the new advances in radiotherapy techniques…challenge of qua

13-17 Sep 20109th July 2009 IRPA – Nairobi ,Kenya 1

Mahmoud Hegazy Ph.D , RSE , MACPSEMSenior Radiation Oncology Medical Physicist ROV- Melbourne , Australia

Lecturer of Medical Physics – Cairo University ,Egypt

The new advances in radioTherapy techniques…challenge of quality

assurance

OBI QA

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Radiation Oncology Victoria

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What is Quality Assurance?

“All those planned and systematic actions necessary to provide confidence that a product or service will satisfy given requirements for quality.”

ISO 9000

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Quality Assurance

In the BSS seen in the context of medical exposure as essential for radiation protection of the patient

Quality Assurance and Control is also important to assess the overall effectiveness of protection and safety measures

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QA and QC

Quality Assurance is the overall process which is supported by Quality Control activities

Quality Control describes the actual mechanisms and procedures by which one can assure quality

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Consequences for radiotherapy

A good acceptance testing and commissioning program is fundamental for any QA activities

QA activities are typically a subset of the tests and procedures used for the commissioning of a unit

QA applies to both physical and clinical aspects of the treatment

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Treatment records must be kept of all relevant aspects of the treatment - including Session and Summary Record information Records all treatment parameters Dose Calculations Dose Measurements

Particular emphasis is placed on QA of dosimetry

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Treatment records

Must contain all relevant information

Can be in electronic format

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A QA system itself and its outcomes must be critically reviewed.

External audits are recommended to verify that the checks are not only done but that they also achieve what they are supposed to do

Every good system requires an independent look at times

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A Comprehensive QA Program typically comprises

Quality Assurance Committee Policies and Procedures Manual Quality Assurance team Quality audit Resources

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OBI-QA

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Rapid Arc


Introduction , ..OBI in general…. The On-Board Imager system is designed to correct for motion

and setup errors of patients undergoing radiation therapy.

The OBI system provides three imaging modes:1-Two-dimensional 2-D radiographic acquisition,2-Fluoroscopic image acquisition, and 3-Three-dimensional 3-D cone-beam computed tomography

CBCT acquisition.

The fluoroscopic images are used to verify the gating thresholdsof the respiratory gating system to account for intra-fraction i.e., respiratory motion.


The radiographic images manage inter-fractional motion and setup errors.

Using the 2D2DMatch and 3D3DMatch analysis tools a user can register the acquired kV or CBCT images with their associated reference image like DRR or planning CT for CBCT

Couch corrections are then downloaded to the linear accelerator and the couch is moved remotely.

Continue…

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OBI…QA…Puzzle


Needs of QA Program The use of this new technology

necessitates a comprehensive quality assurance QA program to maintain and monitor system performance characteristics, which have been established at the time of commissioning.

The QA program has three components:

1- Safety,2- Geometry, and 3- Image quality


The most critical tests are those that evaluate the geometric accuracy of the OBI system, since the OBI system is intended for repositioning of the patient before/during treatment.

All the geometric tests assume that the location of the MV isocenter is known and can be identified independently.

SO , the tools used to identity the location of the MV isocenter like wall lasers, field light are assumed to be calibrated.

Continue…


The OBI system

The OBI system consists of a kV x-ray source KVS and a kV amorphous silicon detector KVD mounted on the linear accelerator using robotic arms.

In the treatment room, an infrared pendant extends and retracts the robotic imager arms, while, at the treatment console, a control box OBI control console extends and retracts the OBI and MV imager arms remotely.


Safety and functionality QA

Door interlock : X-ray generator locked if door opened.

Warning lights : During x ray on, all warning lights should be illuminated.

Warning sound :During x-ray on, the OBI console should sound an acoustic warning.

Collision detection and interlock : Press covers and paddles of the KVD and the KVS. Check that the Clinac motion interlock trips, stopping all motions.

Hand pendant motion enable bars : Release motion enable bars on the hand pendant while retracting/extending the arms.

Tube warm-up : Press footswitch in fluoroscopic mode for 20 seconds with the x-ray

Functionality : Check data transfer from the information system to the treatment workstation 4D ITC, to the OBI workstation, and to the mechanical systems.


Continue…

The safety QA should be performed before any patient is treated on a daily basis

It is more efficient to create a test “warm-up” patient to be used each day during morning linear accelerator QA which Includes:

1- At least one kV setup field for the tube warm-up. 2-The kV setup field contains a reference image.3-Gantry angle and position information of the KVD.

The test plan is delivered exactly like a treatment for a normalpatient; the patient scheduled, the plan retrieved from the database, and the setup field moded up on the treatment workstation 4D Integrated Treatment Console, 4DITC, which sends the data to the OBI workstation


Geometrical accuracy QA

The geometrical accuracy QA tests evaluate the accuracy and stability of mechanical hardware devices as well as some of the software functions.

1. OBI isocenter accuracy2. Magnification accuracy3. Run-out during arm vertical travel4. OBI isocenter accuracy with gantry rotation

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1- OBI isocenter accuracy:

The OBI isocenter accuracy QA test evaluates whether the digital graticulegenerated by the OBI application coincides with the treatment MV isocenter.


2. Magnification accuracy:

Changes in SAD and SID will affect image magnification.However, it is very difficult to measure changes in SAD and SID radiographically, because even a relatively large change in SID or SAD will result in only a small change in image magnification.

SO

A physical measurement is the most accurate.


3. Run-out during arm vertical travel

This test checks that a vertical motion does not have any longitudinal or lateral components. We moved the gantry to 90° so that the detector was pointing up, removed the cover, and marked where the ceiling laser hits the imager. Care was taken to ensure that the gantry was exactly at 90°. We then moved the image vertically from −50,0,0 to −30,0,0 and measured the displacement of the center of the KVD in the longitudinal and lateral directions.

The tolerance is 2 mm.


4.OBI isocenter accuracy with gantry rotation :

This test verifies stability of the OBI isocenter as a function of gantry rotation. The cube phantom was placed on the treatment couch with the marker located at the isocenter. OBI images were acquired at gantry angles 0°, 90°, 180°, and 270°, which locate the KVS and KVD to take right lateral, anterior, left lateral and posterior images, respectively. The displacement should be less than 2 mm.


Image quality QA

The goal of the image quality QA is to establish baseline for image quality parameters and to monitor these parameters over time. Corrective action recalibration/repair could be initiated if theparameters went outside their tolerance.

Radiographic image quality For Contrast resolution and spatial resolution detection using the

Leeds phantom to monitor both contrast and spatial resolution over time.

The phantom has 18 disks of 8 mm diameter each with contrasts ranging between 16.7% and 0.9%, and 21 bar patterns ranging between 0.50 and 5.00 lp/mm.


Beam QualityBeam Quality


Physicists need to be trained on:

OBI system as a new modality. OBI calibrations. Basic OBI maintenance and QA. Plan preparation for use with OBI. Clinical functionality using kV/kV and MV/kV matching. Marker Match workspace, and Third party software use with the OBI.


Radiotherapists need to be trained on:

How the OBI system communicates with the Clinic and the verification system.

How to use the OBI system. Basic morning QA procedures. How to acquire KV and MV images. How to perform a marker match utilizing 3D image

sets from Pinnacle .


Summary Program of Quality assurance need to established for

maintaining of quality for OBI system.

Primary focus on geometric accuracy and precision, secondary focus on dose and image quality.

An integrated daily check should be implemented into routine clinical use with a 15 minute time penalty.

Training for the staff is required to achieve the benefits of the new technology and guarantee the proper use on time .

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Thank You For

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the new advances in radiotherapy techniques…challenge of qua

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