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FastPlanReference Guide

VERSION 5.5

Abstract The FastPlan Reference Guide (100028914‐01) provides reference information and procedures for using the FastPlan software application.

Notice Information in this reference guide is subject to change without notice and does not represent a commitment on the part of Varian. Varian is not liable for errors contained in this reference guide or for incidental or consequential damages in connection with furnishing or use of this material.This document contains proprietary information protected by copyright. No part of this document may be reproduced, translated, or transmitted without the express written permission of Varian Medical Systems, Inc.

FDA 21 CFR 820 Quality System Regulations (CGMPs)

Varian Medical Systems, Oncology Systems products are designed and manufactured in accordance with the requirements specified within this federal regulation.

ISO 13485 Varian Medical Systems, Oncology Systems products are designed and manufactured in accordance with the requirements specified within ISO 13485 quality standards.

CE Varian Medical Systems, Oncology Systems products meet the requirements of Council Directive MDD 93/42/EEC.

HIPAA Varian’s products and services are specifically designed to include features that help our customers comply with the Health Insurance Portability and Accountability Act of 1996 (HIPAA). The FastPlan system uses a secure login process, requiring a user name and password, that supports role‐based access. Access rights to view or modify patient data are granted on a per‐user basis. When a user views or modifies data on the system, a record is made that includes which data were accessed, the user name, and the date and time the changes were made. This establishes an audit trail that can be examined by authorized system administrators.

Trademarks BRW is a trademark of Radionics Sales Corporation.The Common UNIX Printing System, CUPS, and the CUPS logo are the trademark property of Easy Software Products.FastPlan, ImMerge, IsoDrag, and IsoDrop are trademarks of Varian Medical Systems, Inc.Leksell Stereotactic System is a registered trademark of Elekta.Postscript is a registered trademark of Adobe Systems Incorporated.UNIX is a registered trademark of The Open Group.© 2004, 2007 Varian Medical Systems, Inc.All rights reserved. Printed in the United States of America.

Contents

CHAPTER 1 INTRODUCTION...................................................................................... 1User Interface ...................................................................................................................... 3

Stereotactic RadioSurgery 5.5 Login Manager Window............................... 3Select Operator List................................................................................................ 4Stereotactic Radiosurgery Treatment Planning Window ............................ 9

Treatment Planning Overview ....................................................................................... 11Image Set Transfer and Selection...................................................................... 12Transferring Image Sets....................................................................................... 12Validating Image Set Transfer............................................................................ 12

Manual Organization ....................................................................................................... 13Visual Conventions .......................................................................................................... 14

Notes, Cautions, and Warnings ......................................................................... 15................................................................................................................................................ 15Contacting Support .......................................................................................................... 15

Ordering Additional Documents...................................................................... 16Communicating Via the World Wide Web .................................................... 16Sending E-Mail...................................................................................................... 16

Precautions ......................................................................................................................... 17Equipment Specifications .............................................................................................. 18Equipment Classifications ............................................................................................. 18

CHAPTER 2 CT LOCALIZATION ................................................................................19Initiating the CT Localization Process ......................................................................... 19Autoregistration ................................................................................................................ 21

Selecting the Optimal Bar Threshold.............................................................. 22Adjusting Images for Brightness and Contrast ............................................ 24Bar Registration .................................................................................................... 24Process Frame-Based........................................................................................... 26

Error Messages.................................................................................................................. 27Process Frameless............................................................................................................. 35Reviewing and Saving Processed Images................................................................... 35

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CHAPTER 3 MRI-TO-CT CORRELATION ...................................................................37Labeling the Image Sets ................................................................................................. 37Starting the ImMerge Process....................................................................................... 38

Loading and Previewing the Image Sets ........................................................ 38Initial MRI Voxel Scaling ..................................................................................... 39

Point Matching Tools....................................................................................................... 39Image Set Display................................................................................................. 39Image Set Slice (Frame) Display....................................................................... 40Slice Magnification ............................................................................................. 40Color Map.............................................................................................................. 40SYNC Button .......................................................................................................... 41Additional Display Options................................................................................ 42

Merging the Image Sets (Point Matching)................................................................. 43Landmark Selection Modes .............................................................................. 44Selecting a Set of Registration Landmarks .................................................... 45Storing a Set of Registration Landmarks........................................................ 45Reentering a Landmark ..................................................................................... 46Point Merge Process ........................................................................................... 46Point Merge Error Messages.............................................................................. 47Deleting a Landmark.......................................................................................... 48

Finer Adjustments........................................................................................................... 49Translate Tool ....................................................................................................... 49Rotate Tool .............................................................................................................. 51Scale Tool................................................................................................................ 52Undo/Redo............................................................................................................. 53XForm ...................................................................................................................... 54

Evaluating the Point Merge ........................................................................................... 54Visual Evaluation.................................................................................................. 54Quantitative Evaluation ..................................................................................... 56

Saving the Correlation Results ...................................................................................... 57Saved File Names ................................................................................................. 58

AutoFusion ......................................................................................................................... 58

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CHAPTER 4 CONE PLANNING..................................................................................61Preplanning........................................................................................................................ 62Starting Cone Planning.................................................................................................. 64Cone Planning Window Layout..................................................................................... 65

Menu Descriptions.............................................................................................. 66Planning............................................................................................................................. 69

Finding the Region of Interest .......................................................................... 70Creating and Placing Isocenters ....................................................................... 70Treatment Arcs...................................................................................................... 77

Evaluate the Plan.............................................................................................................. 82Translate through the Volume.......................................................................... 82

Settings Tab ....................................................................................................................... 83Image Settings...................................................................................................... 83Isodose Settings ................................................................................................... 85Dose Engine Settings .......................................................................................... 87

Optional Views.................................................................................................................. 91Histograms......................................................................................................................... 95

Dose Arc Histogram............................................................................................. 97Dose Cross Plots............................................................................................................... 98Prescription and Slides................................................................................................... 99Removing an Image Set ................................................................................................ 104

CHAPTER 5 AUTOPILOT TREATMENT PLANNING MODULE .................................105Using Autopilot.............................................................................................................. 106

Case and Targeting System............................................................................. 106Building the 3D Model ..................................................................................... 106AutoPilot Tab ...................................................................................................... 106Entering Parameter Data ................................................................................. 108Isocenter Placement and Calculation ............................................................ 110Modifying the Treatment Plan......................................................................... 113

CHAPTER 6 PHYSICS CONFIGURATION PROCEDURES ..........................................117Establishing the System Configuration ..................................................................... 118

Saving the Linac Specifications ...................................................................... 122Printing the Linac Specifications.................................................................... 122Exiting the Configuration Mode..................................................................... 122

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Required Measurements .............................................................................................. 122Output Factor...................................................................................................... 122Tissue Maximum Ratio (TMR) .......................................................................... 123Off-Axis Ratio ...................................................................................................... 124Measurement Methods.................................................................................... 126

TMR Data Entry ................................................................................................................ 127Login Instructions ............................................................................................... 127Entering the TMR Data ..................................................................................... 129Interpolating the Data ...................................................................................... 130Plotting TMR Data............................................................................................... 131Calculating and Saving the TMR Table .......................................................... 132Saving the TMR Measured Data ...................................................................... 133Loading TMR Data.............................................................................................. 134

OAR Data Entry ............................................................................................................... 134Login Instructions .............................................................................................. 134Entering the OAR Data....................................................................................... 137Plotting OAR Data .............................................................................................. 139Calculating the OAR Tables............................................................................... 141Saving the OAR Tables ....................................................................................... 141Loading OAR Data .............................................................................................. 142Printing the OAR Tables .................................................................................... 142New Collimator Integration into Already Configured FastPlan System 142

Dose Calculation and Model Limitations ................................................................. 145Outline of Dose Calculation ............................................................................ 145Establishment of Beam Ray/Patient Surface Intersection....................... 146Static and Arc Beams......................................................................................... 146Dose Grid.............................................................................................................. 147Monitor Unit Calculation ................................................................................. 147Limitations of Model ......................................................................................... 147

CHAPTER 7 WEBFAST ............................................................................................149Features ............................................................................................................................ 150Starting WebFast............................................................................................................. 151Searching........................................................................................................................... 151Viewing Images ............................................................................................................... 152

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Image Display Options................................................................................................... 155Changing Brightness (Level) and Contrast (Window) Levels ................... 155Zooming In and Out .......................................................................................... 156Panning................................................................................................................. 156Other Display Options ...................................................................................... 156Mouse Interaction Summary ........................................................................... 157Keyboard Hotkey Summary............................................................................. 158

Film and Multiplanar Views......................................................................................... 159Contour Tool ................................................................................................................... 160

APPENDIX A PRINTER SETUP................................................................................... 165Adding a New Printer .................................................................................................... 165Printing a Test Page........................................................................................................ 166

APPENDIX B BUILDING 3D MODELS ....................................................................... 1673D Head Contour Model ............................................................................................... 167

Intensity Threshold Level ................................................................................. 167Rebuilding the 3D Head Contour ................................................................... 1683D Tool Bar ........................................................................................................... 170Editing a Model.................................................................................................... 171Clipping a Model ................................................................................................. 171Deleting a Model................................................................................................. 172Rotating a Model................................................................................................. 172Attributes Tool ..................................................................................................... 173

Model Settings Tool ....................................................................................................... 174Building 3D Models of Internal Objects or the Skull ................................. 174Setting the Transparency Level........................................................................ 175Translating Through the Volume .................................................................... 175Selecting the Model Name and Volume ....................................................... 175Manual Trace Tool .............................................................................................. 176Changing the Color of the Model ................................................................... 177Restoring the Transparency Level................................................................... 178

Isodose Shells .................................................................................................................. 178

APPENDIX C MLC PLANNING .................................................................................. 179

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APPENDIX D FASTPLAN ARCHIVER ......................................................................... 181User Interface ................................................................................................................... 181Archiving Patient Files................................................................................................... 185Restoring Patient Files................................................................................................... 186Data Format..................................................................................................................... 188Configuring Network Drives........................................................................................ 188

Setting up File Sharing on a Windows PC.................................................... 189Connecting to Windows Share from FastPlan............................................ 189

APPENDIX E DICOM EXPORT .................................................................................. 191Transferring Data from MLC Application ................................................................. 192Transferring Data from Cone Planning Application .............................................. 194Structure Sets .................................................................................................................. 195

APPENDIX F DICOM IMPORT.................................................................................. 197

APPENDIX G IMAGING PROTOCOL ........................................................................ 199CT Imaging ...................................................................................................................... 200

Imaging Protocol ................................................................................................ 201Image Set Review ............................................................................................... 201Image Set Archive or DICOM Transfer........................................................... 201

MRI Imaging ................................................................................................................... 202Basic Technique ................................................................................................. 202Imaging Protocol ............................................................................................... 203Image Set Review .............................................................................................. 203Image Set Archive or DICOM Transfer.......................................................... 203

viii FastPlan Reference Guide

Chapter 1 Introduction

FastPlan is a treatment planning system for linear accelerator‐based stereotactic radiosurgery (SRS).

The FastPlan Reference Guide details how to do treatment planning for linear accelerator‐based SRS with FastPlan.

Stereotactic radiosurgery (SRS) is a unique combination of neurosurgery and radiation oncology in which multiple small beams of radiation are precisely focused on intracranial targets. SRS was developed in the late 1940s by Lars Leksell to create intracranial lesions using orthovoltage X‐rays. In the following years, gamma rays, heavy charged particles, and megavoltage X‐rays have been utilized to target arteriovenous malformations, benign tumors, and malignant tumors.

Advances in imaging techniques, most notably computed tomography (CT) and magnetic resonance imaging (MRI), furthered the development of SRS. These imaging techniques provide the radiosurgeon with a three‐dimensional database from which to view the intracranial anatomy and plan treatment. Using these three‐ dimensional databases SRS was the first clinical application of virtual simulation, a technique by which the patient’s entire treatment plan is designed using a virtual patient recreated in the computer from imaging studies. Yet, because of expensive delivery equipment, laborious planning software, inadequate computing power or a combination of the three, SRS is often very costly and/or time‐ intensive.

The FastPlan Stereotactic Radiosurgery Treatment Planning System is a treatment planning system for linear accelerator‐based SRS. Straightforward treatment planning techniques within the FastPlan application allow the radiosurgeon to easily localize the targeted lesion and perform virtual simulation. Coupling patented algorithms with state‐of‐the‐art computer technology allows the radiosurgeon to quickly and efficiently optimize the treatment plan. Once the optimal plan has been determined, the FastPlan system then provides step‐by‐step instructions for quality assurance and treatment delivery using treatment hardware.

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The primary goal of the FastPlan Stereotactic Radiosurgery Treatment Planning system is to assist you in achieving a radiation treatment plan: a treatment plan that conforms to the target, as closely as possible, as defined by the radiation isodose shells with minimal normal brain included.

Figure 1 flowcharts the FastPlan application.

Figure 1 FastPlan System Application Flowchart

2 FastPlan Reference Guide

User Interface

This section describes the major windows that open when you are running FastPlan.

Stereotactic RadioSurgery 5.5 Login Manager Window

When FastPlan starts running, the Stereotactic RadioSurgery 5.5 Login Manager window (Figure 2) opens.

Figure 2 Stereotactic RadioSurgery 5.5 Login Manager Window

In general, the Stereotactic RadioSurgery 5.5 Login Manager window and other windows linked to it are similar to those described in the Patient Positioning 2.2 Operator Login Manager Reference Guide (Part No.

Introduction 3

970737A). This section describes those features that are unique to the current application. You should refer to the Patient Positioning 2.2 document for a description of any features not described here.

Select Operator List

The Select Operator list contains all authorized operators (users) of the system, by name, in alphabetic order. The Administrator, which appears at the top of the list, is a permanent account that has access to all system functions.

The list can contain up to 10 items without requiring scrolling. If there are more than 10 items, the scroll bar becomes active. Pressing the up or down arrow once causes up to the previous or next 10 items, respectively, to appear in the list.

To the right of each operator name is a row of mini‐icons (Figure 3), each of which represents a system function available to the operator. These icons are identical to those appearing on the application startup buttons (see “Application Startup Buttons (White)” on page 5).

Figure 3 Mini-Icons

Clicking an operator name selects that operator. The selection appears highlighted in yellow. Selected operators are expected to type their unique password to begin using the system. (The cursor is in the first space of the Enter Password text box.


Application Startup Buttons (White)

Each application startup button (Figure 4) starts a system application:SRS Planning: Starting this application is described later in this chapter and throughout this document.WebFast Q/R: This application is described in Chapter 7 on page 153.Physics: This application is described in Chapter 6 on page 121.Archive: This application is described in Appendix D on page 181.DICOM Import: This application is described in Appendix F on page 201.

The top‐level buttons are highlighted or dimmed depending on the access rights of the current operator. To successfully access a button function, you must have entered your password correctly.

Figure 4 Application Startup Buttons

When the application starts, its window replaces the Operator Login Manager window. As soon as the selected application exits, the Operator Login Manager window reappears and the button menu returns to the top‐level menu. If at least five minutes of inactivity have occurred, the password text box is cleared.

If a password has expired, the operator is not allowed to start any applications until the password has been changed in the Change Password mode, described later.

Function Buttons (Blue)

The bottom row of buttons (Figure 5) provides built‐in functions.

Introduction 5

Figure 5 Function Buttons

Service Button

This button is available only to operator Administrator, unless the administrator grants access to other operators.

The Service button opens a second level of buttons to perform service‐related functions (Figure 6). Seven blue buttons are aligned in two rows:

Install Patch CD allows you to install patch CDs supplied by the Support organization.Open SSH [Secure SHell] Tunnel allows remote access to the workstation by service and support personnel. This function has been superseded by SmartConnect.Printer Configuration opens a browser window with a web-based tool for setting up the default printer.Test Colors displays a screen with three horizontal color bands. If the monitor colors are correct, blue, green, and red color bands appear from top to bottom, respectively. If one or more of the color bands is black, check for a bent pin on the VGA connector.Restart SmartConnect restarts the remote access services used by service and support personnel in the event of a problem with these services.Delete Log File deletes the system log file associated with DICOM export.Full System Backup opens another level of buttons with options for archiving system configuration and physics data, and all patient data. This option requires an external USB hard drive to be connected to the FastPlan workstation, and the drive must be formatted with the FAT32 filesystem. Full or selective backup of patient data can also be performed using the archiver application. (See Appendix D.)


Below these buttons is a green Back button, which returns you to the main window.

Figure 6 Service Screen Buttons

Below and to the right of the Back button is an orange button labelled Varian Service Use Only, which allows access to configuration, service, manufacturing, and similar functions, and which should be used only by authorized personnel. When you click this button, a message (Figure 7) appears asking you to confirm that you are authorized to use these functions.

Figure 7 Varian Service Use Only Button Confirmation Message

Introduction 7

After confirming by clicking Yes, a second level of buttons appears, with three orange buttons (Figure 8) aligned in a row:

root shell allows performing low‐level expert maintenance access to the system.Sysconfig is used primarily during installation or by the site administrator for changing application settings.system info provides hardware information for manufacturing.

Below these buttons is a green Back button, which returns you to the previous window.

Figure 8 Varian Service Use Only Buttons

Edit Users Button

This button is available only to operator Administrator, unless the administrator grants access to other operators.

The Edit Users button allows the site Administrator to add and edit operator identities and access rights.

Change Password Button

The Change Password button provides unrestricted access to the built‐in mode for operators to change their personal passwords with the on‐screen keyboard.

Power Button

The Power button provides operators with unrestricted control over workstation power options. Pressing this button changes the screen.


Stereotactic Radiosurgery Treatment Planning Window

After turning on and booting up the system, the Stereotactic RadioSurgery 5.5 Login Manager window (Figure 2) opens.

Under Select Operator, click your operator name, then under Enter Password, type in your password. Click SRS Planning. The Stereotactic Radiosurgery Treatment Planning window (Figure 9) opens.

Figure 9 Stereotactic Radiosurgery Treatment Planning Window

Available exams list

Introduction 9

This is the first actual FastPlan window. It consists of five areas:Available exams list is located in the upper right. It consists of a listing of all patients and their associated image sets (CT and MR).Image information area, providing information on any selected patient image set. This information appears in the following data boxes:

NameIDDiagnosisPhysicianDateAvailable images

Function button area, consisting of three buttons:View Attributes File button, which opens a window containing details about the selected image set.Remove Patient button, which removes patient information from the FastPlan database and available exams list, following archiving of the patient data. See “Removing an Image Set” on page 105.Refresh Patient List button, which refreshes the available exams list following the removal of one or more patient image sets.

Stereotactic Image Manager area, consisting of three application buttons:

WebFast SRS, which is described in Chapter 7 on page 153CT Localization, which is described in Chapter 2 on page 19ImMerge, which is described in Chapter 3 on page 37

Treatment Planning area, consisting of two application buttons:Cone, which is described in “Starting Cone Planning” on page 67MLC, which is described in Appendix C


Treatment Planning Overview

The FastPlan system software guides you through all the processes necessary to prepare a treatment plan. The application software uses patented algorithms capable of rapidly updating dosimetry results and providing the treatment team with critical planning metrics on demand. These algorithms use the full volume set of patient CT data, eliminating the need for slice‐by‐slice contouring of critical structures by the surgeon or medical oncologist.

The FastPlan software has a hierarchical structure and all SRS (Stereotactic Radiosurgery) functions are accessed from the Stereotactic Radiosurgery Treatment Planning window (see Figure 9 on page 9). The treatment planning proceeds in a sequential manner and certain functions are not available until the completion of other functions. Options in gray text are not available until a previous function has been completed. Upon exit from a main function, the program always returns to the Login Manager.

The treatment planning process includes:Image set transferImage set selectionCT localizationMRI‐to‐CT correlationTreatment planning

This chapter discusses the transfer, selection, and processing of the stereotactically acquired CT image set. Chapter 3 addresses the correlation of the MRI and CT image sets. Chapter 4 provides step‐by‐step instructions on how to plan a treatment using the information provided by the correlated image sets.

Note: FastPlan can process only CT scans with an image resolution of 512x512 and MR scans with an image resolution of 512x512 or 256x256. Other image resolutions are not supported and therefore will not be loaded into any of the FastPlan modules.

Introduction 11

Image Set Transfer and Selection

Chapter 2 describes the imaging protocol required for use with the FastPlan system. When imaging is complete, the next task is to transfer the patient’s image information (both CT and MRI) from the scanner or scanner media to the active memory of the FastPlan system.

Transferring Image Sets

The FastPlan treatment planning process begins with the transfer of the patient’s image sets (CT and MRI) from the scanner via DICOM to the FastPlan workstation. More than likely your workstation has adequate hard drive space available to accommodate numerous FastPlan image sets.

To maintain adequate hard drive space, make it a practice to archive and remove each patient image set after the radiosurgery procedure is completed.

For instructions on removing exams to free up disk space, see “Removing an Image Set” on page 105.

Transferring Archived Media

See Appendix D on page 181.

Transferring Image Sets Using DICOM

To retrieve scans directly from the scanner, the FastPlan system must be part of the local area network. Since network protocols differ from system to system, exact network transfer instructions are provided to you at the time of the DICOM installation.

Validating Image Set Transfer

The available exams list (Figure 9) displays all patient image sets currently saved in the /home/linac/exams directory on the workstation’s hard drive. The patient image set appears on this list only after it has been transferred.


Manual Organization

This manual is organized into chronological tasks. Any caution or warning relating to a particular instruction appears immediately prior to the instruction. The expected results, error recovery techniques, and termination conditions are provided for each action. This manual is organized into eight chapters and seven appendices:

Chapter 1, “Introduction,” on page 1 describes the FastPlan system and user interface; and provides an overview of stereotactic radiosurgery treatment planning and organizational information; and describes visual conventions used in the manual, precautions, and equipment specifications and classifications.Chapter 2, “CT Localization,” on page 19 describes how the patientʹs raw scanner images are read in and used to create a slice stack in the stereotactic coordinate space, corrected for any table tilt or spin present during the scans.Chapter 3, “MRI‐to‐CT Correlation,” on page 37 describes the ImMerge application, which is used to correlate (align) the patient’s spatially less‐accurate MRI image set with the patient’s spatially more‐accurate CT image set. This results in a transformed MRI image set which is used to plan the radiosurgery treatment.Chapter 4, “Cone Planning,” on page 65 describes how this application performs treatment planning (using cylindrical collimators) on the stereotactic CT and MR data sets.Chapter 5, “AutoPilot Treatment Planning Module,” on page 107 describes this application that provides tools that enable, in some instances, fully automatic treatment planning functions.Chapter 6, “Physics Configuration Procedures,” on page 121 describes these linac‐specific procedures, which are performed during the FastPlan system installation.Chapter 7, “WebFast,” on page 153 describes the WebFast application, which is a web server and a full‐featured DICOM network application that can receive DICOM images over standard TCP/IP connections and make those images available to any Java‐enabled web browser.Appendix A on page 169 describes how to add a new printer to the FastPlan system and how to test the printer setup by printing a test page.

Introduction 13

Appendix B on page 171 describes how to build 3D renderings of the skin, skull, tumor, and isodose shells of the patient’s image set, to visualize anatomy, isocenters, and the dose distribution.Appendix C on page 183 describes how to use the MRI Planning module to review CT and MRI data sets and perform a data export to the Eclipse system.Appendix D on page 181 describes how to use the archiver application to archive and restore patient data, including image sets.Appendix E on page 195 describes how to export DICOM data from FastPlan.Appendix F on page 201 describes how to import DICOM data from CDs and DVDs into FastPlan.Appendix G on page 203 describes the imaging protocols to use for making both CT and MRI scans for use in treatment planning.

Visual Conventions

This guide uses the following notational conventions to help you locate and identify information.

Italic text is used for emphasis, examples, new terminology, text that you type, and book titles.

Bold text identifies menu names and commands, items you can click or select on the screen, keyboard keys, and names of hardware controls.

A monotype font identifies file names, folder names, text file contents, and text that either appears on the screen or that you are required to type in.

View > Options indicates selecting a main menu, then selecting a command from that menu. In this example, click the View menu, then click the Options command in that menu.

This symbol, when found on equipment, represents type BF applied equipment as defined in IEC 601‐1/EN60601‐1.


Notes, Cautions, and Warnings

Contacting Support

Support services are available without charge during the initial warranty period. If you seek information not included in this publication, call Varian Medical Systems support at the following locations:

To contact the support location nearest you for Service, Parts or Support, see the list at the Varian Medical Systems website:

Worldwide Listing—http://www.varian.com/sein/sup205.html

Note: Notes identify additional information about using FastPlan that can help you obtain optimum performance from the hardware or software.

CAUTION: Cautions identify important information about actions or conditions that can result in minor or moderate injury to personnel or can result in damage to hardware or data.

WARNING: Warnings identify important information about actions or conditions that can result in serious injury.

North America toll‐free telephone support +1.888.827.4265

Global telephone support +1.702.938.4807

Global telephone support for treatment planning

+1.702.938.4712

Introduction 15

http://www.varian.com/sein/sup205.html

Ordering Additional Documents

To order additional documents, call the following:

Communicating Via the World Wide Web

If you have access to the Internet, you will find Varian Medical System support at the following location:

Oncology Systems — http://www.varian.com/oncy/

Then click Support from the menu list along the left side of the window.

Sending E-Mail

Send your e‐mails to the following locations for support:

North America +1.800.535.5350 (Press 1 for parts)

Global +1.702.938.4700

Information Management Systems

[email protected]

Digital Imaging Management Systems

[email protected]

Delivery Systems [email protected]

Treatment Planning [email protected]

Brachy Therapy Systems [email protected]


http://www.varian.com/oncy/

[email protected]

[email protected]

[email protected]

[email protected]

[email protected]

Precautions

The FastPlan Stereotactic Radiosurgery Treatment Planning system should be used only as an aid in planning radiation therapy. The clinician should not rely solely on the system for treatment planning as it is the responsibility of the clinician to identify the treatment volume correctly and to perform a final check on the correctness of the treatment plan dosimetry.

CAUTION: The FastPlan system should be used only by qualified medical professionals who have been thoroughly trained and are experienced in its use, and, if relevant, have been trained on the particular equipment especially regarding protective measures such as radiation protection.

CAUTION: This software has been thoroughly checked and tested before its release. The software produces a mathematical model of a treatment plan. Varian Medical Systems cannot be held responsible in any way for any inaccuracies of any nature resulting from use of any software.

WARNING: Do not use the FastPlan system instrumentation on patients suspected of having Creutzfeld Jakob Disease (CJD).

WARNING: The equipment must be used in accordance with the procedures contained in this manual and must not be used for purposes other than those described. The information on the equipment is subject to change without notice.

WARNING: Incorrect operation, or failure to maintain the equipment in accordance with the schedule of maintenance, relieves the manufacturer or his agent from all responsibility for consequent non-compliance, damage, injury defects, and/or other malfunction.

WARNING: When using FastPlan with the Optical Guidance Platform (OGP), it is necessary to use Optical Guidance Platform version 2.6 (or later) software. Consult your Service engineer if you have an earlier version of IR camera positioning software than Optical Guidance Platform 2.6. Using an earlier version of OGP than 2.6 may result in mistreatment.

Introduction 17

Equipment Specifications

Equipment Classifications

The FastPlan system is Class 1, Type BF applied equipment that is enclosed without protection against the ingress of water

The FastPlan system is not suitable for use in the presence of a flammable, anesthetic mixture with air or with oxygen or nitrous oxide.

The FastPlan system is suitable for continuous operation.

Table 1 FastPlan Environmental Specifications

Specification United States Outside the United States

Operating Temperature

50° to 86° Fahrenheit

10° to 30° Celsius

Input Voltage 100–120 Volts 220–240 or 100–120 Volts

Maximum Current 8 Amps 4 Amps or 8 Amps

Power Dissipation 900 Watts 900 Watts

Shipping and Storage ‐15° to 150° Fahrenheit

‐26° to 66° Celsius

Humidity 10% to 80% non‐ condensing

10% to 80% non‐ condensing


Chapter 2 CT Localization

The CT Localization program reads in the patientʹs raw scanner images and creates a slice stack in the stereotactic coordinate space. During the CT Localization process, fiducial marks corresponding to the localizer frame bars are found in each image. These marks are used to calculate image position in the stereotactic coordinate space (with respect to the localizer frame). Images are inserted into a 3D volume and the volume is resliced, compensating for any table tilt or spin present during the scan.

In addition to transforming the data set to a stereotactic coordinate space, CT Localization validates data integrity and reports possible anomalies reflected in the scan, such as potential patient motion, data distortion, or large data misalignment.

Frameless data sets should still be passed through the CT Localization step, to confirm the absence of a frame in the data and create an axially sorted slice stack.

Initiating the CT Localization Process

To begin the CT localization process, in the Stereotactic Radiosurgery Treatment Planning window (Figure 12):

1. Select the patient’s exam in the available exams list.This selected patient becomes the active patient image set. Selecting the patient exam activates the CT localization, image‐set merging, and treatment planning options.

2. Click CT Localization.When the CT Localization window (Figure 10) opens with the current raw image viewer in the upper left corner, the following message may appear:

Undefined patient orientation during the scan. Please confirm whether orientation is Head First Supine.

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3. If the message appears, and if the orientation is head‐first supine, click Yes. Otherwise, click No.

Note: The FastPlan treatment planning system supports only head‐first supine orientation of the patient during a scan.

The message closes and another window opens with the message Running autoregistration and a progress indicator. When autoregistration is complete, the window closes.

Figure 10 CT Localization Window, Input Data Tab


Autoregistration

Autoregistration is a process that attempts to automatically find all the fiducial marks in the raw image set. If the sysconfig option allow auto‐registration (CTLocalize) is turned on (the default setting), Autoregistration is launched automatically at the start of CT Localization. You can also launch this process at any time from the Input Data tab of the CT Localization window by clicking Auto Find under Bar Registration. Autoregistration detects the localizer frame in the CT data volume (if any frame is present) and marks the locations of fiducials in the images on the Input Data tab. The message All bars have been found appears at the bottom of the first image after Autoregistration ends (Figure 11). You must carefully review the marked fiducials across all the images. If no frame is found, the message No bars found. Frameless ?? or use Seed Bars option appears at the bottom of the first image. The data set is likely to be frameless (that is, the localizer frame is absent such as with the use of a bite‐block).

Note: The Autoregistration process uses Bar Threshold to find the fiducial marks in the images. The default threshold value is selected to work for most scanner types and scan settings. However, occasionally you may need to adjust this threshold value. In case Autoregistration fails to detect the fiducials and you can clearly see the presence of the localizer frame in the images, you should adjust the threshold and repeat Autoregistration by selecting the Auto Find option. To find the optimal threshold value, see “Selecting the Optimal Bar Threshold” on page 22. If repeated threshold adjustment and Auto Find does not work, try using the Seed Bar Locations option as described further in “Bar Registration” on page 24.

CT Localization 21

Figure 11 Head Frame Image Set Showing All Six Fiducials

Selecting the Optimal Bar Threshold

The optimal bar threshold value for fiducial detection is a minimal CT value that allows you to clearly distinguish fiducials as clean white blobs. Although the default threshold value works for most scanner types and scan settings, occasionally the Auto Find and Seed Bar Locations options may fail to find fiducials in the image, even though the localizer frame is clearly visible. In this case, you must manually adjust the threshold.


To set the optimal threshold for a specific loaded data set:

1. Use the scroll bar next to the image viewer to select one of the middle images where the fiducials are clearly visible and free of artifacts.

2. Under Image Settings, move the Window slider all the way to the left (a value of 1).

3. Set the Mean slider value to 900 and slowly increase the value until the fiducials in the image appear as rounded clean blobs.

4. Under Bar Registration, adjust the Bar Threshold slider to the selected value of the Mean slider.

5. Repeat the Auto Find or Seed Bar Locations operation that you have been performing.

Note: If you find the need to adjust the default bar threshold value on most of the data sets you are processing, and the new value is consistent across many data sets, you should set this new value as the default CT Bar Threshold value in the sysconfig option set CT localization threshold value. After this change, the CT Localization application will use your new default threshold.

Cursor Readouts

As the cursor moves on the image canvas, the actual X and Y coordinates and the CT pixel intensity value of the cursor appear in the upper left corner. The X coordinate (horizontal axis) values range from 0 at the left border to 511 at the right border. The Y coordinate (vertical axis) values range from 0 at the top border to 511 at the bottom border.

The CT pixel intensity values are the Hounsfield values assigned by the CT scanner for the varying densities of the image.

CAUTION: Use care when using pixel coordinates. They do not provide the program with a reliable basis for determining coordinates or tilt and spin and the resulting image set is not stereotactic.

CT Localization 23

Adjusting Images for Brightness and Contrast

To enhance the image display, adjust the image‐setting sliders (Figure 10). The Mean slider adjusts the image brightness. The Window slider adjusts the image contrast. Use one of two methods to move the slider:

Drag the slider: Place the cursor on the slider, press and hold the left mouse button, then move the mouse to the left or right of the handle.Step the slider: Place the cursor on the slider to the left or right of the handle, then press and release (click) the left mouse button.

Bar Registration

Prior to selecting any of the bar registration options, choose the correct head localizer type in the CT Frame list. The currently available choices are VMS (same as SNT) and BRW frames.

Although the Autoregistration process is expected to work for most scans, in occasional cases there may be a need to use other semiautomatic and completely manual alternatives for bar registration (Figure 12). In addition to the Auto Find option, there are two other options for bar registration:

Seed Bar LocationsMark manually in current frame

Figure 12 Bar Registration Panel


The Seed Bar Locations option guides you through the markup of all localizer frame fiducials in a single image. Their locations are automatically refined and then tracked through the rest of the images. This option employs a centroid‐finding algorithm that refines the user selection and positions a red mark precisely at the center of the white blob. If during the bar registration the red mark does not appear following the left‐click around the blob, the bar threshold requires adjustment. See page 22 for how to select the optimal bar threshold.

The Mark manually in current frame option allows to you to manually select fiducials in a single frame. This option overrides the automatic bar localization setting and instructs the computer to place the centroid of the bar at the point you click. Use this setting when:

There is too much artifact in the image.Bars are too close to the skull for the automatic centroid‐finding algorithm to properly function.Both Auto Find and Seed Bar Locations fail, even after repeated Bar Threshold adjustments.

The number of bars that should be marked depends on the type of the frame: a VMS frame contains six bars while a BRW frame contains nine bars. Mark each bar by left‐clicking the mouse next to the white blob on the slice corresponding to the localizer bar intersection with this slice (see Figure 11). Start marking bars from the thickest bar (the largest blob) situated on the left and continue in a clockwise direction. Failure to follow these guidelines may lead to the following error messages:

Bar #1 should be the largest bar.Bars have been selected out of order or the localizer is physically misaligned.

If either of these messages appears, click OK and reselect the bars starting from the largest in a clockwise order.

Regardless of which process you use to perform bar registration, you must visually inspect the fiducial marks to confirm that the red marks correspond to the centers of the white blobs created by the localizer frame bars on the CT images.

CT Localization 25

Process Frame-Based

When localizer frame bars are registered in either a single image (using the Seed Bar Locations option) or all the images (using the Auto Find option), the Process Frame‐based option becomes enabled. To perform frame‐based processing:

1. First review the fiducial selection to ensure it was done properly.

2. Under Localize, click Process Frame‐based (Figure 10 on page 20).

3. Observe how tilt, spin, and the location of each image is computed from its fiducials, then images are inserted into a volume, and the volume is resliced to obtain stereotactic slices.A progress indicator is displayed and red messages at the bottom of the image describe the current status of the process. When processing is complete, the window changes to the Output Data tab (Figure 13).

Figure 13 CT Localization Window, Output Data Tab


Error Messages

If problems occur during the CT localization process, one or more error messages may appear, along with associated buttons. These are both described in this section.

Table 2 Error Messages

Message Unable to proceed. At least 30% of the slices should contain detected localizer bars in order to process this whole data set. Please verify localizer bar marks in each frame and use manual bar selection when marks are missing. Discard data set when significant patient motion is noticeable.

Button(s) Ok

Explanation Fiducials corresponding to the localizer bar locations were not detected in many slices. The axial span of the CT scan is usually larger than the localizer frame length and not every slice in the scan contains the localizer frame. However, the localization algorithm requires that at least 30% of the slices have valid fiducials. Failure to automatically detect fiducials in some frames may be a result of significant changes in the CT values throughout the scan or of patient motion.

CT Localization 27

What to Do Adjust the image settings by setting the Window slider all the way to the left to a value of 1 and adjust the Mean slider to the current Bar Threshold slider value. Use the scroll bar to move through all the slices and carefully review every slice containing the localizer frame to ensure that fiducials are clearly visible as white blobs. Adjust the Mean slider if necessary to obtain the best fiducial signal. Set the Bar Threshold slider to the selected Mean slider value and repeat localization by clicking Process Frame‐based. If repeated failures occur, slowly review all the slices for consistent slow motion or lack thereof of each fiducial. Patient motion, if present, appears as large, abrupt, frame‐to‐frame deviations of fiducial locations. If you do detect patient motion, discard the data set and order a rescan of the patient.

Close the message window by clicking Ok.

Message Unable to proceed. At least 70% of the slices containing bars should be localized with high precision in order to process this whole data set. This data set may contain some distortion or localizer bars may be marked incorrectly. Please review bar marks in each frame.

Button(s) Ok

Explanation The localization algorithm positions each slice in the stereotactic space (with respect to the localizer frame) and verifies the precision of this registration. This message indicates that the registration precision is not high enough for a large number of the slices and localization cannot proceed.

Table 2 Error Messages (continued)


What to Do Carefully review each frame and verify that the red fiducials marks correctly correspond to the white blobs of the localizer frame bars. If you have used the Mark manually in current frame bar registration option, ensure that the bars were selected in the correct clockwise order, starting with the largest bar on the left. Verify that the correct CT frame type was selected in the CT Frame list and that the correct number of fiducials is visible (six for the VMS frame, nine for the BRW frame). Redo bar registration, if necessary, and repeat localization by clicking Process Frame‐based. If the problem persists, suspect distortion in the data set and rescan the patient if necessary.


Message Computed localize parameters deviate significantly among the slices. Please revisit the fiducial marks. High deviation may indicate presence of patient motion in which case rescan is advised.

Button(s) Ok

Explanation The localization algorithm positions each slice in the stereotactic space by computing tilt and spin and the axial location of the slice. The algorithm verifies the consistency of tilt and spin values throughout the scan to confirm scan integrity (or ʺrigidityʺ), corresponding to the absence of patient motion. This message indicates that the deviation in localization parameters (that is, tilt or spin) is very large, and therefore patient motion may be present.


CT Localization 29

What to Do Review all the slices and verify the consistent slow motion or lack thereof of each fiducial. Patient motion, if present, appears as large, abrupt, frame‐to‐frame deviations of fiducial locations. If you do detect patient motion, discard the data set and order a rescan of the patient.


Message Large misalignment warning. Average spin angle in this data set is S, average tilt angle is T. Please confirm validity of the scan in order to proceed with localization.

Button(s) Cancel and Localize

Explanation This message indicates that the average table/localizer frame spin or table tilt detected in the data set exceeds 5 degrees. Values greater than 5 degrees are unusual for SRS CT scans and represent a large misalignment.

What to Do Proceed with localization by clicking Localize or stop the localization by clicking Cancel. If you choose to proceed, the localization algorithm compensates for tilt and spin and transports the data set into the stereotactic space.

Message Spin angle is too large. Cannot process image‐set. Spin = S degrees.

Button(s) Ok



Explanation A table or localizer frame spin of greater than 30 degrees was detected in this data set. The maximum allowed spin for processing is 30 degrees.

What to Do Validate localizer bar selection and ensure that the bars were selected in the correct clockwise order, starting with the largest bar on the left. Verify that the correct CT frame type was selected in the CT Frame list and that the correct number of fiducials is visible (six for the VMS frame, nine for the BRW frame). Repeat localization if any changes to bar registration have been made. Contact Varian Customer Support if the problem persists.


Message Tilt angle is too large. Cannot process image‐set. Tilt = T degrees.

Button(s) Ok

Explanation A table or localizer frame tilt of greater than 30 degrees was detected in this data set. The maximum allowed tilt for processing is 30 degrees.


CT Localization 31

What to Do Validate localizer bar selection and ensure that the bars were selected in the correct clockwise order, starting with the largest bar on the left. Verify that the correct CT frame type is selected in the CT Frame list and that the correct number of fiducials is visible (six for the VMS frame, nine for the BRW frame). Repeat localization if any changes to bar registration have been made. Contact Varian Customer Support if the problem persists.


Message For slice with axial A spin of S degrees significantly differs from the average Slice Stack spin of SA degrees. Patient might have moved during the scan. Do you want to discard the slice or apply average localization correction?

Button(s) Discard and Apply Average

Explanation The localization algorithm positions each slice in the stereotactic space by computing tilt and spin and the axial location of the slice. The algorithm verifies the consistency of the tilt and spin values throughout the scan to confirm scan integrity (or ʺrigidityʺ), corresponding to the absence of patient motion. This message indicates that spin deviation in a particular slice is very large, suggesting the possible presence of patient motion or incorrect fiducial detection for this slice.

What to Do Discard this slice by clicking Discard or apply an average localization correction to this slice by clicking Apply Average.



Message For slice with axial A tilt of T degrees significantly differs from the average Slice Stack tilt of TA degrees. Patient might have moved during the scan. Do you want to discard the slice or apply average localization correction?

Button(s) Discard and Apply Average

Explanation The localization algorithm positions each slice in the stereotactic space by computing tilt and spin and the axial location of the slice. The algorithm verifies the consistency of the tilt and spin values throughout the scan to confirm scan integrity (or ʺrigidityʺ), corresponding to the absence of patient motion. This message indicates that the tilt deviation in a particular slice is very large, suggesting the possible presence of patient motion or incorrect fiducial detection for this slice.

What to Do Discard this slice by clicking Discard or apply an average localization correction to this slice by clicking Apply Average.

Message Could not localize image #I with desired high precision.

Button(s) Ok


CT Localization 33

Explanation The localization algorithm positions each slice in the stereotactic space (with respect to the localizer frame) and verifies the precision of this registration. This message indicates that registration precision is not high enough for a specific slice. The algorithm will discard the localization parameters for this slice from the computations and apply average parameters to this slice.

What to Do Carefully review the resulting data set, especially around the particular axial slice that generated this message. If this problem is encountered with many slices, the second error message listed in this section appears and localization is stopped.

Message Error reading in the _attributes file.

Button(s) Ok

Explanation This message indicates that either the patient /home/linac/exams directory or the _attributes file in this directory does not have read permissions.

What to Do Contact Varian Customer Support for assistance.




Process Frameless

A loaded scan is considered frameless if a head‐localizer frame was not used for immobilization during the scan (usually such a scan would use byte‐block immobilization). To start frameless processing:

1. Under Localize on the Input Data tab, click Process Frameless.You are asked to confirm that the loaded scan is frameless.

2. Visually confirm that the loaded data does not contain a head‐frame, adjusting image settings if necessary.

3. Click OK to proceed with frameless processing.Slices are quickly sorted axially and inserted into the volume.

Reviewing and Saving Processed Images

After localization is complete, carefully review the processed images using the scroll bar and save them.

A window may open with the message The file, XXX.ss, exists. Ok to overwrite? and an OK and Cancel button. (XXX is the filename of the image file.) Click OK.

The window closes and another window opens with the message Image file was successfully written and an OK button. Click OK. The window closes and the Stereotactic Radiosurgery Planning window returns.

CT Localization 35

Chapter 3 MRI-to-CT Correlation

An MRI image set provides excellent visualization of the pathology of the lesion and the overall anatomy of the brain. Unfortunately, an MRI image set too often includes unpredictable magnetic field aberrations. These aberrations can result in peripheral distortion of the image set that can lead to distortion in the location of the stereotactic reference fiducials and subsequent errors in the treatment planning.

A CT image set with stereotactic reference fiducials does provide a process by which stereotactic coordinates of any point selected on the CT image set may be calculated accurately. Regrettably, many of the targeted lesions are poorly visualized on CT, thus contributing little or no information when planning a radiosurgery treatment.

The FastPlan system recognizes the need for these two different imaging modalities and includes a process known as ImMerge.

The ImMerge process, through a matching of at least four landmarks and a series of proprietary algorithms, allows you to rigidly correlate (align) the patient’s spatially less‐accurate MRI image set with the patient’s spatially more‐accurate CT image set. This results in a transformed MRI image set which is used to plan the radiosurgery treatment.

This chapter discusses the complete ImMerge process.

Labeling the Image Sets

The ImMerge system refers to the image sets as the reference image set and the working image set. In the FastPlan system, the reference image set is the stereotactically acquired and processed CT image set. The patient’s MRI scan is referred to as the working image set.

37

Starting the ImMerge Process

Loading and Previewing the Image Sets

To begin the image set correlation and load the reference and working image sets: In the Stereotactic Radiosurgery Treatment Planning window, under Stereotactic Image Manager (Figure 9 on page 9), click ImMerge.

The ImMerge 5.5 window opens (Figure 14) and the program loads both the reformatted CT image set as the reference image set as well as the associated MRI image as the working image set.

Figure 14 ImMerge 5.5 Window

Note: The stereotactically acquired CT image set must be processed through CT Localization in order to begin the MRI‐to‐CT correlation process.

Note: Failure to follow the MRI scanning protocol defined in “MRI Imaging” on page 14 may cause problems with the loading or processing of the image sets.


Wait until the exam is 100% loaded. The time to load an exam depends on the size of the image set and the amount of workstation memory. In the event information is missing from the image set, an error alert message appears. Usually recovery instructions are included in the message.

Preview the working image set following the instructions found in “Preplanning” on page 62.

Initial MRI Voxel Scaling

When the working image set (MRI) is loaded, it is automatically scaled to match the voxel dimensions of the reference image set.

Point Matching Tools

The correlation process consists of selecting, storing, and computer matching at least four corresponding landmarks on each image set. This section discusses the tools you can use to synchronize the image sets so that the points you select are in similar planes and slices.

Image Set Display

The image sets appear side‐by‐side in the ImMerge window (Figure 14). The reference image set always appears on the left of the window and the working image set on the right side of the window.

The image sets default to the axial orientation when they first appear. In the lower left corner of the image pane are three small images (scout views) depicting axial, coronal, and sagittal orientations. To change the orientation, click on the image with the orientation you wish to view. That orientation then appears in the pane.

Note: Check the patient name and ID to ensure that the proper data has been correlated.

MRI-to-CT Correlation 39

There are two other methods you can use to change the image orientations. These include:

Select the appropriate toggle switch to the right of each image set display pane: A (axial), C (coronal), and S (sagittal).Place the cursor in the pane and press the A, C, or S key on the keyboard.

Image Set Slice (Frame) Display

Moving the scroll bar (found to the right of each image display pane) changes the image which is displayed in the pane. Clicking either above or below the scroll bar handle advances the displayed slice by the amount indicated in the Step data box just below the scroll bar.

Slice Magnification

High levels of image magnification are helpful to fine‐tune the landmark selection. The magnification levels range from one to eight. Each image set is separately magnified by:

Right‐clicking in the desired display pane.Dragging the cursor over the desired magnification and then releasing

Color Map

Clean, clear, and sharp image displays make it easier to select and match the landmarks. The Color Map window (Figure 15) allows you to enhance the image display by adjusting the contrast parameters and selecting the pixel color intensity. To access the Color Map Window, simply right‐click in the desired image‐set pane and select Color Map from the pop‐up window.

Level and Width Slider Bars

There are two slider bars:Level slider: Changes the overall image brightness.Width slider: Changes the image contrast.


Figure 15 Color Map Window

Color Maps

There are four color map options:Gray Scale [default]: Displays the pixel intensities in shades of gray ranging from black to white.Heat Scale: Displays the pixel intensities ranging from red to yellow.Photo Scale: Displays the pixel intensities visible to the human eye sight.Rainbow Scale: Displays the pixel intensities in different colors ranging from black to white.

SYNC Button

When matching landmarks it is important that the landmark appear in the same plane and slice in both of the image sets. Clicking SYNC aligns the reference and working image sets so they are on the same plane, slice, and point, and appear at the same magnification level.


The right arrow synchronizes the working image set to the parameters established for the reference image set. The left arrow synchronizes the reference image set to the parameters established for the working image set.

Additional Display Options

Eight different overlays, found on the palettes below the images, can concurrently appear on the image sets. To display an overlay, click the button to the left of the overlay label. See Table 3.

Table 3 Overlay Display Options

Overlay Description

Grid Places a grid in the pane.

View Center Marks the center of the pane with a red cross hair.

Image Center Marks the center of an image with a yellow cross hair.

Dual Cursor Displays a green cross‐hair cursor at the corresponding position on both the image‐set panes. Left‐clicking and dragging the mouse repositions the green cross‐hair cursor provided Dual Cursor mouse mode is also selected.

Line Displays a blue line, provided the line was drawn with the “line mouse mode.” The length of the line appears in the upper left hand corner of the pane.

Bone Removes the bone from the image.

Circle Retains the circle on the image. The radius of this circle appears in the upper left corner of the pane.

Landmarks Marks the location of all saved landmarks with a green circle.


Merging the Image Sets (Point Matching)

The correlation of the two image sets literally combines on the computer screen both the MR and CT image sets and aligns the MR image set with the spatial coordinates of the CT image set. See Figure 16.

Figure 16 Example of Merged Image Sets

Remember that the correlation process consists of selecting, storing, and computer matching at least four corresponding landmarks on each image set. You can select any points that can be seen in both

CAUTION: It is imperative that you carefully and accurately select the landmarks before performing a Point Merge. Any adjustments made to the transformation after the Point Merge worsens the mean and maximum registration error of the defined landmark, but may improve the overall correlation.


image sets and are not coplanar or colinear. To maximize the accuracy of the correlation, select points distributed over the volume. The recommended landmarks are both orbits and at least two internal anatomical structures.

Your objective is to precisely match the corresponding points within a mean point marking error of less than 1.6 mm and preferably a mean point marking error of less than 1 mm.

“Point Matching Tools” on page 39 discussed the tools you can use to synchronize the image sets. This section explains the tools you can use to assist you with point matching.

Landmark Selection Modes

The Point Merge program requires you to precisely select and match a minimum of four corresponding landmarks. One set of landmarks may be the very center of the orbit. Another may be a unique point somewhere on the tentorium cerebelli.

Select the landmarks by pointing on the image and then clicking. The landmark coordinates are set to the location at the center of the red cross hairs. There are two toggled mouse modes to help you mark the exact point in both image sets:

Select Pts: This is the default mouse cursor mode.Circle: When selected, a circle appears, to aid in the marking of the center of a spherical object, such as the orbit.

Clicking and dragging within the interior of the circle repositions the circle. Clicking and dragging at the edges of the circle, resizes the circle. Releasing the mouse button sets the landmark coordinates to the location of the center of the circle.

There are four other mouse modes:LineDual CursorRotateTranslate

These modes are useful when measuring, positioning, and refining the landmarks. See “Finer Adjustments” on page 49 for further information.


Selecting a Set of Registration Landmarks

The instructions for selecting landmarks are very simple. Your objective is to precisely select the landmark in both image sets. You must individually select and store each set of landmarks.

To select the landmarks:

1. Select the mouse mode (see “Landmark Selection Modes” on page 44).

2. Select the desired image orientation (see “Image Set Display” on page 39).

3. Place the landmark. Click on the desired location on the image.

4. Adjust the location of the landmark in all three views (axial, coronal, and sagittal).

Once the landmarks are defined in both the reference and working image sets, store the points following the instructions in “Storing a Set of Registration Landmarks” on page 45.

Storing a Set of Registration Landmarks

Once an acceptable set of landmarks is marked within the image sets, the next task is to store the points for use by the Point Merge program. To add a set of landmarks to the Points list:

1. Click Point Match above the reference image.The POINT MATCH panel (Figure 17) opens at the bottom of the window.

1. Click Add at the bottom of the panel.A small dialog box opens.

2. Type a name for the landmark in the dialog box.

3. Click OK.The small dialog box closes. The landmark, bearing the name you entered, appears in the Points list (Figure 17) and the coordinates of the landmark appears in the coordinate text boxes. Also a small, thin, green circle appears on the images to mark the location of the most recently added point.


Figure 17 Point Match Tools

After adding a landmark, it may be displayed anytime by selecting and highlighting the landmark name in the Points list and clicking Go To Selected Pts.

Reentering a Landmark

To reenter a landmark:

1. Select the point in the Points list.

2. Click Go To Selected Pts.

3. Adjust the landmark’s location in all orientations.

4. Click Add.

Point Merge Process

When all the landmarks have been added (at least four points), click Point Merge (Figure 17).

If the points (landmarks) match within the established parameters, an acceptance message displays along with the current mean error. In addition, a shift in the working image set occurs (Figure 18). The acceptable parameters are referred to as the mean and maximum registration errors:

Largest acceptable mean registration error is less than 1.6 mm.Largest acceptable maximum registration error is less than 2.8 mm.

Note: Once the landmarks are merged (see “Point Merge Process” on page 46), you can no longer add points.


Figure 18 Example of Working Image Set “Shift”

Point Merge Error Messages

An error message appears only if the point merge is unsuccessful. One of a set of error messages may appear. See Table 4.

Table 4 Point Merge Error Messages

Error Message Recommended Recovery

Correlation not within mean tolerance of 1.6; greatest error at landmark xxxxx

The landmark identified in this message is the worst point in the match and needs to be reentered. See “Reentering a Landmark” on page 46.


Deleting a Landmark

Inaccurately entered and stored landmarks contribute to a higher than acceptable point merge registration errors. The usual procedure is to delete the point from the Points list and then select and add again. To delete a point:

1. Select the point in the Points list.

2. Click Delete (Figure 17).

The landmarks cannot be colinear. The point merge process aborts if the landmarks are found to be colinear. You may need to delete one or more of the landmarks before selecting and adding new landmarks. See “Deleting a Landmark” on page 48.

The landmarks are coplanar; continue with match?

In most instances, this point merge should be aborted. Some of the selected landmarks are in the same plane as another set and thus should be deleted and reentered.

Table 4 Point Merge Error Messages (continued)

Error Message Recommended Recovery


Finer Adjustments

A successful Point Merge operation transforms the working image set. This section discusses five tools you can use to adjust the transformed working image set and accordingly, refine the registration. These tools include:

TranslateRotateScaleUndo and RedoXForm

These tools are located above the reference image set and working image set panes. Each time you select a tool, a tool‐specific palette appears below the image set panes.

Translate Tool

When you select the Translate tool, you can use it to reposition the working image set. The image set can be translated left/right or up/down. The sections below describe three different translate techniques:

SemiautomaticManualMouse‐controlled

Semiautomatic

To semiautomatically translate the working image set by translating to match landmarks in both the reference and working image sets:

1. Click Translate.

2. Select a corresponding landmark in both the reference and working image sets.

CAUTION: It is imperative that you carefully and accurately select the landmarks before performing a Point Merge. Any adjustments made to the transformation after the Point Merge worsens the mean and maximum registration error of the defined landmark, but may improve the overall correlation.


3. On the Translate palette, click Constraint.

4. Select the desired translation plane (that is, Horizontal, Vertical, or 3D).

5. Click Show Results.

6. Observe the new position of the working image set.

7. Visually verify and compare the match between the reference and working image sets.

Manual

To manually translate the working image set:

1. Click Translate.

2. On the Translate palette, click Move Along Axis.

3. Select the desired translation direction (that is, AP, LR, or SI).

4. Type a value in millimeters to translate along the selected axis.

5. Click either Step Up or Step Down to achieve the translation.



Mouse-Controlled

To use the mouse mode to translate the working image set:

1. On the Mouse Mode palette, click Translate.

2. Left‐click and drag the image to a new location.




Rotate Tool

When you select the Rotate tool, you can use it to reposition the working image set. The sections below describe three different rotation techniques:

SemiautomaticManualMouse‐controlled

Semiautomatic

To semiautomatically rotate the working image set:

1. Click Rotate.

2. On the Rotate palette, select the direction of the rotation (that is, clockwise, counterclockwise, or auto).

3. Click a point on the working image set to specify the center of the rotation.The red cross hairs mark this point as the center of the rotation.

4. Click Line from the Mouse Mode palette above the working image set pane.

5. Use the left mouse button to draw a line on both the reference and working image sets.

6. Next to Angle, click Match Lines.



9. Visually verify and compare the match between the reference image set and working image sets.

Manual

To manually rotate the working image set:

1. Click Rotate.

2. On the Rotate palette, select the direction of the rotation (that is, clockwise, counterclockwise, or auto).


3. Click a point on the working image set to specify the center of the rotation.The red cross hairs mark this point as the center of the rotation.

4. Next to Angle, click Other.

5. Type the angle in degrees to rotate in the selected direction.




Mouse-Controlled

To use the mouse mode to rotate the working image set:

1. Click Rotate on the Mouse Mode palette.

2. Left‐click and drag the image to a new location rotated about the red cross hairs.



Scale Tool

When you select the Scale tool, you can use it to scale the working image set. The sections below describe two different scale techniques:

SemiautomaticManual

For either method, you must indicate the type and the direction of the scaling.

Relative scaling sums the user‐specified scale value with the current scaling parameters to achieve a total scale value. Absolute scaling assigns the user‐specified scale value as the total scale value.


Semiautomatic

To semiautomatically scale the working image set:

1. Click Scale.

2. On the Scale palette, select the scale type.

3. On the Mouse Mode palette, click Line.

4. Use the left mouse button to draw a line on both the reference and working image sets.

5. Click Constraint.

6. Select the plane to be scaled.

7. Click Match Lines in the Value Box.

8. Click Show Result.

9. Observe the new scale of the working image set.

Manual

To manually scale the working image set:

1. Click Scale.

2. On the Scale palette, select the scale type.

3. Click Constraint.

4. Select the plane to be scaled.

5. Click Other in the Value Box.

6. Type the value to scale the image.

7. Click Show Result.

8. Observe the new scale of the working image set.

Undo/Redo

The ImMerge system software maintains a complete list of the actions performed by the user, including the Point Merge. Any and all user adjustments, including Point Merge, may be undone in the reverse sequential order in which each function was performed.


To undo an action, click Undo (located above the reference image set pane) once for each action you want to remove. Only the most recent undo action may be repeated by clicking Redo.

XForm

The current transformation parameters may be viewed at any time following Point Merge. To display the current transformation parameters, click XForm (located above the reference image set pane).

A pop‐up window appears. The Total Translation, Total Scaling and Rotation values currently applied to the working image set appear.

To display the mathematical transformation matrix, click Matrix.

Evaluating the Point Merge

Now that the image sets have been correlated, you have access to a variety of tools which enable you to qualitatively and quantitatively compare the correlated image sets.

Visual Evaluation

The ImMerge system enables you to combine the correlated image sets by several methods in order to perform a visual comparison of the merge results. These viewing modes are accessible in one of two ways:

Clicking Mode on the working image set display panelClicking View, then Verify Window

In all of the modes your objective is to visually verify that the anatomy of the reference image set corresponds to the anatomy of the working image set. As an example, using the slider bars, move the images to verify that the ventricles in the reference image set should “fit” with the ventricles from the working image set.

Note: When choosing to undo the Point Merge, a message appears asking you to confirm your choice.


Split Mode

When you select Split mode, the image displays are divided between the reference image set, which is always to the left and bottom, and the working image set, which is always to the right and top. The portion of each image set that appears is controlled by the slider bars. See Figure 19.

Figure 19 Split Mode

Blend Mode

When you select Blend mode, the image display combines the pixel intensities of both image sets. When the slider bar is at the far right, the view displays full reference image set pixel intensity. Conversely, when the slider bar is at the far left, the view displays the full working image set pixel intensity.


Window Mode

When you select Window mode, the image display provides a subsection, or window, of the reference image set superimposed onto the working image set. You control the size of the window by moving the horizontal and vertical scroll bars located below and to the right of the image display. You control the position of the window by the location of the mouse while you click the middle mouse button and drag the cursor within the image display.

Interlace Mode

When you select Interlace mode, the image display is an alternating band of the reference image set and the working image set. The thickness of the bands is controlled by the vertical scroll bars.

Blink Mode

When you select Blink mode, the image display continuously switches from the reference image set to the working image set at a rate of once per second when in “SlowBlink” mode and a rate of twice per second when in “FastBlink” mode. The mouse cursor must be in the image display for the blinking to begin. When the cursor is removed from the image display, the blinking stops.

Quantitative Evaluation

The Point Merge process calculates a mean and maximum registration error between the landmarks that were identified. If the landmarks match within the established parameters, an acceptance message displays along with the current mean error. See “Point Merge Process” on page 46.

You may also request this information at any time following an acceptable Point Merge. To view the mean and maximum point merge error information, click View Errors. See Figure 20.


Figure 20 Registration Errors Window

Saving the Correlation Results

To save the correlation results of the session:

1. Choose View > Verify Window.The Match Verification window opens.

2. Visually verify the results of the point merge. See “Visual Evaluation” on page 54.

3. Click the box next to Correlation Verified.The box turns yellow to indicate the acceptance of the results of the point merge.

4. Click Save or Save and Exit.A window displaying the message “Saving correlation” appears. Do nothing until the save process is complete. The directory and filename of the saved transformed working image set appear. The transformed working image set is saved to the patient directory associated with the reference image set.

Note: To accept the results of the Point Merge, you must click the box next to Correlation Verified before saving and/or exiting the program.


Saved File Names

In addition to the transformed working image set (txMR[patient name].img), two other files are automatically saved to the patient’s directory:

autosave.reg—the accepted point mergeImMerge.log_[datetag]—the session log file

AutoFusion

The AutoFusion feature of ImMerge 5.1 provides an automatic alternative to the preexisting manual point match. Once the reference and working image sets load, you can start AutoFusion by clicking a single button (Figure 21).

Figure 21 AutoFusion Button


Once started, ImMerge displays a progress indicator until automatic fusion is complete (Figure 22). You can examine and approve the results using the existing verification workflow.

Figure 22 AutoFusion Complete Message

After AutoFusion finishes, you must open the Verify window and inspect each slice in all three views (AP, LR and SI) to verify that AutoFusion worked correctly.

ImMerge 5.1 features a more flexible dialog box for loading working image sets. In the case where ImMerge cannot find an exact match for the working set, the new Load Working dialog box (Figure 23) opens. This dialog box contains the most likely working set matches to the reference set: that is, those matches whose name or patient ID, but not both, match the reference. If ImMerge cannot identify likely working sets, all working sets are listed. You can sort the entries in the Load Working dialog box by patient name, modality, exam date, patient ID, or the number of slices.

When you click Translate, ImMerge 5.1 opens a tool (Figure 24) for the fine adjustment of image translation.

First decide the dimension in which you want to translate the images: AP, LR, or SI. Then type the size of the translation increment in millimeters in the text box. The up and down buttons apply the translation, one incremental step at a time.

ImMerge 5.1 supports only the following CT and MR resolutions:512x512 CT image sets512x512 or 256x256 MR image sets

The minimum number of slices in the CT and MR slice stacks that is supported by the current version is three.


Figure 23 Load Working Dialog Box

Figure 24 Fine Adjust Tool

The current version of the AutoFusion algorithm is optimized to work on the CT scans obtained with the standard FOV of 25–40 cm. If AutoFusion is unable to find a correct match, you may need to use PointMatch on the high FOV (45–50 cm) CT scans.


Chapter 4 Cone Planning

The Cone Planning module provides all the necessary tools to perform treatment planning (using cylindrical collimators) on the stereotactic CT and MR data sets. Cone Planning includes:

Defining one or more isocenters.Using these isocenters as the focus for multiple arcs with adjustable and displayed parameters.Viewing the individual and combined contribution of arcs to the dose distribution.Viewing the maximum dose and dose distributions.Displaying and evaluating the dose distributions in axial, coronal, sagittal, oblique planes, or 3D models.Calculating dose volume and dose arc histograms and dose cross plots.Prescribing appropriate doses.

Planning is done on CT and MR data sets, while preplanning is done on the MR volume only. Running Cone Planning on the MR data set automatically starts Preplanning mode. Running Cone Planning on the CT data set automatically starts Planning mode.

Note: This is a software instruction manual. Refer to Linac Radiosurgery, A Practical Guide (Friedman W. A., Buatti J. M., Bova F. J., etal. Linac Radiosurgery A Practical Guide. New York: Springer‐Verlag New York Inc., 1997) for treatment planning strategies and clinical guidance.

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Preplanning

FastPlan has introduced a new Preplanning capability that allows a drastic shortening of the time that the patient needs to wear an SRS head frame on the day of the treatment. Preplanning can be done on an MR data set, days ahead of the SRS or SRT. On the day of the treatment, following the CT scan, CT Localization, and MRI‐CT fusion, preplans are automatically mapped onto the CT volume, requiring minimal adjustment and final dose review and resulting in a much shorter planning process.

To initiate Preplanning mode, select an MR data set and start Cone Planning (see “Starting Cone Planning” on page 64). The first time you launch Cone Planning on each MR data set, the Previewer window (Figure 25) opens, requiring you to review the MR slices before MR volume creation. Carefully review all the slices and click Dataset Verified. The MR volume is created and loaded into the Cone Planning module. You can then mark isocenters, load arcs, adjust arc parameters, draw contours, and perform the rest of the planning operations on this MR data set. The only functionality that is disabled in Preplanning mode is the ability to print the plan details. This is done to prevent erroneous treatment in nonstereotactic coordinates based on the MR volume. You should save the preplan, which you can reload later for review. You can export the preplan to Eclipse for plan comparison with MLC but no Monitor Units will be exported.

On the day of the treatment, following acquisition of the CT scan, CT Localization, and MRI‐CT fusion, the preplan is automatically transformed from MR onto the CT volume. This is done when the MRI‐CT fusion results are being saved and you are prompted to confirm this transformation. All the plan parameters and any present contours are converted into the stereotactic coordinates defined by the localized CT volume. The transformed plan is then saved under the same name as the preplan but it is now associated with the CT data set. When Cone Planning is then evoked on this CT data set, the converted plan can be loaded, reviewed, and adjusted if necessary. When the converted plan is loaded, a message appears: This plan has been originally done on MR data set and subsequently transformed to CT space.


Figure 25 Previewer Window

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Starting Cone Planning

To run Cone Planning:

1. In the Stereotactic Radiosurgery Treatment Planning window, select the patient from the available patient list.

2. Under Treatment Planning, click Cone.The Cone Planning (Dosimetry) window (Figure 26) opens.Depending on the type of modality (CT or MR) and stereotactic type (frame or frameless), one or more messages may appear.

3. Click OK to acknowledge or approve each message.

Figure 26 Cone Planning Window

When Cone Planning is run on a CT data set, this application automatically searches for a matching fused MR data set. If no matching MR data set is found, a message appears: No MR data--continuing with CT only. If one fused MR data set is


found, it is automatically loaded. If more than one fused data set is found, a dialog box (Figure 27) opens with information on each of the fused MR data sets and you can select which data set you want.

Figure 27 Select Fused MR Data Set to Load Dialog Box

Cone Planning Window Layout

The Cone Planning window (Figure 26) has four image‐set display panes on the left and a tools palette on the right. All the tasks associated with treatment planning are accessible from this window.

This window allows you to easily access the tools you need to prepare the treatment plan.

Three of the image‐set panes display the axial, sagittal, and coronal views, generally referred to as the orthogonal views. The fourth pane (in the lower right) displays an Auxiliary view. At any one time a generated 3D, Plan, Prescription, or Optional view can appear in this pane.

To the right of each of the orthogonal view panes is a scroll bar. At the top of each scroll bar (and in a vertical toolbar to the right of the Auxiliary display pane) is a “home” button (with a house icon). Clicking this button recenters the view.

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At the bottom of each of the scroll bars (and in the vertical toolbar to the right of the Auxiliary pane, depending on what is displayed), there is a “slide” button (with a camera icon). Clicking this button automatically creates a slide of the image and displays the “captured slide” in the Auxiliary display pane. A prompt appears for you to type a file name. If you fail to type a name, the program assigns one. The program‐assigned name ties the view to the image: for example, “Axial” is a capture of the Axial orthogonal view. To show the last slide acquired, move the cursor over the Auxiliary pane and right‐click. In the resulting PaneOptions menu, click Slide View. You can view the complete set of slides in the Prescription and Slides tab.

Menu Descriptions

The treatment planning tasks are grouped functionally and are summarized in Table 5. The eight menu tabs associated with these tasks are in the lower right corner of the window. The next sections describe the tasks associated with each phase of the treatment planning process in further detail.

Table 5 Cone Planning Tabs

Tab Description

Planning Allows for the creation and modification of arcs and isocenters.

AutoPilot Automatically suggests the optimal location of isocenters and the selection of arcs for a defined structure.

Settings Allows for the adjustment of the image set and isodose displays.

Optional Views Allows for the creation of a 3D model and 3point and beam’s eye views.

Prescription and Slides

Allows for dosimetry (plan) verification, hard copy printouts of the plan, and viewing of slide files.


The File (Table 6), Layout (Table 7), and Options (Table 8) menus, found on the menu bar, provide you with display and file maintenance choices:

Histograms Allows for the creation and view of dose volume and dose arc histograms.

Dose Cross Plots Allows for the creation and view of dose cross plots.

Export Allows for the export of DICOM data (for example, to optical positioning systems or to Eclipse).

Table 5 Cone Planning Tabs

Tab Description

Table 6 File Menu Functions

Function Action

Load Plan Loads a previously saved plan.

Save Plan Saves the current plan.

Print Screen Tool Opens a UNIX screen‐capture program.

Quit Ends the treatment planning session.

Note: When saving a plan file, always specify a file name. If you do not provide one, the file is named after the folder containing it.

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Table 7 Layout Menu Functions

Function Action

4 View Displays the default view of the three orthogonal views (axial, coronal, and sagittal) and the auxiliary view.

Axial View Only Displays the full screen, single axial view.

Sagittal View Only Displays the full screen, single sagittal view.

Coronal View Only Displays the full screen, single coronal view.

Auxiliary View Only Displays the full screen, single auxiliary view.

Table 8 Options Menu Functions

Function Action

Isodose Curves Displays the isodose curves on the three orthogonal views.

Intersection Dose Displays the dose at the intersection of the cross hairs.

Maximum Dose Displays the maximum dose as a purple cross hair.

Isocenter Marker Displays the isocenter as a yellow cross hair.

Contours Displays the outline of the intersecting 3D model.

View Center Displays the red cross hairs through the center of the image.

Text Displays the text associated with the coordinates, dose, and orientation.


Planning

The Planning tab includes the options for adding, deleting, and changing arcs and isocenters in order to shape the volumetric dose.

Selecting any one of the options in the Planning tab automatically displays the planning tools. The Planning Tools palette is divided into three sections:

Top section contains the arc tools.Middle section contains the isocenter tools.Bottom section contains the Digitally Reconstructed Radiographs (DRR) or scout view.

The tasks that lead to the creation of the plan are:Finding the region of interest (ROI).Selecting the isocenters and controlling their positions in stereotactic space.Adding arcs to determine the optimal treatment plan

The information in the sections that follow assumes that no previous plans have been created or saved. If this assumption is not true, you may load a previously saved treatment plan by choosing File > Load Plan.

Start/Stop Angles Turns on or off the display of the arc stop/start angles in the plan and Prescription views.

Table 8 Options Menu Functions (continued)

Function Action

Note: If the image display panes appear dark on startup, adjust the settings in the Settings tab. See “Image Settings” on page 83.

Note: When both CT and MRI volumes are present, the three orthogonal views show MRI slices by default. For information on how to switch between CT and MRI volumes or blend both, see “Settings Tab” on page 83.

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Finding the Region of Interest

The first task associated with the creation of an isocenter is to identify the anatomical region of interest of the tumor. Use the scroll bars to the right of the image panes to scroll through the pathology until the point of interest is in view. Then, place the cursor on the point and click, or use the resection handles in the image borders.

High levels of image magnification are helpful in selecting and refining the point of interest. Placing the cursor in a view pane and right‐clicking provides you with an image magnification menu. To change the magnification, place the cursor in the view pane, right‐click, drag to the desired magnification, and release.

Creating and Placing Isocenters

The Isocenter tools allow you to select the point(s) where the linac radiation arcs converge and to control their positions in stereotactic space.

To create an isocenter, the coordinate data in the text boxes must transfer to the controlled Isocenters list (Figure 28). There are multiple ways in which to obtain the coordinate data:

Use the IsoDrop tool.Type the coordinates.Select a single orthogonal view.

Figure 28 Placement Tools Panel


Using the IsoDrop Tool

The IsoDrop tool allows you to place an isocenter using the mouse. This is the recommended method to obtain the isocenter coordinates. To use the IsoDrop tool:

1. Click IsoDrop in the placement tools panel (Figure 28).

2. Place the cursor on the target anatomy.All the views automatically update to this position.

3. Adjust the IsoDrop targeting circle to the desired location in all three views.

4. Verify that the coordinates in the text boxes match the coordinates reported in the upper left corner in the orthogonal views.

5. Click the transfer arrow.

6. Click IsoDrop in the placement tools panel to deactivate this tool before choosing another isocenter.

Entering the Coordinates

This method for creating an isocenter is seldom used. However, you may find it useful for refining the coordinates of an isocenter.

To enter the coordinates:

1. Type the coordinates directly into the text boxes.

2. Click the right transfer arrow.

Editing an Isocenter

Highlighting an isocenter in the controlled Isocenter list and clicking the transfer arrow causes a message prompt to appear requesting you to select from one of the following three options:

Overwrite the highlighted isocenter.Create a new isocenter using the coordinates in the text boxes.Cancel this transfer operation.

Note: Using the IsoDrop tool is the recommended way in which to obtain the isocenter coordinates in order to create a new isocenter.

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To edit a single isocenter location:

1. Click IsoDrag<one> in the placement tools panel (Figure 28).

2. Place the cursor over the desired isocenter marker in the image.The cursor changes and the marker turns red.

3. Click and drag the marker to the desired isocenter location. Release the mouse button.

or

1. Highlight the desired isocenter listed in the controlled Isocenter list (Figure 28).The coordinates of this isocenter appear in the text boxes on the left.

2. Type the new coordinates.

3. Click the data transfer arrow on the Isocenter panel.The edited coordinates transfer to the controlled Isocenter list.

Using the IsoDrag Tool

The IsoDrag tool allows you to move the isodose curves in one of the three orthogonal views. This action moves the dose distribution causing the isocenters to shift yet still preserves the relative spacing among all isocenters. Even though the movement occurs in one view, all three views update and display the new dose location. The IsoDrag tool is helpful after the isocenter(s) and arc(s) have been created and you want to make minor modifications to the placement of the entire dose.

To use the IsoDrag tool:

1. Click IsoDrag<all> in the placement tools panel (Figure 28).

2. Place the cursor on the dose distribution and drag it to its new location.

Note: IsoDrag is an effective tool to use when you need to make minor modifications to the dose distribution.


Deleting Isocenters

The process of deleting an isocenter also removes all the associated arcs.

To delete a single isocenter:

1. Highlight the desired isocenter listed in the Isocenter list (Figure 28).

2. Confirm the isocenter by observing its position in the orthogonal views.

3. Click Isocenters, then drag to Delete.

To delete all isocenters:

1. Click Isocenters, then drag to Delete All.

2. Confirm or reverse this action by answering the confirmation question.

Isocenter Spacing Tool

When the dose distribution plan includes at least two isocenters and you want to alter the space separating the isocenters, use the Isocenter Spacing tool.

To use the Isocenter Spacing tool:

1. In the Isocenter Spacing and Weighting panel (Figure 29), click Isocenter Spacing.

2. Under Move, click the isocenter to move and under Relative To, click the isocenter that it is to move relative to.The current and suggested new isocenter spacing are displayed.

3. If a different value is to be used in calculating the spacing, type the value in the New text box.

4. To move the isocenter, click Apply.

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Figure 29 Isocenter Spacing Tool

Isocenter Weighting Tool

For complex, multi‐isocenter plans it is often difficult to achieve acceptable conformality. This is because the interaction of the arcs assigned to neighboring isocenters results in an uneven weighting among isocenters (Figure 30).

The Isocenter Weighting tool is used to assign a desired isocenter dose to an individual isocenter’s set of arcs or to all of the isocenter’s set of arcs.

Figure 30 Isocenters with Unequal Weights, Arcs with Equal Weights

The four isocenters are arrayed in a line and assigned five equally weighted arcs each. The medial isocenters have greater weight than the lateral isocenters, resulting in an uneven dose distribution.


Using the FastPlan system Isocenter Weighting tool, an equal weight is assigned to all isocenters as displayed in Figure 31. This results in a more uniform dose distribution.

Figure 31 After Using Isocenter Weighting Tool

The Isocenter Weighting tool (Figure 32) allows you to specify a desired weight and then “weight” the arcs of one isocenter or the arcs of all isocenters to reflect this dose. The Isocenter Weighting tool is most effective when used in conjunction with the isocenter spacing tool. Clicking Isocenter Weighting (Figure 32) displays a list of the current isocenters in the plan. The list identifies the isocenter number, the total number of isocenter arcs, and the dose value of the isocenter.

Figure 32 Isocenter Weighting Tool

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To weight the arcs of just one isocenter:

1. Highlight the isocenter.

2. Type a desired weight.

3. Click Apply.

To weight the arcs of all the isocenters:

1. Type a desired weight.

2. Click Make All Equal.

There are both Desired Weight and Actual Weight parameters. You are allowed to enter only the Desired Weight. If you do not select the Rebalance Wts check box, then the Desired Weight value becomes the Actual Weight value, and the Arc or Isocenter Weight value would be expected to be the same as requested. If you select the Rebalance Wts check box, then the weights of all the arcs in all the isocenters are recalculated based on the desired values and the other physical isocenter parameters and the resulting Actual Weights are posted. These Actual Weight values are close to the requested Desired Weight values but are not identical. After rebalancing isocenter weights, a message may appear stating that an isocenter has been assigned zero weight. This implies that the requested dose can be achieved without the contribution from this isocenter.

Isocenter Dose Contribution Tool

The Isocenter Dose Contribution tool (Figure 33) displays the dose contribution of each isocenter to the Max Dose point and that point’s location. In addition, the dose contribution to the axial, sagittal, and coronal centers, as well as each isocenter, can also be displayed.

To use the Isocenter Dose Contribution tool:

1. In the Placement Tools panel (Figure 28), click Isocenters, then click Isocenter Dose Contribution.

2. Select the point to be displayed in the Isocenter Dose Contribution tool (Figure 33).


Figure 33 Isocenter Dose Contribution Tool

Treatment Arcs

The treatment arcs panel (Figure 34) provides you with treatment planning tools to manipulate the planning parameters in order to determine the optional treatment plan.

Figure 34 Treatment Arcs Panel

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The most commonly used tools in radiosurgery treatment planning are:

Arc weighting (arc elimination and change in collimator size)Altering of the arc stop and start anglesUse of multiple isocenters

Refer to the University of Florida Treatment Planning Algorithm help window available from the Help menu.

The FastPlan system includes the parameters listed in Table 9, which you can adjust to optimize the treatment plan.

Table 9 Treatment Arc Parameters

Parameter Definition

Isocenter This number represents an isocenter listed in the controlled isocenter list (Figure 28). To change, type any number associated with an isocenter.

Weight This number represents an arc weight. To change, type a new weight.

Collimator This value represents the size of the collimator. To change, click the button and drag to the desired collimator size.

Table This value represents the treatment couch angle. To change, move the slider bar until the desired angle appears. Confirm the angle by observing the dotted line in the AP scout which indicates the arc position through the patient’s head.

Start This value represents the gantry start angle. To change, move the slider bar until the desired gantry start angle appears. Confirm the angle by observing the dotted line in the auxiliary image which indicates the collimator width and arc start angle.


To change (edit) a specific arc or controlled set of consecutive arcs:

1. Select the arc to edit. To select consecutive arcs, drag the cursor over the arcs. To select nonconsecutive arcs, hold down the Ctrl key while selecting the desired arcs.

2. Specify the new parameter(s). Use the slider(s) or type in the dialog box(es) one or more of the desired parameters listed in Table 9. Observe the effect of these changes in the visual representation in the Auxiliary and/or scout image.

3. Click Apply and drag to the desired parameter(s) to edit.The parameter(s) for this arc or set of arcs are altered and the treatment plan is updated.

Functions

The functions in the Arcs menu allow you to add, change, or delete an arc from an arc set. Then, you can save this modified arc set template with a new name. Furthermore, you can select the functions which will cause the arc rays, stop and start angles, and isodose curves to appear in the views.

The Apply function allows you to associate the modified parameter with a specific arc.

To load an arc set template:

1. Select an isocenter from the controlled isocenter list (Figure 28).

2. On the treatment arcs panel, click Arcs, then click Load Set.

3. Select one of the standard arc sets (Figure 35).

Stop This value represents the gantry stop angle. To change, move the slider bar until the desired gantry stop angle appears. Confirm the angle by observing the dotted line in the auxiliary image which indicates the collimator width and arcs stop angle.

Table 9 Treatment Arc Parameters (continued)

Parameter Definition

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Figure 35 Select an Arc Set Dialog Box

4. Select the relative contribution of the new set of arcs.You can choose to fix the weight at the isocenter to a certain value (default choice) or set the dose at the isocenter as a percent of the maximum dose (Dmax). The latter option is intended to be used when a single arc is being added to conform the isodose to a desired shape. If the latter option is used for a multiarc set, a warning message appears. The Rebalance Wts check box allows you to control whether the weights of all the arcs at all the isocenters should be recalculated, taking into account the desired weight of the new arc set. Rebalancing is on by default when the fixed weight at the isocenter has been selected.


5. Click OK.The adding arcs action updates the arcs that appear in the Treatment Arcs panel and also displays the projection of the arcs in the AP scout view and the auxiliary plan view.

To add custom arcs:

1. Specify the new parameters. Use the slider(s) or type in the dialog box(es) one or more of the desired parameters listed in Table 9.

2. From the Arcs menu, click Add.An arc is added to the treatment plan. The new arc along with its parameters appear in the treatment arc panel. Since this is now the active arc, it is highlighted. In addition, the image in the auxiliary view updates to the table angle defined by this arc.

To delete an individual arc:

1. Select the arc to delete.

2. Observe the selected arc’s position in the scout view.

3. Click Arcs, then drag to Delete.The arc is removed from the treatment arcs panel. However, it is not removed from the arc set template unless the current arc set is saved as a new template.

To delete all arcs:

1. On the treatment arcs panel, click Arcs and then drag to Delete All.

2. Confirm or reverse this action by answering the confirming message.

To save the current arc set as a template:

1. Click Arcs.

2. Drag to Save Set.

Note: During the FastPlan system installation, standard arc set templates are created and saved on the system. You can select these arc sets in the Load Arc Set dialog box, in the Files list (Figure 35).

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To display arc rays, stop and start angles, or isodose curves:

1. Click Arcs.

2. Drag to the desired Show option.When selected, Stop angle appears in red and Start angle appears in green in the auxiliary view.

Evaluate the Plan

The FastPlan system offers you various options for viewing, inspecting, and evaluating the planned dose distribution to ensure that the:

Plan conforms to the target as closely as possible.Critical brain structures near the target receive the lowest possible dose of radiation.

These options include translating through the volume using the programs listed in the Settings menu (see “Settings Tab” on page 83), viewing the images in arbitrary oblique planes and as 3D models (see “Optional Views” on page 91), and viewing the dose volume histograms (see “Histograms” on page 95).

Translate through the Volume

The first evaluation technique is to translate through the volume based on a selected slice increment. Using the translate scroll bars to the right of the orthogonal views, you can examine the entire image set in three planes.

To step through the volume:

1. Click the Settings tab.

2. Click Image Settings.

3. Select the translation step size.

4. Move the translate scroll bars to the right of the orthogonal views.


Settings Tab

The Settings tab contains the options for adjusting the image displays. These include:

Image SettingsIsodose SettingsDose Engine Settings

Image Settings

Clean, clear, and sharp image displays make it easier to define the region of interests and ultimately create and evaluate the treatment plan. The Image Settings tool (Figure 36) allows you to enhance the image display by:

Selecting the preferred image modality (CT, MR, or CT/MR Blend).Adjusting the contrast parameters.Choosing the pixel color intensity.

To access the Image Settings window:

1. Click the Settings tab.

2. Click Image Settings.

Image Set: CT, MR, Blend

If both CT and MR image sets were obtained for the patient and were processed through the ImMerge program (see Chapter 4), you may toggle between image sets by clicking either CT or MR or use the slider bar to blend both image sets. See Figure 36.

Use the slider to blend the images. When the slider bar is at the far left, the view displays the CT image set. Conversely, when the slider bar is at the far right, the view displays the MR image set.

Mean and Window Adjustments

You are able to enhance the image display by adjusting the contrast parameters:

Adjusting the Mean slider changes the overall image brightness.Adjusting the Window slider changes the image contrast.

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Figure 36 Image Settings Panel

Color Map

Another technique for enhancing the image display is to vary the pixel color intensity. There are three scales:

Gray Scale [default]: Displays the pixel intensities in shades of gray ranging from black to white.Heat Scale: Displays the pixel intensities ranging from red to yellow.Rainbow Scale: Displays the pixel intensities in different colors ranging from black to white.


Isodose Settings

The Isodose [Display] Settings tool (Figure 37) allows you to visualize the prescribed dose distribution throughout the volume.

Isodose Styles

There are three isodose styles:Line: Displays an isodose line.Wash: Displays a translucent color wash isodose overlay on the two dimensional images.Solid: Displays the dose distribution as a solid wash.

Isodose Colors

There are three isodose color styles:Color: Displays the isodoses in user‐selected colors.Mono: Displays the isodoses as all white.Gray: Displays the isodoses in shades of gray.

Click the box(es) to the left of the desired color(s) to select the isodose colors. Type the isodose percentages levels in the dialog box, or use the slider bar and drag to the desired isodose percentage.

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Figure 37 Isodose Display Settings Tool


Dose Engine Settings

The Dose Engine Settings tool (Figure 38) allows you to select the default settings for isodose calculation. These settings are listed in Table 10.

Figure 38 Dose Engine Settings Tool

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Table 10 Dose Engine Settings

Field Description

Normalize Method Toggles between two normalization methods:

To Maximum—Normalize to the maximum dose in the three dimensional dose matrix.To Isocenter—Normalize to the isocenter. Type an isocenter number in the dialog box.

Max Search Method Determines the method by which the system searches for the point of maximum dose. Select among:

Gradient—Allows the system to search for the maximum dose point utilizing a gradient based method which significantly improves computation time while not compromising calculation accuracy.Fast Gradient—Allows the system to search for the maximum dose point using a fast gradient method.Exhaustive—Forces the algorithm to examine every point in a dose matrix at a resolution of 1 mm within an axial plane and 2 mm axial slice thickness to determine the point of maximum dose.


Arc Resolution The FastPlan system’s calculation algorithm approximates arcs as multiple static beams. The Arc Resolution option lets you choose how closely spaced these static beams should be. The default setting is 10 degrees, which speeds calculation and does not significantly affect calculation accuracy. Select among:

10 Deg5 Deg 1 Deg

Isodose Resolution Determines the grid upon which the dose is calculated. Select among:

Full—Calculates the isodose lines on a fine matrix around the target, and uses a coarse grid (5 mm) outside of the region of interest.Coarse—Allows the computation to proceed entirely on the coarse matrix, which has a 5 mm resolution.

While the coarse grid increases calculation speed, it may be inappropriate for regions containing steep dose gradients.

Fine Matrix Resolution

Defines the fine matrix resolution. The default value is 1 mm. However, the selections are:

1 mm2 mm3 mm5 mm

Table 10 Dose Engine Settings (continued)

Field Description

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Show Coarse Mtx. Toggle between On and Off to display or not display, respectively, the bounding boxes for the coarse dose calculation matrices.

Show Fine Mtx. Toggle between On and Off in order to display or not display, respectively, the bounding boxes for the fine dose calculation matrices.

Contour Threshold Determines the external head contour. Type a value in the dialog box.

Save Settings Click to retain these values.

Table 10 Dose Engine Settings (continued)

Field Description


Optional Views

The second plan evaluation technique is to choose arbitrary oblique planes and 3D models to view the images. These options are available to you under the Optional Views tab. The oblique views are referred to as the “3‐Point View” and the “Beam’s Eye View.” To access these views, click the Optional Views tab (Figure 39), then select the desired view button.

Figure 39 Optional Views Tab

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3-Point View

The 3‐Point View program allows you to select three points, generate the plane defined by these three points, and display the reformatted CT with the dose distribution superimposed.

To generate the 3‐Point View:

1. Click 3‐Point.

2. Click each point of interest and then click one of the following options:

Import CircleAxial CenterSagittal CenterCoronal CenterIsocenter 1Head Contour CenterTarget 1 Center

orYou may manually type the coordinates for each point of interest.

3. Once you have chosen all three points, click Generate.The CT slice is reformatted with the superimposed dose distribution and appears in the auxiliary pane.

Beam’s Eye View

The Beam’s Eye View program allows you to examine the reformatted CT slice as viewed along the axis of the radiation beam from the source of the beam.

The Beam’s Eye view of the reformatted CT appears based on selected parameters.


To generate the Beam’s Eye view:

1. Click Beam’s Eye.

2. Determine the point of interest by clicking Import and then clicking one of the following options


3. Type the coordinates for the point of interest in the AX, LAT, and AP text boxes.

4. Type the values for the table and gantry angles.

5. Select the collimator size.

6. Click Generate.

7. Using the scroll bar, step through the reformatted CT slices either toward the patient or toward the gantry.The isodose curves are not visible while you are moving the scroll bar; however, there is a superimposed circle to indicate the collimator diameter of the associated beam.

3D View

The FastPlan system automatically generates an external head contour model the first time you select the 3D View. You can optionally build multiple 3D renderings of varying transparencies of the skin, skull, tumor, and isodose shells following the instructions found in Appendix B. These 3D model displays allow the clinicians to visualize the anatomy, isocenters, and the dose distribution.

To access the 3D model:

1. Click Optional Views.

2. Click 3D View.

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Lightbox View

The Lightbox View program allows you to generate a virtual lightbox display of either 4, 6, 9, 12, or 16 reformatted CT image slices with the superimposed dose distribution. The Lightbox view is based on user‐selectable parameters, specifically, the number of images, image orientation, slice spacing, and image center.

To generate the Lightbox view:

1. Select the Lightbox View check box.

2. Determine the view center for the lightbox images. Using the Import button, select from the following:

CircleAxial/Sagittal/Coronal centerIsocenter or head contour centerManually type the coordinates for the view center in the AX, LAT, and AP fields

3. Select the Image Orientation of the lightbox images:AxialSagittalCoronal

4. Select the Slice Spacing for the lightbox images:1 mm2 mm3 mm4 mm5 mm

5. Select the Number of Images to be generated:4691216

6. Click Generate.


Histograms

The third evaluation technique is to view the dose volume histogram (DVH). You can select from one of three methods for calculating the dose volume histogram:

SphericalCubicStructure

To initiate the calculation of a dose volume histogram:

1. Click the Histograms tab.

2. Click Dose Volume Histogram for the desired volume.

Spherical Method

The spherical dose volume histogram method calculates a dose volume histogram for a user‐defined sphere emanating from the isocenter. This method is valid only for single isocenter plans.

To calculate the spherical dose volume histogram:

1. Select the prescribed dose.The default is 1500 cGy.

2. Select the prescription isodose.The default is 80%.

3. Select the dose axis maximum.The default is 1800 cGy.

4. Select the volume axis maximum.

5. Select the spherical radius.The default is 10 cm.

6. Click Generate.Once the calculations are complete, the dose volume histogram appears. Use the sliders and observe the display in the upper right corner of the DVH window.

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The dose volumes may be written to an ASCII file in tabular format by clicking Save at the top of the DVH tab. The range of dose indicated by the software settings [0 ‐‘Dose‐Axis‐Max’], which is equally divided into 240 “dose bins,” determines the resolution of the data.

Cubic Method

The cubic dose volume histogram method calculates a dose volume histogram for a user‐defined cube.

To calculate the cubic dose volume histogram:





5. Specify the cube by providing the cubic bounds.


Structure Method

The structure dose volume histogram method calculates a dose volume histogram for a structure of interest that has been outlined on multiple planes, such as a 3D model.

To calculate the structure dose volume histogram:






5. Select the name of the structure file from the list.


Dose Arc Histogram

The Dose Arc histogram shows the percentage of the dose that each arc contributes to the total volume. As with the Dose Volume histogram, a Dose Arc histogram can be generated for cubic and spherical volumes as well as for built structures.

The Dose Arc histogram shows a scale that you can view to determine the percentage of each arc, or you can highlight an arc and the arc number and the percentage of dose to volume appears in the upper right corner.

The Dose Arc histogram is a tool that can be used in conjunction with arc weighting. You can view the percentage of dose to volume that an arc contributes and weight this arc differently in order to change the dose distribution.

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Dose Cross Plots

The Dose Cross Plot options allow you to generate orthogonal dose cross plots through a point of interest.

To initiate the Dose Cross Plot output, click the Dose Cross Plot tab. The Dose Cross Plot tool (Figure 40) opens.

Figure 40 Dose Cross Plot Tool


To use the Dose Cross Plot option:

1. Click Import.

2. Determine the point of interest by clicking one of the following options:


orYou may type the radii of the cross plots into the Radius (mm) text box.

3. Click Generate.Three orthogonal cross plots appear.

4. Use the mouse to move a slider across the plots.The distance from the origin (D) appears in millimeters along with the percentage dose in the upper right corner of each cross plot.

Prescription and Slides

The Prescription functions allow you to set the prescribed dose, view the slide rack, preview the plan, and output the plan to a printer.

To initiate the Prescription output, click the Prescription tab. The prescription output tool (Figure 41) opens.

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Figure 41 Prescription Output Tool

Inspecting the Arcs

The FastPlan system forces you to inspect each arc before allowing printout of the dosimetry forms. Inspecting each arc ray confirms that the contour correctly fits each arc. Therefore, examine each arc ray, and if required, take the appropriate corrective action.

1. Adjust the contour of the arc, if necessary.

2. Click Trace Patient Contour.

3. Press and hold the mouse button to trace the arc’s intersection with the patient surface.

4. Click Accept.The status of the arc changes to Inspected.

5. Click Next.


Confirming the Dose Distribution

1. Examine the dose distribution around the ROI and critical structures.

2. If you are satisfied with the distribution, click Dose distribution reviewed and inspected.This action certifies that you have reviewed the dose distribution and enables you to instruct the program to print the dose distribution plan.

Slides

The Slide Rack panel includes the options to display a slide in the auxiliary view, print a slide, and delete a slide.

Figure 42 Slide Rack View

To view a slide, click on a slide listed in the Slide Rack panel. The slide (Figure 42) appears in the auxiliary pane. If any of the plan parameters have changed, a warning message appears. The message indicates that the slide may or may not be correct.

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To print a slide:

1. Highlight the desired slide in the dialog box.

2. Click Print Slide.The slide is printed.

To delete a slide:

1. Select a slide listed in the Slide Rack panel.

2. Observe the slide in the auxiliary window. When the desired slide appears, click Delete Slide.

Print Options

Next to Print, there are three options:Instructions button: Clicking this button sends the checklist and instruction set to treat the patient to the printer.Plan w/Image button: Clicking this button opens a small dialog box (Figure 43).

Figure 43 Print Dialog Box

Clicking Directly to printer causes printing to begin.Preview button: Clicking this button opens a window displaying the DOSIMETRY FORM. After you have viewed the plan, you can edit it directly in the window and save it. Click Close to close the window.


Under Slide Rack, there is also a Print Slide button. Clicking this button causes the same result as clicking the Plan w/Image button, described earlier in this section.

If a problem occurs with printing, in the print dialog box, click Preview in web browser. A web browser opens displaying a preview of the print job. You can print the plan from the web browser.

Saving the Plan

If you want to save the plan, choose File > Save Plan in the top menu. Cone Planning also performs an automatic plan save. In the case of an abnormal application exit, you can relaunch Cone Planning and find the latest plan under the name auto.save.plan.

Exporting to ARIA

If you want to export the radiosurgery treatment plan to the ARIA oncology information system, see Appendix E.

Note: The printouts provide an average depth for each treatment arc. This enables a “rough” hand calculation of monitor units. While this value is not exact, it will be within approximately 2% of the correct value.

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Removing an Image Set

The Remove Patient program allows you to erase an exam from the hard drive. To retain sufficient hard drive space, the recommended procedure is to permanently archive the exam to a CD or DVD, and then to remove the exam from the hard drive.

To remove an exam:

1. In the Stereotactic Radiosurgery Treatment Planning window (Figure 9), select a patient’s name in the available patient list.

2. Click Remove Patient.The patient’s name disappears from the list.


Chapter 5 AutoPilot Treatment Planning Module

AutoPilot is a module of the FastPlan Treatment Planning system for radiosurgery. It provides tools that enable, in some instances, fully automatic treatment planning functions. AutoPilot requires the input or selection of specific initial treatment planning parameters. The software then delivers a final treatment plan that may be optimized based on the initial parameters.

AutoPilot may be used in conjunction with FastPlan’s forward‐planning tools or independently of them to create a treatment plan. Depending on your level of experience, you may find it easier to continue with forward‐planning approaches for targets of simple geometry and use AutoPilot for more complex targets. Since treatment plans created with AutoPilot can be produced using a “one button” fully automatic approach or in steps, you may interactively use FastPlan’s manual and automatic planning tools for plan optimization.

The FastPlan AutoPilot Treatment Planning module is intended for use only as an aid in radiation treatment planning. It is indicated for planning the radiation treatment of small cranial lesions, such as arteriovenous malformations, pituitary tumors, pinealomas, acoustic neuromas, and malignant neoplasms.

The clinician should not rely solely on the system for treatment planning. It is the responsibility of the clinician to identify the treatment volume correctly, perform a final check on the correctness of the treatment plan dosimetry, and ultimately accept the plan.

The FastPlan AutoPilot Treatment Planning module should not be used for any medical conditions that are contraindicated for radiation treatment using a linear accelerator. Such contraindications include the inability to adequately define the lesion boundaries or the inability to plan a dose that adequately minimizes radiation exposure to surrounding tissue.

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Using Autopilot

A sample case is used to demonstrate the use of AutoPilot. This case is provided as a FastPlan demo on all systems and is identified as DemoAcoustic. The target is an acoustic lesion that would typically require a treatment plan using between two and four isocenters to produce a conformal result. DemoAcoustic consists of a stereotactically localized CT and stereotactically merged MRI data set.

Case and Targeting System

1. Launch FastPlan.

2. At the Stereotactic Radiosurgery Treatment Planning window, select DemoAcoustic as the desired case.

3. Under Treatment Planning, click Cone to start Cone Planning.

4. Find the acoustic lesion of interest and manually contour the target using FastPlan’s 3D contouring tools. See “Contour Tool” on page 160.

Building the 3D Model

After the contouring process is complete, build the 3D model:

1. Using the Settings tool, select color and transparency for both the target model and the cranial model that provide good visualization of each 3D reconstruction in relation to each other.

2. Click Show Isocenters to enable automatic 3D visualization of isocenter placement as AutoPilot creates each isocenter.

AutoPilot Tab

Selecting the AutoPilot tab changes the planning tools on the right side of the window while maintaining the 2D and 3D images on the left. Refer to Figure 44. A description of each planning parameter follows.


Figure 44 AutoPilot Tab

Planning Target displays a pull‐down menu with the names of all 3D target models for AutoPilot to use in treatment planning.AutoPilot Arc Set displays a pull‐down menu of all predefined FastPlan arc sets. This is the same collection of arc sets available from the Load Arcs option on the Planning tab.

Note: While AutoPilot works with any valid FastPlan arc set, it is recommended that the standard five‐arc, clockwise set be used for most plans. This is commonly stored with the name std-5-cw.

Max. Isocenters is a text box that allows you to type the maximum number of isocenters in the plan. This hard limit applies to isocenters found using IsoFind and Full Auto IsoFind as described below.Normal Tissue Weight allows you to select how conformal the plan should be to the boundary between the target and healthy tissue. The boundary is defined by the target contours. The Low, Medium, and High settings are predefined. Selecting High causes dosimetry to conform strictly to the boundary of the target. The

Isocenter displaybox

AutoPilot Treatment Planning Module 107

Medium and Low settings allow isocenters and doses to extend increasingly beyond the target boundary. Most treatment plans should start with an initial setting of High or Medium. If desired, you can also select the Manual option and type any decimal value greater than zero. The higher the value, the smaller the extent of isocenters and isodose lines beyond the target boundary (that is, the more normal tissue is spared).Rebalancing optimizes individual arc weights based on initial isocenter weights as defined in the Des[ired]W[eigh]t text box. Rebalancing applies to a plan with more than one isocenter. You can rebalance at any time by clicking Apply Desired Wt. The DesWt text box and Apply Desired Wt button are described later in this manual.1 Isocenter optimizes isocenter weight for single isocenter plans. It is recommended that 1 Isocenter be selected for all plans with one isocenter.IsoFind places each isocenter, up to the maximum number specified in the Max. Isocenters text box, one at a time in the isocenter display box. This permits step‐by‐step optimization of the treatment plan. You can change the maximum number of isocenters at any time.Full Auto IsoFind automatically places each isocenter, up to the maximum number specified in the Max. Isocenters text box, consecutively without stopping. This permits optimization of the entire treatment plan.

Entering Parameter Data

To enter parameter data:

1. Type parameter data into the required text boxes. See Figure 45.

2. Under Planning Target, click the button.

3. Select Target 1 from the selections that appear in the pull‐down menu.In actual practice your selection may be different depending on system configuration.

4. Under AutoPilot Arc Set, click the button.


5. Select the standard five‐arc, clockwise set from the selections that appear in the pull‐down menu. This is commonly named std-5-cw.

6. In the Max. Isocenters text box, type 4.

Figure 45 Autopilot Parameter Text Boxes

7. Under Normal Tissue Weight, click Medium.In actual practice other selections may also produce a conformal plan.

8. Select the Rebalance check box because this is a plan with multiple isocenters.


Isocenter Placement and Calculation

For this example a plan will be produced in steps by using IsoFind. (AutoPilot can also automatically produce a plan with four isocenters by using Full Auto IsoFind.)

1. Click IsoFind.AutoPilot calculates the first isocenter and displays relevant parameters in the AX, LAT, AP (stereotactic coordinates), Weight (isocenter weight), Col. (collimator size), and SetPt. (set point) data boxes.

2. Click the down arrow directly below these data boxes to accept the parameters.The parameters move to the isocenter display box and the first isocenter is spatially placed in the 2D and 3D image fields. See Figure 46.

3. Click IsoFind.AutoPilot calculates the second isocenter and displays relevant parameters in the AX, LAT, AP, Weight, Col., and SetPt. data boxes.

4. Select the down arrow directly below these fields to accept the parameters.The parameters move to the isocenter display box and the second isocenter is spatially placed in the 2D and 3D image fields. See Figure 47.

5. Click IsoFind.AutoPilot calculates the third isocenter and displays relevant parameters in the AX, LAT, AP, Weight, Col., and SetPt. fields.

6. Click the down arrow directly below these fields to accept the parameters.The parameters move to the isocenter display box and the third isocenter is spatially placed in the 2D and 3D image fields.


Figure 46 Isocenter 1

7. Click IsoFind.AutoPilot calculates the fourth isocenter and displays relevant parameters in the AX, LAT, AP, Weight, Col., and SetPt. data boxes.

8. Click the down arrow directly below these data boxes to accept the parameters.The parameters move to the isocenter display box and the fourth isocenter is spatially placed in the 2D and 3D image fields.A message appears indicating that the maximum number of isocenters has been reached (Figure 48).

9. Click OK to close the message.


Figure 47 Isocenter 2

Figure 48 Isocenter 4 Warning Message


Modifying the Treatment Plan

The acceptability of the treatment plan produced by AutoPilot depends on a number of factors you can control. These include the quality of target contouring, tissue weight selections, and the number of isocenters. You may revise the suggested treatment plan using several modification tools.

Adjusting Set Points

SetPt. allows you to modify the weights of all arcs simultaneously by changing isocenter weight (set point).

Isocenter 2 is currently weighted at 500, evenly with the other three isocenters. To change the weight of Isocenter 2:

1. Select isocenter 2 in the isocenter display box to highlight it.

2. In the SetPt. text box, type 400.

3. Select the down arrow directly below the SetPt. text box to display the new value in the isocenter display box.

4. Click Apply Setpoints to accept the new value.AutoPilot immediately recalculates the dosimetry, rebalances the isocenters, and displays the modified plan. See Figure 49.


Figure 49 Modifying the Plan by Changing the Set Point

5. Click Wt. Stats to numerically review changes to the plan made by set‐point modifications.A dialog box (Figure 50) appears showing the relative dose contribution by each isocenter as a function of weight.

6. Click OK to close the dialog box.


Figure 50 Wt. Stats Dialog Box

Manual Planning

You may interactively switch between AutoPilot and FastPlan’s manual planning tools. Assume that a set point adjustment to Isocenter 2 was not desired, but that a modification to a particular arc or isocenter spacing was preferable.

To change the plan manually:

1. Click the Planning tab to access FastPlan’s main planning window (Figure 51).

2. Make the necessary changes to the plan.

3. Click the AutoPilot tab to return to AutoPilot.


Figure 51 FastPlan Main Planning Window

Deleting Isocenters

Any single isocenter may be deleted.

To delete Isocenter 2:

1. Select isocenter 2 in the isocenter display box to highlight it.

2. Click Isocenter and drag the cursor to Delete.The isocenter is removed from the isocenter display box and the plan is modified accordingly.

All isocenters may be deleted simultaneously if you want to start a new plan from the beginning. To do so: Click Delete All. The remaining isocenters are removed from the isocenter display box.


Chapter 6 Physics Configuration Procedures

Access to these functions is limited to users who have the privileges to run the Physics program.

The physics configuration procedures are performed during the FastPlan system installation. All of the data is machine‐specific and must be obtained on the linear accelerator to be used for treatment.

The FastPlan system’s dosimetry algorithm uses Tissue Maximum Ratios (TMR) and Off Axis Ratios (OAR) to determine the dose at any point within the irradiated volume.

This chapter describes the:Details of the fitting algorithms.Measurement required for the fitting algorithms.Recommended measurement techniques.

WARNING: The FastPlan system contains beam data for installation and training purposes. This data is not intended for clinical use. Use only measured machine-specific beam data for clinical use. Using the default beam data may result in serious injury or death to patients.

Note: If you are adding a new collimator to an already configured FastPlan system, the Physics module should be reconfigured, taking into account this new collimator. For a complete description of the reconfiguration process, see “New Collimator Integration into Already Configured FastPlan System” on page 142.

117

Establishing the System Configuration

The Configuration window (Figure 52) stores information specific to a particular site. Once correctly set up, the configuration does not need to be changed unless there are changes to the site or upgrades.

Figure 52 Physics Configuration Window

To establish or change the system configuration:

1. Log on as the Physics user.

2. Choose Physics > Configure.

3. Enter the required information in the Configuration window. Refer to Table 11 for the text box descriptions.


Table 11 Physics Configuration Parameters

Parameter Requested Information

Name of Institution Type the institution name.

Make & Model Type the linear accelerator manufacturer and model.

Machine Id. Type the linear accelerator identification number.The Linac_ID is used by record‐and‐verify systems to identify the incoming RTP. The record‐and‐verify system should be configured with the proper Linac_ID.

Positioning system Select the option button for either positioning system:

FloorstandCouchmount

Gantry Home Angle Click the button. Drag the cursor to select either of two angles:

0180

Couch Home Angle Click the button. Drag the cursor to select either of two angles:

0180

Gantry (+) Rotation Click the button. Drag the cursor to select either of two positive rotation directions:

ClockwiseCounter‐Clockwise

Physics Configuration Procedures 119

Couch (+) Rotation Click the button. Drag the cursor to select either of two positive rotation directions:

ClockwiseCounter‐Clockwise

SRS Technique Click the button. Drag the cursor to select either of two SRS techniques:

SRS_ARCARC

MU [Monitor Units] per Deg[ree].

Position the mouse cursor in the MIN (minimum) text box and type the number of monitor units per degree to indicate the fastest arc rotation speed. Position the cursor in the MAX (maximum) text box and type the number of monitor units per degree to indicate the slowest arc rotationspeed.

Energy Level (MV) Type the linear accelerator’s energy in MV.

Dose Rate (MU/min) Type the linear accelerator’s dose rate in MU/min.

Field Size (mm) WARNING: The recommended field size is between 50x50 and 60x60 mm but should not exceed 65x65 mm. Exceeding this limit will cause

extra leakage outside the cone mount, which may result in excessive radiation dose to the patient.Type the linear accelerator’s field size in millimeters.

Max MU Linac Type the linear accelerator’s maximum allowed dose per treatment in MU.

Table 11 Physics Configuration Parameters (continued)



Source‐axis‐distance (mm)

Confirm that the value in this text box is set to 1000 mm. Otherwise, type in 1000.

CT Frame/Localizer Click the button. Drag the cursor to select one of the two supported localizer frames:

VMS [SNT]BRW

Customize Printed Setup Procedure button

Opens a text editor (gray) window which enables you to customize the default setup procedure sheet that prints out with the prescribed plan. Place the cursor inside the gray window, then type any modifications. Once the modifications are entered, click File, then drag to Save. Again, click File, then drag to Exit. These actions edit and save the modifications as the new default setup sheet until otherwise modified.

COLLIMATORS How many collimators?

Type the total number of collimators. Next type the size in millimeters, output factor, and ID for each collimator. The output factor is the dose at the depth of Dmax as a function of collimator size, normalized to unity for a standard field size: for example, 10x10 cm for a source‐to‐axis (or isocenter) distance (SAD) = 100 cm. It follows that the output factor is a relative measurement against the calibration for the linear accelerator in use.

Table 11 Physics Configuration Parameters (continued)



Saving the Linac Specifications

To save the linac specifications, click Update.

Printing the Linac Specifications

To print the linac specifications, click Print.

Exiting the Configuration Mode

To exit the configuration mode, click Close.

Required Measurements

Several measurements are required:Output factorTissue Maximum Ratio (TMR)Off‐Axis Ratio (OAR)

Output Factor

WARNING: The field size defined in the linac configuration must be used for all measurements and the same field size should always be used for treatment. Using a different field size will cause the machine output to differ from the conditions defined in FastPlan and could lead to higher or lower delivered dose.

The output factor is the dose at the depth of Dmax as a function of collimator size, normalized to unity for a standard field size: for example, 10x10 cm for a source‐to‐target distance (STD) of 100 cm. Therefore, the output factor is a relative measurement against the calibration for the linear accelerator in use.

An output factor is required for every circular collimator you use for radiosurgery. The FastPlan system assumes that your accelerator has been calibrated to deliver 1 cGy per MU to isocenter at a depth of Dmax. Many institutions calibrate their accelerators to deliver 1 cGy per MU at an SSD of 100 cm at Dmax.


If this is true of your institution, you must account for this in the collimator output factors. For example, if you have an SSD calibration that delivers 1 cGy per MU at a depth of Dmax = 1.5 cm for a 100 cm SSD setup, you must multiply your output factors by (101.5/100)^2, or about 1.03, due to the inverse square effect.

Tissue Maximum Ratio (TMR)

TMR, in a water phantom irradiated by a photon beam, is the ratio of absorbed dose at any point along the beam axis to the dose at the same point with the surface of the phantom moved so that the point is at the depth of maximum absorbed dose. During measurement, the source‐to‐detector distance should be 100 cm with measurements taken with increasing depth. TMR is a function of depth, beam quality, and collimator geometry.

The function TMRTOOL accepts measured TMR data and fits the data to two separate analytic functions. In the buildup region, which is assumed to extend from the surface to 1 cm beyond the depth of dose maximum, TMR values are linearly interpolated from point to point. TMR values between the shallowest value entered and 0.1 cm are obtained by linear extrapolation of the two shallowest data points. Beyond the buildup region, TMR values are fitted to the exponential expression:

where μ = the effective linear attenuation coefficient for the collimator entered. Use this algorithm for each collimator with measured data entered into the system.

These data can be entered from a minimum depth of 0.5 cm to a maximum depth of 30 cm. Data need not be entered for every depth, but resolution of the measured data must be fine enough to smoothly define the curve. The recommended minimal data set should contain measured data in 0.5‐cm increments from the surface to 1.0 cm past the point of dose maximum, and measured data in 1.0‐cm increments to define the exponential region.

TMR d( ) A e μ d⋅–( )⋅=


Consider taking the TMR data with a minimum of two measuring devices:

DiodeTLDsIon chambers

Any collimator for which data are not entered has its data calculated by linear interpolation from the measured collimator data. While data should be measured for a representative set of collimators, TMRTOOL determines the TMR for all collimators with data entered for a minimum of three collimators.

Off-Axis Ratio

The off‐axis ratio (OAR), in a water phantom irradiated by a photon beam, is the ratio of absorbed dose at any point to the absorbed dose on the beam axis at the same depth.

OAR data at three different source‐to‐target distances (STDs) are required. Measure the OAR data at a depth of at least Dmax or 1.5 cm for a 6 MeV beam for at least three collimators. Sample the data every millimeter (that is, 1.0‐mm spacing) regardless of STD used and collimator size. Three STDs are required with constant depth because OAR demonstrates a small dependence on STD, but is virtually independent of depth.

OARTOOL accepts the measured OAR data and applied a curve fit algorithm using the following modified Cunningham model:

where:r = radius at the point of interestr0 = collimator radius corrected for source‐to‐target distance

OAR 1 0.5 α1 R β R2⋅+⋅( )–( )exp⋅–= r r0≤( )

OAR t 0.5 t–( ) α2 R⋅( )exp( )+= r r0>( )

R r0 r–( ) P⁄=


where

and SS = source sizeSCD = source‐to‐collimator distance

Note: These latest two values are used to calculate the penumbra. Both have a very small effect on the quality of curve fitting. Therefore, if they are not known precisely, it is acceptable to use the following standard values: SS = 0.3 cm, STD = 60 cm.

STD = source‐to‐target distancea1, a2, b, and t are curve‐fit parameters determined by OARTOOL.

The two modifications to the standard Cunningham model are:In units with large focal spot sizes, the shoulder of the OAR curve is difficult to fit for small collimators. The term b is required to adequately fit the measured data. b defaults to 0.1 cm for collimator diameters greater than or equal to 1.8 cm and 0 for all other collimators.OAR exhibits a small dependence on the collimator‐to‐target distance. Since SCD is fixed, data are represented as a function of STD. A minimum of data at three different STDs needs to be used to model this dependence.

The “isolated coefficients” a1, a2, and t are computed for each STD and collimator. To generate the OAR data for one collimator, these coefficients have to be predicted for other values of STD. Any other value of STD is predicted by linear regression of coefficients calculated for the three STDs entered for this collimator. The resulting coefficients are known as “regressed coefficients.”

To generate fits for all of the collimators, an average of the regressed coefficients is used. The resulting coefficients, “average coefficients,” are linearly related to STD but independent of collimator. The curve‐fitting program avoids oversensitivity to one set of inaccurate data by fitting a straight line to the reciprocals of a1 and a2.

P SS STD SCD–( ) SCD( )⁄( )μ=


Measurement Methods

Due to the small fields used in stereotactic radiosurgery, partial volume effects are noticeable if large volume ion chambers are used. A large volume detector for radiosurgery measurements is a Farmer type chamber (0.6 cc); it demonstrates marked partial volume effects. While these effects may be deconvolved from the measured data, the recommended higher resolution detector systems are:

DiodeTLDsFilm

The data obtained using all three techniques must agree.

Choose diodes with a small area and with energy response suitable for beam data acquisition. Use this diode with a solid tissue‐equivalent phantom that accepts the diode.

Build a second solid water phantom, which accommodates TLD chips. Mill a section in the center to accept a solid row of TLD chips. Allow for a placement of a TLD anywhere along the phantom length. Stack the TLDs on edge during measurements.

Collect the film data using a phantom which prevents the introduction of artifacts.


TMR Data Entry

The FastPlan system includes a spreadsheet for easy entry of your department’s TMR data. Once entered, a program can interpolate the data and create the binary look‐up tables used for computing dose. Selected plots depicting the relationship of the TMR data to the collimator size and of the TMR data to the depth provide you with visual representation of the fit of the interpolated data.

Login Instructions

To login as a Physics user:

1. At the Stereotactic RadioSurgery 5.5 Login Manager, click Physics.The Stereotactic Radiosurgery Treatment Planning window opens.

2. Choose Physics > TMR Data Entry.The TMR Data Entry window (Figure 53) opens.

Figure 53 TMR Data Entry Window

The TMR Data Entry window is divided into two primary regions:Plot canvasData spreadsheet


The tasks associated with entering, processing, printing, and saving the TMR data are listed in one of two menus:

File (Table 12)Output Table (Table 13)

On the right side of the plot canvas are two task‐related control buttons. Selecting Clear Plot erases the plot canvas. Selecting Fill Columns interpolates the measured data you entered and automatically updates the values in the appropriate collimator cells.

Table 12 File Menu Commands

Command Function

New Clears the TMR Data Entry window and empties the spreadsheet cells.

Load Loads data previously saved to a file. A list of saved files appears in the tmrtool window.

Save Saves the TMR table to a file.

Print Prints the contents of a file using a Postscript printer.

Print to File Saves the contents of a file to a Postscript file. Unless otherwise specified, the file saves to tmrtool.dump.

Exit Quits the TRM Data Entry program.

Table 13 Output Table Menu Commands

Command Function

Process Tables Interpolates the entered data to create the binary look‐up tables for all collimators used by the FastPlan system for computing dose.

Print Tables Sends the contents of the TMR table file to a Postscript printer.


Entering the TMR Data

The TMR Data Entry table (Figure 53) contains a spreadsheet for the input of the measured data for each available collimator. As a convenience, you need to type the measured data for only three collimators. The entered data, however, should represent the entire range. From this minimal information, the program is able to interpolate the values for the remaining cells and collimators.

The collimator sizes automatically appear in the spreadsheet and represent the entries made to the hardware configuration file at the time of setup. The two sections of TMR data you must enter are:

Depth of maximum doseMeasured data

Depth of Maximum Dose

Maximum dose depths are integers ranging from 8 to 35 which indicate the depth in millimeters of the maximum dose. Type the depth of maximum dose value for each collimator.

The TMR at the depth of the maximum dose should be 1.000. TMR values should not be less than zero. Values should increase in the buildup region (that is, depth is less than or equal to the Max Dose Depth) and then should decrease.

Measured Data

The TMR Data Entry table contains a column for the input of measured data for each available collimator size. Each column supports up to 60 values at depth increments of 5 millimeters. The values range from 5 mm to 300 mm.

Make Individual Table

Interpolates the entered data to create an individual binary look‐up table for a specific collimator.

Table 13 Output Table Menu Commands (continued)

Command Function


Enter the data for a minimum of three collimators covering the widest possible available range. Include a minimum of five data points beyond the depth of maximum dose.

Enter the measured data into the appropriate input cells. Type in the floating‐point value. The preferred TMR value format is D.DDD—one digit before the decimal point and three after. Extra precision is truncated.

TMRTOOL checks the data values as you enter them and provides you with a warning message of an inconsistent entry.

Note: The TMR at the depth of the maximum dose should be 1.000. TMR values should not be less than zero.

Interpolating the Data

Clicking Fill Table instructs the program to interpolate the data for the remaining collimators (Figure 54). The interpolated data values appear in the spreadsheet in a light blue text. This differentiates the interpolated data from the manually entered data.

The interpolated data cannot be saved, only viewed.

Figure 54 Example of Interpolated Measured Data Values

To remove the interpolated data from the TMR spreadsheet, click Unfill Columns.


Plotting TMR Data

The FastPlan system graphically represents the TMR data in relation to the collimator size and also the depth. Multiple plots of the same relationship, each in a unique color, may display on the plot canvas. However, it is not possible to simultaneously display the TMR vs. Depth and TMR vs. Collimator Size plots.

On a TMR plot, the curve appears without any points for columns filled entirely with interpolated data. Data points (the small squares in the plot window) only appear for the manually entered data points.

TMR vs. Depth (in millimeters) Plot

To plot TMR versus depth, click any one of the collimator buttons. The plot automatically appears on the plot canvas. The values for A and Mu appear in a legend to the right of the plot.

Clicking any one of the other collimator buttons results in the display of multiple plots, each in a unique color. To clear any one plot from the canvas, click the collimator button the plot represents. To clear all the plots, click Clear Plot.

The cross hairs represent the position of the cursor and display the coordinate values.

TMR vs. Collimator Plot

To plot TMR versus collimator, click any one of the depth buttons. The plot automatically appears on the plot canvas (Figure 55). The legend to the right of the plot displays the slope and the intersect value.

Clicking any one of the other depth buttons results in the display of multiple plots, each in a unique color. To clear any one plot from the canvas, click the depth button the plot represents. To clear all the plots, click Clear Plot.


Figure 55 Example of TMR vs. Collimator Plot

Calculating and Saving the TMR Table

The Output Table menu (Table 13) contains the tools to create and print the TMR tables.

Calculating the TMR Table

Clicking Process Tables interpolates the entered data and creates the binary look‐up tables used by the FastPlan system for computing dose. This process automatically saves the information in the $SRSHOME/lib/tmr directory.

Making an Individual Table

Clicking Make Individual Table interpolates the data for a specific collimator and creates the binary look‐up table used by the FastPlan system for computing dose. This process automatically saves the information in the $SRSHOME/lib/tmr directory.

This tool is very useful for adding collimator data after the initial configuration process is complete.


Saving the TMR Measured Data

Clicking Save from the File menu (Table 12) writes the manually entered TMR values to a file in the $SRSHOME/lib/data directory (Figure 56). Entering a file name or highlighting an existing file instructs the computer to save the data. By default, the file is saved with the .dat suffix. This file can then be reloaded when TMR tables need to be regenerated, such as when a new collimator is being added.

Figure 56 TMR Data Save Tool


Loading TMR DataClicking Load from the File menu (Table 12) opens a window which lists the saved TMR measured data files. Highlighting the name of the desired file and clicking OK instructs the computer to display the contents of the file in the TMR Data spreadsheet. Only the manually entered TMR values appear.

WARNING: If the warning message Column does not fit into hardware defined Collimators appears, you are attempting to load a file created for a linac with a different collimator set than the current actual. No data will be loaded. When the linac hardware configuration described in the loaded file and that of the current system differ, a different warning message appears: Linac parameters differ from the selected TMR table parameters. This data cannot be used for treatment. Testing purposes only. Are you certain you want to proceed with loading? Loading such a file for other than testing purposes and using the generated tables for patient treatment may cause serious injury or death.

OAR Data Entry

The FastPlan system also includes a spreadsheet for the easy entry of your department’s OAR data. After you enter the data for three collimators, a program can interpolate the data for all the collimators and create the binary look‐up tables used for computing dose. Selected plots, depicting the relationship of the OAR data to the manually entered data, to the interpolated data, and to the average OAR value for the three selected collimators, provide you with visual representation of the fit.

Access to these programs is limited to users who have the privileges to run the Physics program.

Login Instructions

To login:

1. The physics program window opens.

2. Choose Physics > OAR Data Entry.The OAR Data Entry window opens (Figure 57).


Figure 57 OAR Data Entry Window

The OAR Data Entry Window is divided into two primary regions:Plot canvasData spreadsheet

The tasks associated with entering, processing, printing, and saving the OAR data are listed in one of two menus:

File (Table 14)Data (Table 15)

On the right side of the plot canvas are two task‐related control buttons:

Clear Plot: Erases the plot canvas.Average Plot: Averages the OAR values for the three collimators and graphically displays the result.


Table 14 File Menu Commands

Command Function

New Clears the OAR Data Entry window and empties the spreadsheet cells.

Load Loads data previously saved to a file. A list of saved files appears in the OARTOOL window.

Save Saves the OAR table to a file.

Print Prints the contents of a file using a Postscript printer.

Print to File

Saves the contents of a file to a Postscript file. Unless otherwise specified, the file saves to oartool.dump.

Inspect Tables

Saves the contents of the OAR binary look‐up tables to a print file and sends this file to the Postscript printer.

Exit Quits the TRM Data Entry program.

Table 15 Data Menu Commands

Command Function

Make Table Interpolates the entered data to create the binary look‐up tables for all collimators used by the FastPlan system for computing dose.

Force Central Axis Changes the value of all the OAR entered data to one. The algorithm which interpolates the entered data to create the binary look‐up tables uses an OAR value of one in place of the actual OAR value.


Entering the OAR Data

The OAR Data Entry window (Figure 57) contains a spreadsheet for the input of the OAR values for each available collimator. As a convenience, you need to enter data for only three collimators. The entered data, however, should represent the entire range. From this minimal information, the program is able to interpolate the values for the remaining cells.

The collimator sizes automatically initialize in the spreadsheet and represent the entries made to the hardware configuration file at the time of setup. The three types of OAR data you must enter are:

Source‐to‐target distancesMachine dataOAR values

Source-to-Target Distances

Determine for which three collimators you intend to enter OAR data. Type the source‐to‐target distances for each collimator in the STD cells associated with each of the tables (Figure 58).

Figure 58 Example of STD and OAR Data Cells


OAR Input Spreadsheet

Enter the OAR data for each collimator’s three STDs in the cells associated with each of the tables (Figure 58). The preferred floating‐point value format is D.DDD, one digit before the decimal point and three after. Extra precision is truncated. OARTOOL checks the data values as you enter them and warns of an inconsistent entry.

Machine Data Entry

Type the value in millimeters for source size and source‐to‐collimator distance (Figure 59). D.DD is the preferred OAR value format: one digit before the decimal point and two after. The range for Source Size is 0.10 mm to 10.0 mm. The range for source‐to‐collimator distance is 500 to 701 millimeters.

Figure 59 Example of Machine Data and Plot Tool


Plotting OAR Data

The FastPlan system graphically represents the OAR data in relation to the manually entered data points, the interpolated data, and as an average value. Multiple plots, each in a unique color, may appear on the plot canvas.

On an OAR plot, the curve appears without any points for columns filled entirely with interpolated data. Data points (the small squares in the plot window) appear only for the manually entered data points.

OAR vs. OAD (Manually Entered Points)

To plot OAR vs. OAD, click the desired STD plot button. The plot automatically appears on the plot canvas (Figure 60) and the STD button text is highlighted to indicate that the specific STDs OAR values are plotted. A legend displays the collimator size and the STD value for each plot, as well as the a1, a2, b, and t values.

Figure 60 Sample Average OAR Plot


Clicking on any one of the other two STD buttons results in multiple plots each in a unique color (Figure 61). To clear any one plot from the canvas, click the STD button the plot represents. To clear all the plots, click Clear Plot.

Figure 61 Sample Multiple OAR Plots

Interpolated OAR Data vs. OAD

To plot Interpolated OAR Data vs. OAD, type the desired STD value for a specific collimator. The plot automatically appears on the plot canvas. A legend displays the collimator size and the STD value.

Clicking any one of the other collimator buttons results in multiple plots each in a unique color. To clear any one plot from the canvas, click the collimator button the plot represents. To clear all the plots, click Clear Plot.

To check the accuracy of the interpolated data, plot three collimator/STD combinations. The interpolated plot and the plot of manually entered data for each collimator/STD combination should be nearly identical. The interpolated plot appears as just a curve—with no data points.


Average Value OAR Plot

To plot the average value OAR plot, click Plot Average. The plot automatically appears on the plot canvas (Figure 60). A legend displays the average OAR a1, a2, b, and t values for the three collimators.

To clear the plots, click Clear Plot.

Calculating the OAR Tables

Clicking Make Tables from the Data menu interpolates the entered data and creates the binary look‐up tables used by the FastPlan system for computing dose. This process automatically saves the information in the $SRSHOME/lib/oar directory.

Calculating the OAR Table with a Forced Value of 1.0

Clicking Force Central Axis from the Data menu interpolates the entered data with a value of 1.0 at the central axis (oad = 0) when creating the binary look‐up table used by the FastPlan system for computing dose. This process automatically saves the information in the $SRSHOME/lib/oar directory.

This tool is very useful for adding collimator data after the initial configuration process is complete.

Saving the OAR Tables

Clicking Save from the File menu (Table 14) writes the manually entered OAR values to a file in the $SRSHOME/lib/data directory. Entering a file name or highlighting an existing file instructs the computer to save the data. By default, the file is saved with the .dat suffix.

Clicking Inspect Tables from the File menu saves the contents of the OAR binary look‐up tables to a print file and sends the file to a Postscript printer.


Loading OAR Data

Clicking Load from the File menu (Table 14) opens a window that lists the saved OAR data file. Highlighting the name of the desired file and clicking OK instructs the computer to display the contents of the file in the OAR Data spreadsheet.

WARNING: When the linac hardware configuration described in the loaded file differs from that of the current system, a warning message appears: Linac parameters differ from the selected OAR table parameters. This data can not be used for treatment. Testing purposes only. Are you certain you want to proceed with loading? Loading such a file for other than testing purposes and using the generated tables for patient treatment may result in serious injury or death.

Printing the OAR Tables

Clicking Print from the File menu (Table 14) prints the contents of the OAR data file to a Postscript printer.

Clicking Print to File from the File menu prints the contents of the OAR data to a Postscript file and writes the file in the $SRSHOME/lib/data directory. Clicking Inspect Tables from the Data menu (Table 15) saves the contents of the OAR binary look‐up tables to a print file.

New Collimator Integration into Already Configured FastPlan System

When adding a new collimator to a FastPlan system where OAR and TMR tables have already been configured, perform the following procedure:

1. At the Login Manager window, click Physics.The Login Manager window closes and a small unnamed (Physics mode) window opens.

2. Choose Physics > Configure.The Configuration window opens.


3. Under COLLIMATORS, type the size, output factor, and applicator ID for the new collimator in the next empty row of text boxes.

4. In the How many collimators? text box at the top, type the new total number of collimators.

5. Click Update in the lower left of the window and then click Close.The Configuration window closes and the small window reopens.

6. Choose Physics > Configure again.The Configuration window reopens.

7. Ensure that the new collimator is now listed and that all the collimators are sorted by size.

8. Click Close.The Configuration window closes and the small window reopens.

9. Choose Physics > OAR Data Entry.The OAR Data Entry window opens.

10. Choose File > Load.The Oar tool opens.

11. In the Files list, select the file containing the OAR measurements created during the original system configuration.

12. Click OK.The Oar tool closes.

13. From the main menu, choose Data > Maketable to regenerate the OAR tables for all collimators.

14. Exit the OAR Data Entry window.

15. In the Physics mode window, choose Physics > TMR Data Entry.The TMR Data Entry window opens.

16. Choose File > Load.The TMR Tool opens.

17. In the Files list, select the file containing the TMR measurements created during the original system configuration.

18. Click OK.

19. The TMR Tool closes.


20. From the main menu, choose Output table > Process Tables.A message opens asking if you want to proceed to regenerate and store new tables for all collimators.

21. Click OK.The message closes, a progress indicator appears briefly, and then another message appears telling you that the new tables have been created.

22. Click OK.The message closes.

23. Exit the TMR Data Entry window.

24. Exit the Physics mode window.

Now the new collimator integration process is complete. You must perform the standard dosimetry verification tests to verify the validity of the OAR and TMR tables.


Dose Calculation and Model Limitations

This section describes the model with which FastPlan calculates doses, as well as the limitations of this model.

Outline of Dose Calculation

The dose, D, at any point, P, in the beam is determined as:

where:d = depth to point PS = collimator diameterTMR (tissue maximum ratio) = ratio of absorbed dose in water

along beam axis to the dose at the same point in space with the phantom moved such that the point is at the depth of maximum dose

OAR (off‐axis ratio) = ratio of absorbed dose at point off of beam central axis to the dose at the same depth on the beam central axis

OF (output factor) = ratio of output for the particular collimator at point of maximum dose to the output for calibration field size

SCD = source‐to‐calibration distance for the linear acceleratorSPD = distance from the source to point P

D d S P, ,( ) TMR d S,( ) OAR dmax S P,( )( ) OF S( ) SCD( )2( ) SPD( )2⁄⋅ ⋅=


Establishment of Beam Ray/Patient Surface Intersection

WARNING: This method of calculation may be used incorrectly if the contour threshold is set incorrectly, or if the program incorrectly identifies a nonpatient surface as the external contour. Examine each arc ray and take appropriate corrective action, if required.

For each arc the system draws a number of static beams. Each of these static rays is determined starting from the radiation source and progressing toward the isocenter. The ray is drawn along this path from the external contour to the isocenter. The position of this intersection is recorded with the data for that beam, in order to determine the average TMR for the arc in question.

The FastPlan system forces you to inspect each arc before allowing printout of the dosimetry forms. Examine each arc ray; and if required, take the appropriate corrective action. Corrective actions may be:

Altering beam parameters to exclude the nonpatient surfaceAdjusting the contour threshold to ignore the nonpatient surfaceAdjusting the contour by right‐clicking in the main view and tracing along the correct contour

Static and Arc Beams

The FastPlan system algorithm approximates arc dosimetry calculations as multiple static beams. To determine the average TMR for the arc, the system draws a static beam at user‐specified arc increments (1, 5, or 10 degrees). The system then averages the TMR from all of these beams to determine an average for dosimetry calculations. The dose contribution for any particular arc is normalized to 1.0 at its isocenter and then multiplied by its weight.

Note: The printouts provide an average depth for each treatment arc. These are provided to enable a “rough” hand calculation of monitor units. Monitor units calculated by hand using these average depths are not exact, but will be within approximately 2% of the correct values.


Dose Grid

When the dose calculation is initiated, dose is calculated for an array of points on two 45x45 matrices. One grid is coarse, with a point separation of 5.0 mm in the center of stereotactic space. The other grid is fine, with a point separation of 1.0 mm and centered on the isocenter of the current display plane.

Monitor Unit Calculation

The monitor unit calculation is broken into two portions:Calculation of reference dose from the average TPR and the tumor doseCalculation of the monitor units from the reference dose and collimator output factor:

Reference Dose = Tumor Dose/TPR

and

Monitor Units = Reference Dose/OF

Note that the arcs are provided only relative weightings during the planning process, and their true relative dose weightings are not assigned until the time of dose prescription. The number of times the weights need to be “repeated’ to deliver the prescribed dose is indicated by the ratio of the tumor dose to the relative arc weight.

Limitations of Model

This model has several limitations, described in this section.

Tissue Inhomogeneity

Tissue inhomogeneity is not considered, and all CT values are treated as having water equivalent densities once the entry point has been determined. This is generally acceptable in the head, since most beam paths are through approximately water equivalent densities. For example, skull density is approximately 1.4 times that of water, and the skull thickness is approximately 0.75 cm. This means the


equivalent thickness of the skull is 0.75*1.4+1.05 cm, resulting in a 0.3‐cm error. For a 6MV beam, attenuation is approximately 4%/cm, resulting in a dose error of 0.3‐cm*4%/ cm=1.2% error.

Beam paths that traverse air cavities result in slightly higher errors, and you may want to alter beam entry points to avoid large path lengths through these cavities. For beams that enter or exit through cavities, realize that these areas are treated as having water equivalent densities.

Oblique Entry of Beams

The beam axis is assumed to always be normal to the patient contour, and no consideration is made for beam obliquity. Due to the small field sizes encountered in radiosurgery, this error is negligible.

Backscatter

No consideration is made for the absence of backscatter near the cavities or where the beam exists the head. This results in the displayed dose near the surface being slightly higher than the actual dose.

Off-Axis Ratio

The OAR is assumed to be independent of depth, and only dependent on STD. Since the collimators are small and span only the central area of the linear accelerator’s flattening filter, this assumption applies quite well.

Small Collimators

There are minimum practical limits to the size of detectors used for beam measurements. This means that is difficult to calibrate the physics models for the collimators with diameters less than 12 mm since it is likely the detector spans the whole of the central peak dose area. The effect is the most significant when measuring CCF.


Chapter 7 WebFast

This chapter describes how to use the WebFast application of FastPlan.

WebFast is a web server and a full‐featured DICOM network application, which can receive DICOM images over standard TCP/IP connections and make those images available to any Java‐enabled web browser. If your computer is connected to FastPlan, through either the hospital intranet or the internet, you can just open your browser, log into WebFast, and select the patient whose images you want to view (Figure 62).

Figure 62 Using WebFast to Access Patient Images

149

WebFast is set up to make the DICOM images coming from the scanner immediately available for viewing through your browser. It is also possible to configure WebFast so that you can remotely view the postprocessed (that is, CT‐localized or fused) images.

The possibility of remote image viewing and contouring offered by WebFast can be used to enhance and improve the collaborative effort among the different personnel involved in the neurosurgery process.

Features

The following is a summary of the main WebFast features:DICOM Storage Class Provider (SCP) status that gives the ability to receive images from remote DICOM client devicesPatient or Study root queries based on any combination of patient name, referring physician, patient, or exam IDSecure web transmission (https) when using the browserSingle image display consoleThumbnail sketches of all images for instant retrievalPixel inversion (black to white and vice versa)Cine loopPan and zoomText Overlay TogglingPredefined CT Window/Levels for anatomical structuresOn‐screen display of 3D patient coordinates within an imageAuto Level/Window based on a user‐defined region of interestAbility to select images in a film view for display in the main windowJPEG Image button that captures a “snapshot” of the main display window image for presentationsImage contouring


Starting WebFast

To start the WebFast application:

1. Open your browser and go to the WebFast server website. (Acquire the web address, username, and password from the administrator of your WebFast server.)If the FastPlan IP address is <FastPlan IP>, then the URL you must type in your web browser is : https://<FastPlan IP>

2. Under Login, type your username and password and click Login.

3. Optionally, you can start WebFast directly from the Stereotactic Radiosurgery Treatment Planning window. Under Stereotactic Image Manager, click WebFast SRS.A web browser window opens and a connection is made to the local WebFast server.

Searching

After you successfully log in, a Search window opens. Here you can type the name or ID# of the patient(s) you want to search for. (You must type at least three characters.) If you want to list all available patients, type all in the text box.

Once you have started the search, the results of that search are listed in a search results window (Figure 63). If your search fails, a single line appears with an error message in it, explaining the cause of the failure. If your search succeeds, each patient appears on a separate line.

WebFast 151

Figure 63 Search Results Window

Viewing Images

To see the list of image series available for viewing, click the corresponding link. For example, if you click a link appearing under Study ID, all the image series under that study are shown (Figure 64).

To view the images in the series, in the View Images columns, click Entire Series. This starts the WebFast image viewer (Figure 65).

Features of the image viewer include the following:Main display area: Images are shown in a 512x512 area on the left. Images that are not 512x512 are scaled to fit within this area while maintaining their original aspect ratio. The DICOM information (such as patient name, ID, and image number) is also shown. If you want to remove all textual information from the image, choose Options > Hide Text Overlays on the right.


Figure 64 List of Study Image Series

Figure 65 Image Viewer

WebFast 153

Status bar: Across the top of the main display area is a status bar. This text informs you of what image is being loaded and whether errors occur during loading. Since WebFast is a multithreaded application, you do not have to wait for all the images to load before viewing a specific DICOM image. The status bar tells you when loading is complete: Idle (Finished Loading).Thumbnail section: The image viewer contains a “filmstrip” on the right side of the main display area with thumbnails of the downloaded images. When you select a thumbnail, the corresponding expanded image is displayed in the main display area.Values: Coordinates and pixel values automatically change with the movement of the mouse cursor across the image. The coordinate values shown are real 3D DICOM patient coordinates. WebFast labels DICOM coordinates as shown in Table 16.

The pixel values shown represent the degree of brightness, which corresponds to density (or other factors) in the image.Cine loop: Clicking the play button launches a cine loop representation of all the downloaded images. These controls operate in the same way as those on a VCR or other video or audio player. You cannot record data.JPEG Image button: This button allows you to load the image currently in the main display area to your web browser. From your web browser you can then save a local copy of the image in JPEG

Table 16 DICOM Coordinates and Their WebFast Labels

DICOM Coordinate WebFast Label

Positive DICOM X L (for left of patient)

Negative DICOM X R (for right of patient)

Positive DICOM Y A (for anterior of patient)

Negative DICOM Y P (for posterior of patient)

Positive DICOM Z S (for superior of patient)

Negative DICOM Z I (for inferior of patient)


format to your system hard drive. The text overlays are not included with the image, which is useful if you are going to e‐mail the image to colleagues or include it in presentations or reports.

Image Display Options

This section describes how to adjust various viewing settings.

Changing Brightness (Level) and Contrast (Window) Levels

You can change Window/Level settings in several ways:Type the desired Window and Level values (Figure 65) and press Enter.Select one of the predefined Window/Level values from the Window/Level Presets menu.Use the mouse:

To change the brightness (Level), hold down the Shift key and left mouse button while dragging the mouse either forward or backward.To change the contrast (Window), hold down the Shift key and the left mouse button while dragging the mouse either left or right.To change both the brightness and contrast simultaneously, hold down the Shift key and the right mouse button while drawing a rectangle over a portion of the image. The settings for this portion of the image become the values for the entire image.

WebFast 155

Zooming In and Out

You can change the magnification of an image in several ways, by using the mouse:

To zoom in, hold down the left mouse button to open a magnifier over the desired area of the image. The magnifier follows the mouse cursor around the image.orHold down the right mouse button while dragging the mouse away from you.To zoom out, hold down the right mouse button while dragging the mouse toward you.

The difference between the two methods is that in the first method, if you release the left mouse button, the magnifier closes.

Panning

Panning functions only when the image has already been zoomed in.

To pan around the image, hold down the Alt key and the left mouse button while dragging the mouse.

Other Display Options

From the Options menu, you are presented with additional image display choices:

Hide Text Overlays: Removes all textual information from the image.Hide Graphics Overlays: Removes all graphic overlays (such as contours) from the image.Flip Images Up/Down: Rotates the image so that it appears upside down.Flip Images Left/Right: Creates an exact mirror‐image.Colormap: Applies different color maps (SPECTRUM, FIRE, or ICE) to the image.Invert Pixels: Turns black pixels into white pixels, and vice versa.


Mouse Interaction Summary

Table 17 summarizes all the available mouse interactions you can use while viewing images.

Table 17 Mouse Interactions for Image Viewing

Action Mouse Button/Keyboard Key Direction of Mouse Motion

Magnify Left

Zoom in Right Away from you

Zoom out Right Toward you

Pan Middle (or Left+Alt)

Level(Brightness)

Left+Shift (Left+Ctrl fine‐tunes)

Away from/toward you

Window(Contrast)

Left+Shift (Left+Ctrl fine‐tunes)

Left/right

Auto Window/Level to area of interest

Right+Shift

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Keyboard Hotkey Summary

Table 18 provides a list of useful keyboard hotkeys you can use while viewing images.

Table 18 Hotkeys for Image Viewing

Key(s) Action

Arrow (up/down/left/right)

Navigate through the images. Pressing the down/right arrow keys displays the next image, while pressing the up/left arrow keys displays the previous image.

d Displays the DICOM tag values relative to the image in the main display area.

z Displays debug information, including heap usage.

i Toggles scaling interpolation on and off.

s Smooths the image.

a Enables autosmoothing.

f Updates all images in film view (see the next section).


Film and Multiplanar Views

The Film View button (Figure 65) allows you to see all the currently loaded images in film view (that is, side‐by‐side). The film view (Figure 66) works like the main display only with respect to the mouse interactions. Note that these film‐view windows utilize a lot of system resources (RAM), so closing them will increase your computer speed.

Figure 66 Film View

From the film view panel you can enter the Multiplanar viewing mode by clicking Multiplanar. In this viewing modality, you can inspect the image set from different orthogonal planes at the same time (Figure 67). You can scroll through the image set by pointing and clicking one of the views. For example, to scroll through the sagittal

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and coronal planes, point and drag the mouse cursor on the axial slice. To scroll through the axial and coronal planes, point and drag the mouse cursor on the sagittal slice, and so forth.

You can also display a 3D maximum intensity projection reconstruction by left‐clicking the lower right pane.

Figure 67 Multiplanar Viewing Mode

Contour Tool

WebFast allows you to draw and save contours as DICOM RT structures.

To create and save a new structure set:

1. Click Contour (Figure 65).The Contour tool window (Figure 68) opens.

2. Click Create New Structure.The Edit Structure Attributes window opens, with two tabs.


Figure 68 Contour Tool Window

3. Click the Structure Name tab and type a structure name.

4. Click the Display Color tab and select the color of the structure.

5. Click Ok.The Edit Structure Attributes window closes.

6. In the “film strip,” select the slice you want to start contouring.

7. The slice appears in the display area.

8. Position the mouse cursor over the image and start drawing the contour.The contour tool allows only closed contours. Any open contour is automatically closed when you click Accept (see the next step).

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9. To accept the contour you drew, click Accept.orTo discard the contour, click Discard.The tool allows you to draw bifurcated structures, that is, structures that consist of multiple closed contours (for example, eyes). To draw such a structure, draw a contour, accept it, then draw a second contour on the same slice, accept it, and so forth.

10. To contour the next slice, click Next.orSelect the slice from its thumbnail image in the “film strip”.

11. To navigate through the slices, click Next and Previous.

12. When you have finished contouring, click Done Editing.

13. To generate the DICOM structure set file, click Publish New RTSTRUCT.

14. To delete all the contours from a slice, at any time during the contouring, click Done Editing and then Clear All.

15. To delete an entire structure, select that structure from the Existing Structures table at the top of the window and click Delete Existing Structure.

16. To edit the name and display color of a structure, select that structure from the Existing Structures table and click Edit Existing Structure.

The structure set you created and saved is listed under the patient’s image series as illustrated in Figure 69.

When you close the Contour tool window, and return to the image results list, when you click on the corresponding Entire Series link under View Images, the image set that was used for drawing the structure is downloaded with the contours overlaid (Figure 70).


Figure 69 New Structure Added to List

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Figure 70 Images Overlaid with Contours


Appendix A Printer Setup

This appendix describes how to add a new printer to the FastPlan system and how to test the printer setup by printing a test page.

Adding a New Printer

To set up a printer for use with the FastPlan system:

1. In the Login Manager window, click Service.

2. In the next window, click Printer Configuration.A web browser opens with a Printer application.

1. Click Add Printer and type username root and the associated root password. If you do not know the root password, contact Varian Service.

2. Click OK.

3. Fill out the name, location, and description of the printer.These are arbitrary and are useful only to users for future identification.

4. Input the following data in the subsequent menus:Device: AppSocket/HP JetDirect Device URI: socket://<ip_address_for_printer> Make: RAW Model: Raw Queue (en)

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Printing a Test Page

To print a test page:

1. Return to the printer menu.

2. Click Print Test Page.The printer should either print immediately or audibly warm up before proceeding.


Appendix B Building 3D Models

Using the FastPlan system 3D reconstruction techniques, it is possible to build multiple 3D renderings of varying transparencies of the skin, skull, tumor, and isodose shells of the patient’s image set. Clinicians can use these 3D models to visualize anatomy, isocenters, and the dose distribution.

This chapter describes how to build and edit 3D models from the Cone Planning module.

WARNING: When building structure models using the isosurface (ISO) segmentation method, only areas overlaid with red are used in the volume calculations, To compute accurate volumes for DVH calculations, be sure the entire structure is overlaid in red.

3D Head Contour Model

The FastPlan system automatically generates an external head contour model each time you select the 3D View. If the model is unsatisfactory, you may rebuild it.

Intensity Threshold Level

The FastPlan system uses intensity threshold leveling to determine which areas in the 2D images to include in the 3D model. By adjusting the thresholds, you begin to see a solid red line outline the surface of the anatomy you intend to model. Only image areas with intensity (brightness) above the lower threshold level and below the upper threshold level are incorporated in the 3D model. The intensity threshold level determines the exact size and shape of the image space surface.

If you set the threshold too high, you tend to “fill‐in cracks” and the fine details are not seen in the 3D model. If the threshold is set too low, parts of the desired anatomy appear to “drop out.”

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Rebuilding the 3D Head Contour

The tasks associated with rebuilding the 3D head contour include:Setting the intensity threshold levelsEditing the model to remove “noise” and unnecessary pieces of the image

To rebuild the 3D head contour:

1. Click the Optional Views tab.

2. Click 3D.

3. Click Build Models.The 3D build tool (Figure 71) opens.

4. Confirm the Model Name reads Head Contour.

5. Magnify the orthogonal views.

6. Observe the red outline around the patient’s skin.

7. Move the Lower Threshold slider through the threshold range until a solid red line outlines the patient’s head as seen in the orthogonal views.

8. Click Build.The elapsed time required to build the 3D model depends upon the size of the image set and the amount of workstation memory. While building, the “working” message appears. Do nothing until the model is completely built.

9. Click Close.

10. The 3D build tool closes.


Figure 71 3D Build Tool

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3D Tool Bar

The tool bar icon inside the 3D view (Figure 72) has three modes and four buttons. The tools make it convenient for you to rotate and translate the 3D model and to also return the model to its home (by default, anterior) orientation.

Figure 72 3D Tool Bar

To rotate the 3D model using the tool bar icon:

1. Click the Rotate icon.

2. Move the cursor onto the 3D model.

3. Left‐click and drag the cursor across the model in the intended rotation direction.

4. Click the Point and Click icon to return to the point‐and‐click mode.

To translate the 3D model using the tool bar icon:

1. Click the Translate icon.

2. Move the cursor onto the 3D model.

3. Left‐click and drag the cursor across the model in the intended translation direction.

4. Click the Point and Click icon to return to the point‐and‐click mode.


Editing a Model

The edit option in the 3D view panel removes visual noise and unnecessary pieces of the image, such as a scanner head rest or scatter. The edit program finds all pixels contiguous to the pixel you initially select and displays these in white. You then have the option to either select and retain those pixels or to select and remove those pixels.

To access the Edit tool:

1. Click Build Models.

2. The build models tool opens.

3. Click Edit Models.The Edit tool opens.

The recommended technique is to:

1. Click on the patient’s anatomy, such as the nose or forehead.

2. In the Edit tool, click Select.

3. Observe as the tracked pixels turn white.

4. In the Edit tool, click Retain.

5. Repeat the editing process until you are satisfied with the results.

Clipping a Model

Clipping is another technique that you can use to remove undesired parts of a model. While the Edit option tracks all points contiguous to the point you select, the Clipping option allows you to redefine the 3D area.

Remember, it is the solid red line surrounding the surface of the anatomy that determines what is included in the model. Adjusting the anterior, posterior, inferior, superior, left, and right slider bars (Figure 71) moves the boundary lines. Everything within the boundary lines is kept; everything outside the boundary lines is dropped.

The recommended technique is to clip the image using the slider bars in the 3D build tool before you build the 3D model.


To clip after the 3D model is built:

1. Click Clipping.The Clip tool opens.

2. Use the slider bars to adjust the boundaries of the model.

Deleting a Model

The Delete Models option removes any one model or all models associated with the patient image set. After clicking Delete Models, click All (Figure 73) to display a list of the models. To delete a model, highlight the model you wish to delete or click All, then click OK. Wait until the watch icon disappears before beginning another operation.

Figure 73 3D Model Delete Tool

Rotating a Model

The Rotate tool (Figure 74) includes slider bars and buttons that cause the model to rotate. These slider bars include:

Azimuth slider: Allows you to rotate the model by individual degrees to the left or to the right.Elevation slider: Allows you to rotate the model by individual degrees in the superior or inferior direction.Roll slider: Allows you to roll the model in any direction.


There are also six view buttons:AnteriorPosteriorLeftRightSuperiorInferior

Clicking any of these buttons rotates a model in 90‐degree increments.

Figure 74 Rotate Tool

Attributes Tool

The Attributes tool reports the volume of all these models in cubic centimeters.


Model Settings Tool

Clicking Model Settings opens the Model Settings tool (Figure 75), which allows you to fashion the model. This tool allows you to change the color, visibility, cut mode, type, and data, and the color wash of each model.

Figure 75 Model Settings Tool

Building 3D Models of Internal Objects or the Skull

The FastPlan system software allows you to build 3D models of the skull, tumor, vessel, artery, or isodose shell. The steps involved in building a 3D object are:

Resetting the skin transparency levelFinding the best representation of the object in all viewsSelecting the model name and image‐set volumeTracing the objectChanging the model colorRestoring the transparency level

Note: The blue virtual probe may still be visible in the 3D view, along with the isocenter shell and associated purple bounding box if an isocenter has already been established.


Setting the Transparency Level

Set the transparency of the 3D skin model to 0%. This action temporarily clears the 3D view so that only the newly built model appears in the 3D view pane.

To set the transparency to 0%:

1. Click Model Settings.The Model Settings tool opens.

2. Click Visibility, and drag to 0%.

Translating Through the Volume

Find the best representation (largest volume) of the tumor or vessel in each slice using the translate scroll bar to the right of each image in the main window. Moving the scroll bar allows you to step through the data set slice by slice.

Selecting the Model Name and Volume

If you used the ImMerge system program to correlate the image sets, you can build models using either CT or MRI image sets. Furthermore, to prevent overwriting the skin model, be certain to select a model label other than the default skin label.

To select the model name and volume:

1. In the main window, click Build Models.The Build Models tool (Figure 72) opens.

2. Select the model name.

3. Select the volume.

The blue virtual probe may still be visible in the 3D view, along with the isocenter shell and associated purple bounding box if an isocenter has already been established.


Manual Trace Tool

Using the Manual Trace tool to build a model enables you to free‐hand trace the perimeter of the object. The preliminary trace appears in blue. When accepted, the trace color changes to green and becomes the active trace.

The Manual Trace tool opens a “working canvas” that appears on the left and an options menu (Table 19) that appears on the right.

Table 19 Manual Model Trace Tools

Command Function

Accept Turns a blue preliminary trace into an active green trace.

Up Displays the slice previous to the currently displayed slice.

Down Displays the slice following the currently displayed slice.

Nearest Trace Superimposes the green active trace in the closest image to the currently displayed image. This trace appears as a blue preliminary trace.

Cancel Clears any green active traces as well as any blue preliminary traces.

Clear All Clears any green active traces as well as any blue preliminary traces. Make certain the pertinent image is displayed.

Light Box Displays the light box images.

Close Exits the trace module and returns you to the 3D Build tool.


To build a 3D model using the manual trace method:

1. In the main window, click Build Models.

2. The Build Models tool opens.

3. Under Segmentation, click Manual Trace.A virtual light box opens. If the soft tissue is not visible, adjust the Mean and Window settings.

Note: A new trace may be drawn on the new image, or the nearest active trace may be superimposed on an image.

4. Scroll through the images and click on a frame that contains the pathology of interest.The image appears on the canvas.

5. Outline the pathology of interest. Left‐click and drag around the perimeter of the object.The outline appears in blue, indicating a preliminary trace that is not included in the 3D model until it is activated.

6. If you are satisfied with the trace, click Accept.The trace color changes to green, indicating that this is the active trace. The enclosed anatomy is included in the 3D model. If you are not satisfied with the trace, click Cancel and restart the tracing process.

7. Continue modifying the traces until all anatomy desired in the 3D model is outlined in green in all applicable frames. Make certain no undesirable anatomy is outlined in green, as it will also be included in the 3D model.

8. Click Close.

9. In the 3D Build Model tool, click OK.

10. Edit, as necessary (see “Editing a Model” on page 171).

Changing the Color of the Model

The model appears in the default peach color. To change the color:

1. In the main window, click Model Settings.The Model Settings tool opens.


2. Click Color in the appropriate model row and drag to the desired color.If the model you are interested in does not appear, scroll through the window to view all the built models.

Restoring the Transparency Level

Restore the transparency level(s) of model(s), if earlier they were set to 0%. To change the transparency level:

Click Model Settings.The Model Settings tool opens.

3. Click Visibility in the appropriate model row and drag to the desired value.

Isodose Shells

Use the 3D models to construct an isodose shell at the desired percentage level. To do so:

1. Click Dose Vol Res to set the isodose resolution as 1 mm, 2 mm, or 5 mm.

2. Adjust the bounds of the isodose shell using the slider bars.The default is 20 mm x 20 mm x 20 mm centered at the average coordinates of all defined isocenters.orDrag the handles of the magenta bounding box. Set the percent level for the isodose shell using the slider. The default is 80%.

3. Click Generate.An isodose shell is generated and washed onto the 3D model as a translucent shell.

As new isocenters are added, new isodose shells are washed onto the 3D model.


Appendix C MLC Planning

In the Stereotactic Radiosurgery Planning window, under Treatment Planning, clicking MLC launches a module that allows you to review CT and MRI data sets and perform a data export to the Eclipse system, where actual MLC planning is performed. This module contains two tabs: Export and Settings. For a description of Export functionality, see Appendix E. For a description of Settings functionality, see “Settings Tab” on page 83.

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Appendix D FastPlan Archiver

The archiver application archives and restores patient data to and from CD, DVD, network file share, or USB removable drive. The data is stored either compressed or uncompressed and has a built‐in checksum function to guarantee data integrity.

The archiver is backwards compatible with archived CD‐ROM data from FastPlan 5.0 and 5.1 systems. Newly archived data cannot be read on any version of the software prior to FastPlan 5.5.

User Interface

The user interface consists of two tabbed lists: Archive and Restore. On the left margin of the window are labels for patient details and buttons for user actions.

The Archive tab (Figure 76) shows all “active” patients that are currently on the system and are available to FastPlan. In this tab, you can choose to archive or delete multiple patients at once. For each patient in the list, the following information is provided in the list column headings. Clicking any of these labels sorts the data accordingly.

Patient: Patient nameMod: Image modality: for example, CT, MRI, PETSize (MB): Megabytes of space occupied on the local diskCompressed Size: Predicted megabytes of space which would be occupied on the archive medium if data is compressed. This value is updated by the system overnight and may not always reflect the correct size of the data. The value appears as N/A for data sets that are less than a day old.Archived: Indicates whether data has ever been archived.

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Figure 76 Archive Tab

The Restore tab (Figure 77) lists patients stored on any of the supported archive media. From this tab, you can restore multiple patients back to the local disk. The following columns are available in this list (in addition to patient name and modality):

Archived Size (MB): Actual space (in megabytes) occupied on the archive media, whether compressed or uncompressed.Archive Date: Date and time when the archive was created.On Local Disk: Indicates whether this data is found on the local disk (for example, if the patient has been previously restored or never deleted). Does not necessarily indicate that archive data and local disk data are identical.

Figure 77 Restore Tab


The patient detail information (Figure 78) on the left side shows the following information:

NamePatient IDDiagnosisPhysician nameDate of image creationNumber of images available for planning (for localized data sets.)

If more than one patient is selected, then the Size of selected data data area (Figure 79) shows the sum of predicted storage capacity occupied for all selected data, both uncompressed (raw) and compressed (archived). This may be used for optimizing space utilization on CD or DVD media, such that the maximum number of patients can fit on a single disk.

Figure 78 Patient Detail Information, One Patient Selected


Figure 79 Patient Detail Information, Multiple Patients Selected

The buttons on the lower half of the left margin represent all of the available actions. These buttons include:

View Attributes File(s): Opens an editor window that shows the raw attribute data for the selected patient(s). For multiple patients, the editor displays multiple tabs. Available in both Archive and Restore modes.Refresh Patient List: Forces the data in the list to be reread from disk, if an update is needed. The list updates itself automatically every five minutes. Available in both Archive and Restore modes.Select Fused MR(s): If one or more planned CT data sets are already selected, selects associated MR data sets based on fusion data. Does not select unfused data sets. Available only in Archive mode.Remove Patient(s): Permanently deletes selected data from the system. If any unarchived data is selected for removal, a warning message appears. Available only in Archive mode.Restore Patient(s): If one or more patients are selected, restores data to the local disk. Available only in Restore mode.


Archive Patient(s): If one or more patients are selected, archives data to the selected medium. Available only in Archive mode.Eject CD/DVD: If the archive medium is either a CD or DVD, ejects that medium from the drive.Exit: Returns to the Login Manager window.

Archiving Patient Files

To archive patients:

1. Click the Archive tab.

2. Select the patients to archive.

3. Click Archive Patient(s).An archive dialog box (Figure 80) opens.

Figure 80 Archive Dialog Box

The Use compression check box determines whether the data is compressed before archiving. Typically, compression reduces the amount of occupied space by approximately a factor of three. However, it may also be slower than storing data uncompressed, since compressing (and uncompressing) takes time. If storing a single patient on a CD, for example, it is not necessary to use compression. On the other hand, if you are trying to fit as many patients as possible on a single CD or DVD disk, then compression is more efficient.

If storing data to a CD or DVD, you should choose the correct button. The archiver cannot automatically detect the type of disk in the drive tray, and if you click CD to write to a DVD, or vice versa, an error message appears. If the amount of selected data exceeds the usual


capacity for a CD or DVD, then the archiver issues a warning message. The archiver assumes, conservatively, that a CD has a capacity of 650 MB and a DVD has a capacity of 4.5 GB.

If you are using an external USB drive, first make sure that the drive is plugged in to the FastPlan computer, before clicking External USB drive. If a failure message appears, your drive might be incompatible with the system. The drive must be formatted as FAT32.

The Network drive option may be used if you have a Microsoft Windows file share on the network that has already been configured for use with FastPlan. This option may not be compatible with all types of Windows network drives.

For network and external USB drives, a warning appears if you are attempting to archive an exam that already exists on the archive destination. You have the options to overwrite or cancel.

Restoring Patient Files

To restore patients:

1. Click the Restore tab.

2. Select the patients to restore.

3. Click Restore Patient(s).A restore dialog box (Figure 81) opens.

Figure 81 Restore Dialog Box

Clicking CD/DVD reads data from your FastPlan CD‐ROM drive. CD archive data from a previous version of FastPlan (prior to version 5.5) is read and restored.


For the External USB drive option, make sure the drive is plugged in, as described earlier. The Network drive option works only if preconfigured, as described earlier.

When data is restored from any source, the archiver first checks if the data is already present on the systemʹs local disk. If so, a dialog box (Figure 82) appears with a listing of every patient found on the system.

Figure 82 Dialog Box Listing Patients Already on Local Drive

Clicking Erase & Overwrite first removes data from the local hard drive and then restores it from archive. Any changes to the data made after archiving are lost. This could be useful if you suspect that the data has been damaged or compromised. The Overwrite option overwrites archive data over existing system data, but it may preserve new files that have been added to the patient folder, such as MRI fusion data or new plans. The Skip option skips over any data that appears to be on the system and restores only data that is not already on the system.

If data is restored from an archive CD made with a version of FastPlan prior to 5.5, then the archiver automatically performs an overwrite, consistent with the behavior of the old archive utility.


../../../../../../../C:/Archive

../../../../../../../C:/Archive

../../../../../../../C:/Archive

Data Format

Data is archived in either tar or tar‐gzipped format, depending on whether compression has been activated. The files are written flat to the top‐level directory in the archive destination. For each patient directory, two files are generated that appear as follows:

3651b2b5359625d0584c8c53ae3746c4.attr

3651b2b5359625d0584c8c53ae3746c4.tgz

The file with the .attr extension is a copy of the _attributes file inside the patient directory. The _attributes file is a plain‐text file generated by the FastPlan DICOM receiver for all incoming image data. The presence of the .attr file allows the archiver to quickly retrieve information about all the patients in the archive. The file with the .tgz extension is the tar‐compressed patient directory. (For uncompressed tar files, the extension is .tar).

The name of the file pair is not a random sequence, but a 32‐byte md5 hash of the full patient directory name. The name is hashed to guarantee compatibility across all different types of archive file systems, whether they be ISO9660 for CD or DVD or FAT32 for USB file systems.

Configuring Network Drives

A Windows file share folder may be configured as a network drive. The share could be on a departmental file server or a shared folder on a Windows PC.

Note: Avoid the use of spaces in folder names. If you want separation between words, use an underscore (_) instead.

The following example demonstrates how to do this on a PC.


Setting up File Sharing on a Windows PC

As an example, suppose we want to use the following folder to store FastPlan archive data:

C:\Archive\Fastplan

We can set up C:\Archive as a shared folder and specify FastPlan as a subfolder. In Windows Explorer, right‐click on C:\Archive and click Sharing.

In the resulting dialog box, enable sharing and set up the desired permissions. Make sure that at least one user has Full Control of this share.

Connecting to Windows Share from FastPlan

You must have the appropriate rights to perform this activity.

To connect to a Windows share:

1. At the Login Manager window, click Service.

2. At the next window, click Varian Service Use Only.

3. At the resulting prompt, click Yes to confirm that you are authorized to continue.

4. Click Sysconfig.A configuration window opens.

5. Type r to run archiver.

6. Type c to configure the Windows File Sharing server for archiving.The Windows File Sharing for network archival dialog box (Figure 83) opens.


7. Type values for the parameters as follows:IP of Windows sharing PC or server: Type the static IP address of the Windows computer used for sharing.Name of Windows share: In the earlier example, the name of the share would most likely be Archive.Sub‐folder within share: If there is a folder (or set of folders) within the share, then this text box should be filled. For the example above, this would be Fastplan.Username: The name of a user with a valid account on the Windows computer, who has access to the share.Password: The password for the same user.

8. After the text boxes are filled, click Ok.The dialog box closes.

9. Type t to test the connection.If no errors are reported, the connection succeeded.

Figure 83 Windows File Sharing for Network Archival Dialog Box


Appendix E DICOM Export

This appendix describes how to export DICOM data from FastPlan.

The Cone Planning application includes an Export tab from which you can export DICOM data (Figure 84).

Figure 84 Cone Planning Export Tab

You can access the Export tab in two ways:From the Stereotactic Radiosurgery Treatment Planning window, under Treatment Planning, when you click MLC.Directly from within the Cone Planning application when you click the Export tab.

When you click DICOM Export, the DICOM Export dialog box (Figure 85) opens, which allows you to select which DICOM data to send and what destination to send it to.

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Figure 85 DICOM Export Dialog Box

Transferring Data from MLC Application

You would typically use the MLC button to transfer localized CT or fused MR images to the Eclipse planning system. When you click MLC, the Cone Planning application starts in export mode. In this operating modality, the only tabs available to you are the Export and Settings tabs (Figure 86).

You are able to export only images from the MLC button: the RT Plan and RT Dose check boxes in the DICOM Export dialog box are always disabled.

To transfer localized CT or fused MR image sets from the MLC button:

1. Select the patient in the Stereotactic Radiosurgery Treatment Planning window.

2. Click MLC.When Cone Planning is run on a CT data set, this application automatically searches for a matching fused MR data set. If no matching MR data set is found, a message appears: No MR data--continuing with CT only. If one fused MR data set is found, it is automatically loaded. If more than one fused data set is


found, a dialog box (Figure 87) opens with information on each of the fused MR data sets and you can select which data set you want. Click OK and the dialog box closes.The Cone Planning application starts in export mode.

3. Verify that this is the image set you want to transfer.

4. Make any necessary changes to the image settings from the Settings tab. (See “Settings Tab” on page 83.)

5. Click DICOM Export.The DICOM Export dialog box opens.

6. In the Destination list, select the destination for the export and select the check box(es) corresponding to the data you want to transfer.

7. Click Send.A progress indicator informs you of the status of the data transfer process.

Figure 86 Export and Settings Tabs

DICOM Export 193

Figure 87 Select Fused MR Data Set to Load Dialog Box

Transferring Data from Cone Planning Application

After a plan has been created and approved, you can transfer it to Eclipse, a patient positioning system, or a record‐and‐verify system via DICOM from the Export tab. To transfer the plan:

1. Go to the Export tab and click DICOM Export.A dialog box opens, asking if you want to create a dose volume for transfer purposes.

2. If you are transferring the plan to Eclipse and want to compare the dose distribution of the FastPlan plan with a corresponding plan created in Eclipse, click Yes.The application generates a dose volume for export. Creation of the dose volume may take some time, depending on the complexity of the plan; for a plan consisting of 20 fields, for example, it may take between 3 and 4 minutes (the more fields, the longer it takes, since the software computes the dose contribution relative to each field in the plan).


orIf you want to send plan parameters to a patient positioning system, or a record‐and‐verify system, you do not need to transfer the dose volume, so do not create one.

3. In the DICOM Export dialog box, select the check boxes corresponding to the data you want to transfer and click Send.The plan is sent. Notice that only approved plans can be transferred. If your plan has been saved but not approved, you cannot transfer it.

Structure Sets

There is no option for sending structure sets as such from FastPlan. Each time you export an image set and a plan, the system creates a simple DICOM structure set, consisting of the isocenter(s), in the background and transfers it to link the images to the plan.

DICOM Export 195

Appendix F DICOM Import

This appendix describes how to import DICOM data from CDs and DVDs into FastPlan.

1. Insert the media with DICOM data into the CD/DVD drive.

2. At the Login Manager, click DICOM Import.The Z‐Remote Teleradiology Application (also referred as ZShuttle) window (Figure 88) opens, along with an instruction window.

Figure 88 ZShuttle Window

3. Follow the instructions displayed in the instruction window (Figure 89) to transfer DICOM images to FastPlan.

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Figure 89 DICOM Import Instruction Window


Appendix G Imaging Protocol

Radiological studies are an integral part of the FastPlan Stereotactic Radiosurgery Treatment Planning system. The FastPlan system relies on the information from CT and MRI computer‐processed images to accurately plan the treatment and dose selection.

A stereotactically acquired CT scan is a requirement for treatment planning using the FastPlan system.

Typically, a patient is imaged with both MRI and CT. Then, using the ImMerge application software, the MRI image set is correlated to conform with the results obtained by the CT image set. The fused image sets provide the clinician with the functional or structural image detail from the CT and MRI scans.

The following sections specify the imaging protocol to use when scanning patients for a FastPlan system procedure.

CAUTION: Failure to follow the imaging protocol may affect patient data set loading, image quality, or localization accuracy.

Note: Acquisition of new scanners or modifications to existing scanners may require updated drives or software on your FastPlan system. Contact your local sales representative to determine if modifications are necessary.

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CT Imaging

Attach the CT localizer to the base ring affixed to the patient’s skull prior to imaging. The preferred imaging protocol is to start the scan at the top of the patient’s head. Obtain a series of sequential, 1‐mm‐thick axial slices down to the ring. This strategy improves image quality and ImMerge efficiency.

As an option, you can start the scan at the top of the patient’s head. Obtain a series of sequential, 5‐mm‐thick axial slices down to the area of the target lesion. Change to 1‐mm‐thick slices through 0.5 mm below the target region. Resume 5‐mm‐thick slices and scan to the ring. This strategy provides maximum resolution through the target region, but, by using thicker slices in the nontarget brain regions, it reduces the number of scan slices, scanning time, and computer memory requirements.

Scan as quickly as possible to eliminate patient movement. If you think there is motion, repeat the scan. Axial slices are preferred. One‐millimeter helical scans reformatted to 1‐mm axial slices are acceptable. While the technique is scanner‐dependent, high kV is typical; mA is variable. There can be no tube‐cooling delays. If necessary, use a lower mA.

Contrast agents may be injected before or intravenously fed during the scan to maximize lesion enhancement on the CT images.

The FOV (field of view) of the acquired images should be between 29 cm and 35 cm in order to include the outlying fiducial rods for subsequent CT localization.

CAUTION: Properly plan each patient’s case prior to any stereotactic procedure. Evaluate all anatomical and functional considerations revealed on preexisting diagnostic imaging. Consider all clinical constraints, which may be relevant to the choice of stereotactic procedural strategy, selection, or use of instrumentation, and anesthesia methods.

Note: The FastPlan system supports the VMS and BRW stereotactic localizers. The VMS and SNT localizers are identical.


Imaging Protocol

The following imaging protocol must be used throughout the image set because the FastPlan system is designed to accept only certain parameters:

Contiguous, nonoverlapping axial slices1‐mm slice thickness throughout the target region1‐mm to 5‐mm slice thickness throughout the nontarget regionFOV between 29 cm and 35 cm to encompass the entire cranium and the outlying fiducial rods (roughly equivalent to a small abdominal scanning field)Square matrix 512x512 or 256x256 (MR only)Scan from the top of the head through at least 0.5 cm below the target region

Image Set Review

Before removing the patient from the scanner bed, the surgeon or radiology technologist should examine the scans to make sure:

Patient orientation is correct.Imaging protocol is followed.Total pathology or region of interest is visible.Entire patient head and localizer are visible.No motion artifact is present.

Image Set Archive or DICOM Transfer

Archive the image set to a tape or optical disk in an uncompressed file format. Certain GE scanners, by default, archive in a compressed file format. These GE file formats are acceptable for use with the FastPlan system.

Note: Attach the CT localizer to the base ring affixed to the patient’s skull prior to imaging.

Imaging Protocol 201

The FastPlan system uses the DICOM 3.0 standard for network‐based image transfers. Site‐specific image‐set transfer instructions are provided at the time of the FastPlan installation and in‐service training.

MRI Imaging

Acquiring MRI images involves:Basic techniqueImaging protocolImage set reviewImage set archive or DICOM transfer

These subjects are discussed in the following sections.

Basic Technique

Acquire the images using the standard MRI diagnostic MRI head coil. Scan the entire head so that it will be easier to identify landmarks and therefore the system will be able to more precisely correlate the MRI image set with the CT image set. If this is not feasible, at a minimum, the scan should include the mastoids and the orbits since, typically, the area of interest should fall within this anatomy.

The recommended scan technique uses volumetric image acquisition with a modified T1‐weighted sequence (SPGR, TR = 19.2 and TE = 4.2). This technique allows rapid image acquisition to minimize movement during the MRI acquisition. The volumetric scan also allows

Note: Slice descriptions should be used to discern between fused CT and MRI data. The series description always reports “CT” in fused cases.

Note: This technique assumes that the MRI image set will be correlated with a stereotactically acquired CT image set using the ImMerge application software. Since the MRI image set does not require a stereotactic head ring, the patient is routinely scanned the day before treatment. Contrast agents may be injected to maximize lesion enhancement on the MRI images.


1‐mm‐thick slice acquisition. While it is not mandatory that the slice thicknesses be identical for image fusion, the smaller slice thickness provide maximum image resolution. If 3D acquisition is used, reformat the scan to 1‐mm axial slices.

Imaging Protocol

The following imaging protocol must be used throughout the image set because the FastPlan system is designed to accept only certain parameters:

Contiguous, nonoverlapping axial slices1‐mm slice thickness throughout the target region1‐mm to 5‐mm slice thickness throughout the nontarget regionFOV between 22 cm and 26 cm to encompass the entire craniumSquare matrix 256x256 (MR only) or 512x512Entire head scan or at a minimum from the orbits through the mastoids

Image Set Review

Before removing the patient from the scanner bed, the surgeon or radiology technologist should examine the scans to make sure:

Patient orientation is correctImaging protocol is followedTotal pathology or region of interest is visibleEntire patient head is visibleNo motion artifact is present

Image Set Archive or DICOM Transfer

Archive the image set to a tape or optical disk in an uncompressed file format. Certain GE scanners, by default, archive in a compressed file format. These GE file formats are acceptable for use with the LINAC SCALPEL system.

Imaging Protocol 203

The FastPlan system uses the DICOM 3.0 standard for network‐based image transfers. Site‐specific image‐set transfer instructions are provided at the time of the FastPlan installation and in‐service training.
