AAPM REPORT NO. 54

STEREOTACTIC RADIOSURGERY

Report of Task Group 42Radiation Therapy Committee

,:. Michael C. Schell (Chairman)Frank J. Bova

David A. Larson (Consultant)Dennis D. LeavittWendell R. Latz

Ervin B. PodgorsakAndrew Wu

!

June 1995

Published for the

AmericanAssociation of Physicists in Medicineby the American Institute of Physics

STEREOTACTIC RAD1OSURGERYTable of ContentsI. INTRODUCTION .................................................................................. 1

A. Clinical Introduction ..................................................................... 1B. Introduction For Administrators ................................................... 3

If. RATIONALE FOR RADIOSURGICAL TREATMENTS ................... 4

A. Non-Malignant Lesions ................................................................. 5B. Malignancies .................................................................................. 5

III. THE ACCURACY OF STEREOTACTIC RADIOSURGERY .......... 6

IV. STEREOTACTIC RADIOSURGERY TECHNIQUES ...................... 8V. ACCEPTANCE TESTING ................................................................. 1 I

,',• A. Introduction .................................................................................. 1 1B. Accurate Localization .................................................................. 1 1

DISCLAIMER: This publication is based on sources and information C. Mechanical Precision ................................................................... 1 1

believed to be reliable, but the AAPM and the editors disclaim any 1. Linac Gantry, Collimator, and Couch (PSA) ....................... 12warranty or liability based on or relating to the contents of this 2. Lasers ...................................................................................... 12

publication. 3. Patient Docking Device ........................................................ 13

4. Frame Syste m :....... .:............................................................... 13TheAAPMdoesnotendorseanyproducts, manufacturers, orsuppliers. 5. Target Verification Devices .................................................. 13Nothing in this publication should be interpreted as implying such 6. SRS System Verification Test ............................................... 13endorsement. D. Dose Delivery ............................................................................... 15

E. Patient Safety/Machine Interlocks ............................................. 15Further copies of this report ($10 prepaid) may be obtained from: E Gamma Knife Acceptance Tests .................................................. 15

VI. DOSIMETRY .................................................................................... 16

A. Linac Systems ............................................................................... 16American Association of Physicists in Medicine 1. Dose Measurements .............................................................. 16

One Physics Ellipse • Off-Axis Ratios .............................................................. 20College Park, MD 20740-3843 • Scatter Correction Factors ............................................ 21

• Collimator Scatter .......................................................... 21International Standard Book Number: 1-56396-497-X • Tissue-Maximum Ratios ............................................... 21

International Standard Serial Number: 0271-7344 B. Measurement Summary ............................................................... 211. Linacs ...................................................................................... 21

©1995 by the American Association of Physicists in Medicine 2. Gamma Knife Units ............................................................... 223. Phantoms ................................................................................ 22

All rights reserved. No part of this publication may be reproduced, 4. Dosimetry Calculation .......................................................... 22storedinaretrievalsystem, ortransmittedinanyformorbyanymeans • Planning Parameters ...................................................... 24(electronic, mechanical, photocopying, recording, or otherwise) • Gamma Knife ................................................................. 25

without the prior written permission of the publisher. VII. QUALITY ASSURANCE ............................................................... 26A. Introduction .................................................................................. 26

Published by the American Institute of Physics, Inc. B. Probable Risk Analysis and QA .................................................. 27500 Sunnyside Blvd., Woodbury, NY 11797 C. Treatment QA ................................................................................ 28

1. Check Lists ............................................................................. 28

Printed in the United States of America 2. Target Position Verification .................................................. 30

3. Laser Check ............................................................................ 302. Couch-Mounted Frame System ............................................ 63

4. Pedestal Mount System ......................................................... 31 • Dynamic Stereotactic Radiosurgery5. "Known" Target Test During Localization:Recommendation to SRS Manufacturers ............................. 31 at McGill University ...................................................... 63

6. Head Ring Movement Test ................................................... 32 C. Dedicated Radioisotope SRS Unit--The Gamma7. Verification of Treatment Setup ........................................... 32 Knife Technique ........................................................................... 648. Secondary Test ....................................................................... 33 1. Apparatus ................................................................................ 64

D. Stereotactic Couch Mount ........................................................... 33 2. Target Localization ............................................................... 661. Overview ................................................................................ 33 3. Dose Calibrations and Measurements ................................. 662. Target Verification/The Joint Center for 4. Absorbed Dose Profiles ........................................................ 67

Radiation Therapy .................................................................. 34 5. Mechanical Alignment Accuracy ......................................... 703. Patient Alignment .................................................................. 35 6. Results .................................................................................... 704. Alignme_ht Verification of a Couch-Mounted XVI. Appendix V. EXAMPLE GAMMA-KNIFE QA PROGRAM .....71

Frame (McGill) ....................................................................... 36 XVII. Appendix VI. EXAMPLE RAD1OSURGERYE. Routine QA .................................................................................. 37 PROCEDURES AND CHECKLISTS ........................................ 72E QA Program for a Gamma Knife ................................................. 39 XVIII.APPENDIXVII. DYNAMIC STEREOTACTIC BRAING. Stereotactic Frames and Quality Assurance .............................. 42 IRRADIATION PATIENT CHART (SAMPLE) ........................ 81

VIII. FUTURE DIRECTIONS ............................................................... 43 REFERENCES ............................................................................ 83A. Image Correlation ........................................................................ 43B. Multiple Fractionation ................................................................. 44C. Real-Time Portal Imaging ............................................................ 45D. Conformal SRS ............................................................................. 45E. Robot-Guided Linac ..................................................................... 49

IX_ SUMMARY ...................................................................................... 49X. ACKNOWLEDGEMENTS ................................................................ 50XI. APPENDIX L PROBABLE RISK ANALYSIS FLOWCHART:

EXAMPLE ........................................................................................ 5 IXlI.APPENDIX II. PROBABLE RISK ANALYSIS FLOWCHART:

EXAMPLE ...................................................................................... 5 IXIII. APPENDIX Ilia. SRS QA SCHEDULE ....................................... 52XlV. APPENDIX lllb, LINAC QA SCHEDULE ................................... 52XV. APPENDIX IV. STEREOTACTIC RADIOSURGERY

TECHNIQUES ................................................................................. 53

A. Heavy-Charged-Particle Therapy .............................................. 531. Heavy lons--LBL .................................................................. 532. ISAH: Irradiation Stereotactic Apparatus for Humans ...... 533. Beam Characteristics ..................................... . ....................... 534. LBL Stereotactic Frame ................................ _....................... 545. Treatment ................................................................................ 56

B. Linear Accelerators in Radiosurgery ......................................... 571. Pedestal-Mounted Frame Techniques ................................. 57

• The initial configuration at the Joint Center ForRadiation Therapy. ........................................................ 57

• University of Florida Technique .................................. 61

ii i iii

I. INTRODUCTION

A. Clinical Introduction

Stereotactic radiosurgery (SRS) of an intracranial lesion, or radiosurgery,combines the use of a stereotactic apparatus and energetic radiation beams

to irradiate the lesion with a single treatment. Stereotactic Radiotherapy(SRT) utilizes the stereotactic apparatus and radiation beams for multiplefractions or treatments. SRS and SRT are essentially two-step processes con-

sisting of: (1) accurately defining the shape and location of the lesion andthe neuroanatomy in the reference frame of a stereotactic frame system withCT, MRI or angiography; and (2) developing and delivering the planned

,', treatment. The treatment techniques produce a concentrated dose in the le-sion with steep dose gradients external to the treatment volume. The rapiddose falloff from the edge of the treatment volume provides dramatic spar-ing of normal brain tissues.

SRS was first developed by Leksell in the late 1940s to destroy dysfulLc-tional loci in the brain using orthovohage x rays (Leksell, 1951). Heavycharged panicles, gamma rays, and megavoltage x rays have been used inthe intervening decades to irradiate arteriovenous malformations as well asbenign and malignant tumors.

This report describes the techniques for stereotactic external beam irra-diation with heavy charged particles from cyclotrons, x rays from electron

"- linear accelerators (Linacs) with nominal beam energies between 4- and 18-MV, and gamma rays from the "gamma knife" using 201 _Co sources. Thefirst three-dimensional treatment of a brain lesion with a megavoltage unit

took place in April 1948 (Kerst, 1975). The first combined use of an x-rayunit and stereotactic frame occurred in 1950 (Leksell, 1951, 1983). This

report is written primarily for clinical medical physicists who are co.sider-ing acquisitioning and cmnmissioning of a SRS program at their facility. Itis extremely important to understand the importance of quality assurance inevery step of the SRS treatment process. As with brachytherapy, the dosewith SRS is administered in one or a few applications. However, the dose

rate for SRS is such that the dose is typically delivered in less than one hourfrom the start of treatment, unlike low-dose-rate brachytherapy, which is

typically administered over several days. It is imperative therefore that athorough and methodical quality assurance program for SRS be developedat each institution. Safety precautions include the implementation of inter-locks on the patient support assembly (couch) motion and the gantry mo-tion, which limit the arc or rotation of the equipment and prevent patientinjury. No therapy department should consider undertaking SRS without tilepresence of at least one clinical medical physicist (as defined by the AAPM,1985) at each procedure. The quality assurance requirements demand thatevery step be checked by a physicist and independently rechecked by a

1

B. Introduction For Administrators

second expert (clinical medical physicist or a board-eligible medical physi-cist). A joint statement has been issued on this subject by The American Table I contains time estimates for various tasks that are involved withAssociation of Neurological Surgeons and The American Society for Thera- commissioning a linac-based radiosurgery procedure. These time estimatespeufic Radiology and Oocology (Lunsford el al., 1994). The statement de- deal solely with the time requirements for collecting the physical data and

fines radiosurgery, but also recommends that training be received by the testing the hardware and software of a radiosurgery installation. For ex-radiation oncologist and physicists. It also specifies that the oocologists and ample, it is estimated that it would take approximately 10 weeks for a de-physicists be board certified or eligible for board certification, partment with a scanning film densitometer and the appropriate ionization

Typical abnormalities that are treated with SRS are single metastasis chambers to commission a commercial radiosurgery package. Such pack-(Starm et al., 1987), solitary primary brain tumors (Larson et al., 1990), ages are currently available from RSA, Inc. (Brookline, MA) and Leibingerarteriovenous malformations (Betti et at., 1989; Colombo et al., 1987; and Fischer LP (Metairie, LA). To fabricate the treatment hardware (the

Fabrikant el al., 1985 and1984; Kjellberg et al., 1986; Saanders el aL, 1988; tertiary collimation system) for the stand or the couch mount systems wouldand Steinar, 1986)'!and benign conditions (Barcia-Salofio et aL, 1985) or take approximately 0.7 yr. To install a prefabricated hardware system andtumors, such as pituitary adenoma and acoustic neuroma (Kamerer el al., write a treatment planning software package for radiosurgery would take

1988). Overviews of clinical applications of SRS/SRT have been presented 2.3 yr. To design the entire system in-house and install the hardware andby Flickinger and Loeffler (1992), Luxton el al. (1993), McKenzie et al. software would require almost 3 yr. These time estimates do not include the

(1992), and Podgorsak et al. (1987, 1988, 1989, 1990, and 1992). SRS gen- background efforts regarding the coordination of the disciplines of radiationerally consists of identifying a target in the patient's brain that is to be irra- ontology, neurosargory, and neuroradiology. A considerable amount of time

dinted by the intersection of one or more heavy charged particle beams, bymultiple noncoplanar arcs with a linac, by dynamic rotation with a linac, or

by the intersection of _Co beams at the isocenter of the gamma knife. TABLE I. Time Estimates for Commissioning a Radiosurgery Program.Target identification begins with the fixation of a stereotactic frame to t_stimated Project Times (weeks)

the patient's skull. Imaging techniques, such as computerized tomography(C_, magnetic resonance imaging (MRI) and/or angiography, pinpoint the TASK TIME

target within the stereotactic frame. The location and geometry of the target Stereotactie Equipment Evaluation 2 wksis then transferred to a treatment planning system that calculates dose distri- Treatment Planning Systembutions in three dimensions. The treatment planning system must be ca- a) Evaluate commercial package 1 wkpable of computing dose distributions from either the combination of b) Develop treatment planning 2 yrs

Dosimetry Measurements 2 wksnoncoplauararcs or the intersection of the _°Co beams, For linac-besed Treatment Delivery Hardwareradiosurgery, the arc geometry can be varied to provide a concentrated dose a) Setup commercial package 3 wksto the selected target while minimizing the dose to critical structures sur- b) Adapt a prefabricated system 12 wksrounding the target. The gamma knife achieves similar results by selective c) Design & fabricate 28 wks"'plugging" of holes in the helmet (Flickinger, 1990). Final System Test 2 wks

Routine OA 0.5 days/monthThe clinical rationale or indications for radiosurgery are discussed in Plan and Treat a Radiosurgery Case 8-t2 hr/patient

Section II. Factors contributing to the net uncertainty of the SRS treatments (DepenOing onare reviewed in Section 111, which describes the tolerances encountered in Complexity)each SRS technique. A brief introduction to the radiosurgical techniques ispresented in Section IV and detailed synopses of five techniques are in the TIME ESTIMATES FOR FOUR OPTIONS:appendices. Acceptance testing requirements for the pedestal-mounted and Commercial Package 10 wkscouch-mounted frames are contained in Section V. The beam and dosimetry Adapt a Prefabricated System andWrite Software 2.3 yrsrequirements are describedin Section VI. Requirements of quality assur- Fabricate Hardware/Buy Software 0.7 yrsante programs for the hardware, software, and treatment procedure are re- Design and Fabricate Hardware/viewed in Section VII. Current research efforts in SRS are summarized in Write Software 2.7 yrsSection VII1.

2 3

_r

is invested in coordinating the quality assurance programs of each depart- A. Nonmalignant Lesionsment and establishing the team required to execute a radiosurgery proce-dure. Finally, there are time estimates for planning and treating a typical Stereotactic radiosurgery has been used for nonmalignant lesions such asradiosurgery patient. It usually requires 8 hr of 1.5 physicists and dosimetrists arteriovenous malformations and acoustic neuromas. Arteriovenous malfor-

to plan and treat the patient. This begins with acquiring imaging data early mations are congenital anomalies that develop from aberrant connectionsin the day, entering the data sets into the computer, establishing the appro- within the primitive arterial and venous plexus overlying the developingpriate contours and surfaces of the tumor and normal tissue structures de- cortical mantle. During embryological maturation, this region of abnormalveloping a plan, and reviewing the plan with the radiation oncologists, the vasculature is incorporated into the brain parenchyma. Initially, the cerebralneurosurgeons, and finally treating the patient. The routine QA of vasculature adjacent to tbeAVM develops normally. However, becauseAVMsradiosurgery hardware and software requires approximately 0.5 days per lack a normal capillary bed and the associated hemodynamic resistance,month, local blood flow through the AVM is increased and vascular dilation gradu-

In summary, the time requirements for installing and commissioning a ally ensues. This shunting of blood through the AVM may result in a bloodradiosurgery proce_dure are substantial. The time requirements for treating a steal phenomenon. The lack of a normal capillary bed implies that the yes-

typical patient per week amounts to 20% of a typical weekly patient load. sels of tbeAVM provide no nutritive function. Therefore, tissues deep withinThis procedure represents a significant increase in the staffing require- the AVM may be nonfunctioning and sclerotic. The approximately 2-3%ments of the physics section of the department of radiation oncology, per year risk of bleeding is the primary reason for treating the AVM. TheWe recommend an additional 0.3 FTE medical physicists/patient/week standard treatment is surgical resection, if it can be performed safely. Tbe(board-certified or board-eligible radiotherapy medical physicist) to immediate goal is to eliminate the risk of hemorrhage. In cases where thesupport an ongoing radiosurgery program. We recommend a minimum AVM is relatively inaccessible, especially if centrally located in the speechof 0.2 l--ll_ medical physics years be allotted for the acceptance and corn- area or in the brain stem, radiosurgery may be considered.missioning of a commercial linac-based SRS system. Radiosurgery is a very The radiosurgical principles appllcable to the treatment of AVMs are evolv-time-consuming procedure requiring a high degree of attention to detail, ing, and thus far are similar to established surgical principles: (1) Within theThe consequences of understaffing and misadministration are a significant nidus of the AVM, radiosurgery may be destructive because there is usually" " little normally functioning tissue therein; (2) One should not pursue arteriesand grave risk to the patient.

or veins beyond their normal attachment to the nidus to avoid damaging•lormal tissue: (3) Obliterating a final feeding artery only improves tissue

II. RATIONALE FOR RAD1OSURGICAL TREATMENTS nutrition whereas obliterating any other artery only worsens tissue nutri-tion; and (4) Total obliteration of the AVM is of vastly greater benefit than

Radiosurgery has been used to treat a variety of benign and malignant partial obliteration. Usually the obliteration of AVMs after radiosurgery islesions as well as functional disorders. In many categories, however, only a not complete for 1-3 years.small number of cases have been treated. Results have not been reported Stereotactic radiosurgery for small-volume AVMs appears to achieve aand indications are far from established. Kihlstrom reported 1311 gamma high obliteration rate at the end of 2 years with a low complication rateknife unit radiosurgical procedures performed at Karolinska Hospital be- (Alexander et al., 1993). There are several limitations or disadvantages totween 1968 and 1986 (Kihlstrom, 1986).The most frequent reasons for treat- stereotactic radiosurgery for the treatment of AVMs. The obliteration of themerit were arterioveaous malformations (AVM) (41%), acoustic neuroma larger AVMs is not readily achievable with stereotactic radiosurgery with a

(14%), and functional radiosurgery (14%). Chierego et al. (1988) listed 150 2-yr follow-up. Microembolization in conjunction with stereotacticpatients treated with a linac-based system in Vicenza.: The most frequent radiosurgery is currently under evaluation for treatment for the largerAVMs.categories were AVM (44%) and malignancy (33%). The natural history of Other sites of treatable benign lesions include pituitary adenomas, acrontegalyinoperable arteriovenous malformations may be favorably influenced by Cushings disease, and Nelson's syndrmne (Levy et al., 1989 and Alexanderradiosurgery as discussed below. The risk of hemorrhage is 2-3% per year et al., 1993). [See also Friedman (1993); and Hosobuchi (1_87).]and 6% immediately posthemorrhage. The nidus of the AVM is a blood steal

B. Malignanciesfrom the adjacent parenchyma. Hence, it is generally assumed that the adja-

cent tissues are dysfunctional and that radiation damage to this tissue would It may be argued that radiosurgery as the sole treatment modality, withresult in minimal additional neurological deficits, its dose localization characteristics, is contraindicated in the treatment of

4 5

The definition of a tumor with CT (or AVM with angiography) depends

primary malignant intracranial lesions, where tumor cells arc known to in- on the resolution of the image and the relationship of the macroscopic ira-filtrate beyond the borders of abnormalities seen on CT or MRI (Halperin et age with the microscopic extent of the disease. The first factor is a conse-al., 1989; Hochberg and Pruitt, 1980; and Wallner et al., 1989). The role of quence of the dimensions of the voxel. The pixel dimensions are typicallyradiosurgery in radiation oncology may be analogous to that of interstitial 0.7 mm by 0.7 ram, and the separation between slices is not less than 1.0brain implants as a high-dose boost following the standard course of exter- mm. Therefore, an object's location cannot be known better than to withinhal beam therapy (Halperin et al., 1989). Mehta et al. (1993) have per- 1.5-2.0 ram. The mechanical position uncertainty in any orthogonal axis offormed a prospective analysis of the toxicity and efficacy of stereotactic a stcreotactic frame is 0.6 ram. The gantry rotation axis, collimator rotationradiosurgery boost when combined with external beam radiotherapy for the axis, and table rotation axis should coincide within a sphere of 1 mm radius.treatment of newly diagnosed glioblastoma (GBM). External beam radia- The net uncertainty in target localization and treatment delivery is then 2.0tion therapy was delivered to 54 Gy with 1.8 Gy per fraction times 30 frac- mm for an AVM and 2.4 mm for a tumor when summed in quadrature (Table

tions. The stereotactic radiosurgery boost ranged from a maximum of 25-35 II). Note that the net uncertainty increases to 3.7 mm when a CT slice sepa-Gy. Their preliminary findings were that no significant toxicities were en- ration of 3 mm is employed. This net uncertainty is far less than the clinicalcountered and the necrosis rate was 10% at a follow-up of 13.5 months. The knowledge of the AVM or neoplasm.data evinces at best a minimal improvement in survival. SRS application to AVM definition can be limited by factors other than the detector resolu-

the treatment of metastases has been found to provide improved local con- tion. The nidus of an AVM may be partially obscured by arteries or veins. Introl if applied in conjunction with whole brain irradiation (Fuller et al., this case, the location of the nidus may only be known to within 5 mm. In1992). Fonber discussion of the use of SRS for malignancies is located in the absence of this uncertainty, orthogonal angiograms permit the locationSection IV. of an AVM in the stereotactic frame coordinates to within 1 ram. The l-ram

limit derives from the radiologists ability to identify a unique poim fromIlL THE ACCURACY OF STEREOTACTIC two views. However, the extent of the nidus cannot be determined frmn the

RADIOSURGERY orthogonal radiographs, preventing the optimum plan of irradiating the tar-

Accuracy limits not only reflect the technical limitations of the frames get while sparing normal tissue.and treatment units, but also reflect the current knowledge of the neurologi- Similar uncertainties exist for certain brain tumors, but it is caused bycal abnormality and its radiation response. Two SRS techniques report un- the invasive nature of the malignancies. The relationship of the macroscopiccertainties in target alignment with the beam focus of 0.2-0.4 mm in patient CT image with the primary brain tumor is a matter of current study (Halperinposition, whereas the linac setup uncertainty is 1.0 mm (Friedman and Bova, et al., 1989; Hochberg and Pruitt 1980; Kelly et al., 1987; and Wallner et1989 and Wu et al., 1990). Although the techniques differ in accuracy, it is al., 1989). Halperin et al. obtained antemortem CT scans of glioblastomaunclear whether the difference is clinically significant. The uncertainty in multiforme (GBM) tumors in 11 patients. In nine cases, autopsies indicateddose delivery is a result of two processes: (I) target definition and (2) the that the tumor extended beyond a I-cm margin around the contrast-enhanc-machine tolerances of the dose delivery apparatus (including the frame). A ing areas. Furthermore, the differences between survival rates for wholereasonable perspective on accuracy requirements for SRS should include brain irradiation versus partial brain irradiation are not statistically signifi-(I) the current accuracy in external beam therapy; (2) the net result of un-certainties in SRS; (3) the resolution of the target image; and (4) the rela-

tionship of the image to the lesion itself, macroscopic and microscopic. TABLE II. Achievable Uncertaintiesin SRSThe accuracyof patient setupin conventionalexternal beam therapy has Stereotactic Frame 1.0 mm 1.0 mm

been investigated by several groups, including that of.Rabinowitz et al. Isocentric Alignment 1.0 mm 1.0 mm(1985). The variation in setup was determined from the differences between CT Image Resolution 1.7 mm 3.2 mmsimulation and port films. The standard deviation in treatment-to-treatment Tissue Motion 1.0 mm 1.0 mmvariation was 3 mm. However, the average discrepancy between the simula- Anglo (Point Identification) 0.3 mm 0.3 mmtion films and port films was 5 mm when the brain was the treatment site. Standard Deviation of 2.4 mm 3.7 mmThe mean deviation exceeded 7 ram. Hence, the benefit of stereotactic 1o- Position Uncertainty

calization and treatment is the ability to plan and treat a target with reduced (by Quadrature)

position uncertainty.

76

Collimator,201

cant.This lack of differencebetweentreatmentsis a resultof the failure of SeamSources201 r UpperHemisphericalShieldexternalbeam therapy to control bulky disease.Currentexternal irradiation

techniques alone are insufficient for tumor eradication; "focal" (brain im- + 4a0plants or SRS) treatment is required to help eliminate the original tumor. Itis further speculated that when the primary tumors arc controlled, manypatients will have recurrent GBM outside the abnormal region as shown byCT or MRI.

The uncertainties in dose delivery by any of the above SRS techniques ,HyOrauuicPowerare significantly less than the clinical knowledge of the location and extent __ .... /

oftbe lesion as determined by CT or MRI. The accuracy in dose delivery tothe target of linac-based radiosurgery is a significant improvement over con-ventional techniques and approaches that of the heavy-charged:particle fa-cilities. Until technology affords accurate target localization, the differences THE RADIATION UNITin position accuracy wig have minimal impact on treatment delivery. How-ever, the impact of the net positionaccuracyon the planning processshould FIGURE 1. The cross-sectionalview of the gamma knife irradiator.The 201be foremostin the mindsof the oncologistandphysicist.Table II illustrates sourcesare focused at one locus.The stereotacticframe positionsthetargetthe uncertaintiesin SRS delivery for two cases:(]) ]-mm slice thickness at the intersectionof the beams. (Wu et al., 1990.)and (2) 3-ram CT slice thickness.

IV. STEREOTACTIC RADIOSURGERY TECHNIQUES

SRS is a nonstandard radiation therapy technique by nature of the means _ _..,., _=........of delivery of the target dose.Two basic approacheshave beentaken in the _ ''""' ®_°='_"_'_,"_", ="="" "-" ""¢"_" .....

past: (1)modification of standardlinear acceleratorswith the addition of _ _ _ _I _-_

tertiary collimation and stereotactic frame system or (2) the use of a dedi-cated a_Co unit. Linac-based radiosurgery delivers a narrowly collimated x-ray beam while rotating about the target. The target is positioned at the

center of linac rotation. The process is repeated for a number of treatment _/couch angles, Thus, the target is caught in a cross fire of x-ray beams whichdeliver a lethal dose to the target and a sublethal dose to the surrounding t

normal tissues. The gamma knife unit delivers a comparable dose by meansof the simultaneous irradiation from 201 cobalt beams. The dose distribu- .b ....... _ ......... _,_.......... _ ............

tion is concentrated in a localized small volume by the intersection ofbeams_) )__ __ )K._/_' '

from up to 201 Co sources (gamma knife unit shown in Figure 1) or of the "_multiple arcs from a linear accelerator. The small treatment volume andrapid dose falloff are also characteristic of brain implants, yet the technicalaspects of SRS are considerably different from those of.brachytherapy. "_ _-,_ _, __

Figure 2 illustrates the beam entry patterns for (I) the gamma knife unit;

(2) a single 360 ° arc in the transverse plane of the patient; (3) a fournoncoplanar arc geometry; and (4) the dynamic radiosurgery approach (b, a,e, and g, respectivelyin Figure 2). These four approachesproduce isodose FIGURE 2. Beam-entry patternson a patient's skull forvarious radiosurglcalsurfaceswith shapesthat are unique to the SRS. The dose-volume histo- techniques. (Podgorsak, E.B. Physics for radiosurgery with tinearaccelerators, in "Stereotactic Radiosurgery", Chapter 2, pp. 9-34,gramshave been found to be approximately equivalentamong the four ap- NeurosurgeryClinics of NorthAmerica, Vol. 3, edited by D. Lunslord,W.B.proachas(Phillips et al.. 1989; Scbell et al., 1991; andSerago, 1992). Stan- Saunders Company, Philadelphia,PA, 1992.)

8 9

ERRATA SHEET AAPM REPORT NO. 54

Helium Ions vs 6-MV X raysdard arc geometries yvere routinely used for many lesions in the mid-1980s.

Advances in treatment planning software allow for beam's-eye-view plan- 100 __ /

ning which facilitates dose optimization to the target and avoidance of criti-

cal normal tissues. The shapes of the isodose surfaces can be modified to 75 HeliumIons 1.27omminimize the dose to critical structures by changing the arc geometry withlinacs. The gamma knife unit collimators can he plugged to prevent beam

passage through vital tissue. At most centers, each treatment plan geometry so _Nx_.j X rays 1.25 nmis adjusted to minimize normal-tissue dose and maximize target dose, as isthe case with conventional external beam planning. Irregularly shaped le- 2ssions are treated with multiple isocenters with linacs and the gamma knife

unit. The range in collimator size differs between linacs and the gamma o ....knife unit. Linacs use collimator sizes in the range of 5-40 mm diameter, o 0.2 0.4 0.6 o.a 1whereas the gamma knife unit has four collimator diameters: 4 mm, 8 ram, Radius (cm)

14 ram, and 18 ram. Large lesions require more isocenters with the gammaknife unit than with linacs. RGURE 3. The dose profileof a 230 MeV/u heliumion beam is compare_

withthe dose profile of a 6-MV x-ray beam.The irradiation geometry for heavy charged particles varies between cen-ters. LBL (Lawrence Berkeley Lab) only irradiated through the hemisphere

with the lesion; a four-port geometry is normally employed. The Harvard Sch¢ll et al. (1991) demonstrated that the differences in techniques disap-Cyclotron Therapy Center treats with seven to eleven ports. Heavy charged peered at the 5% dose level as the collimator sizes exceeded 2.0 cm whenpanicle beams have the advantage of stopping at the distal edge of the tar- the geometry of the cranium became the limiting factor. Detailed informa-get. Consequently, the integral dose is approximately a factor of two less tion on five SRS techniques is contained in Appendix IV.than with photon therapy beams. The beam shaping of heavy charged par-ticle beams eliminates the need for multiple isocenters. V. ACCEPTANCE TESTING

Figure 3 compares the beam profiles for helium ions with 6-MV x rays A. Introductionwith 1.27- and 1.25-cm beam diameters. The helium beam yields a more

uniform dose profile than the 6-MV x rays. However, the two modalities The basic requirements for SRS are: (1) accurate localization, (2) me-have comparable profiles. An 8-mm diameter lesion would receive a zero % chanical precision, (3) accurate and optimal dose distribution, and (4) pa-dose gradient from helium ions and a 10% dose gradient with 6-MV x rays tient safety. These four requirements are common to linac-based radiosurgeryif a prescription were based solely on profile data. This comparison sug- and the gamma knife unit. Some tests are unique to the gamma knife unitgests that the primary advantage of heavy ion therapy is in normal tissue and are discussed at the end of this section.sparing, due principally to the finite range of the particles in tissue. Sincethe late 1940s (Wilson, 1946), the advantages of delivering heavy charged B. Accurate Localizationparticles in concentrated doses to tumors while sparing normal tissue havebeen acknowledged. Since the high cost of heavy ion therapy limits its use, The stereotactic localization techniques shall be able to determine themost institutions rely on the gamma knife unit or modified linens. However, coordinates eta well-defined object (pointer or a ball bearing in a phantom)new x-ray-based techniques, such as PEACOCK and ACCU-RAY, have the in the frame coordinate system to within 1 mm for angiography, and 2 mm

potential to enhance the dose delivery of x-ray beams and narrowing the for CT and MRI. A localization test is described in the System Verificationgap between x rays and heavy charged particle approaches (see Section VIII). Test section.

Three groups have compared photon-SRS techniques. The first compari-son used the steepest and shallowest dose gradients as criteria (Podgorsak et C. Mechanical Precision

el., 1989). More recently, Scbell et el. (1991) and Serago et al. (1992) have An essential element of stereotectic therapy is the alignment of the pa-used dose-volume histogram analysis to compare linac-based SRS techniques, tient-frame-based coordinate system with the LINAC coordinate system.

The differences in dose-volumes between the approaches were clinically The alignment procedure puts the treatment target position specified in theinsignificant when the total arc traversal exceeded 400 ° of gantry rotation.

10 11

_r

patient-frame coordinate system at the LINAC isocenter. The alignment pro- 3. Patient Docking Devicecedure typically relies on rigid mechanical devices, including pedestal andcouch-mounted devices, or on registration of patient-based markers. A pre- The patient docking device couples the frame to the treatment machine,requisite of this report is that the radiation oncology department abide by either the pedestal or the couch-mount bracket. The patient docking devicethe recommendations of AAPM Reports 40 and 45 with regard to quality must be as mechanically rigid as possible. Notably, the docking position onassurance and quality improvement of equipment and procedures. AAPM the frame should minimize torque caused by the patient. For the pedestal-Report 40 focuses on comprehensive QA for radiation ontology and AAPM mounted frame system, the origin of the pedestal's coordinate system should

Report 45 deals specifically with the code of practice for radiotherapy ac- be aligned to within 1.0 mm of the gantry/collimator/PSA axes' locus. Forcelerators and machine tolerance limits. Adherence to the recommendations the couch-mounted frame, the patient is brought in alignment with the LINAC

of the aforementioned reports forms the foundation for the SRS QA proce- isocenter using the standard couch motors. These motors, however, are notdures delineated below, accurate or sensitive enough to assure accurate positioning. The patient dock-

, ing device thus must allow a vernier-based or fine adjustment system to1. Linac Gantry, Collimator, and Couch (PSA) precisely align the patient at the desired isocenter/target position. It is the

experience of the task group members that the frame system can be aligt_cdThe overall stability of the isocenter under rotation of all axes----couch, to within 1 mm of the linac coordinate system.

gantry, and collimator--needs to be established before commencing any

stereotactic therapy program. These axes shall coincide within a 1-mm ra- 4, Frame Systemdius sphere for all possible gantry, collimator and PSA angles. (Hartmann etal., 1994) Caution: Some centers correct for the precession of the PSA axis The performance of the components relating to the frame coordinate sys-by changing the target coordinates as a function of PSA angle in order to tern must be verified as to compliance with the manufacturer's specifica-center the lesion during treatment. We recommend correcting the mechani- tions. For example, the BRW pedestal and phantom base axes should becal precession problem (e.g., PSA bearing replacement) prior to commis- accurate to within ± 0.6 mm for each axis. The CT, MRI, and angiographicsioning the SRS procedure. PSA precession correction requires at least two localization procedures must yield target coordinates that differ by less thancoordinate adjustments for each PSA angle. These corrections could be mis- the total uncertainty of the frame system and imaging procedures over theapplied and place the lesion further away from the linac isocenter, coordinate domain of the frame system.

A couch-mount system requires a mechanically stable couch. The most

critical mechanical property is the stability of the couch rotation axis under 5. Target Verification Devicesrotation. It is not necessary for the couch to be infinitely rigid, as such arequirement is unattainable, even in principle. It is necessary, however, for The target verification devices ensure that the patient is treated at thethe couch to be stable under rotation, i.e., as the couch rotates, the mechani- correct target coordinate, that the target coordinate is aligned with the

cal forces on it should not change the torque on the-couch. A couch can be isocenter, and that the patient is aligned with the isocenter. These devicesmechanically stabilized by external supports to increase the stiffness if are calibrated with respect to the frame-based coordinate system. This call-needed, bration needs to be verified and documented upon acceptance.

2. Lasers 6. SRS System Verification Test

Before a particular radiosurgery system is considered ready for patic,tThe most practical room-based reference system is:afforded by wall- treatments, we recommend testing the entire system/procedure (ItJcaliza-

mounted lasers. A set of three lasers--two on opposite sides lateral to the tion through treatment) for geometric accuracy. This comprehensive methodLINAC and one in the ceiling--suffices. These lasers must cross accurately to obtain quantitative results involves the use of hidden targets (steel or leadat the isocenter and must be as parallel as possible. These requirements balls) placed in a head phantom. These hidden targets are localized by CTimply that the laser-mounting brackets must allow very fine movement to

and planar angiograms (MRI may require a more careful selection of phan-allow mechanical movement of the complete laser assembly. The lasers tom and targets) under conditions and with the same equipment used forshould coincide within I mm of axes locus. The lasers should be routinely patients. These targets are next "treated" with a number of fixed beamschecked for drift, representing entrance points spread over theupper hemisphere of the skull.

12 13

A port-film exposure is made for each beam. The displacement of the image D. Dose Delivery

of the steel ball from the center of the field is measured for each of the • The accuracy of the absorbed dose (beam calibration) to the targetbeams. From this information, the geometric error in treatment (i.e.. the shall be uncertain by less than 5%, in accord with AAPM Reportdisplacement of the center of the radiation distribution from the target cen- 2 I.

ter) can be calculated. A summary of the geometric error in the "treatment" • The dose delivery to the simulated radio-opaque target shall beof 18 hidden targets is given below (Lutz et al., 1988): aligned to within I mm for all gantry, collimator, and PSA angles.

• The tertiary collimator system shall reproducibly collimate the beamLocalization Method Average Error In Treatment (mm) with a variation in the full-width at half maximum of 2 mm.

Computed Tomography 1.3 ± 0.6 • The dosegradient in the beam penumbra(from 80% to 20%) shallPlane FilmAngiography 0.6 = 0.2 be greater thanor equal to -60%/3 mm.

These results _gree with the uncertainties ascertained by Yeung et al. E. Patient Safety/Machine Interlocks(1993) and determine a margin (in the absence of medical uncertainty) which The linac should be interlocked to:can be used between the prescription isodose surface and the target bound-ary that assures target coverage for a particular confidence level desired.

It is also possible to measure the accuracy of localization alone via CT or • Limit gantry rotation as a function of PSA position in order to pre-planar radiography, in the absence of medical uncertainty, using the test vent injury to the patient, by means of either software or hardware.targets (plastic or steel balls) that are attached, respectively, to the CT and • Set the secondary collimators to the treatment position. If the SRSangiographic localizer frames. The coordinates of the balls can then be mea- treatment occurs with the jaws opened beyond the tertiary

sured directly by mounting the appropriate Iocalizer to the BRW phantom collimator, the normal brain tissue will receive an excessive andbase and comparing with the coordinates found using the treatment plan- unacceptable dose.ning program. Disable power and immobilize the PSA during the SRS treatment.

An interlock system for certain linacs has been developed to

Localization Error = _(AAP) 2 + (ALat) 2 + (AVert_ _ satisfy the above requirements (DeMagri et al., 1994).

where AAP, for example, is the difference between a phantom base mea- F. Gamma Knife Acceptance Testssurement and a computer calculation.

Radiation Survey of the FacilityIf you use digitally reconstructed planar radiographs or MRI, test

the procedure thoroughly to ensure the images are free of distortions Radiation Leakage TestRadiation Wipe Test

throughout the volume of interest. Positional errors as large as 4 mmcan occur when digitally reconstructed radiographs are used for local- Timer Constancy and Linearity Testsization. Timer Accuracy Test

One interesting observation is that if the linac and the radiosurgery appa- Timer On-Off Errorratus are accurately aligned and nlechanically stable, then the average inca- Safety and QA checks:sured errors in "'treatment" (hidden targets in a phantom) will be approxi- a) Door interlockmately the same size as the measured localization errors. The fact that 1o- b) Emergency-off switches

calization and treatment errors presented here are exactly the.same is just a c) Beam on-off lightscoincidence. Furthermore, these results do not suggest that the treatment d) Audio-visual systemapparatusdoes not introduce error. Rather, they suggest that for a well aligned e) Couch movementsystem, errors introduced through the treatment apparatus are smaller and f) Micro switches verify the helmet alignment with

randomly directed with respect to the errors in localization (particularly CT the _Co source locus to -+0.1 mm.localization). Furthermore, uncertainties in measurements of the test target g) Hydraulic system. The hydraulic system is designed to with-coordinates by the phantom base contribute to the "localization error", draw the patient/couch from the gamma knife unit and close

14 15

Slqmtotlcllc Boom proffiett (I 2.5 _ ¢_41)

12

1.0

the gamma unit door in the event of n power failure. A hand ,-Y"- i- "_pump serves as a backup in case of hydraulic fluid pressure o_loss. These systems must be tested, h " "_"_"

h) Dose profiles of each helmet shall be measured by plugging _ o_ _ _.

200 of the 201 collimators in each helmet. Film dosimetry is 0., /

used to obtain the beam profile and background radiation. The _ *background radiation is measured with all 201 collimators 0.2 J

A

plugged. The background is then subtracted from the first film. _........ , .........i) Relative helmet factors. A small ion chamber should be cross- o0,2 ._.s -, .o.s o os _ ,s 2

calibrated against an ion chamber which has a calibration trace- c.,_able to NIST. The cross-calibrated ion chamber is used in a (a) s_.,.._n_e.,.P,.n,..m_,_c_smal ! phantom to calibrate the 18-mm helmet, with the cham- _=bet centered at the beam locus. Film, diodes and/or TLDs should

be used to calibrate the 4-, 8-, and 14-mm helmets. ,.o =/_..O_ .... _.j) Availabilityof operatingmanualandsafetyposting. 0JJ

VI. DOSIMETRY

0 j \A. Linac Systems 0_

1. Dose Measurements .... J ""..O0

The dosimetry of small x-ray fields is complicated by two factors: the ._ ._ orelationship between detector size and field dimensions and the lack of equi- (b)librium in lateral charged particles. Figures 4 (a)-(c) and 5 illustrate the st.,.o_._,_e..mP,*_l..o0.o,_c,_,)

beam profiles for both the linac and gamma knife as a function of collimator tz

diameter. The large dose gradients in the typical SRS penumbra relative to ,.0 .., . _: .

lution.theconventional fields require dosimetry techniques with higher spatial reso- 0J /_'P _'_° t. I

Dose distributions for stationary fields have been determined in water ......

baths and polystyrene slabs with ion chambers, TLDs, and film (Friedman _ 0s --_o_.and Bova, 1989; Rice et al., 1987; Wu et al., 1990; and Olsson et al., 1992). bThe effect of detector size on penumbra width has been reported by Dawson o.,

et al. (1986) and Rice et al. (1987). Beam profile measurements with a o_ 9 \'. ]

detector diameter of 3.5 mm or less can reproduce the penumbra width to _ '_'.within I mm. Dawson et al. investigated the penumbra width as a function o.o.......... 3

of ion chamber diameter for large photon fields. Extrapolation to zero de- (c) "_ .2 -, _lector diameter provided a correction factor for the 90%-10% width of the

penumbra. Rice et al. (1987) determined that the corrections to penumbra FIGURE 4 (n)-(c). Beam profiles lot 12.5-, 22.5-, and 30-ram diarneter fields.widths ranged from 0.3-1.0 mm when beam profiles (I.25-3.0 cm in diam- The beam profiles were measured with three densitometry systems(Welhofer, Lumisys laser film digitizer and the Truvel film scanner). Note thaleter) were measuredwith a 3.5-mm diameter detector, the beam profiles are essentially equivalent. These data are not to be

Transient electronicequilibrium exists at the point of measurementwhen substitutedlot actual beam data by the reader.the measurement point is farther from the beam edge than the maximum

1716

mm for a 6-MV x-ray beam. It shall be noted that these TMR values, beam

tO0 [ profiles, and output factors are representative for a 6-MV x-ray beam, butshall not be substituted for the reader's beam data. The beam profile film• "- data were measured with three instruments. The first instrument is a laser

f__ film digitizer with an effective aperture of 0.5 mm. The second instrument76 is a scanning film densitometer by Truvel with an aperture of 1 mm. Thet : I UNIVERSITY

I • tI OF PITTSBURGH third densitometeris the Wellhofer with an effective aperture of 0.8 mm.! _ tI GAMMAKNIFE Note that the beam profiles obtained with the laser film densitometer,o

o _ : _ Wellhofer and the Truvel densitometry system are comparable to witi_in a• i _ t Collimator Size50 millimeter. It is estimated that the uncertainty in position in the beam pro-

(Z:

. i ....... 8mm file (edge) is approximately ± 1.0 mm (Schell etal., 1993). h is important to• ; t ..... 14mmIt _ ,, lSmm directly calibrate each scanner using the film calibration that is performedt. _ t at the time of each measurement since the response can vary between25 t • t• : _ the scanning densitometer and the manual densitometer. Therefore, each',. -.. ,, densitometer must be calibrated separately.

%%. -% %%.•.

O.5 1.O 1.5 2.0 21.5X PLANE ICml

FIGURE 5. The beam profilesare illustratedfor the four beam diameters of --o--12.5mmcoil Ithe Gamma Unit (4, 8, 14 and 18 ram). o 22.5mmcoil£t 3Omm coil I TMR curve (12.5122,5130mm coil)

1.1 b i i i I I I _ I I I I

range of electrons. However, effective transient equilibrium is observed _ Tbecause the x-ray beam has a continuous photon energy distribution, weightedtoward the lower energies, and the secondary electrons are forward peaked, o.9Bjarngard etal. (1990), measured the dose on the central axis as a functionof field diameter from 0.7 mm to 8.5 mm. They determined that the electron 0.sfluence for the 8.5-ram field was measured correctly when the detector di-ameter was 2 mm or less. For field sizes 12.5 mm and greater, the central 0.7

axis dose measurement can be achieved with a parallel plate ionization cham-ber such as the PTW Model N23342 (PTW Freiburg, Germany), which has o.s

a 3-mm diameter collecting volume. Dose calibration can also be achievedwith the RMI plastic scintillation detector (RMI, Middleton, Wl) (Beddar et o.5al., 1992 and Meger-Wells etal., 1993).

The field-size dependence of output factors has been measured from 12.5- 0.435 mm with cylindrical and parallel-plate chambers. The inner ion chamberdiameters of 3.5 mm and 5.4 mm, small compared to the 12.5-mm field 0 s 10 is 20

diameter, enable output factors to be measured accurately to within 0.5% Depthlnpolystyro_o

(Rice etal., 1987) and related to the dose calibration of the linac (AAPM FIGURE 6. 6-MV TMR data are shown for the 12.5-mm, 22.5-mm, and 30.0-Task Group 21 Report, 1983). mm collimators for depths between 1.5 em and 20 cm. Note the TMR

Figures 4, 6, and 7 are plots of the beam profiles, tissue maximum ratios increases 8% at d=10 cm as the field diameter increases from 12.5 to 30.0(TMRs), and output factors for field collimator sizes of 12.5, 22.5, and 30 ram.

18 19

Stereotactlc Output Factor Curve

beam. Figures 4 and 5 illustrate the beam profiles for the 6-MV linac and0.98 _ gamma knife unit.0.90 _ .................

-Sca,erCorrecto co0.94 The total scatter correction factor, S, as a function of field size is a prod-0.92 uct of the collimator scatter, S, and the phantom scatter, S (Khan et al.,

1980). Phantom scatter factors are inferred from the total scatter and colli-

0.90 mater scatter factors.

O.99 • Collimator Scatter

The dose in phantom is independent of collimator scauer from the ter-0.86 i! tiary collimator for a 6-MV x-ray beam (Bjarngard et al., 1990). Collimator

0.64 .......................................... [......... scatter is dependent on the secondary collimator setting and independentof

the tertiary collimator diameter. S is illustrated in Figure 7 for the 6-MV0.82 _ beam. The data were obtained with a PTW Model N23342 palallel platechamber. The chamber volume is 0.02 cm 3 and a collecting volume diam-

0 2 4 6 0 1O 12 14 eter of 3 mm.

Area(em2)• Tissue-Maximum Ratios

FIGURE 7. 6-MV output factors at isocenter and at d=, for collimatordiameters 12.5--40.0 mm. The variation of tissue-maximum ratios (TMR) with collimator diameter

. at largedepthsisapproximately10%for6 MVand9 MVx rays(Arcovitoet al., 1985; Rice et al., 1987; Houdek et al., 1983; Serago et al., 1992; and

The following data acquisition procedures are adequate for field diam- Jani, 1993) for field diameters in the interval between 0 cm and 4 cm. Theeters greater than or equal to 10 ram. Beam profiles require high spatial principal diminution is from the lack of lateral electronic equililJrlum. Theresolution and film has been shown to be the most efficient dosimeter. Film TMR data in Figure 6 were acquired with the PTW parallel plate cha.d)er.

analysis can be performed by a scanning isodensitometer with an aperture

of 1 mm or less or with a laser film digitizer. These approaches yield equiva- B. Measurement Summarylent results to high-resolution TLDs. The uncertainty Of the beam radiusmeasurements can be greater than 1 mm. This uncertainty should be mini- 1. Linacsmized. Tissue maximum ratios and output factors should be acquired with

• Measure beam profiles with film, diodes, plastic scintillators,parallel plate or thimble ionization chambers that have small collecting vol- thermoluminescent dosimeters or ionization chambers. Film is theume diameters, e.g., 3 mm or less. The phantom material should be within dosimeter of choice. The detector dimensions must be 2 mm or less.

the guidelines of the TG-2t Report of the AAPM. Diodes must be used with caution, due to the angular response of thedetector.

• Off-Axis Ratios • Measure tissue-maximum ratios and total output factors (S,) wilh

Off-axis ratios (OAR) have been measured for 6-MV x-ray beams as a ionization chambers with diameters less than or equal to 3 ram.function of depth in a polystyrene phantom and in air. The variation of the • Use phantom materials and calibrate in accordance wilh the AAPMscaled profile with depth (constant SDD) is less than 2% (Rice et al., 1987). Protocol: TG-21: a protocol for absorbed dose from high-energyHence, some radiosurgery computer codes (Schell et al., 1991) use OAR beams.tables for each collimator which scale with the geometric projection of the • The PTW Model N23342 parallel plate chamber and the Capintec

20 21

cylindrical 0.07 cm_chamber (with the cylindrical axis aligned withthe beam axis) are examples of detectors for TMR and output factormeasurement (see Kalend et al., 1993).

2. Gamma Knife Units

• The aforementioned dosimeter types are appropriate for the gammaknife unit if the dimensions are no greater than I mm x I mm x Imm.

3. Phantoms

Polystyrene (Rice ei al., 1987 and Wu et al., 1990), anthropomorphic (Seragoet al., 1992 and Smith et al., 1989), water, and water-equivalent plastichave been used to measure the dose output and dose distributions of smallfields (dose verification). Existing anthropomorphic phantoms usually re-

quire measurement modifications for the smaller field sizes that are en-countered in SRS (Smith et al., 1989); additional adaptations are required (e)for use with the frame. Finally, anthropomorphic phantoms vary in size and am,,Dka

heterogeneity between institutions. For these reasons, members of the task A,oi,,,_,,s_o,,__,,,.,.group (Schell and Wu) have modified the gamma knife unit phantom designto accommodate field sizes encountered with the linacs as well as the gamma

knife unit. The phantom design is depicted in Figures 8 (a) and (b). The film BONDEDJO,NT

cassettemustbe opaqueto Cerenkovradiationin orderfor the film responseto be a result of x-ray radiation absorbed dose. SCREWS

The dose distributions for rotating fields can be acquired with spherical

phantoms. Dose rate calibration and dose distributions for the gamma knife F_LMON_

units have been determined with a 16-cm diameter polystyrene phantom Z PuTwhich can contain a cassette for TLDs or film. Cassettes for TLDs and sheetfilm accommodate field sizes from 4-18 mm. This film cassette design was

modified to accommodate field diameters up to 35 ram. Water-equivalent DOWE_-_plastic (WEP) by RMI was used to construct a 16-cm diameter sphere andcassettes for TLD and film dosimetry, (see Figure 8). This phantom designcan be used with both linac and gamma knife units. The standard WEP- ,_

BONDED Obased design enables dose distribution for the two SRS techniques to be

hINT

compared and minimizes dosimetry corrections. 40ram

4. Dosimetry Calculation (b)

The approximately spherical geometry of the human head and its tissue FIGURE 8 (aHb). The side and top views o| the water-equivalentphantomare shown in (a) and (b), respectively.The large film cassette allowsfor thedensities make the dose calculation algorithm relatively simple yet accurate linac-produced dose distributions to be measured as well as the smallerto within 2.5% for cylindrically symmetric fields. The dose algorithm re- gamma knife fields. The film cassette also accommodates TLD ribbons forported by Rice et al. (1987) incorporates off-axis ratios to represent the output calibration.

22 23

beam profile at depth, tissue attenuation, inverse-square/fall-off of dose,and dose output versus field size. Tissue heterogeneity occurs from bone slice separations typically between 3 and 10 mm. Target definition requi_estissue. The dose perturbation for beam energies between 4 MV and 10 MV smaller slice separations (CT and MRI) of 1-3 mm depending on the size ofis I-2% for a beam passing through the skull. The current arc geometries the lesion. Target definition is the enhancing region or the surgical defect in

and gamma knife source arrangement minimize the effect of oblique beam the tumor bed. The treatment volume, depending on the radiation oncologist,incidence on the measured dose distribution by entering the surface over 2_ can be the target volume with the margin of overall uncertainty of dosesteradians. The algorithm by Pike et al. (1987) is based on the Milan and delivery (Lutz et al., 1988 and Winston and Lutz, 1988). When the uncer-Bentley (1974) two-dimensional algorithm but provides the radiosurgical tainty in dose delivery exceeds the separation of the target from a criticaldose distribution in three orthogonal planes through the machine isocentar, structure, there are occasions when the patient should be treated with a more

Factors contributing to the net uncertainty of the dose delivery to the accurate technique (heavy ions, surgery, etc.). Size and location of AVMs istarget have been reviewed in Table 11.The principle factors are the uncer- determined from paired angiograms (Siddon and Barth, 1987).tainty in the frame,, the dose delivery system, movement of the brain within The dose to extracranial critical organs has been measured and was _ckthe skull, and the l:esolution of the target by the imaging modalities. Total ported relative to the isocentric dose for the gamma knife by Walt_m el aLuncertainty is on the order of 2.4 mm. The appropriate choice of the dose (1987) and for linac-based radiosurgery by Podgorsak et al. (1992):

calculation grid size has been addressed by Niemierko and Goitein, 1989. Organ Dose (°/o)The analysis of factors affecting the accuracy of dose estimation were di-vided into two factors: dose accuracy and position accuracy. Beam profile Eyes 2.5was represented by the Fermi function and it was shown that the limiting Thyroid 0.2factor is the accuracy in the dose, whereas the accuracy in the position was Breast 0.06normally less demanding. It was also shown that the maximum uncertainty Gonads 0.02

does not occur at the midpoint of the penumbra, but at the 80% and 20% Dose-volume histograms (DVH) have been used to cmnpare various SRSisodose llnes--the shoulder and heel of the beam profile. This is particu- modalities (Phillips er al., 1989; Schell et al., 1991; Serago et aL, 1992).larly pertinent to linac-based radiosurgery because the dose prescription is The DVH analysis complements the treatment planning process. Software

normally in the neighborhood of the 80% isodose surface. Given these fac- packages such as XKNIFE and PINNACLE are capable of calculating dose-tots, the appropriate grid size has been shown to be on the order of 2 mm. A volume histograms of the lesion and normal structures with sufficient speed2-mm grid spacing will produce a 1-2% uncertainty in the dose, whereas a so as to serve as a guide in optimizing the plan. Since fast 3-D dose algo-4-ram grid spacing will produce approximately 3_,% uncertainty in the rithms are required for critical treatment plan evaluation, a maximum timedose (Niemierko and Goitein, 1989). limit for DVH calculation should be 30 seconds.

The planning code should directly overlay the dose distributions on the The tissue response, normal or otherwise, as a function of dose and vol-appropriate CT image (transverse slice or reformatted), MRI or angiographic ume is not well known. Consequently, DVH analysis is valuable for theimage. Reformatted CT images in the plane of each arc are recommended. understanding of tissue response in clinical studies. Lyman and Wolbarst

This reconstruction allows the user to visualize the peak dose in the plane of (1987) have proposed an algorithm based on DVH analysis to estimate corn-the arc. The multiple arc geometries are simulated in treatment planning plication rates as a function of dose in normal tissues. Flickingeretal. (1990)software codes by many stationary beams (usually the stationary beams are have used DVH analysis to model complication rates in normal tissue andseparated by angles of 5-10°). The complex beam geometries can make have shown that these rates follow the trend reported by Kjcllberg (1983

conventional treatment plan calculation times intolerably long. The task and 1992). An RTOG protocol (#90-05) has been designed and i,lplemcJucdgroup recommends the use of software packages that are capable of calcu- to determine the radiotoxicity of single fraction radiosurgery as a functionlating the dose distributions on ten CT images from five noocoplanar arcs of dose and volume.(500 ° total traversal) in 1 min or less. This time requirement will reduce thetotal planning time to less than I hr.

• Gamma Knife

• Planning Parameters In addition to the X, Y, and Z coordinates of the target and the gamma

The definition of the patient geometry is obtained from CT scans with angle, the distances from the center of the stereotactic frame to 24 preselectedpoints on the surface of the skull are measured with a special plastic helmet

2425

LZ9_

'lunouJqanoaoqlJOlunomI_lSopadaql'(q)pu_(e)'Illx!pu_ddvu!soldtu_xooqls_qans'Sl_mOlu!om9i_axg1_zna_o4a!4_'slso*VOaugnoJo41(£)pu_:luaml_oJ!qo_aJOjV_)aql uo_:_j.toaaJ'esal_u!pJooaaqlI_qlpueaz!slq_!JoqlS!JO1_tU!IiOaoq]leq]

ffu]_la:aqa,(qp_t.J!ldtuaxas],(l!.lo]Jdlsaq_!qaq,L'_Jaqds!tu_.ql:3_JJOaoqlu!(_)'.s[s,(r_u__s]Jolq_qoJduop_suqs!qa[qM',(ffolopoqlotuult!sopaJnpaa'oldm_,xaJOj'aa_ldlaaJJO_aqlu]s!JalUa_OS]aqllt_qluo!l_tu.n.JUO:_lens]^I_-oJdS_]S_ql(l):sofft_lsaaaqlo]s_[iddeuff[s_.po:_u_JnssV,(l!l_n0aq,L"V0slI!Inq'_l_aqaal_u!pJooaoq!jo,(_Jn:x_eoqlo,',_qIousaoppuusaluu!pzooosa!s,(qdit_a[patuuo,_lalOSs_snaojuo[laasffu[_OllOJaq,L"(l_661',(oo)Ipuu•ilaq:_s)[iDt_sff,{JOffJnSOJIrl_Upue,(ffOIO]pezlnq,(ffOlOaUOUO]lU[p_J.Ioj,(luo

oqluo_l,_.qa_qlOldn-_l_qus!$!q.L"J_lU_OS]_qlql[t6,(lllOll_U_sSO.lffjolu_umff]l_oqluo_l_q:__ql,(qp_U]Idtua_s]la^Olpuoaasaq,L"pauue:_s_.Jloutut_JffoJd,(.mu!ld]as!p]qntu_,([[.mssaaous]S_ISu]oDueJnssu,(ill,end)

._qo_,a^r,tIplno,v,lua]ludaql'paJJn:)_os[qlJ1"_tu_,.tja_uo_j_J._A_[_]olpueuo!lanpo-quI"V_L_)ii_p_lDquo]l_uiJOjSU_t_o]l?Al!pJOO3oql_I?,[nDIE_3louplnoa_uo'sut_asJL3,_qlu!alq!s[^]ou_J_N_spoJuo]lez!le,3Olaqlj!'oldiuexozod"paoaoJdoiluaull_,_.l__OlI_,louplno_JoJza_qlJOluaull_Jlatlluol,_,dtu!JOU!Ul_a^_q_]_)N!V_IflSSVJ_J_I"[Vfl_)"IIAplnot_I!'paz.m._,_oJOJJ_i]i_j]_J_}q_As_3uP,lsu!sapn[au!la^al_IS[Jlsat_Ol

_q,L"SJOn_) jI_l]duapugploq,(qpau!ufflss]lua[ledaqlolla^O[_lSlZ]saqff!q.uo!le].oq]pu_sJallaIploq£qpa!j[uff[ss!_ls!zjo[at,o[puo._asaq,L"]uoj,(zuu!p.toaql-nfftJuoafinalsuo^!ffuzojsnoojoqlleI]unoqljo]ndlnooq'lpue'lamlaqJOl,(qDOll]uff!SS[t{JOff_ll_D)[S!JlSa,V,OIoq,L"S_lS]aJOJap.loffU[SV_Z:3tl!U[!_qOlq_l-utU!llOapal:_alaSoqljo]ndlnoOA]lel_.toql'UO.ll_]peJJ[luq!O1Ua^]fflq_t[at_puo,_asaqlU]pat.j[u_!saJ_,(oqlpu_S_lS]JJosla^aIaazqlaau_zaql'(IIx[puad_qluopaseqs]uo[ssasuo]w.[pezJ]q_eo.lOj_m]l]ttotltll_.l!oqlJOuo]le[n:_le3-dv)_ldmux__ldtu!sS!qluI"]ua]lt_daq]ol>Is[JoqljoSLUJ_IU[paz!l]Jo[.td'uo]lnq[JIs[p_sopD_lleJff_ltl!leuyoqlplo[5olpatumnspuepolqlt[ot_s!qat_aput,pa,_]^_J_qu_,,_d_lsq,_e._]"oJnpaaoJd,(.ta_Jnso]pe.tlua[d,(ieJojJapzou]tuoJjuo!lnq!aluoaaql'paaap!suoaazesJ_lUaaOS!uo!le]peJJ!old!llntuU_qA_.pols!ll.mq_,v,oIJ"euosdalsoqls_le,o]ptt![x]puaddv"IIput_Is_a!puaddvu]"s_alt_u!pJooap_z!sap_qlffu]£j!aads£q(l_uo.mapue'lelu_nlls_,s[s,(itmr,pj_ze.lIlln_jjouo!w,:_]ldd_oqljosaldtu_x_t",(|_jeslua[lo]!ffes'asJa^SUeJl)saueldlud[au]zd_JqlaqlollallUJt_daut_Id,(ueu!pa,(t_Id-_dp_m'_aur,Jnsse£1!lenh',(Jlam]sop',(Ja^!lap_sop._u!.mpuo!l[sodla_.ml-s!p_qu_suo]lnq].qs!p_soposI"atunlo^xpletuoqlu!suognq[Jis]posop,_[p,_,uo]l,z]ie,_oIloffJP.ltl[_(:3P, jtl.'sDP,, apnl_u[$_1Sjosl_adst_i_,_!uqa_.L-os!jo,(_[ds!ppuuuo[l_Z!letUJOUoqls,_OllUlu[odua^]fi',_leosopalnlosqe

"uo[lnl]lsu[q._ea,(qpautjapaqOSl_plnoqs_lS[.Ia^[ssaax_jout_ffu!u!tuJalo(i"papn[aaoa.msaaJnosouffu]p!^oJd'x]zletuoq:lU[tl]]_lu!oduo!|!u[JoP_'q,L"_Jnpaao.MV_)a]j!_ads-uo]lnl!lsu]uesplop(punuo[lmgsu]q_eaJojpatutunsa.msa_Jnos10ZIIt_mo.tjsuo!lnq!zlUO_)"pasns[tuuoqodinq,_u]ql!,_tua|s,(s[_np]^]pu]aqlffu]u_!sapJOjinjdlaqs!V_Idoq.L"at,]sejolu_[oljjao:_uo!lurlu_lleJU,gu[I_tl,L"algoJdosop_.q]tuoJjpau!elqos!-so3x_s],(1]l!qeqoJdI_]l]u]aqluoqt__ls!Jaqlo3np_Jolpaufi'!sap_Js[olnpoaoile._s!xe-jjooq,Lll_le_lqOIffU[SeJOsu[nulzoJ[l_[luauodx_uo[l_nu_lluJeaulI-oadOLLL"poss0sses!,(Jn['u]JO,(I]llquqozdaqJ_unaoouea_.m,fu]OJDtlA_, sdolspull'SO]leJs!xe-jJO'me[olenbsOSJ_AIIIgq]ffu[snp_lelnalt_:)aqueoIin_lsoqlle.mpaooJduopasnaojs!UO]lUOllV"Sle[J|tUZ,I$,(SJOSISalI_nla_olUO]l]ppt_u]lu]odelttosopoql',(JlattltU.,(sle[Xe_'u]tunssV"lllql!JO_l'eUO!lelnaleaasopu!'_Jnpa_oJdoqljod_lsqo_a_u[lapotujosls!suo,_VHd"]uoullu_.l|lua]l_'qlu[uo[lua_]ldtu!sJojst_Oll_,Qlatutu,(stueaq[_a]Jpu[[,(ooq,L"tuat_'0t'-edIsJ].IoqlOl_o]zdpotuJojJ._ds[VHd'saSSOlolqeldoa_eunaonpoJdplnot_s!((IriS)oouels[psnaojo1_);3Jnos_q_L"tUOlueqd.talemeu[lu!od_I3uoJ_j;BJ

s.a_h]Utl,_alJOJJOpuP.Jl?,]J10JOqA_'VSVNpuP.,(Jlsnpu]1jl_J3J[P.. _lqlJOjp_dolaAasop_.tllpue'az]sJOletO]llO:_p_tj[aodsu'SalDoJduo[lt_!pe._OSJ_AStlt_J| 'UOll-.",O511,]1!U],'lJa,_.sanb[tlq3ols[s,(l'e.tlP,_lS!_'ulB.lffoJdV_)_*q'ljouff!sDpaql-_.mff]juoa[in,isoqlffu!utJapsDJlnb_Ju]eoqalfftl!SeJOj'uo!|elnaleaosoOolpugaJnpa._oJdS_]Soqljouff]sapaqlqloqolpa]lddeaqueasls,(leUt_o^]l"az]sp.lJffaql_lUpallg,(q-aodsoJdoq_L'lualledaqljoluotu|_oJlS!ttl.10,Qnl'uljo_s!JoqlaZ!tLllU!tUOlpao!_aAoqueax!Jl_tuoqluoslu!odoqluaot61aqffu.ta_dS"lSOJolu.ljouo.l_aJu_Inlsa_ns_atuluanbasqnsaqlpuutuals,(sejo(VHd)s[s'(l_uVPJeZeHllne:-Ioqlu!poaaluaaslu!odjox{alt_tu1£xI£_u!palelnal_ast.stue_Iuo!l_!pe.IaqlJojsalffolopoqlatuolsu!euad(V_dd)sls,(lUUV>lS!_lolqeqoJdJoV0a^9I0Zjoqa_a£qpaaa^]laposopaq,L"sa_letu]a!qdeJffolpe]uoffutsodm!_adns-aadsoJd"s!s,(ltmV_lS[_lalquqoJdJoV0a^goadsoadolpalo^apa(][[]t_uollJOjuo!lanpaJ.Iouoll'e:_t.j!uff_tuJadoadaqlql!t_pallold_opa,(t_|ds!paquua-ua_ll_atuos"aaojoJaqJ,'aJnpaaozdS_ISIVSJa^lun_Jotuez_lozdV0It_sJa^.mnputtau_ldlelllffvsZ-Apu_'auuldl_UOaOaZ-X't_ai^au_ldasJa^suez]A-X

jolu_tudolo^apaqls|!q]qo_d"ala'lno,(uIlue[dlUa!s,(qd'saa.mosa_tuo]jaqlJOjpal_[n.olU:_a.tusuo!lnq!_ls!pasoposI".tolu!JdpueJanoldo[qdeJff_pu'etlO!lnl!|su!qa_auoS|tl!t]J1suo:_aq|u[uo!ltt!JffAaq.L"(17661'sauof)tuuz$oJd_amdtuoat_qlImpaqs!ldtUoaattstSu!uueld]uatuleo_J_"_aindtuoaffuIuu_Id

VOpu_a.mpaaoJdS_ISoqlffu[ufflsapu!Injdlaqs]s!S,(leUU_lsl-talqt_qo-Idluatulea.qoql£qpaluazas]atu'_jja[lo_looJolsoq|op]$u.Ifinalsaqljouo!lt_l

VOput_s!s,(itmV_IS!Haiqt_qoad"ff-ntu!sleuo!suatu!p-aa.Iq]'sluatuaJnsuotuosoqluoposu_"aul_Jjaq]olpaqoL'llu

Quality assurance procedures for linac-based radiosurgery have been de-veloped for a variety of frame/linac configurations (LuIz et el., 1988;

Podgorsak et al., 1992; Drzymala, 1991; Serago et al., 1991; and Tsai et al., _ __

1991). The principal features of the QA programs are (I) verification of the

mechanical tolerances, (2) x-ray/light field/laser alignment with isocenter,and (3) verification of the target/tumor with the isocenter prior to treatment.

The QA program at the Joint Center for Radiation Therapy was designedinitially by Lutz and augmented byTsai. Three tests can complement a quality

assurance program for target verification. The localization algorithm/soft- ___

ware can be tested by determining the frame coordinates of a target with apreviously known coordinate. For these purposes a test case can be archivallystored for routine'!sofiware QA. The BRW frame system features an arc

assemblythat employsfouranglesandthe depthto uniquelyidentifya tar-get in BRW space. The arc assembly has been used to mark the scalp as a .............................._"_':::._................function of angles and depth to identify frame slippage between the time of

image acquisition and treatment. The BRW stereotactic fi'ame system in- FIGURE 9. The target simulator (steel ball) is shown attached to the BRVVeludes a verification device known as the phantom base (Figure 9). The phantom base. The phantom coordinate system is identical tu thephantom base was designed for verification of tumor localization in coordinates of the BRW stand. The pointer is set to position the targetneurosurgery. Lutz used the phantom base to set a target (a radio-opaque simulator at the lesion's coordinates. The BRW phantom is also used in QA

procedures to verify the angiographic box localization in SRS. [Lutz eta/.,steel sphere) at the BRW coordinates of the tumor. The alignment of the 1988.)sphere at the isocenter with the x-ray beam confirms the coordinate selec-tio_non the BRW pedestal (Figure 10). The patient is then positioned on thePatient Support Assembly (PSA) and the frame is attached to the pedestal.The treatment configuration of the linac and pedestal mount is shown inFigure 2. . ,

Similar attention should be focused on the graphics display of the treat- Q/ _..___

mentplanningsystem. The position of color-codedisodosecontours rela- otire to the target image are a function of the color gun alignment. Misalign-merit of the color guns in the graphics display unit can displace color.coded

isodose curves relative to the target by more than 1 mm and mislead the --'-%.

planningprocess.Eachstepof the SRSproceduremust be examinedfor the ._consequences of failure.

C. Treatment QA

1. Checklists

Because of the complexity of radiosurgery treatments, the QA programmust include a treatment procedure checklist. The checklist will reflect thetreatment step sequence and should be written in sufficient detail so as tominimize risk of misadministration or injury. Some sample items are: jaw FIGURE 10. The target simulator is mounted o_J the pedestal to vu_iry lh_

target alignment with the SRS x-ray beam as a function of table and gantrysetting, proper diameter collimator inserted, couch disabled, anti-collision angles. (Lutz et aL, 1988.)switches in place, external target test acceptable, head ring check accept-

28 29

able, target coordinates checked, target simulator film acceptable (or corn- tolerance, and that the radiation field is centered around the isoccnter andparable test), laser alignment of patient verified, patient strap in place, etc. beam axis.In general, the critical steps in a radiosurgery treatment procedure should

require confirmation by at least two people. Sample procedures are shown 4. Pedestal Mount Systemin the Appendix IV. Note that one sign-off includes the detachment of theframe from the pedestal before restoring the capability of vertical motion to Three primary tests and one secondary test are suggested to assure thethe patient support assembly, positional accuracy of a patient treatment.

• "Known" target test during localization.

2. Target Position Verification Head ring movement check.Rigorous verification of treatment set-up.

Verification of the target position in the beam prior to irradiation has A secondary, less quantitative test, which to some extem supple-been developed at the heavy charged particle therapy centers [Goitein et al. ments the three main tests.(1982) and LymPh et al. (1989)]. A pre-treatment radiograph is obtained These tests will be illustrated with the Joint Center lbr F.adiatio. "lhClallyfrom the beam's-eye view and compared to the digitally reconstructed ra- approach to radiosurgery (Lutz et al., 1988) which utilizes BRW s_ereotac-diograph of the treatment plan. When the positioning differences are less tic biopsy equipment and patient head support independent of the couch. Inthan 1 mm, patient irradiation is initiated. Similar efforts have been re- particular, the first and third tests utilize the BRW phantom base which canported by Serago et al. (1991), using orthogonal port films. Jones et al, position a pointer at any desired target coordinate relative to a head ring.(1989) used fiducial markers embedded in the scalp as a stereotactic frame.

A linac-moanted x-ray tube/simulator has been used to verify patient post- 5. "Known" Target Test During Localization: Recommendation to

lion prior to treatment by means of the angiographic Iocalizer (Schell et al., SRS Manufacturers1991). Methods for target coordinate verification are described below forthe pedestal-mounted and couch-mounted frame approaches. The requisite equipment for this test is not available commercially. The

task group recommends that the SRS system manufacturers modify the flame

3. Laser Check systems to accommodate this coordinate transformatlou algorithm test, Thelocalization test, which checks the process, involves placing a target of

A couch mount system derives its accuracy from lasers fixed in the room. "known" coordinates external to the skull, but relatively near the ime_.alThe first check confirms that the lasers indeed intersect with the isocenter target, during angiographic or CT localization procedures. The external tat--within the desired tolerance, get is attached to the localization frame (CT or angiography). Following CT

The initial laser alignment procedure is best performed using a calibrated or angiography, the frame, with the external target attached, can be placed

mechanical pointer. The Joint Center for Radiation Therapy uses a Mechani- on the BRW phantom base. The phantom base is then used to measure thecal Isocenter Standard (MIS) that bolts on the base plate of the PSA. The coordinates of the external target. These results are the "known" coordi-MIS is also used in the initial morning check to verify visually check the nares. The coordinates of the external target are also calculated using thealignment of the lasers, same films or CT slices, computer hardware and software as used to calcu-

The test involves aligning a radio-opaque marker to the point marked by late the patient's treatment target coordinates. Only when these externalthe crosspoint of the lasers. This alignment procedure depends on the par- target coordinates compare favorably with the BRW phamom base mca-ticulars on the stereotactic hardware. A set of films taken at various gantry- surements ("known" coordinates), would one proceed with the calcutatloncouch angle combinations allows a determination of the alignment between of the patient's target coordinates. Note, this test is valid ooly if the Iocafizet"the radio-opaque marker and the isocenter, and the centricity of the radia- is correctly affixed to the frame during the imaging acquisition. An in-tion field. A film test with the calibrated MIS allows a quantification of any correctly attached Iocalizer will produce incorrect target coordinates°misalignment of the three axes of rotation and the shift of the MIS itself. The coordinates of the patient's treatment target should be calculatedThe film test before a patient treatment thus becomes a second test and independently by at least two people or by two independent software pro-documentation of the alignment, grams. If possible, two different methods and/or computers should be used

The films become part of the treatment record and document that the and compared. If the target is localized by CT, the thinnest possible slices,laser intersection point corresponds to the LINAC isocenter within a desired consistent with the use of contrast, should be taken through the target to

30 31

minimize the localization error. The size and shape of the target needs to be The film holder is attached to the collimator and the film is exposed withcarefully evaluated so that treatment planning decisions (number of the accelerator's beam at eight standard turntable/gantry positions. This filmisocenters, collimator diameters, pattern of arcs, etc.) are meaningful. It verifies the alignment of the entire system over the range of possible gantryshould be noted that two planar radiographs are often inadequate to deter- and turntable movements. If the steel sphere is centered within the accept-mine either the exact shape or size of a target (Born and Friedman, 1991). able limits of all eight exposures, it is reasonable to conclude that the set-up

has been correctly aligned for the treatment of the lesion at the specified

6. Head Ring Movement Test location.This verification procedure will detect subtle problems with the linac as

The BRW arc system (or its equivalent in another system) can be used to well as misalignment of the supplemental collimator or BRW floor stand,insure that the BRW head ring has not movedbetween its initial placement and mistakes such as incorrectly setting the intended coordinates. This veri-

and treatment (Tsai et al., 1991). After the head ring is secured, the BRW fication procedure checks all positioning aspects of the treatment subse-

arc system is attached. Using the arc system and its pointer, three or four quent to determination of the target coordinates. After verification, the tar-points on the scalp are marked at specific values of 0_, [3, 7, A, and depth, get simulator is removed and the patient is attached via the BRW bead ringChoose "easy" numbers for the angles, since the only constraint is that the to the floor stand without making any alterations.

points be distributed. Just prior to treatment, the arc system is again at- The target simulator test cannot detect an error ia the target cuutdlnatcstached to the head ring with the patient's head in the same position as be- regardless of the"cause of that error. Nor can this test detect an error causedfore. The three or four marked scalp points are then confirmed to be at the by slippage of the head ring on the patient's head. These potential problemssame values of cz, [3, "/, A, and depth, thus establishing that the head ring were covered in the first two tests.

has not moved. An equally rigorous test for target positioning for a couch-mount systemduring set-up in which the patient's head is supported on the couch is de-

7. Verification of Treatment Setup scribed by Serago et at. (1991).

In the BRW based system, the target simulator test (Lutz et al., 1988)8. Secondary Test

verifies that the treatment equipment is set up correctly to the target coordi-

nates and that the entire system is properly aligned. Alignment and setup are A general, less quantitative supplemental test can be used which checksverified by simulating the patient's lesion with a small steel sphere posi- for errors in the localization process and/or treatment setup, providing the

tioned at the target coordinates and making radiographic exposures with the target can be visualized on CT. At the CT console, distances frmn the le_iongantry and couch in eight representative positions (Lutz et al., 1988). After center to the head surface, along the three principal axes, are measured.the collimator and the BRW floor stand are secured in place, one person These measurements are made from two CT slices: o_ae through the cctlter

aligns the floor stand to the correct coordinates while a second person sets of the lesion (or nearly so) and one through the top of the head. (The differ-the phantom base to the identical coordinates. The BRW phantom base al- ence in table position between these two slices is the "Lesion Center to

lows theprecise mechanical identification of the target's position in BRW Superior" distance.) These measurements are made as part of the localiza-space. Next the target simulator is attached to the BRW phantom base (Fig- tion process and carefully recorded. At the time of treatment, after the pa-ure 9). The target simulator contains a section of head ring that attaches to tient has been secured in the treatment position, these same three distances

the top of the phantom base ring. The steel sphere on the arm of the simula- can be measured reasonably accurately (maybe :t 6 mm) on the patient us-

tot is then centered using a magnifying glass as a visual aid on the tip of the ing the lateral and ceiling lasers and a couple of rulers. Successful comple-phantom base's pointer. The vertical coordinate must :be adjusted for the lion of this test, even with its limited accuracy, can be very reassuring.radius of the spherical target and for the thickness of the head ring, whichshould now overlay the phantom-simulated head ring. Next, the target simu-lator is removed from the phantom base and attached to the BRW floor D, Stereotactic Couch Mount

stand in the same manner that a patient's head ring would be attached (Fig- 1, Overviewore 10). The simulator's spherical target then represents the patient's lesionwith its center located precisely at the "best compromise" isocenter, if no A stereotactic couch mount fixates the patient on the couch and relies onerrors have been made. an external reference to define the LINAC or treatment coordinate system.

32 33

The main advantage of the couch mount is complete access to any point in The alignment hardware consists of two assemblies: a rectilinear phan-the patient's cranium, especially for plain transverse arcs and access to the tom base (RLPB) and a laser target localizer frame (LTLF). Both devicesposterior as shown in Figure 11. Elements of a couch mount include: are calibrated with respect to the BRW coordinate system and have scales

• Couch locking devices--Stabilize the couch to ensure mechanical that allow a coordinate to be entered given the AP, LAT, and VERT post-stability and to disable all motions, tions. The RLPB mounts on the couch-mount docking device and allows a

• Lasers--Provide room-based fixed reference, pointer to be precisely positioned to the is*center using the couch motors

• Patient docking device--Rigidly attaches to the couch and allows and verniers on the docking device.the patients frame to be uniquely positioned on the couch. Two people should execute the procedure. The first person sets the target

• Is*center/target verification devices---Allow verification of the coordinate on the RLPB and the second person sets the target coordinate oucorrect target coordinate and its alignment with the LINAC is*center, the LTLF. The RLPB is aligned to the is*center. Couch motions, except d_e

vertical movement, are locked and stabilizers applied if needed. The above

• 2. Target VerificationThe Joint Center for Radiation Therapy laser test is perfornmd. The LTLF is placed on the RLPB. If the lasers al'cparallel, and if the target coordinate on both tile LTLF and die I_,LPB aL'e

The following procedure is specific to the Radionics couch mount as- identical, then the lasers will align with the markers on the LTLF. This pro=sembly and reflects the quality assurance procedure as performed at the cedure thus documents the alignment of the target with is*center throughJoint Center for Radiation Therapy (Tsai et al., 1991). the film test and that the target coordinate is indeed the correct coordinate

through the redundant entry on both devices.In practice, the lasers never are truly parallel even though they cross al

the is*center, and small deviations will exist. The alignment markers on the

LTLF are a macroscopic distance from the is*center, and any divergence ofthe lasers is magnified by this distance• Thus when tile LTLF is idaced o,the RLPB, a small deviation will be observable. This deviatit), should be

below an acceptable tolerance. If not, adjust the LTLF to exactly aligH thelasers at the LTLE Note that this means that the coordinate AP, LAT, and

VERT values now will slightly differ from the prescription coordiLmtes. It is

important to note the objectives of these steps. First, the RLPB/LTLF com-bination verifies that the physicists/therapists correctly entered the targetcoordinate on the RLPB. Secondly, the small adjustments on the LTLF al-low an exact calibration of the state of the lasers with respect to the targetcoordinate. Thus the critical eement is not that the lasers are perfectly col-

linear; instead the critical element is that they are stable from the time thetreatment procedure starts until the treatment is over.

The exact calibrated positions of the LTLF for a givcJL targcl j_,sifi_m a,crecorded prior to the actual pattern treatment. For a patient ucated with

FIGURE 11. A dynamic stereolaetic radiosurgical procedure starts with the multiple isocenters, individual LTLF positions for each target are rc-cnte=cdcouch at +75 ° and the gantry at 30% as shown in part (A). During the on the LTLF without requiring the patient to be taken off the couch. Thistreatment the couch rotates 150° from +75* to -75 °, while the gantrysimultaneously rotates from 30 ° to 330*. Several successive positions much improves the ease of patient setup and throughput.through which the couch and gantry move during the complete radiosurgicalprocedure are shown, starting (A) with the gantry and couch angels of 30* 3. Patient Alignmentand 75°, respectively, through (B) 90* and +45°. respectively, (C) 180° and0°, respectively,(D) 270* and -45 °, respectively,and (E) stoppingat 300* The RLPB is removed from the couch docking device, the couch is low-and -75 °, respectively. (Souhami, L.; Olivier, A.; Podgorsak, E.B.; Pla, M.; ered, and the patient is positioned on the couch and locked in the dockingPike, G.B. Radiosurgery of cerebral arteriovenous malformations with the device. The couch is raised to its original height during the above test. Thedynamic stere*tactic irradiation. Int. d. Radiat. Oncol. Biol. Phys. 19:775-782, 1990.) patient's weight, however, will induce an unavoidable shift even in the mosl

34 35

im

mechanically stable system. The LTLF is placed on the patient's frame, andis aligned to the lasers once again using the couch docking device verniers.Note that the LTLF prior to placement on the patient was calibrated to the It-exact configuration of the lasers for the treatment coordinate. Thus this align- ([_ Lipmerit of the LTLF once again will align the target coordinate to the lasersand thus to the isocenter. The LTLF thus affords a direct method to assess

the padent-weight induced effect on the mechanical assembly and a method '1to correct for this effect. This procedure thus reduces torque effects andincreasesthemechanicalaccuracy. I I

I Ilcm

4. Alignment Verification of a Couch-Mounted Frame (McGill)

The collimator alignment is a cddeal step in treatment because the preci-sion of the treatment itself depends heavily on the accuracy of the collima- zWY

for placement. The collimator is placed onto the lianc tray holder, which isattached to the linac head. The proper collimator position is obtained with a_

thehelpofceiling-andwall-mountedlasersthatareperiodicallycalibrated _l eto indicate accurately the linac isocenter location. The alignment procedureis as follows: The couch table top is raised to the isocenter and the gantry

positioned off-vertical, so that the dot produced by the vertical ceiling laser FIGURE 12. Verification films illustrating collimator alignment, t3ollirnateltO indicate the couch rotation axis is clearly visible on the table top. The diameter: 1 cm, filmat isocenter, perpendicular to the beam. Image (a) is for

position of the dot is marked on the table top, the gantry is placed vertically, a single vertical beam, images (b) and (d) are for two parallel-opposedvertical beams (gantryangles: O" and 180°), and images (c) and (e) are forand the collimator position is centered with the help of the light-field localizer two parallel-opposed horizontal beams (gantry angles: 90" and 270").lamp around the mark on the table top representing the couch rotation axis. Images (b) and (c) result from a well-aligned eel,mater, and images (d) andThe collimator plate is then immobilized with four pressure screws. (a) result from a collimator shifted 1 mm laterally from the optimal position.

The alignment of the collimator is verified with radiographic film in threesteps. First, a film is suspended horizontally at the isocenter and exposed to

a parallel-opposed beam with the gantry at 0 ° and 180". Next, another film beams (second step) are shown in Figure 12 (c) and (e). Parts (b) and (c) of

is placed vertically through the isocenter and exposed to a parallel-opposed Figure 12 are for a well aligned collimator, while parts (d) and (e) representbeam with the gantry at 90° and 270 °. Finally, a third film is placed horizon- a collimator shifted 1mm out of alignment. It is evident from Figure 12 that

tally through the isocenter onto the couch table top mid rotated with the even a slight misalignment of the collimator ca. be easily detected widi d_e

couch during irradiation with a vertical beam. With the three-step process radiographic test procedure involving two parallel-opposed beanls.above, any misalignment of the collimator can be easily detected with the Figure 13 represents the third step of the alignment test, which checksradiographic film. The radiosurgical treatment is not given unless the re- the coincidence of the couch rotation with the collimator alignment. Part

salts of the alignment procedure are within the accepted tolerances. (b) results from a couch (fihn) rotation in a vertical beam from an alignedAn example of the radiographic films obtained during an alignment pro- collimator and shows an excellent coincidence between the couch rotation

eedure for a l-cm diameter collimator is given in Figures 12 and 13. Part (a) axis with the vertical beam axis. Part (c) results from a couch (film) rotationof both figures represents the radiographic image of a single, vertical l-cm in a vertical beam from a collimator shifted by about lmm from the aligned

diameter beam. Images of vertical parallel-opposed beams (first step) are position. The misalignment of the couch rotation axis with the beam verti-shown in Figure 12 (b) and (d), while images of horizontal parallel-opposed cat axis is easily noticeable, and die treatment would not be giveu under

36 37

several disciplines, and the equipment is likely to be used by a v;aicty o_

,_ _ health professionals in different departmentS (Schell and Kooy, 1994), There-M U fore. the task involves coordinating personnel as well as QA of apparatuses

and procedures. Tile QA program should include:

|" ",1 Stereotaetic Frame: Phantom base + pointeror analogousdevices| | CT IocalizmI I AngiographicIdealizer

1 1¢M Target pointerand frame pedestal elcouch mourl_

Therapy i_actdlle: Uose calibradtmFrarrle alignl_e_l¢wi_hy_.(_y za,,_

couch eccentricity or precessiu.X-ray field alignment wi_h isocenter

beam profiles

Software: Dose calculation

._r_. Frame coordinate/Imagecoordinatetransformation

Digitizerlineafity

FIGURE 13. Verification films illustrating couch alignment. Collimator Graphics display irrlage aligr=._er.diameter'.1 cm. film at isocenter,perpendicularto the beam. Image (a) isfor Filrn imager distortionasingieverticalbeam andimages (b)and (c)arelorcouch (lilm) rotatingfrom 1) Gamma If.nile do_e owHz_y75' to -75" in a vertical beam. Image (b) results from a well-aligned 2) DRR distortio_ _or char_j_dcollimator,and image re) results from a collimator shifted 1 mm from the particlesoptimal position.

these circumstances. Alignment of the lesion with isocenter is achieved by Fo QA Program for a Gamma Knife

positioning the patient such that the lasers align with the x, y, and z coordi- The quality assurance (QA) program is divided between daily, monthly,nates on the Idealizer grid. semi-annual and annual checks.

Before the patient is ready to be treated each day, doo_'interlocl_, beth d_

E. Routine QA elapsed-time timer and the remainiug-thne limer, audio-visual syste.,s, cme_'-gency-off buttons, console lamp tesl, radiation _md_ors aud _lyd_au_ic I_fe_

The QA progranl at any SRS installation should rouiinely inspect the sure must be cbecked for safety purposes.hardware/software performance to ensure compliance with the original speci- The timer constancy, timer linearity, ti.tcl accm'acy, o.-olf t:_ u_, u u.fications. Several QA protocols have been or are about to be published for nion centricity, radiation output, and tile relative helmet factors uced lo beradiation oncology (AAPM Report No. 13; ACMP Report No. 2, Svensson, checked. The timer constancy, linearity and accuracy are checked over die1990; AAPM Report No. 40; AAPM Report No. 45; and Van Dyk et eL, range of clinical use. An ionization chamber coupled with an electrometer

1993). These existing QA protocols for radiation oncology should guide the is placed at the center of an 80-mm radius polystyrene spherical phantoulinstitution's QA program for SRS. Such a program should also include all and the focus of the beams. Multiple exposures are made using diflerentaspects of the planning and treatment process. The QA program involves time intervals and the 18-mm collhnator helmet with all collimalors open.

38

I I II I I I I II

A spread of the electrometer readings of a constant time setting determinesthe constancy and reproducibility of the timer and the dosimetrie system. Aplot of the average electrometer readings versus time intervals determinesthe timer's linearity. The "On-Off" error calculation, (o0, is based on the

same method used in a teletherapy machine, where ct =[nR2-R,]/n[(R,)-R2].This procedure is repeated monthly at the University of Pittsburgh.

The radiation output of the machine is measured using an electrometerwith an NIST-traceable ion chamber placed at the center of an 80-ram ra-dius sphere of tissue equivalent material which is positioned at the focus of

the 18-ram collimator. At the University of Pittsburgh, a Capintec ModelPR05P ion chamber was used with a Capintec Model 192 electrometer. Thedose output measu_'ed for the gamma knife is referred to the dose to water.

The percent discrepancy between the measured output and the anticipatedoutput should be within :t 3%. The relative helmet factors are verified usingdiodes or thermoluminescent dosimeters. The diode (PTW 9111), or LiFchip is placed at the center of the spherical phantom and the focus of theradiations. The ratios of the readings obtained from the 4-, 8-, and 14-mmhelmets to the reading for 18-mm helmet are determined as the relative

helmet factors. This procedure is repeated annually.Trunnion eentrieity is checked using the trunnion test Idol supplied by

the manufacturer. The trunnions are.responsible for the accurate placemento(a target in the X dimension. The trunnion test tool is a cross-shaped appa-ratus that is attached to the interior of the collimator helmet. The trunnions ,-/should read 100 when they are fully inserted and come in contact with the /center of test tool. This procedure is performed monthly. I , I . I .... 1

Radiation/mechanical isocenter coincidence is checked by irradiation of -s -2.5 0 2.5 5.0a film in a specially designed tool. The mechanical/radiation isocenter toolis basically a light-tight aluminum film cassette, containing a small piece of el! axis (cmlfilm (2.3 x 2.5 cm). At the center of the cassette, a pin is used to pierce atiny hole on the film which indicates the mechanical isocenter of the ma- FIGURE 14. The X-axis dose profile of a film exposed with the 8-ram

collimatorhelmet. The filmwas puncturedwith a pin to indicatethe centerofchine. The film is irradiated, and thenscannedwith a densitometer.Figure mechanical focus(the dip at the center o! the profile). (Wu et al., 1990).14 shows the position of the pinhole as the mechanical center, and the cen-ter of the radiation profile measuring by the half-width of the half-maxi-

mum. The discrepancies between the two centers along X, Y, and Z direc- ment of the microswitches. As a result, the contrul col_solc _huuld st_l_ thetions were approximately 0.25 mm. treatment. This test should be performed monthly.

The engagement of two microswitches located at the :base surface of the Couch movement time is the interval time during which _hc paticu_ may

helmet indicates the proper positioning of the helmet. To test their sensitiv- be exposed to radiation in the case where treatment is interrupted right afterity, a special tool, which is simply a ring that simulates the helmet docking it is initiated. When the treatment is interrupted, the couch moves the pa-with the central body, is provided by the manufacturer. After seating the tool tient out of the unit, and the shielding door closes completely. The couch

on the helmet's four anchor posts, a small sheet of brass approximately 0.1 travel time is adjusted to the minimum, typically within 30_.0 sec. This testmm thick is inserted into the space between the top surface of the helmet is performed monthly.base and the bottom of the tool to create a 0.1-mm gap. This small gap Furthermore, the treatment planning aspects of quality assurance shouldcauses misalignment of the docking of the helmet and improper engage-

4140

include the computer output check, and relative collimator helmet factor VIII. FUTURE DIRECTIONS

verifications. This procedure is performed monthly. Also, on a semi-annual This section delineates areas of development which have yet to be staa-basis leak testing of the source is required. Dose profiles should also be dardized. Five areas are described: (I) image correlation (CT and MRI), (2)

verified on acceptance or after a source change, multiple fractionation, (3) real-time portal imaging, (4) conformalradiosurgery and, (5) a robot-guided linac.

G. Stereotactic Frames and Quality AssuranceA. Image Correlation

The majority of SRS applications use one of five stereotactic frames:Brown-Roberts-Wells, Tipal, Leksell, GilI-Thomas_osman, or Riecbert/ MRI contains distortions which impede direct correlatio, with CT data

Mundinger. Excellent reviews of the technical aspects of the stereotactic at the level required by SRS (Sumanaweera et al., 1994). Three approachesframes are presented by Galloway and Maciunas (1990) and Macianas et al. are cited below. Magnetic resonance imaging (MRI) and magnetic resonance(1994). The stereotactic frames must be assessed for accuracy as they are angiography (MRA) are capable of resolving tissues I mm in diameter or less.actually used. One point made in Maciunas's article is that phantom tests do The difficulty in MRI stems from the fact that inhomogeneilies in the mag-

not stress the stereotactic frames in the same manner as do actual patient netic field and eddy currents produced within the patient can distort thetreatments and that "clinically encountered levels of weight-bearing by ste- images and produce warping or displacements in the image relative to thereotaclic frames may have a pronounced effecl on their mechanical accu- stereotactic frame coordinate system. Two general precautions can be takenracy." The consequence of this factor is an introduction of an error that is to minimize this. The first is placing the volume of interest in the eemcr ofnot appreciated by the general community. For example, a mean error for a the main magnetic field. Displacements of 20 cm or more froln the center of4-ram slice thickness in the BRW frame system is 2.7 ram, with a 95% the magnetic field can produce gross distortions in the MR image. Thisconfidence level of 4.8 mm. These numbers decrease to 1.9 mm for the precaution will reduce the typical uncertainty in the anomalous displace-mean error and 3.6 mm for a 95% confidence level for a I-ram slice thick- ment of the image to 4 mm.

hess. These numbers.also do not take into account the uncertainty in the A quantitative analysis of the distortion in MR has been reported by Schadtreatment delivery in the linac system or that introduced in the planning el al. (1992) and Ehricke et al. (1992). This group has devised two phan-process of the radlosurgery software. The overall uncertainty is larger when toms to assess warping in the MR image. The first phantom is two-dimen-these numbers are included and are representative of the numbers in Table sional and quantifies the pin cushion distortion in the phantom. The second11.All frames serve the same function: to accurately guide surgical instru- phantom is three-dimensional and quantifies the displacement and warp andments or small radiotherapy x-ray beams to a locus in the brain. Frame tilt of the image plane. Correction of the pin cushion distortion is reportedaccuracy has been found to vary between serial numbers of the same manu- to reduce displacements on the order of I mm using a fourth order two-facturer. As with other apparatuses in radiation ontology, the frame system dimensional polynomial correction. Milfimizatiou of the warp and displace-must be lested initially and routinely for accuracy, ment of the MR plane is achieved by adjusting the gradleln-shiumllug cur-

The task group strongly recommends to the manufacturers that all rents of the magnetic field until the inmge of tile threc-dimensiuual phau-frame systems use the positive valued quadrant of the Cartesian coordl- tom is a faithful reproduction of the three-dimensional phantom structure.nate system. This convention eliminates the accidental omission/substi- Both of these corrective procedures are time-consuming and require a rigor-

tutlon of a negative-valued coordinate. Elimination of negative values ous QA program of the MR unit prior to each radiosurgical procedure, re-therefore reduces the possibility of misplacing the target, suiting in the reduction of the MRI uncertainty from 4 mm to approximately

All frame systems provide localizing devices for angiography, CT, and 1 mm.MRI. Some angiogr-'iphic Idealizers have radiotranslucent scales that allow A second effort has been presented by Kessler and Carson (1992) whichfor direct deduction from the film image of the target coordinates. Other includes the development of a test object for determining the geometricframe systems rely on fiducial markers and require more complex algo- distortion in three-dimensional MRI and other three-dimensional imagingrithms for obtaining the target position, Similarly, certain CT Idealizers en- systems. The phantom consists of sets of three spiral-filled rods which cross-

able direct calculation of the target coordinates, others do not. Simplicity in correlate with the array of simulated images. The position of tile rods alld theIdealizer function and design facilitates target-setup verification on the treat- phase change of the rods allow for the determination of the poshloi_ uf ament machine, point in absolute three-dimensional space and determine the conforl.al map

42 43

to the three-dimensional image coordinate system. The differences between marketed with the RSA XKNIFE system. (See Loeffler: Stereotactic Radio-the coordinates are due to the distortion by imperfections in the magnetic therapy: Rationale, Techniques and Early Results in Stereotactic Surgeryfield of the imaging system. This phantom accesses distortion by the imag- and Radio Surgery," MPPC Press, 1993, pp 307-320.)ing system, but not the distortion from the perturbation of the magnetic Repositioning the patient relative to the linear accelerator can be accom-field by the patient, plished by several techniques. Standard techniques involve a BRW stereo-

A third effort has been presented by Kooy et al. (1993), which utilizes an taxlc floor stand or aser- ne ntersect ons w h the pa eat s head r ng. Newautomated method for image fusion of CT and MRI volumetric image data innovations in patient repositiooing include the use of a low-frequency mag-

sets. The approach uses a chamfer-matching algorithm which ensures qual- ' - aerie field generated by a special source in the accelerator gantry with theity assurance of the procedure and eliminates the requirement for stereotac- patient's spatial coordinates digitized by a field-sensor that is an integraltic fixation of the patient during the MRI study. The accuracy is improved part of the stereotaxie head ring (Houdek et al., 1990). Another reposition-from approximately 6 mm to 1 mm using the image-fusion technique based " ' ing scheme embeds three gold radiographic markers into the scalp. Orthogo-on the chamfer-matc_hing method, nal radiographic films locate the three markers in space during the first

patient set-up. Subsequent patient reposltioning then requires the three mark-

11. Multiple Fractionatlon ers to be oriented in the same locations. This orientation is accomplishedthrough repeat radiographs coupled with computer programs that dctcrmi.e

From the beginning, SRS has been a multidisciplinary effort to deliver a the movements required to provide tile correct position (Jones et .l., 1989).large radiation dose to a well localized, small volume in the brain through Likewise, repositionlng schemes using Molt6 patterns or laser-to.struttedstereotaxis. Although Leksell originally intended to induce lesions with a repositioning planes can be investigated. A repeat-fixation system is offeredsingle fraction to eliminate functional disorders (Leksell, 1951, 1983, and by MEDCO (Cinnaminson, NJ) for multiple fractionation in SRT. This sys-1987), subsequently SRS has been mainly used to treatAVMs and neoplasms, tern will be marketed with a stereotactic frame and a variable attenuation

Furthermore, many treatments pioneered by the heavy-charged-particle cylindrical collimation system.therapy groups have not yet been widely incorporated into the x-ray SRS

teuhniques. These treatments include multiple fractionation, conformal ra- C. Real-Time Portal Imagingdiation therapy, beam's-eye-view treatment planning, and real-time imag-

ing verification of the patient setup. Real-time imaging (Meertens, 1985) should be adapted for vcrlfyi.g pa-Conventional experience indicates that several fractions of SRS will en- tient position to within 1.5 nun of the desired target position v,ith respect to

hance tumoricida[ effects while minimizing normal tissue sequelae. Guide- the machine isocenter. The skull af(ords ma_y analomical laodt_arks. "l'_elines for fractionated stereotactic radiotherapy have been published for pro- use of tile natural landmarks, image reconstruction from the CT ucatmc.Iducing the tumoricidal effect of 70-Gy low-dose-rate '2_1 interstitial ira- planning data in the beam's-eye view, and teal-time ima,glng _,ill allow forplants (Brenner et at., 1991). However, little is known about the benefits framelcss SRS or high-precisiou radiation therapy. Several digitaJly recoil-and risks of SRS. An RTOG protocol (#90-05) has been initiated to deter- structed radiographs (DRR) can be compared with the corresponding real-mine the radiotoxicity as a function of volume. Future protocols will corn- time images to align the skull with the treatment machine's coordinate sys-pare the effectiveness of single versus multiple-fraction SRS and SRS vet- , tern. Again, this is an enhancement of positioning techniques developed atsus brain implantation versus external beam irradiation. _ LBL and other charged-particle therapy facilities (Lyman et al.,1989). See

These studies will require the development of stereotactic frames that also Adler:"Frameless Radiosurgery,"Stereotactic Surgery andRadiosurgery.

accommodate multiple applications with minimal degradation of patient Mud. Phys. Pub. Co. 1992. pp 237-248.repositioning accuracy, as well as minimal personnel time. Several devices

have been reported: (I) the stereotactic frame/mask designed at Lawrence D. Coaformal SitsBerkeley Laboratory (Lyman el al., 1989); (2) the Lailinea frame (Hariz etal., 1990); (3) the Schwade-Houdek frame (Schwade et al., 1992); and (4) Conformal SRS (CSRS) is lhc use or"aJl adjustable Ct_thlOait,I lu cuu['uI*uthe GilI-Thomas_osman frame (Sofat et al., 1992). The first two devices the beam profile to the target cross-section in the beam's-eye view and isare noninvasive, whereas the third frame is attached to the patient's skull for analogous to the collimation of the charged-particle beam to the BEV of theI-2 weeks. None of these have been widely used in SRS at this time. The target for each beam port. Conformal SRS would improve the dose deliveryGilI-Thomas_Cosman frame-has completed beta testing and is currently in approximately 40-70% of the SRS caseload. The absence of CSRS can

44 4$

I I

prevent treatment in instances such as a large nonspherical target within 5 mater assembly at the University of Utah. Whh the photon collimator jawsmm era critical structure. For the rcmainlng SRS candidates, CSRS reduces of the linear accelerator set to define a field 6 cm × 6 cm at isocemer, aathe irradiated volume of normal tissue (Nedzi et al., 1993; Nedzi et al., aperture is inserted at the bottom of the stereotactic collimator to define a1991; and LcaviR et al., 1989). A second benefit of CSRS results in the circular field of the desired diameter at isocenter, which will encompass theeliminationofoneormoremultipleisocenters.MosttargetsareuonspbericaL maximum target volume projection plus a clinically determined margin.

If the target is elongated, conventional SRS techniques reduce the dose to This aperture is chosen from a complete series of aperture inserts that definenormal tissue through the use of more than a single isocenter (Nedzi et al., the field diameter from 1 cm to 5 cm in 0.25-cm increments. These inserts]990 and Serago et eL, 1990). Nonetheless, two overlapping spheres are . : preserve the small geometric penumbra of the standard circular aperture.not likely to conform to the typical tumor. CSRS will permit an additional Immediately upstream (relative to the photon beam) from the circular aper-25% reduction of the normal tissue volume between the 50-80% dose lev-

els, The end result should be the reduction of complications. Difficulties '

experienced with the..multiple-isocenter technique include the increased timerequired to determine the location of isocenters, field sizes, determination =*_

lop uou:_l_ Pt_Tl

of the are geometry to achieve an adequate treatment plan, and the increased .......

treatment time required to double or triple the treatment arcs. _"_:" Z /

Several techniques to implement field shaping have been proposed. One .......... /_ _ _ ./

ClACt_L_;_

technique attempts to shape a single elliptical aperture that can be applied _ ..........across an entire arc without field shape modification during the arc (Serago c%,_=;_,-_

et al., 1990 and Otto--Oelschlager et al., 1994). The single elliptical aper- 1 _':_J'_"°":tur¢ is chosen when it is necessary to encompass the maximum projection of ,,, --the target volume throughout all angles of all arc segments used in treat- _ ......... _ ...........

merit. This technique will be expanded through the development of control .......... _ _ ..........

software that allows the major axis of the elliptical aperture to be rotated

about the beam axis during rotation to more closely conform the aperture to [ ......... _,.:_;,_,"the target shape, Additionally, the elliptical aperture insert can be removed | ....... ,o, ,........

manually from the collimation system and be replaced by a different insertfor each arc to improve conformation to the target volume. However, inmany cases the projected cross-sectional shape of asymmetric lesions changes ",,__",,_,_d

markedly during a single arc as well as from one arc to the next, thereby _"_'_=_"L'-"_"__

making dynamic field shaping necessary to optimize dose distributions. /Existing multi-vane collimation techniques can be applied to small-field _ ,irradiation. However, this application requires a large number of very thin " i '--i "vanes to achieve the required resolution in field shapes. ' ' '

An alternate design uses four independent computer-controlled jaws, eachhaving translational motion (in-out) and circular rotation (around the target-to-isocenter axis) to conform the field shape projected bY the standard elf-

ENd VtEW

cular collimator more closely to the target projection at each increment ofarc (Leavitt et al., 1991). FIGURE 15. Upper right: A limited perspective of the collimator housing tar

The key feature of the dynamic field-shaping design is the use of Jude- dynamic tield shaping. Upper lell: A schematic view of the seconclary circularpendently controlled collimating vanes to shape the circular field defined collimator, the two layered identical dynamic collimator sub-assemblies, andthe primary circular collimator (6 cm in diameter). One collimator vane isby the standardaperture. Thus, the vanes can be reduced in size and mass extended into the field,while the other is retracted. Lower left: An end viewbecause they must only "trim" the existing circular field, rather than pro- illustrating that each motor drive and its respective collimator jaw is rotatedvide all the primary beam attenuation across the entire larger field defined independently and the independent in-out movement of the jaws. (Leavitt et

by the primary photon collimators. Figure 15 illustrates the prototype colli- al., 1991.}

46 47

ture, two pairs of independently controlled tungsten vanes and their associ-ated linear-motion, screw-drive motors mount on two concentric movable simultaneous control and adjustment of these parameters requires consider-

rotating tables driven by belt attachment to motors with integral quadrature- able study.count cncoders for sensing angular position. The vanes, concentric mount- NOMOS Corp. has also introduced a complete conformal SRT planninging plates, and potentiometers are controlled and driven by a microproces- and treatment delivery system (PEACOCK). The treatment-planning algo-sor-based, four-axis controller. The required range of linear motion of each rithm is based on the filtered backprojection techniques which generate thevane is limited to only 2 cm, corresponding to the distance from the outer dose distribution by beam intensity modulation and dynamic collimator-diameter of a 5 cm (at isocenter) aperture to the midline of the aperture. The jaw movement. The treatment volume is irradiated in slices. The net resuhangular range of motion can extend to 360 °, subject to the anti-collision is a dose distribution which conforms to the tumor and minimizes normalconstraints imposed by the second concentrically mounted vane. Immedi- tissue dose. The PEACOCK system is entering beta testing at Baylor andately upstream again, this two-vane configuration is repeated on a second . . the University of California at San Francisco. Similarly, TOMOTHEI_,APYset of two concentric movable rotation tables. This second set of indepen- strives to achieve the same dose delivery goals by meaus of a redesign ofdent vanes compl_ments the first set to define field shapes of four straight the entire treatment delivery system (linac) by mounting the electronsides (a field smaller than the circular aperture), one to four straight sides, waveguide/target on a ring perpendicular to the patient axis (Mackie et al.,and one to four curved sides (circular aperture clipped by one to four of the 1993). Temporally-modulated collimators and beam intensity modulationvanes), or circular (all four vanes withdrawn to the edge of the circular would conform the dose distribution to the tumor as the beam spirals downaperture'), the axis of the patient. This technique has the theoretical advantage of de-

The above-described four-vane collimation system is unable to match livering a homogeneous dose to the target (Carol, 1993).the projected cross-sectional concave view of some target shapes, such as acrescent or peanut shape. In these cases, improved conformation to the tar- E. Robot-Gulded Linac

get cross-section may be achieved through the use of multiple narrow vanes, A mini-linac has been mounted on a robotic arm a,d ¢o.llgtffed I'_JL

each moving independently to describe a curved treatment field boundary, frameless SRS (Cox et al., 1993). The system, Neurotron 1000, can vary theEfforts are now in progress to develop specialized multi-vane collimators source-axis distance as well as the beam path by angle, distance a.d speed.for radiosurgery in which the projected width of each vane will be reduced The Neurotron 1000 tracks the image of the patient anatomy i, real-time

to 2 mm (Nedzi et al., 1991). This capability, coupled with rotation of the and continuously guides the robot arm during the treatmem. Consequently,entire collimator assembly about the principal beam axis, may improve the conformal SRS can be affected by beam manipulation as opposed to corn-

dose conformationin selectedclinicalcases, plex collimation.Dynamic dose-rate control features on new-generation linear accelera- In summary, dynamic conformational field shaping, improved imaging

tots allow the continuous adjustment of dose delivered per degree. This techniques, expanded treatment planning techniques, the incorporation offeature may be incorporated into dose delivery in radiosnrgery. During treat- dose-volume histogram and biological predictive data, and patient position-ment planning, a large number of treatment arcs would be defined. Each arc ing techniques will be extensively investigated. Progress iu these areas willwould then be broken into a number of segments; for each segment the undoubtedly lead to further advances in stereotactic radiosurgery.conformal collimator shape would be determined, and the dose contributionwithin the target volume and the surrounding normal tissue would be calcu-lated for a fixed number of monitor units. Optimization routines would de- IX. SUMMARYtermine the monitor units to be delivered during each. segment, based onevaluation of differential and integral dose volume histograms, which are Stereotactic radiosurgery has evolved to the point where co.m_ercial sys-

weighted by the biological predictors of tumor control probability (TCP) tems, such as XKNIFE, LEIBINGER AND FISCHER LP, the GAMMA-and normal tissue control probability (NTCP) (Lyman and Wolbarst, 1987). KNIFE and the BRAIN LAB are available to the oncology community. TheAdditionally, computer control of the patient couch rotation during treat- basics of these systems will not change significantly with the exception ofmerit suggests additional possibilities for optimizing the dose distribution image correlation and immobilization techniques. Stereotactic radiosurgeryby adding simultaneous couch rotation to conformational vane positioning (SRS) and stereotactic radiotherapy (SRT) present the same accuracy re-and computer-controlled dose rate modulation. The potential advantages of quirements in dosimetry and patient positioning and are at the millimeterlevel. The introduction of the SRS/SRT hardware and software is a complex

48 49

process which must be configured to the institution at the interdepartmental Xl. APPENDIX Ilevel as well as to the SRS apparatus. The system will be used by a team ofradiation oncologists, neurosurgeons, medical physicists, and neororadiologists. PROBABLE RISK ANALYSIS FLOWCHART: EXAMPLE 1The following basic sequence for its introduction is recommended:

1) Establish a multidisciplinary team to determine the treatment _ q' |Set pointer to target

goals. Attach Frame Mount pedestal coordinates2) Determine the accuracy required and present in existing

equipment.Foroxamp,,therototinua,axesofthegantry,col- 1 L Ilimator and PSA should intersect within a l-mm radius sphere. -- J

3) Select the SRS apparatus and perform a prospective risk ' " ]Sc.a Iocafizer et Place patiefzt °n PSA Ianalysis of the SRS procedure, n with CT Mount collimator hold and affix to pedestal J

4) EstablJ:sh an acceptance test. maximum / [5) Acquire the beam-profile data with a detector t_ !

dimension of I-2 mm for the linac and 0.5 mm for the gamma 1 ] )

knife unit. Setcollimator Insertcollimator Treat6) Acquire dose calibration with a detector dimension of 3 mm or 5xson

less for the linac 02.5--40.0 mm diameter fields) and 1 mm x 1 [__ [mmx 1 mm for the gamma knife unit.

7) Establish a treatment procedure and routine treatment QA sched-ule (daily, quarterly and annual).

8) Interlock the gantry/PSA to prevent collisions. XII. APPENDIX 11

Appendix III contains a representative or generic QA schedule for a liuac- PROBABLE RISK ANALYSIS FLOWCHART: EXAMPLE 2based installation. Examples of the gamma knife unit and liuac QA sched-

ules are shown in Appendix IV. Each institution should modify the above _ --1guidelines to optimize the accuracy of treatment delivery at that particular c_c,.r,_o_coo_o,_'r_facility. L A,=a,,_ _ [ ._'rcouJ_r°"""'_ I [ ,m=ST_- [

i _ l i

i i vC_leCk ab'Ic_OI 0 ( IocJtzef t ing Iha _ _ _ P¢_¢_ Pu_i_ll _Jt_'_*__ tK[Jlfl _ lU1_014_ IThe task group would like to express their appreciation for the assistance I I •r .......... __ •[afforded by Drs. Steven Leibel, Hanne Kooy, Robert Kline, Patrick Stafford,

Jatinder Palta, Martin Weinhous, Steven Goetsch. Robert Dryzmala. and _' _'

Douglas Rosenzweig. Dr. Leibel provided considerable insight into the treat- I ,_.,_,T_=_t.,_., _""°°*'"*' [ I _C,,V_'_ COO_t_ [merit of primary brain lesions. Dr. Kooy assisted with the QA procedure for FOW_.o.ct e_c,_eou.,_'ro.s_ i I c_c_Fs_._t'ro,_,,,.,=,_ 1the couch-mounted system. Dr. Rosenzweig as well as Kathi Burton were r _ _

I I ICheek akWm_cnt of O,_ss ar_ton_integral in preparing the manuscript for publication. [ S_lr_w_llCTio:_b_er COOR_,ATE$

i I ,I J I [ '.... ]

i i

C,HECKARCGEOMETRyBYCALCIJL_TI_APp_o XIAATE FOR T_U_ A,X'¢_ $

TAR_ _T COOF4D_T F_ '/_STH F:_iI _OTATIN_ THRU ° A.*_T_y N4OL_ S

50 51

XIII. APPENDIX IliA: SRS QA SCHEDULE XV. APPENDIX IV

PROCESS TEST PERIODICITY STEREOTACTIC RADIOSURGERY TECHNIQUES

I. INPUT DIGITIZER, OUTPUT PLOT A. Heavy-Charged-Particle Therapy

• Square contour Weekly* R. R, Wilson first proposed the use of heavy charged particles iui K'adlt_II. CT SCAN TRANSFER Quarterly*"III. PHOTON BEAMS therapy in 1946 (Wilson). Heavy charged particle therapy has been avail-

1) Point doses (d= d=, 5, 10) Semi-annually* able for several decades (Goiteia et el., 1982). The therapy facility at the2) Lateral profiles Semi-annually* Donner Lab/Lawrence Berkeley Lab is presented as an example of the of-

• Open (d= d ,=, 10) (12.5 mm, 30.0 mm) forts in heavy-charged particle therapy. The treatment philosophies at LBLIV. FRAME SYSTEI_'1) CT Localizat on Pedormance are not identical to those at other facilities. For example, as many as eight

ports through both hemispheres may be used to treat intracranial lesions at2) Angiographic Performance Quarterly3) MRI Performance the Harvard Cyclotron, compared to four purls through one hemisphere al

V. SYSTEM LOCALIZATION LBL.

1) CT Phantom Target Quarterly2) Beam Target on Linac 1. Heavy ions--LBLVI. SUMMATION ALGORITHMS

1) Arc pair Ahhough the initial stcrcotactic hradlatiotl at LBL o¢¢u,'rcd ;. _hc c_LJi)• Equally weighted 1960's, tile current SRS design was developed in 1980 (Lyma. _t t,l., 19_39)* Unequally weighted Semi-annually"2) 5 arc The principal criteria for SRS with a helium ion beam were (l) a uailbr.L

• 270°, 230 °, 190 °, 10°, 50Q field between 10 mm and 40 ram; (2) a range in penclralion dcpd) bclweeuVII. MACHINE SETTINGS 40 mm and 140 mm; (3) the ability to shift the Bragg peak 9ver a 40-ram

. - f) Single stationary Semi-annually* interval; (4) sharply defined lateral and distal borders; and (5) a dose rate2) 4 arcs on spheregreater than 2 Gy/min.

tA . .t mm_mumfrequencyndpeatedora ersotwarechanges.

"*Atminimumfrequencyindicatedoralter any software orhardware 2. ISAH: Irradiation Stereotactic Apparatus.]'or HurnanJs

changes on the CTscanner or treatmentplanningsystem. Irradiation Stereolactlc Apparatus for Humans (ISAH) is a patlent pu_;Iioni_g device for heavy-charged-panlcle therapy (Lyman and ChoJ_g, 1974)

XVI. APPENDIX IIlB: LINAC QA SCHEDULE iSAH maneuvers the patient with 5 deglees of fJcetloc.: iln'ce .lutually o_-thogonal translations and two rotatitms, The base of ISAH is a (}.5-m thick

HARDWARE TEST PERIODICITY granite slab, polished to tolerances of 0.5 microns. The slab call |,e adjusted_erlically and horizonlagy to whhiu 5 cm. A pallc.l m_Jduie is mounled o.

I. DOSIMETRY OF THE LINAC the slab and can rotate on two orthogonal axes. Position accuracy is 0.01 cm

a) Dose calibration monthly and rotational position is uncertain by 0.10 degrees. All motions are el-b) x-ray/light field alignment bi-weekly fected by computer-controlled stepping motors. Should tile difference be-

ll. ALIGNMENT OF GANTRY COLLIMATOR tween the actual patient position and the compuled position exceed the I-AND PSA AXES annually nrnr or I ° limits, treatment is hailed unlil the positi_m error is correcled.

Ill. STABILITY OF THE BEAM SPOT annuallyIV. SAFETY OF PATIENT SUPPORT 3. Beam Characteristics

ASSEMBLY monthlyV. ARC THERAPY TEST quarterlyVI. LASER ALIGNMENT Beam energy degradation and ulodulatiuJ_ _CCu=_3.t_ .L Ul,:_.c_.,. h_,,,,

a) Pedestal mount weekly the patient (Figure 16). ConsequentLy, tile l)eai]n has _¢gligi01c diverge.co.b) Couch mount prior to The peak-to-plateau dose ratio equals 3.09. The distal beam pemambra dl,op_

each treatment from 90% peak dose to 10% in less than 6 mm (Figm'e 17).

52 53

Ill

-- tO

O8

Range modulator _ _ 0so 06- o

4onchamber _ _ Patient collimator >_m

o4- _. 04

_eeom path4

02- 02

IL

O0 50 tOO i50 2 0

Depth in waleZ (cm) Disla;ice I[o111 bU_¢ll _; (CIll)

X_L 9012-3a74

I I I i I I I

FIGURE 16. The helium ion beam delivery line is shown in relation to the I.O-- jur_,J_

ISAH. An x-ray uytube (not shown) is positionedbetween the patient and O.S--beam line to obtain BEV radiographsfor positionverification.(Lyman et al.,Mud. Phys. 13:695-699 1986.) 0.8

o 0.7_, j_, _u,_-_

Figure 3 is a comparison of dose profiles of a 230-MeV/u helium ion _ O E ._oudL_--_-"-_¢=-_t-=_- Ibeam and a 6-MV x-ray beam with beam apertures of 1.27 cm and 1.25 cm, ._ 0.5 _respectively. The two beam profiles are remarkably similar. The principal "_ _/clinical advantage of the charged particle beams over x rays is the finite _ 0.4range of charged particles. The charged particle beams can be range-modu- 0.3lated such that the Bragg peak coincides with the distal side of the target,thus sparingthe normaltissuebehindthelesion. 02

0.1

4. LBL Stereotactic Frame , I I l t I I IO0 20 40 60 80 IO0 120 140

A noninvasive frame has been developed at LBL for stereotactic Depth i(_ wutez Imrnlneuroradiological studies (CT, MRI, and angiography), (Lyman et al, 1989). "The frame consists of a plastic mask, a Lucite/graphite mounting frame, _b_.e ,_

fiducial markers, and a fixation interface to the imaging couches (Figure FIGURE 17. The depth dose prolilos in water are snow, tar (a) a=_ul=Stiilt_¢.l18). The frame allows the patient to be repositioned to within I mm in each 230 MeV/u helium ion beam and (b) a range-modulated beam (stoppingof three orthogonal planes, region is 21.6 mm). The beam cross-section is shown in (c) for tiau 12.7 mrn

The frame is mounted to the ISAH and positioned for the desired beam aperture. (Lyman et al., Mud. Phys. 13:695-699, 1986.)entry and inclination. A radiograph is taken to provide a beam's-eye view(BEV) of the treatment port. The radiograph is compared with a digitallyreconstructedradiograph (DRR) alsoreconstructedfrom the BEV, ascalcu-

54 55

Anteric¢ Fiduc/al

Markers B. Linear Accelerators in RadiosurgeryArch

The use of linear accelerators in radiosurgery was first proposed theoreti-

Mask tally by Larsson etal. in 1974. The first reports on clinical linac-hasedPositk_ng Pin-.. radio.surgery were published I0 years later in 1984 by Belti and Derechinsky

and in 1985 by Colombo etal. and Hartmann et al. These reports were all

Sideptate based on a technique referred to as the multiple noncoplanar converging

arcs radiosurgieal technique.The center of the target is placed stereotaeticallyat the machine isocenter and a series of arcs, each with a different stationary

Yoke treatment-chair position or treatment-couch position, spreads the dose oat-Top

ass-member side the target over as large a volume as possible. Soon thereafter, linac-based radiosurgery started in North America in Boston with a variation o.the multiple arcs technique (Houdek et al., 1985; Lutz etal., 1988; andPosterior Fiauclar

Markers Sehel[ et at., 1991) and in Montreal with the dynamic rotation technique

' "LateralFiduc/a/ (Podgorsak el al., 1987 and 1988).Markers

Several of the current linac-based radiosurgery tectmiques are d_seussed

SupportRod in detail. The discussion focuses on pedestal- and couched-mounted framesystems. A discussion of the physics for radiosurgery with linear accelera-

FIGURE 115.The LBL noninvaslve steroolaclh_ frame is illustrated with the tars has recently been published by Podgorsak (1992).fiducial markers. (Lyman et at, 1989.)

1. Pedestal-Mounted Frame Techniques

lated from the treatment plan. If the two BEVs depict Ihe same port location * The initial configuration al the Joint Center F.r R.dial;uJ_

and angulation, the treatment proceeds. Conversely, the patient setup and Therapyposition is adjusted until the DRR and radiograph are identical.

As in x-ray SRS, the frame immobilizes the patient and establishes a A system has been developed tbr stereotactically described delivery at"reference for target localization. The distinguishing feature is that the frame prescribed doses of radiation to precisely located volumes ranging fi'om 0.6is noninvasive and is used for single or multiple fractions, cm; to 14 cm 3in the brain (Lutz etal., 1988 and Winston and Lutz, 1988). A

Brown-Roberts-Wells (BRW) stereotactic apparatus and a 6-MV linear ac-5. Treatment celerator equipped with a special collimator (1.254.0 cm in diameter) have

been adapted. The 20-ram collimator produces a nearly spherical volume ofA lesion is treated with four ports or beams that traverse only one hemi- 3.6 cm 3 within the 80% isodos¢ surface for a five-arc geometry with 40

sphere and converge on the target. Each port is conformed to the three- degrees between each arc plane. Outside the treatment volume, the dosedimensional shape of the target; hence, the need for multiple isoeenters is declines to 50% of the peripheral target over a distance of 3_, mm. Theeliminated. Intracranial lesions are treated with multiple fractions, with the target can be located with computed tomography or cerebral a==giography.total pholon-exjuivalent dose between 15 Gy and 25 Gy. Field sizes range Radiation is delivered with an arcing beam of x rays, with the turntablefrom 8 mm to 60 ram. The treatment dose is calibrated to an isodose surface (patient support assembly) in a different position for each arc. Typically,value between 70-90% of the maximum dose. (Chen et al., 1979 and Goiteln there are four arc positions, but there are no restrictioJ_s. The exact pattern

etal,, 1982) The CT scan data are acquired with a 5-ram slice thickness to of arcs and arc-weights depends on the treatment goals. The entire systemfacilitate the compensator fabrication for each port. AVM treatments are has been extensively tested for accurate alignment and dose distribution.

• planned from anglograms and MRI (Phillips et al., 1989). The AVM's sur- Errors have been measured for the alignment of the apparatus and the pro-face is contoured at the levels of MR scans corresponding to the CT scans tess of localization. Safety of operation was emphasized throughout theand is incorporated into the CT data set. design and testing phases.

56 57

6_8S

1_:_3I_0},'IR_UO)_J,_,'_JP.H!JOs|oSDt_|]I_H|s!)voll_oa!nboa,([uO_H,L"LLIIU_t{]('_6["le,rezln-O"Jolem!llOO.tO,'331n0_DIllol130(Is3Jtll!_,pno(I01_|joIJOllp,tJ_lJoOqlJO'JOlO_JUOllt_OlJIUpul_elqel'_JlueOeq|Josexeuo!|eloJeqlJosnooleqllepuepue|seql

.•olpeqo_llesletueJio|oeloeJe|soqj."eleldoseqVSdeqluopolunouJpuels -_t?lII'D3tzi?,l_;IplO_Jl21/ttll!.|'/:l![P,llO_OqlJOJOJ$;IUOUtlOj!nboJout_!A_,_uoqo:*fold'"etuejjeqlq|tMUMOqSSuoqmnfiIUO0aJe_oJeqJalUeO_utof.eqj."6t3EfflOI.q [_,.I,'llgIpuP.I_,ltlOJJtt!ap_,mgllga!dglaJ_sqdvJffo!,ffuel_Jq,-1la_)"stld_J_O]_tle....•

S!1U_tlIO_IIP.JJP,JP.OU!IODUOLI_Un)/(I_.JJP,OJ_FIb._0139X11139_I[1!SJO_IJI_III[

I_.!3np!.IpnaIlnojjolos8sllqxoq3!qd_JSO!_tl_oqlJOsgp!sJlloj041Jo

q3v,3'uts!u_qnotula_l.3os-pu¢-ii_qA_I_t_qlJosu_atu£q_tllP,Jjlaz![p.3oI_L3i_'f_

-,qTt_,3o311d_.l_Ol_l_P,.IOlp_13nJl_;tl_3ptl_p,311_!S0p_P,_xoqJ_Z![P.30|V._o

N_I.LVTZI3V30_.I,39HVL

_!too]Xop,_.'lunJ1s,llt.3!l_d_t]luoddnxmposn_!(VSd),(lquIoss_.lJod'_"-t'frIs111_]ll](lDI],L"pOJ!rt[3DJ8U]UO!l]_od0S!3,_JdoqlJOj_lq_Is,(llth".]a!jjnslOU

s!'uol)_,z_..[.?ItomuJl,l_,uo]l!pp_]noql!_A'qgno3]UamlU._J)LIP,!JI_A_L')tt_!led

q3¢_JOjdnlospu_lu_mU,_!l¢u_oIs_saqlJOUOII_3!.I!J,3AlU_tlllP,aJlOldSt_oi

-.lO_!JI_sl!tttJ¢3d_u]uo]llsodItlo!l_dJOpoqlottls!t[l'KllUP_lJodttl!aJOp_['3sl3

-oJd,_,qa|to_qla)lctuKl_lllKl[[[qg[JeAJ!aqlpuestttvoqJaSt_Iaqljoqlp.tmaql

asnv.a=qsJasv_I]uamu_!l_s,mooJaq)ol_._uaJajaJ]noql!aspaqs!idtuoa3_s]

_u!uo[llsodlO_.l_lOl_L"DP,U![OL]I,|0JOlllo30_;]OqlleOlP.tllpJOOOl_Jt_lp_ullII

-JolopnJd_._3v.ldO1_lqnaJ¢so^!Jpos_tll'/_llP.oU!oodS'(,_o|olllUIJOlA_[_

tl![_3[1J3ApIIt_'[P.JOIP.['JO[JOlSodoJo|tIP.$;P,O|p_JJ_JOl)soltlu[pJoo3uu!SD|J_)

ppl!_.ap-_'D¢31'pe.3tls.ltt.7!lP,d_qltl!ql!_lu!odpo!.l!3,_ds,(u_'o3u_q'pu¢'_u!a

p_:oq-_tllOAomI_1|1S,_A!Jpp._l_J_doKIw,nucm'|P,uo,_oqlJOpaW,Jq!l_o_Jql-noJiO.V"_umodo.JCn3J..3pa|pJp,osad31_I_3a_qpUI_'pu_qoJJa3uloJjop_

S_4pUnlSJOOIA_lfl,3tLL"t_u!jl?oq-JoO]js,q3no3_qljo_leldaqlo1,(3_,Jnoo__J__lJ3su[_O]4]UI3-OI_qj_"|JaSU!JOleUl!]103leO[JpU]],(3_UO]da33ei[!_a

._(t.anpo.rdnjqlt_ptmfll3l,_!.rp_tloqpuupouu!d._qu¢3_seqpouS'!s_pff[fe!3pu_Joluaoos!aqlmoJjtu3I;_olspuolx_l["JOUUCtUolq]otlpoad_Jpu_as!oajd-otiss!q,L"punlsA_t_[_[o(]1P_]A,_U!J_OqJO0[l_qlO!p¢oqs,luo!l_d¢q,3¢11¢u!,(Jlue_gqlOllunomplnoqsJOl_luI.o3aq.L"uols_oqlaptslno,tlOlll_.pl_jJO

o|p_sn_qu_qlu¢,3,_u!JAX_ll]_q,L"(uo!l¢|oJs,olqP,luJnl_qlJOs!xP,[_3!laO^JJoll_Jp!d_Jaaotu_u!_u!tlnsaJ'm_aqaqtjouaq_nuod_qlsoz!m!u!mpu_

aqls_qs!lqms_s!ql)q3no3lU_tttlVOlloqluoddnsIt_qls_u]Jvoq_ql_ul,(JJO^Olugulu_!leoqlSaAOJdWtOSl_uoumu.llOo,Q_!Ua,L"stueaqJ_ln3al3alqe.usap

olefdall!olpile.Is.too[.[A_[[[oqlx'_Olpouff!s_pse_OS'_.qaacJJOltt[uVaqlul_qlJOqll_J'stueaqa_ln_ul_lo_la3npoJdstat_.faqlasn¢3_q,(Ja]]anso!pe.t

3u,3mu,_]l,__1_Jn33¢Joj_l¢nb._p'elou/_ll_nsns!pl_Ulqff!IJOja|enbopuu!s.tJOlUJalOO3ujt_OU!lt_uololt_tUtllO3ibuoqu_^uo3oq,L

S,M)IEJOI._3,3P.Oq.L"tlOn03loLJlUI_ff_qlJOuoD!sodOqlJOssolpJ_ffa.lP[:)U"]D_zqu[s_'_at[/JOuo[l[sodI/l_tlJoqlJ]I1_^o

tlO]lP,!p_JanlnoJ]3or|!111pOJaltlO3,_qplnoqs1DffJe]leO[J*qds_qljoOffeLll]'$_XI_,(JlUU8pueolq_luan!joUO[lO_SJOltljo_3uIpue'uo[ssao_jds,xualqeI

¢P,[n3.r[3_ql|l'.tOlff3,'30S[IS.K]OqlIP.S[|3ffJP,lOq|ptt¢poU,_[leS[JOIB¢//![[O3Oq]-uJnlpuu,(JlUl_ff'flusLa|lllOffluoJjsluatuaoelds[puJulL'O-ff'OaqlJOosm_oaq_t,allA_'o3_,ldIt!.tOl_:ttT!llOO/(.112,[IJ_latllql]_JOlP,J_I_DOP,.te_U]lOqlffu!snl_ffJl_lpa^atq,_e.]offst.tou_30s!.[l_3lueq3OlU.Onl|V"la|tlODOSl...OSltUoJdtuo3.lsoq.,aql

o1|1jostldv,J_o!pPJffu!_tupuP,J,'3uooost,,os]uloJdtuo3ls_q,,oql1'_,([_s]3s_p_leUff!sops!loqla_o|1s_so]3_tlJo3sox_'#azqlaq!aJaq__3_dsu!lu[od

-oJdI3ffJP..|[DD1Sle.3!aatldslimUSeffulaeld5qp_v.nlv.^_set_suo!usodq3no3°q.L"(61aanff]d)SUO[|IS|OJI1_ffu.anpalq_lsumtu=upu_(JaIUODOSlOql)]ulod

pUP._(gll/_liP.]ell/DmUB[['V''Z_llla.90S[DqlO]aDJIlO$Uoloqdaql8u[lO_UUOOuommo3ululooslolu[Plnoqs(lolemHio3puu'olqe|uJnl'/,Jlul_i_)soxu[e3ou[Ioqlql],',_pouffH_aoqlsntu1JOSUls.JOl_tU]l[o3_qljos!xei_Jluo3atI.L-lueq.?otui_houlJd_Jqlaq,L'lelluossoSlgouJno3t_i_tolueqooutpooo",(l!l]ql_ 'posnua_qOSlV,o^eqSlJOSUtJalatuelp.ioffJU|pu_ZallmUSqffnoqllt_'Jaluo3os_''"'•

••-III_AI_JO$sRqOq|UOUOI|ISIpBJ_UIZILIOIJOJg'DJOOS,_q|sBuosoqoSRA_(UIU oql1ctu30"t'oltu3;Z'ImoJjaz!su]offueJsuosu!a^lat_L"aJaqds!moq......cJ_^opozo^flOpazesumoq_ql_JOq,,,t'Jo]etmllo3.a_enbseqltat.Dlq[S$Od-JOJ[[l_'oIIVOled"OUI'SOll_13OSS V.Ilel-leA)..lOleJOOO3vjealtl.-]AP,[-9V

S]ttP.qlloo!pP,affosopJodJ_qseSJaA,II_p1]asn'_o_quosoq3s_zol_tU!llO3_eISfLt'V_WddV

IIIIIII

2. Couch.Mounted Frame System

• Dynamic Stereotactic Radiosurgery at McGill University

APPARATUS

The dynamic stereotactic radiosurgical technique was developed in 1_86at McGill University in Montreal (Podgorsak et al., 1987, 1990, and 1992).This technique uses a 10-MV llnac (Varian, Clinac-I 8) as the radiation sourceand two types of commercially available stereotactie frames (OBT frame,Tipal Instruments, Montreal and Leksell frame, Elekta Instruments,Stockholm) for target localization, treatment set-up, and patient immobili-zation during treatment. In contrast to the multiple noncoplanar converging

arcs technique, which spread the dose outside the target area with a series ofarcs, dynamic rotation delivers the dose during a simultaneous and conlinu-ous rotation of both the gantry and the couch during treatment.

The additions and modifications required to make the linac useful t_Ldynamic radiosurgery are relatively simple and consist of extra 1O-cm thicklead collimators to define the small circular fields at the isocemcr (0.5-3.5

cm in diameter), a remote controlled motorized couch-rotatlou capahilitywith a variable speed control, a couch-angle readout and a couch-heightreadout on the machine console, brackets to fasten the stereotactic frame to

" //" the treatment couch, and brakes to immobilize the longitudinal and lateralcouch motions.

The stereotactic frames are compatible with modern imaging equipment,such as CT, MR1, and DSA, so as to allow for accurate target localization(Olivier et al., 1987 and Peters et al., 1987) and, so long as appropriatebrackets arc available, to fasten /he frame to the treatment couch 1o ensure

to the floor stand used in most umhiple converging arcs techniques is antpossible for dynamic rotation because in dynamic rotatltJn the linac headmust pass below the patient. Not being able to attach the frame to the floor

stand could be considered a drawback of dynamic rotation, assuming that

the floor stand offers better frame stability. However, couch mounting on aproperly locked couch offers equal stability and is considerably safer thanthe floor-stand rooanling in cases of inadvertent vertical couch motions.

The stereotactie frames used for dynamic radiosurgery at McGill are com-patible with CT, MR[, and DSA, and their mass is only 800 g, making them

FIGURE 21. The University of FIodda system is shown with the gymbal- easily supportable by the patient when moving from diagnostic to therapeu-mounted collimator arm attached to the linae. (Friedman and 8ova, 1989.) tic equipment..

The frame is fasleacd to the paficm's head wi£h three 1,.,l'Jvc tattoo. IA.sthat penetrate diagonally into the frame's cubic structure. Standard fidt_cial-

marker plates are used to determine the coordinates of the target with CT orMRI, whereas for target localization with the DSA, special magnificationplates are used, Information on the target position obtained with diagnostic

6Z

/ I i iiii iiiiII i ,J t

procedures is transferred to special target-localization plates that are used in lic system, and a control panel (Bradshaw, 1986; Lunsford et al., 1987 andconjunction with wall- and ceiling-mounted lasers for placement of the tar- 1989; and Wu et al., 1990). The radiation unit consists of an almost spheri-get center into the linac isocenter before treatment, cal housing with a shielded entrance door. Inside the housing is a hemi-

spherical central body, which contains the 201 _Co sources (Figure 1). TheTREATMENT TECHNIQUE housing and the central body are made of cast iron; the entrance door is cast

The patient is placed supine onto the treatment couch and the stereotac- steel. The radiation unit weighs approximately 16,800 kg. The treatment

tic frame is fastened to the couch such that the patient's head overhangs tbe table weighs an additional 1,500 kg. The housing opens like a cla_. shell forend oftbe couch as shown in Figure 11. The appropriate couch position is accessing the sources. The upper half of the housing has an outer radius ofdicta ned with the help of wall- and ceiling-mounted las_:r positioning de- 82.5 cm and an inner radius of 42.5 cm. The lower half contains the shieldedvices and the target localization plates on which the target centers are indi- entrance door and a removable sump plug to retrieve objects accidentally

cated. Once the center of the target coincides with the linac isocenter, spe- dropped into the unit.cial brakes immobilize, the lateral and longitudinal couch motions and the The central body, with an outer radius of 42 cm, fits closely wilh thetarget localization plates are removed from the frame to minimize the inter- inner radius of the upper half of the housing; its inner radius is 22.5 cm. Theference of the stereotactic equipment with the radiation beam. The couch is angulation and diameter of the 201 beam channels are machined precisely

then rotated to 75 °, the gantry to 30 °, and the dynamic stereotactic (tolerance 0f0.026 mm) in the central body. Each beam channel consists ofradiosurgical procedure is ready to begin, the source/hushing assembly: a 65-ram thick, 96% lungslen al)oy

During the treatment, the couch rotates 150°, from +75 ° to -75 °, while precollimator and a 92-ram thick lead collimator. All 201 bea.A ch,_nnuls

the gantry simultaneously rotates 300% from 30 ° to 330 °. Thus, each degree are focused 1o a single point at the ceJ_lcr of tbc radialio, uniL (|'oral did-of couch rotation corresponds to 2° of gantry rotation. Several successive tance is 40.3 cm). The sources lie in an arc _: 48 ° from the ccLm'al I)eant

positions through which the couch and gantry move during the complete along the long axis of the treatment table and ::t:80" along tl}e tra_asverse axisradiosurgical procedure are shown in Figure I1, starting (a) with the gantry of the table. No primary beams of radiation are directed out of the shieldingand couch angles of 30 ° and +75 °, respectively, through (b) 90° and +45 °, door. The central axis of the 201 beams intersect at the focus with a me-

respectively, (c) 180° and 0°, respectively, (d) 270 ° and -45*, respectively, chanical precision of ± 0.3 mm.and (e) stopping at 330 ° and -75 °, respectively. The final collimation is accomplished with one of four collimator hel-

During radiosurgery, the radiation beam always points to the target vol- mets. Each helmet has an identical 6-cm thick cast iron shield with an innerume. The beam entry trace on tbe palienrs bead. however, exhibits a pecu- radius of 16.5 cm and an outer radius of 22.5 cm. The 201 channels areliar trace (baseball seam), shown schematically in Figure 2 (g). All points of drilled in each helmet, Removable, 6-era-thick final collimators are 96%the beam entry lie in the upper hemisphere, which results in the beam exit tungsten alloy. They have circular apertures that produce nomi.,al 4-, 8-,

14-, or 18-ram diameter fields at the focus. The apertures of iltd_vldualpoints all lying in the lower hemisphere. This means that in the dynamic collimators can be replaced with occlusive plugs to prcvetlt iJladiat_, otrotation, even though all beams intersect in the target volume, parallel andopposing beams never degrade the optimal steepness of the dose falloff out- critical structures, such as the leJbsof tile eye, or to ahc( the shape of theside the target volume, isodose distribution. Each hehnet is equipped with a pair ol trulmions, which

A couch-mounted frame system is also available from RSA, Inc. serve as the fixation points for the stercotactic frame in the X dimension

(Burlington, MA). This system continues to employ a radio-opaque target (right-left).

simulator system to verify the target alignment in the x-ray beam. This ap- Micro switches on each helmet verify alignment between the helmet andproach offers hard-copy documentation of the target placement in the radia- central body with a positioning accuracy of ± 0.1 ram. Each '_70 sourcetion beam. consistsof 20 pellets,1 mmin diameterandheight,stackedon topof one

another, and encased in a double-walled stainless sleel capsule. Each source

C. Dedicated Radioisotope SRS Unit_The Gamma Knife fits into the source-bushing assembly at tile top of each central body colli-Technique mator. The short distance from the collimator helmet to die pat;era reduces

the beam penumbra to from l to 2 nlln for all sizes of ct)llillla[of hclu)cts.

I. Apparatus The steel door in the radiation unit is 1_.5 cul thick. The upclfiHg aJld oh}s-ing of the door and the n_ovement of the treatment lable in and out of Ihc

The major components of the Leksell stereotactic gamma knife are the unit is controlled hydraulically. In the event of a power failure during aradiation unit, four collimator helmets, a patient treatment table, a hydrau-

64 65

I ] ..... t iIt-

treatment session, reserve hydraulic pressure automatically releases the treat- ion chamber was placed in a polystyrene block phantom at a deptl_ of 8.0ment table and closes the shielding door. If reserve pressure is also lost, a cm to simulate the radius of the spherical phantom. A small 5 × 5 cm2 '_'Cohand pump is available to close the door. Failure of all back-up systems beam was used for irradiation. With the same physical setup, the exposuresrequires manually releasing the table and removing the patient from the were repeated using a 0.6-cm 3, Farmer-type ionization chantbcr and an elec-unit.

trometer, which has a calibration traceable to NIST. Hence, the dosimetry

system was appropriately cross-calibrated. With the micro-chamber in place2. Target Localization at the center of the spherical phantom, which was centered at the focal point

of the lg-mm collimator helmet, dose rates were measured repeatedly atWith Leksell's stereotactic frame attached to the patient's skull, a diag- different positions. The trunnions were adjusted to vary the dose until the

nestle imaging procedure, such as CT, MRI, or angiography is performed to maximum dose rate was found.

localize the target. A three-dlmensional Cartesian coordinate system (X, Y, Because the chamber volume was large relative to the region of unifoonZ) is used to locate the target coordinates in Leksell's stereotactie frame, dose of other col}treater helmets, an additional electronic method was usedThe Z-axis (superior nferior) of the coordinate system lies along the axis to measure the dose rate at the focus of tile 4-, 8-, and 14-nun helmets. A

of the patient, the X-axis (left-right) is in the coronal plane, and the Y-axis small diode was used iu a mariner slmi/ar to the micro-cl_ambcr, lzs rcsl)u,sc(anterior-posterior) is in the sagittal plane. The frame coordinate system is in a polystyrene block phantom at a depth of 8 cm on tile cubalt unit wasoriented such that the center of the helmet (the focus of the 201 sources) is compared to thal in the spherical phantom at life focus of the gamma kJlifc.X = I00, Y = 100, and Z = 100. This system eliminates the use of negativecoordinates. The current mode of the electrometer was used for all dose rate measure-

merits with diodes.

The target is moved to the focal point of the unit by setting the X, Y, and Standard (3 mm × 3mm × I ram) LiF TLD chips also were used and

Z coordinates of the stereotaetic frame and fixing the frame to the trunnions calibrated in the polystyrene block phant'om at a depth of 8 cm for the 5 cmof the helmet. The angle made by the frame between the central source ray x 5 cm field. The TLDs were appropriately annealed and sorted so that theand the horizontal plate is called the "gamma angle" and is read from indi- entire group responded within ± 2% of the mean TLD response. The TLDscaters on the trunnions. The gamma angle is determined by tilting the patient's were given the same exposures that the chambers were given in the polysty-head. When shining a small pen light through each collimator in the hehnet, rene block phantom. A dose-to-water versus TLD response curve was dctex-radiation beams that would pass through the lens of the eye can be pre- mined and fit to a least-square line.dieted. The appropriate collimators are then replaced with solid plugs to A TLD was placed at the center of the 8-el,, _adl,s |]ulystylelLe Sphereprevent the direct exposure of the lens to radiation. If more than one target and exposed at the focus of rue gamma kafife re,it. The 18-m,n heh,,et wasis to be irradiated, this process is repeated for each target, used with all 201 cobalt source collimators open. The TLD respo_se c,l've

was used to determine the dose rate to water per iniuute at the center of the3. Dose Calibrations and Measurements polystyrene sphere. The average reading of 11 TLDs, exposed at every 30°

along the x-axis of the spherical phantom, determined the dose rate.To determine the best dosimetry system for the measurements at the small To determine the "'true" dose rate at the focus of the unit, the transit dose

focal point of beams, several different detectors were investigated. These (the dose accumulated during the table's entry and exit from the lbcus) wasincluded an ion chamber, a silicon diode, LiF thermoluminescent dosimeter subtracted from the total accumulated dose at the focus. The shutter error

chips, and film. All of these detectors were calibrated in a phantom against was determined as for the _'jCo telctherapy machine, using the diffcreuce i_,an ion chamber whose calibration is traceable to the National Institute of exposures measured in an interval of time with due ON-OFF sequence axxdScience and Technology (NIST). several ON-OFF sequences to determine tile transit duse.

The dose output for the gamma knife was first measured using the 18-

ram collimator helmet. A spherical polystyrene phantom 16 cm in diameter 4. Absorbed Dose Profileswas constructed to simulate a human head. The phantom was fixed betweenthe trunnions along the lateral direction and was movable within the helmet. Because lbe ganrma knife unit contains 201 _'Co sources, with eac_t col

The ion chamber (coupled to an electrometer) used for calibration and mea- limated beam focusing at a central point, the dose profile of each individual

sarement was a 0.07-era _micro-chamber small enough for this purpose, beam is a building block for the total dose distribution of multiple beamsBefore measuring dose rates, the dosimetry system was calibrated. The with various plug patterns.

66 67

V

To measurea single beam dose profle, 200 of the 201 collimator open- Singlebeamprofilesat g cm in polystyreneings of the 18-mm helmet were plugged, leaving the central one open. Film spherical phantom

was cut to fit a special polystyrene cassette, which was placed at the center [ i i _ i I I I I i t I Iof a polystyrene sphere, 8 cm in diameter, to simulate a human head. Ap- 100

proximately 1 Gy was delivered to irradiate the film to obtain an optical 9011_ _ I .COLLIMATO RRE====LMET

density of approximately 2. Profiles were measured along the X- and Y-axes a- 4 rnmwith a 0.75-ram aperture, using a scanning densitometer. The density-dose tu 80 b -- 8 film

conversion relation was obtained from calibrated films of the same package _) 70_- _ I _ 1 c--14 mmO-- 18 mm

exposed to the"°Co teletherapy unit. The true single-beam profiles for each C_uj60}- / / / I

collimator size can be obtained by subtracting the background radiation, _- 501- at Ib /c [awhich was measured with all 201 collimators plugged, from the single-beam

profiles shown in Figure 22, and plotted and illustrated in Figure 23. The _ 40_ _ I / I

dimensions of the':50% isodose, or full-width-of-half-maximum (FWHM), rr 30_- // //and the penumbra size, defined by the distance between 20% and 80%, are

measured. Their FWHMs are 4.0 mm, 8.4 mm, 14.0 mm, and 18.0 mm for 2if _ _

4-ram, 8-mm, 14-mm, and 18-mm collimator helmets, respectively. The 10

penumbras are in the I-2 mm range, which is, comparably speaking, large h _ , _ , 2_0 t 2k4for small collimator helmets, but small for large collimator helmets. -0 4 8 12 16

RADIAL DISTANCE FROM BEAM AXIS (rant)

FIGURE 23. The single beam data with the background t_alls,wfissiu.subtracted. The sizes are defined by the 50% wiOths,and penumbrae by the80%-20% distances. (Wu et aL, 1990.)

Singlebeamprofileswithbackgroundat gem"- depthInsphericalphantom

I I I I I I I I I I I I

100

90 a-- 4mmCOLLIMATOR Figure 22 shows the dose profiles of the single beams for all collimatorb-- 8mm COLLIMATOR

80 C--14rnmCOLLIMATOR sizes. Shoulders appear on both sides of all beam profiles because of theILl a d d--18mmCOLLIMATOR radiation transmitted through the plugs and are particularly apparent for tl_eto 70 e-- BACKGROUNDO 4- and 8-mm hehnets. The shoulders are substantial, representing almosta 60 60% of the maximum iutensity of a single beam, because radiation is UanS-LU mitred through all 201 plugs, rather than just one plug.> 50

Most of the 201 collimators remain opcu during patic,t ucaui_c,t. There-

40 _ fore,wemeasureddoseprofilesaswellasisodosedistributionsfromfilmsLU

rr 30 irradiated in two perpendicular planes; that is, the X-Y and X-Z planes atthe center of a polystyrene 8-cm sphere in the gamma knife. The dose pro-

20 filesalongtheX-axisofallfourcollimators(helmetat thefocus)areshown

10 inFigure23.

00 i i i i i J2 i i i 210 t i4 Figure 23 shows isodensity scans of the X-axis dose profiles for the 4-4 8 1 16 2 mm, 8-mm, 14-mm, and 18-mm collimators. The corresponding Y-axis dose

RADIAL DISTANCE FROM BEAM AXIS (ram) profiles (not shown) are much sharper at the edges as a result of the collima-

FIGURE 22. Dose profiles of a single beam measured with all but one tor pattern that spreads out ± 80° in X direction and ± 48 ° in Y direction.collimator of the helmet closed. Due to transmission through the 200 The Z-axis dose profiles may be slightly skewed toward the top because allcollimator plugs, the single beam profiles exhibit high backgrounds. (Wu et of the sources are positioned at the upper hemisphere, tiowever, the snaullaL, 1990.) diameters of the beams make this insignificant.

68 69

F

The relative output factors for the four helmets were measured using 1 XVI. APPENDIX Vmm × 1 mm x I mm TLD chips and a diode coupled to an electrometer atthe focus for each helmet. Both the diode and the TLD chips were calibrated EXAMPLE GAMMA KNIFE QA PROGRAMat a depth of 8 cm in a polystyrene block phantom with the small beam of a6°Co teletherapy machine against ion-chamber measurements. The output The quality assurance (QA) program that we have implemented in ourvalues are very close to those obtained for a single beam and to those pro- facility (Univ. of Pittsburgh) includes the topics of physics, dosimetry andvided by the manufacturer, but there is a 3.5% variation for the 4-ram colli- safety. The actual program is divided between daily, monthly, semi-annualmator helmet, and annual checks. Each item is not only assigned a frequency as dictated

by regulating requirements as a good health physics p?actlce or commonsense, but also tolerances as applicable.

5. Mechanical Alignment Accuracy

PHYSICS:To illustrate the qualitative accuracy of gamma knife irradiation, a small

lead sphere, 4 mm in diameter, was placed at the center of a 20-cm diameter Timer Constancy Munthlyspherical phantom and exposed exactly at the focus. A strip of film was Timer Linearity Monthlytaped to the bottom of the phantom to catch the exit beams from each of the Timer Accuracy Monthlysources. The 8-mm collimator helmet was used. On-Off Error Monthly - 0.03 off.

An aluminum film cassette was made and placed into a film can. The Trunnion Centricity Monthly ± 0.5 raincassette has a pinhole indicating the focal point of a helmet. A cut-out film Radiation Output Monthly ± 2%was then loaded in the cassette, exposed with a 8-mm collimator helmet, Relative Helmet Factors Annual ± 3%and scanned with a microdensitometer with a 0.75-mm aperture. The posi- Anticipated Output vs. Measured Monthly ± 3%tion of the pinhole in relation to the focus was determined. Figure 14 showsthat the density profile is determined by the half width of the half of the DOSIMETRY:

maximum. The position of the mechanical focal point is indicated by the Computer Output vs. Measured Mo,,thly _- 3%pinhole, which is shown as a dip in the plot. Thus, the deviation of the Radiation/Mechanicalradiation focus from the mechanical focus along the X-axis can be deter- lsocenter Coincidence A.nual ± U.4 ...mined. This measurement was repeated along the Z-axis. The overall devia- Dose Profiles After source change or i. thetion from alignment of the unit was calculated from the square root of the acceptance testsum of the squares from the deviations of X- and Z-axes and found to be SAFETY:

approximately0.25mm. TimerTerminationofExposure DailyDoor Interlock Daily 0.5 cm trip point

EmergencyOff Buttons Daily6. Results Beam Status Lights Monthly

All three dosimetric tools--ion chamber, diode, and TLDs--were used Emergency Release Rod MonthlyAudio-Visual Communicationto measure the output at the focus of the 18-ram helmet. Each response in Dailythe gamma knife was related to the dose in water measured by the Farmer Systems

ionization chamber on the U_Counit according to the mo_;t recent American HehnetPermanentMicroswitchRadiati°nMouitor AnnualMonthlylUucti_)-al0.1mm triptCStpoiut

Association of Physicists in Medicine protocol. The deviations among the Hand Held Radiation Monitor Daily ± 10% Annualdosimetric tools were less than 0.5%. We detected no appreciable direr- Couch Movement Time Deviation Monthly < 0.5 min from intiattional dependence of the ion chamber, TLD, and diode measurements within couch movement calibrationthe geometry of the gamma knife.

7170

V

SAFETY (Continued):

Emergency Instructions Monthly semi-annual training Procedure for CT Scanning (all patients)Operating Instruction Availability Monthly

NRC Postings Monthly Taking CT scans for reconstruction in treatment planning (CT

Leak Tests 6 mos. <0.005 pCi localization optional).Emergency Power AnnualTest timers' battery backup

through power loss/return cycle Monthly t"l OPTIONAL--Start IV for contrast injection (mandat_ry f_r CTlocalization).

* Many of the checks are not required by regulation. C] Attach CT table adapter to table.

XVII. APPENDIX VI O Place patient on table and attach head ring to table adapter.r'l Attach CT Iocalizer cage to head ring.

EXAMPLE RADIOSURGERY PROCEDURES AND [3 Take scout view of patient's head.CHECKLISTS 1:3 Examining scout view, adjust gantry till as necessary to make gaa-

(University of Florida - Gainesville) try plane parallel to head ring plane.{:! Take scans of patient's head according to one of the l'ollowi.g:

Procedure for Patient's Room/Clinic • If aagio tocalizatlon is i.tended, take 5 mm thick sca.s 5 ..,,apart starting above he patient s head and ending at the li.g, h

General patient preparation and ring attachment, contrast is desired, begin injecting I or 2 slices above the top ofthe target. Radiologist input may he helpful.

17] Administer pre-operative medication. • If CT will be used for localization, proceed as above except inI:1 Attach head ring using most posterior and most anterior position, the vicinity of the iarget using 3 mm thick scans 3 mm apart for

Make sure the word ANTERIOR is above the patient's nose. increased resolution. Begin contrast injection before starting 3I"1 Ensure that top of CT Idealizer cage clears top of patient's head. x 3 scans.173 Ensure the anglo Iocalizer cage clears patient's head and nose. [:1 Remove CT Idealizer cage from ring.1:3 Attach emergency wrench to head ring. 1_ Unbolt patient from table adapter and remove patient.

Transport patient to angiography/CT. C] Remove adapter from table.. * , r

[:] Archive the co_Jplete C 1 exa ]n_at o. o 112 l.pd l'oJuse m tJcaL-ment planning.

Procedure for Patients Undergoing Angiography {7] Take patient to roo.t or outpatl¢.| holdi.g a_ca tu ¢,alt doL*"/btLeat-Obtaining anterior and lateral angiograms for localization, ment planning process.

O M ' ' ' -eke patient s head as comfortable as puss hie with cushmns/braces.I_ Radiologist perform selective transfemoral catheterization. Procedure for Treatment Plamtlng

I_ Attach ring support brace. Plan the patient's treatment using CAD (Computer-Aided Dosimetry)_I Attach anglo Iocalizer cage. tools. There are two basic types of plans: anglo localization and CT local-1_ Position patient in fields, ization. This procedure indicates the differences between the two.1:3 Take non-injected scout films to verify patient positioning. 1:3 Sign on to the Son system wilh user name and password.

O Ensure full size cut film. {7] Start the appropriate planning script with either the comlllaad sirs/Adjust patient as necessary to include target and all 8 fiducial points utilsdguangio or strs/utils/goctloc.on both films. Retake scouts if needed. O Answer the questions as the script promp{s tt_r tt_e patie.t's troupe

O Runinjectedangloseries, andhospitalnumber.O Select best target views for later localization. O For angiogramlocalization:

Transport patient to CT. The script will automatically start the anglo localizatio.

program. Verify that the digitizer control box is turned on. Tape72

patient films to the digitizer, side by side. For each of the Repeat the trace procedure for tiffs view.two films: As was described in anglo localization, select between gco-

a) OPTIONAL--Select contour entry and enter the patient's ex- metric center, center of mass, or a user input center to obtainterior or skull contour for frame of reference, the best isocenter location.

b) Select point entry and enter all 8 of the fiducial points. Save the data before exiting.c) The program will prompt if it discovers that the view is up- The entire CT localization process may be repeated, if desired.

side down based on the positions of the fiducial points. [] If more than I pass was made through the selected localizationd) Select target entry and trace the outline of the patient's program, the script will prompt for selection of one of the sets of

lesion. When finished, hit the target trace button again to data.compute the geometric center and center of mass for the view.

• Examine the BRW coordinates and skew distance in the r'l The script will automatically start the dosimetry program.[] Perform the treatment plan in accordance with detailed instruc-

checklisa window. Cycle between geometric center and center tions on the use of the gamma 2 program.of mass'to minimize the skew distance. 171 Remember to generate a hard copy of the dose di_tclb,_._,, a.dOPTIONAL--If the skew distance seems excessively large or save the data before exiting the program.

other considerations make the computed center unacceptable, O The script will prompt for a dose prcscriptiu, ulhd isud,_,se Ii_td.the user may enter a user center to lock in the isocenter Enter the prescribed dose and the percent line to which the doselocation. Save the data before exiting the angio program, value is given.

• The entire anglo procedure may be repeated if desired. _ When the script prompts, request a hard copy of the treatment in-171 The script will automatically start the tape reading program, formation.I_ Input the required data to select a patient and examination from

those available on the tape. Procedure at Radiation Therapy of Gainesville

The program will reconstruct all slices from the examination and Assemble apparatus onto accelerator, verify alignment, and treatplace them on the disk. patient.The script will automatlcally start the CT processing program.

171 To process the CT's: I"1 Make sure the film proccssul i_ tuf££ddvii.Adjust mean and window for comfortable viewing. [] Move the tool cart into the accelerator rooHl fur easy access tuTrash images until an image with separated rods is visible, tools and parts.

D Remove the table top uod place it to one side, out 0f the way.Select the position button and enter the position of the localiz-ing rods beginning with the thick rod and proceeding [] Remove the touch guard from the accelerator.[] Remove the inside corner floor boards.

clockwise. D Replacewithradiosurgerynotchedfloorboards.Save the processed image. D Place radiosurgery table top onto table, making sure that adapterPress the run button to continue processing the remaining im- slides down onto alignment cone.ages. i"1 Raisethetabletolevel15.If an image is present after the run, press trash until the pro- [] Rotate the table to 50°.

gram exits. [] Position A-frame over lltJur, makl.g sure that real feet slid,.: all the[] To perform CT localization: way into 'U' brackets in pit.

The script will automatically start the CT localization program. [] Insert leveling ratchet into needle hearing in A-flame _ith theAdjust mean and window for comfortable viewing, handle pointing towards tbe accelerator.

• Page through axial slices until target appears largest. [] Roll alignment apparatus over A-frame being careful riot to bump• Outline the target with TRACE function. When through, press table or A-frame.

TRACE again to compute geometric center and center of mass. I_ Carefully lower apparatus onto A-frame. Maintain alignment of• Position cursor over either of the two centers and pivot the holes in plate with holes in A-frame so that pins may be easily

imagetopara-sagittalview. inserted.

74 75

v

/"l Insert three alignment T-pins through apparatus base plate into the 3. Recheck coordinates on floor stand.A-frame. 4. Manually move gantry completely through the range of the

C] Remove wheels from apparatus and place to one side. arc.[] Install table float modification in control system. 5. Set machine for correct MU's and rotation direction. Note thatCl Check floor stand leveling. If necessary, adjust level with ratchet the gantry should always rotate away froal tile floor stand.

by reaching through access hole in base plate. 6. Administer radiation.D Set accelerator'collimator rotation to 0° and primary field size to i'1 After last arc, unbolt patient from floor stand.

5 x 5 cm. ["1 Remove table stop collar and lower table to a safe level.

C] Attach gimble bearing plate to accelerator collimator, i7 Remove head ring from patient and remove patient from table.Cl Remove collimator clamp from apparatus arm. Insert designated t"l Following the reverse of the assembly procedure, disassemble the

collimator through hole in arm into gimble bearing. Make sure that apparatus and store the components.collimator geats firmly on lower lip of hole in arm. Reinstall the Cl Remove the table float modification from the control system.

collimator clamp and tighten. Parts List for Stands[] While one person sets floor stand coordinates to target coordinates,

another person setup phantom pointer on phantom base to the same C] Appropriate medicadoii l'ul anxiety.coordinates, i7 Xylocaine.

C] Install phantom pointer on floor stand using adapter. [:1 Syringe.[] Place a piece of white paper behind phantom target ball. Turn on t'l Head Ring Assembly.

field light and rotate gantry about target, observing location of bali's O Wrench.shadow on paper. If shadow appears to move relative to field, re- 17 CT Localizer Cage.check floor stand settings and phantom setting. Repeat until suc- r'l Anglo Localizer Cage.cessful. O Angio Table Support Bracket.

1_ Attach film holder to apparatus arm. [] CT Table Adapter.[] Preparea strip of filmapproximately2" wide. [] Ruler.[] Insert film strip into film holder. At several different gantry angles, [] Computer Tape.

expose the fihn to 55 Mid, repositioning the strip for each expo-sure.

[] Develop film. Examine film and verify that the phantom ball iscentered in the radiation field in each exposure. Retain film strip

for patient records.O Remove film holder from apparatus arm.[] Remove phantom pointer and adapter from floor stand.f"l Place patient on table and clamp head ring to floor stand.[] After adjusting table height to maximize patient comfort, securely

clamp retaining collar to table ram, preventing table slippage.[] Recheck floor stand level, adjusting if necessary as above.CI Turn on lasers and observe the position of the lasers on the patient's

skin. Verify that the position is in accordance with the known posi-tion of the target. Turn off lasers.

[] Following the computer generated list of actions, treat the patientusing the following procedure for each arc:1. Set floor stand coordinates to new isocenter if required for

this arc.

2. Rotate floor stand and table to correct angle.

76 77

ISOEFFECTIVE DOSE CURVESGRAPH OF FIELD SIZE VS. COLLIMATOR SIZE

20_ .. ......... ,.................................. ,,,,,,;: ; ;;;;;_:;:; .................... F]¢]d(rrt_)[Ifl4_tl_:: ::::,, ; ::::;_.___

!5: : ,. ,. : ! ! ! ] !! ! !!I Illi i i.U,,_l_tttt_it ........ I[ ...... I I II bFfHtHII_-_H+HIJ_]It_|_,_+H 32.0

',,_ 3o.o

8t:__ _,__ 2_.o¢_ _ _,._Z, ;i;;;_-!!!!=lllhdiii]h,,.,'.P.-- 26.0

.................... "ri _ I "'_,_4: ::::::: : : 24.0

-': :!_ !!!!___ II_I_L___I 220_=_ ...... ._.__?._4_q_

_[_ _V'L_Ua_otor __================================================-"'........:_'-_::: :::::::::;:},!L:_.!_il[ 20.0

......_,,,,,,,',,-_,T111_q,,____

! J;i ..........'.......................311 I ""': .....III :::',',::',::[l::',:_,_P._.,,I_ _6ol I I II II[IIIINI I

;;llllllh.,,,lII[Ii+HII_IIIlIlI.,,,, ,,, ,, ]1f_'_, d,,,,,.,,,.llllll_,..,_rJ_, _4.o

/, 12.0

AVM dose determination. Isoeffective doses for proton beams of various 10.0 !

diameters from 7 mm to 50 mm. The bottom fine of the 4-sided figure s.orepresents the one percentile isoeflective dose for cerebral necrosis in the

normal brain. Note that for a small beam (7 ram), the one percentile dose is 6o5000 fads. For a larger 50 mm beam, the one percentile isoeffecSve dose is1100 rads. Isoeffective dose is different for each different beam diameter.Since the injured brain has a larger threshold for necrosis than normal brain, 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 Collim (on0we operate with a margin below the one percentile line to provide a margin ofsafety.

Note--Field size measured lit transa_ial pla_ th:ou£1h isoce.ter i_ /atrialdirection. Isedose curves generated by standard four u_c d_stHbUhOH.

7879

V

MAXIMUM ANGLE FOR VERTICAL OFFSET XVIII. APPENDIX VII

DYNAMIC STEREOTACTIC BRAIN IRRADIATIONPATIENT CHART (SAMPLE)

250

MtGifl Univtf_it yUepartmem of Radiation Oiicotogy

Division of physics

240 Pati_l #: Trvatmezlt _:Patient name: Trealmem ullit;Hospitah Total presc_i0eddose (cGy):Patient #i Dose Maximum (cGy):

*_ Diagnosis: prescribed isodose line (IL):230m

oNumber of Treatments

,_ Treatment number

_ _._0 Date of treatment l

._ Prescribed dose for ....

thistreatment (TO)210Physicians

Physicists I _200

Oo,m=o,°aoete,,oLi°aoo'ioa'o'lI ""m'l J0"°°"_iC°tlimat°ram,ter 05 0.8 1 I 25 1.5 i.75 2 2.25 2.5 2.75 3 3.5 4 I

B

D et (cm): "-50 -40 -30 -20 - f 0 0

RelativeooseFactQr 054 06g 074 O7g 082 085 067 088 08g 09 09t 0.92 0.94Axis! Coordinate (ram) RDF (A): ...........

Steteotactic flame: OBT Lekself

Maximum angle to which the gantry can be rotated based on the axialcoordinate setting of the floor stand. This constraint must be taken into Lo_]_z_beJ_bo.*: C_,ui.,,t,,_ x= ;_ = ;¢ _ ___.

account when defining arcs in the patient's treatment plan. T,Jmo_votu,.e: _ c,,,'Talget v01unle: , Gill3

_ooo0bei00tt I [ I I I I

80 81

rDYNAMIC STEREOTACTIC BRAIN IRRADIATIONPATIENT CHART (SAMPLE) CONTINUED REFERENCES

I. AAPM Policy Statement, 1985. The roles, responsibilities, and status of the clinicalCalculate total [6quJre_ MUfrom equation: medical physicist, 1985 Presidential Ad H0c Committee. E, C. McCullough. B. E.

Bjamgaard and J. A, Oey¢.

100xTO = [ ] 2. AAPM Report 13. Physical aspects of quality assurance in radialion Iherapy. (AmericanMU= D_.=(10)xRDF(D)xlLxCf = Association of Physicists in Medicine, New York, 1984).

3. AAPM Report 21: A protocol for absorbed dose from high-energy beams, Report ufwhereO_mt_(10) = t.05 cGylMU,TD is theprelw.dbedtumordose. IL is thepreSCribedis0doseline. AAPM Task Group 21. Mud. Phys, 10:741 (1983).RDF(A) is Ihe relativedose fa_or forthe collimator and _ is the correctionfactor for the stereotaetic 4. AAPM Report 40. Comprehensive QA for Radiation Oitcology: Report of AA PMframe (O,SS). Radiation Therapy Committee Task Group 40. 1993 (sublnhtcd for publication).

Gantryangular interval: A = 180 -0, = 5. AAPM Report 45. AAPM code of practice for radioiharapy accelerators: Report of................................... AAPM Radiation Therapy Task Group No. 45, 1993 (submltled for publicafio_O.

MaximumMU per ganhv angularinterval: B = (180 - 0,)x 4.99 = ....................... 6. ACMP Report 2. Radiation control and quality assurance in radiation oncology; asuggested protocol. (American College of Medical Physics, Madison. WI, 1986),

': 7. E. Alexander I11. J. S. Loeffler, and L. D. Lunsford. Stereotacti¢ radi.surgery. (McGraw

Total MU Hill, New York. NY, 1993).Esgmatedaumberofangularlntervalsrequirea: C = -- -- = •.................. 8. G. Arcovito, A. Piermattei, G.D'Abramo andP. A. Bassl "DoseBeeasure._eltsand

D calculations of small radiation fields for 9-MV x rays." Mud. Phys. 12, 779 (1985).' g "

AdjustedCupwardstothenearestevennumbel: D = ...................... 9. J.L. Barcta-ga or o, P. Rodan, G. Henaadez, andG. L. Lopez. Rado. ugcaltreatl_entof epilepsy.' Appl. Neurophys'ol. 48. 400 (1985).

10. A. S. Bcddar, "Dosimetry of stereotactic radiation fields using a miuiature plusli¢

CalculatedMU per angularInterval:E = Total MU t scintillator detector." Mud. Pi_ys. 19, 790 (I 992) (abstract).D 1I. O. O, Belli arid V. F Derechlasky, "t|yperscte¢t;vc eacephali¢ _l:Jd_allon wmlhti.c_l

accelerator," Acta. Neurocldrurgica., S,JppL 33, 385 (19841.E12. O. O. Betli, C. Munali, and t¢..Rosier, "Sler¢olaCtlC radiosurgeJy w;th the ldt¢.l

Calculated ana set MUper degree: _ -- (must be less than 4"801= _ acceleralor:trealmentofarleriovenous alfor "a o s, Neuros,,rgery. 2q, 31111_),13. B.E. Bjarngard. J. S, Tsai. and R. K. Rice, "Doses oa central axis of imrrow 6-MV x-ray

FRACTIONALTREATMENT MU IOOS 11 FRACTIONALTREATMENTMU tOOS 11 beams," Med. Phys. 17,794 (1990).

1 "1. Gaatr-/(CW) 0=to 180" . • 6 11. Gant_ (CCW) 01 to 180" _: 14. F.J. Bova and W. A. Friedman, "Slereotactic aaglography: an inadequate dalahase lotradiosurgery?" Int. J, Radial. Oncol. Biol. Phys. Z0, 891 (1991).

2. Gaatry(CW) 100*t00r 12. Oantp/(CCW) 180" to0j15. J. D. Bradshaw, "The stereotactic radlosurgery unit ill Sheffield." Clin, Radiol. 37. 277

2 3. Gant_ (CCW) 01 to 180" . ' 7 13. Ganlly(CW) 01 to 180° (1986).4. Gantry(CCW) 180"1o0i 14. GantP/(CW) 180"1o01 _ Ifi. D.L Brenner, M.K. Martel, andE. LHall,"Fracdonatedregimens forstereotactic

radiotherapy of recurrent tumors in Ibe brain." lnl, J. Radial. OncoJ. Biol. Phys. 21, 8193 5. Gant_(CW) 0,10180* . • 8 15. Gantry(CCW) 0l 10180° (1991).

6. Gant_ (CW) 180" to Of 16. Gantp/(CCW) 180° to Oi 13. M. Carol. Slereotactic Surgery and Radiusurgcry, (Mud. Phys. Pub. Co, Madlsoth, WI,

4 7. Gnatty (CCW) Or to 180° . • 0 17. Gantry (CW) 0=to 180° 1993). pp. 249-326.

8. Gant_(CCW) 180° to0, 18. Gantry(CW) 1800to0r lB. G.T,Y. Chea, R.P, Siugh, J.R. Castlo, elul,"TicatJILcmpla.J*i.£1oihc_vy_,JH

5 g. GaateT(CtAO O_ to 180" . ' 10 19. Gaatry(CCW_ Ot IotB0 ° therapy,'llnt. J. Radiat. OacuLBioI. Ph_s, 5, 1809(1979).19. G. Chlerego, C. March¢tti, R. C. Avanzo, et .t, "DOSitleeLLIC£oLts;dclallol_s _JJ__.ul_ipb.:10. Gantry(CW) 180° 10 0e 20. Gantry (CCW) 180" to0, arc slereotaxic radiotherapy," Radiotherapy a_d Ontology. 12, i41 /tggg)

I I 20. F. Colombo. A. Benedeui. L. Casentini. et .1,, "Linear accelerator _udlosurgely ofTOTALMU GIVEN l _ arteriovenous malformations," AppI. Neurophysi0L SO. 257 (1987).2 I. F. Colombo, A. Benedelti, F. Pozza. et al.. "Exlernal ster¢otacti¢ irradiatiou by linear

accelerator," Neurosurgery. 16. 154 (1985_.22. F. Colombo. A. Benedetti. P. Pozza. et ul.. "Stereotactic radiosurgery ulilizing a linear

acceleralor." Appl. Neurophysiol. 48, 133 41985),23. R. Cox, W. P. Haneman, and S, W. Brain, "Dose distributions produced by a robot-

mounted linac (abstract)," Mud. Phys. 20, 889 0993).• .... . W,24, D.J. Dawson. N. J,Schroeder, and J. D. Hoya, Penu bral ileasurcmems ater for

high-energy x rays." Mud. Phys. 13. I01 11986).25, C. E. DeMagri. V. Snfith. M. C. Sebell, el ul., "hderlock system for ll.ear accele_atur

radiosurgery." To be submltted to hal, J. Badlat. ghoul, Biol. Phys. 1995.26 R, Drzymala, "Quality assurance for It.at-based stereotactic radiusurge_y i,, ttualby

assurance in radiotherapy p ys cs, Proc. A net _a College of Mcd _ul P y_ _.s Sy ,G. Slarkshall and J. tloclon, eds, (Medical Physics Pub.. Madlsvlh WI. 1991).

82

t'8

"(uo!m3!lqndlajpoll!uiqns)'ss;u_oJdu!glod;_H"8£61-1NId:_dbt'(t'66|'V:)"(L'_61)£01'£I"s'(ttd"lO!f_"to3uo'aJouIJo^]l"q_l[e.uo.eN_JotujaA"1;D_'u_.v,¢"l),"tu_$oJd,(l:_J_S_tu_s.(spue,(_JaU_

f,.q"IP-•.uo!ss!4"s;_!^_ple_[poulJe_l_nuJO=,snoqlflu!nln_oJu!s!S.(leUn_ls[8.'souor"o"_"0giopoql:_lln:lit'_d_t-_lllIIO!l_!p_Jjouo[Ir,Z!ul!ldo.'lsJ_qlo3A'Vpueut:tu,('l".L'f"_L"(6861)11_'[;"lo:mo"uIJaqU_d_CH";_!Jn3opu_]+.+slU_ldUl!u!_qu!ul;Hs,('_;alll_Jj

'(_fi61)[fT_'_f'¢(J._ffJnsozn_N,,'_poql_I_tI_JtJOuo_;tJl?dtuo3_3u_loJ;_lI_UJalX_ueJO;_sn_q_..'Inla's!s!_["_]'f'uosJ;_qdo|s[Iq_)"V"¢I's_uofTI'6_'piins.qld!:_u!Jd:/;J_Jnso[pt_J_[|3P,IO._J_IS.,"]r_I_'J-_SZOI"'_)'_'._!u_[!qZ"d'uol'¢n']"D'_L"(P;_q_lqndufl)[66["sa3_e.,i._s._o[o311offol_!peJ"suo_ezlue8Jo

"(R_61)[L£'l,I"s/;qdlO]H'losuo"le]P_}l'f"lUl,,']oleJ_t333__u_3qIi_qjouoll_lipal:)3e;_qluouolsslululO:_ulol""spJepuuls_3uulnss'e,(l[l_=nbOHV_)f"8_'m_U!lnql!_,(JOffJnso!pnJ3!13elO_*J_lSJOJIIl_lS_V+.']_31I?[_"N'U°lStl!/_"_["_['z|rt']'A_'_/."(Poqsilqndun)L_61's_,_l,_l_s,(_o[o3uouoll_lpez"sumc.zlu_$10 "(6861)""

I_1'bi_"_'J_g'Jnso_n.aN,.+_Jlu)lmuttmD_rloso_t,,10i_S;_l_lSpoliUfllSJUoql_'u!sn;ue3qit_yJouo!etp;u:*_aquouolssltuluo_ulof"spJ_pu_soou_n_sl_.(ii_nbOHV_)r";t, '""(£661u!nJq_tI_o,(h_JnsolpnJ_!l:_nlo:_J._;S."1nI_'JmlpurlT)'J._$u!_3!ld['PJOJSUn'l'(3"3"_L"'ld'uol_l_ot]'ss;/Id_)_1)"_kdn.lalllolpn.I.Iofn_p[._alull'opfi_yuoqpul_tthuff"'_l"S'9t. "(L_fiI)_'05"{o!s/Cqdom'_N"lddv..',(z:*_Jnso!p_.lJoJ....

t_fi6)f61Lbf,(J_JnsnJnaN,.'£Ja_nso!pnH_tl._oazal_noa3JOd_S_L£_olo_uO_ojsplo=Juo!|e!p_JII_tUSJO,(Jl_tu!soo.'so.(_d"A'fpue'ua_ntluvA"IN"f":lapnoH"A"d"_t'p.n,(_otoTpn8_!ln.'ufn_¢_t.IJoj,(t:,u_oSint:,u._ttV:_q.Lplm,Q_3.m_:o!pn__!l_nlo_.t_lS"(S_61)69b'_I"s'(qd"p_IN,.'sosaIieueJoe_uli1etus

i*o_:_Jc,d_ls_i._.o_,qJnSi,_:_1_oolnoNjo.olm!_ossVu_:_!smuVaqJ./;qp_J_d_JdloJ_nb!uq3_l,(d_J_qlO[p_l3!13t_1o_1_|S.,_'/nla'U_A"_q"["_'SO_(_?d'A"["_pnoH"A"d"t,t.

'"(L_61)_t,i_'05"lo!s,(qdoJn_N"lddv,,'suo!lmuJoJl_lUsnou_ao!J_Lm[t_!ue.J_nJlu!la,_qpl!ll;1ll!_:lloq_tlll¢_j[_.tlr_nOI/.'3AO!I_LI'R[_!lll3J3_Jlll![OIll_ll[t,'?_JI_L_I_OJ_J_Jn1¢o![_t?]JOUOI_tp_JJIO[31Ll_d_-,(At_;_q 313_O_1;)_..'U_UI,(']"fpu_'Ul_31Jq_"f+lq3nqOSOH"._"_t'

"(lg61)91£'_OI.'muols_lqoll$JO,(de_qloipe._:_qlulsuolldtunssv.'1inJd'Vpue_J;)qtl_OH"H"_"|1_Plln3S"J!q_)rr137,'tl!_lq.rollJOA_o_Jn_;o!pr_Jput_pOql;*Ul3!1_,1o_3_1:¢Oq.L.,'ll_S_Oq".L7'_9'(_61)

'(£_61)_;_[['It""s'(qd"o+t]"lo3u"e+p_l'f•u!'_ql3e./oc_aa:_:_Jeauq_euot_Jzlpla (OJIpeff L6L'gt,"_(JIn!q3gscl'ffJnsOmON"loJnoN"f,'_ffJnso!pnJ3!131_|ooJ;)1_. 'ii;_s_lol'.L"1"L9"(L861)09'6_ul^otu8u=sn.QaSmsummp_I_Jq=oD,,"lna'ram$"A'laS_lqoS"t_'uuemUreH'H"D"0t'

"s_H'roman,.'spu_Ji_nlnjpilesntnlSluos;,Jd".(_Jnso!pnJ3!13_)o'_J_lS.,'liPS,:r1"O"O"99"(£661)18_''$1_"s.(qd'lO!g"lo3uo'(6_6()690['L!"s£ffd"l_!Pe8"f"lul+"J°l_'=al_33t*Jeau[I_tuo_jsuo!le!ptuJ!tUe_lluaSaa^uo33!13_looJ;_l'_

"lo!FI'o3110"ln*pn_l+f'luI.'ttl_ls_s._c,imil!llO3oun^-!l[mu_!ulnu_pnjouo!t_nln^Opu_JO_31]Jn33_ptl_UO!$]3;_Jd_'*'[19Ill+OSPd_S'X['_1+s_cIJ!_[-J;_n_g'_]'uut_luLlcH"H"_)"6[:"(0661)Lg'/.["*($OLO3UOpug.(dP.J;_qlo!pe_1

I,_!I_lli_ell_ld+ll!:/_dnhal|l.( 166"_nl )U°]I'_I_"Lt_?; I'I_"l's_qdla'J=ll_OlN.io_fl. °ouo'H"f.l_.!p _H'tlne_lS'f "_.lul'f ,,'FJ_Jnso!pnJ'll!^n_'I "CI"(]"g9..,'JOl_JOlO3Z_l_ al_u_Iqllt_slOUtlnlutmqJouolelpuJJiol3_1o_.1_spo_UOl3e_lj_7!+,_!ldonl_rl]¢ltlll'_pl_l3urnKCI.."'1nI_'n_ql_H'd'_*sqq!_)"V"d'II!^P._.'I"CI"(I"_'9JOJpoqlomo^!_^u!-uou7."'1nla'qo_Jo'l"0"d'llO_iS'_3!JU;_H"_1"z!JuH"|",_"8£

'(t'Lfil_i_l_'£I'l°lg"s'(qd'z:,qL"e:_ti_Ol°!P_Hn3V,,'lln_s"(6861)Lb£1'.'I"s_qd'[o!l]"lO3UO"l_!pe_"f"lUl,.'SUO!I_I_dO:_.L_)q|!_,(mOl_U_t_v_llll._lllrf_ncalir1:4_lnl:_ni1s[[i?lll_jOiiO!ln!p_J.tl."'Kqm_"FIpli_'u_pu!"]"_'ltoss/13,']"_]"£931qd_8odoL"Ulg*L¢OUll_;od uIpos'eqSl'g,(l_u__;OlllJOjl[ntu_wos_lqOll8i_uou:ae]dml

,,'_:c_Inl.nJqjoollrrpnJJ3113nto_:_lS,'t:_,qt:_l"_¢"S'IIn_l"g"d'1osJn'l"Y"O'i_9"(i_861)ggO_'8"s£qd"lO!g"l°:_uo"ln!Pa_"f"lUl,,'_p!u_d"(£661)"s_(qd"Io!R"lo3uo"ln!P_H'r"lul,,'8u!uu_tdlu_Ull_OJI,(JoSJnso!p_.lpogl_q3_^_otIqllasuoulleO.i8uluueld.,"l_la".(Ju:_o"H'slu_qv'IN"u!:=!oD"IN"9£

plm.(dnJ_tllo!p_J:_!l_mo_Jms_ojno!snJ_nU,l."1.#a's_uJn9'c/"_J_Hun^'_',(oo_"H"19"(0661)181'8I"Su[Joou!SuEI'(I66t3£89'|Z"s,(qdlo!9"lO:_uo"l_¢!pe_l"f"Ul,,'suo!s;'lI_lUeZ_zulJole31potuotg.,'£1oSJnso.lnou.31_eo=oS,,"seun3elN'f"_1pue_e_Olleo1"H"!;£

_'l_ffmso!p_.j313t_o_;__;.mJSu!uunld|u:_ull_=:_LL,. "lnla'lzp_N"V+1']zP_N'q"(ooN"H"09"(i_661)£1t''(£861)St'i;'1£"_Jnso.m=N"U!l:),/u!_qoqlJouo!lmuJoJIcUlsnouo^o]Ja_l_'£Z:"s,(qd"1o!0"lo3uo"I_[p_H"i"'lUl..'UO!l_!p_xQu!eaqoloq_,lue^nlpejooou_uodtu!oql

io.;.((l_j_qluIP,_IttoloJd'Ve::x'f_ffnJ_,,"'1"I_'suo,(1"_;'s!^r_(1"_q"N'ffJaqllol_'51'N"_I'6_:_os_ls_otuumaq._oJ_(s_8.m_oip_._31_,_o_aS,,"Inla"/_'[PV"f"ue[de)_"(_"['J_llnd'0"H"el."(986DL['Lt'"s_H"U!lO"uuv.'suo!leuuoJlmusnou_^o!_o_Je'(686t)t.£_2'Z£"lOm=N

"SJnS'UlOlS,(s/;JOSmsopuJ_pJO_JO,(s_;_^uRaq.L'e^o_"f"d,put_'u_tup_lJd"V"A_'££

"9R61'lm!dsoHmloq_oz$'(0661)Ef'l'61"s'(qd'_xl_'r!lr_lt_+_UO!*';._p!_rt_:_3!ffOlO_Ul_p!d;_-_J_ffmsoipnJ31:_o_oS..'umJslql_I'-["Lg"o11]"1o3uo"mp_["f"uI.,'elnmJoj31slSoIpattJSou_qq_.(J_$Jnsop_Jo_J_[_33a

•(13nJlsqn)(i_661)n_!J=_lVquoNJo,(i;_!ooSIt_3!ffOlO!p_H_t_au[I_oJsuo!l_3!ldtuooJOUO!lmU]lS'_. ,'uosJ_r']'V"(1pue'11_q3s"_)'IN'Ja_u[_13!ld"D"1"'_£_1Io_rtlth"*_lltlnnmlv,,*llIOllinqduO!LIoIslp;_ntu!poJ_JId_:Sgl;*s,(s_u!_._ml"(066l)

_i+:IOl"o!t_[n¢ll!S;t_tv"ttlJO.IJ."_l pllP,"ff!s_p13=_qo)'¢;_.L.,'ltout_1'dpueJ=ISSON"1'P_!'9_CSL'61"sgqd"1o!1]"l°3uo+lt_!pe_+f"luI.'l!Ufl_mm_DIlOS_:_loql8u!snSu!_13olqtueoq"(gL61)oai_OlOSqI_8uidnqsomnlo^uOUllt_;UL'.ln;_'pu_leN"CI"'I'zl.¢_l'V'Ja_O._3.ld_)"f'[£

L61_'Z>sgttd"pop_,'s!ou!lllJo/;l!S+o^!uR:_1InmJ+J;=lls_n_)-uoJlelo_].'lslaN"h_'(_"_;"i_661Joqluo^oN"(L_6[)sgR'99"_snso_noN"r..'s'¢us_ldorytoil_Ie:uP.J3ezuip_e_zunm'01t,#o_Jno3j;=qg_ljoJ:/doSJnso!pe3[13U|O_J_IS'.(8oio3tlOpu_B,(8OlO!p_B_3!lnode+aqI

sa!sdo!q3]|3_1ooJ_15p_seq-oSetUh,"lr_la'uods!_I"g'O'uoddno-smuneo':_',(liON'f"d"1,_;Joj.(a,:,oSu_3t_tuy--Su=]aatuoUiuolosicnuu_qlp£"aoUJ=_l'fpue_;_SuR3!I_"O"f"0£"(8861)I_9'/.6"lo_u_g"I"lou!qH"1olo'uu'¢',,'s_mom_u_!lsno3_"(_861)H'i_$'H)I'ddn$"soEI'lm,pn_l,,'_p_oslplelnost=^leuel3J;_uJOJ/d;_.msope_

JojItlOmll_:_Jio^]l_UJOlI_u_:oj!u__tutUeD,,'JOll!lN'_pu_'p.=ojsun']"O"l'J:_Jotut=N"(]"£_;_1tl_l_Sml];_13[gted'P°SJetp'(ae_H-'la_lu_ld"V"Npu_'umu,("I".L'f'luml!lqed"1"f'6"_"(3_Jsq_)(£661)'91_6'0_"s,(qd"pow.',(J_SJnsotpt_Jullu:_m_nsae_tu:>sop'(t'861)6L1_'/._'Io!PcEI'f"l_].,'suo!lmu.=oJleUJsnou=^ouotze

onlosq_JOJ_ltu_q3uol0z,uollie_nmultuV."lnla'n_'V'Suoqz'V'puole>l"V+_d;,apjolu_ue:ullojpoqom:u=pJoslplelnoseai¢!ugJ3mlu".mJgJaSJnso!pv..z"(0861)0£_'.6's_(qd_e_KI88eJguol-X^_I_t_eo_u_lS,,'lq3nqosoH"3.pue'uem£"l"J."f'lue_[pqed'l"f"8_

'p._[_.'stl_:_q,(I]Jo'¢,(ffJ;_u=JOLl_'!qptle09IOqo_JOJsdo_uo:_o!elsmnm.xmu-J*e_s"(_661)_£'9|",(qdu_omo,L"lssV"dmo3"d".,+_u!uueldplmotn_ulnml_nul-onss!JOuols!^oH"lna'ool'r'pu_q:_,q:_s"_'uqe>I"IR'd"H;O!l_elO_=lS,ioj,(qde_8o!SueHP_joosn,,"lr_la'uumuop_D+O'pelI:_S"H"1':_l:_!lq_I"H"Li_

76. J.T. Lyman, M. H. Phillips, K. A. Frankel, el al., "Sleteotacric frame for neuroradiology• , gand charged porhc e Bragg peak radl_urgery of n racran al d .orders, Int. J. Radial 100. E. B. podgor_k, A. Olivier, M. Via, "Physical aspects of dyaamic stereotuctlc

OncoL Biol• Phys. 16, 1615 (1989). radiosurge_," Appl. Neurophysiol. SO,263 0987).77. J. T. Lyman and C. Y. Chong, "ISAH: a versatile treatment positioner for external 101. E. B. Podgorsak, A. Olivier, M. Pla, el at., "Dynamic slercolacric radiosu:gcry," ha J

radiation therapy," Cancer. 34, 12 0974). Radiat. OncoL Biol. Phys. 14, 115 (1988).78. R.J. Maciunas, R. L. Galloway, J. W. Latimer, "The application accuracy of stereotacfic 102. E. B. Podgorsak, G. B. Pike, A. Olivicr, et ,I., "Radiosurgery with high energy photon

frames," Neurosurgery. 35, 682 (1994). beams: a comparison among techniques," Int. J. Radiat. Oacol. Biol. Phys. 16, 85779. T. R. Mackle, P. J. Reckwerdh S. Swerdloff, et al., "Tomotherapy: a proposal for (1989).

optimized dose deliver/of radiotherapy," Mud. Phys. 20, 875 (1993). 103. E. B. Podgorsak, G. B. Pike, M. Via, et u/., "Radiosurgery with photon beams: physical80. M. R. McKenzic, L. Souhami, E. B. Podgorsak, et al., "Photon radiosurgery: a clinical t,_pects and adequacy of linear accelerators," Radiotherapy and Oncology. 17,349

review," Canadian J. Ncurol. Sci. 19, 212 (1992). (1990).81. MEDCO (private communication), 104. 1. Rabinowitz. L Broomberg, M. Gohein, el al., "Accuracy of radiation field alignment

• ,t82. H. Meertens, Digl a processing ofh gh-energy photon beam magcs, Mud. Phys 12 in clinical practice," Int. J. Radial. Oncol. Biol. Phys. 2, 67 (1985).

I I (1985). 105. R K Rice, J. L. Hansen, G. K. Svensson, el ,I. "Mca.suremcnts of dose distribu0oas in

83. C. M. Mcger-Wells and T. R. Mackie, "Dosimetry of slereotactic radiosurgcP/beams small beams of 6-MV x rays," Phys. Mcd. Biol. 32, 1087 (1987).• _t q[

using a plastic scm!tllatmn detector, Mcd. Phys. 20, 890 (199.). 10ft. W. M. Saundcrs, K. R. Winston, R. L. Siddon, el _l., "Radiosurgery for arleriovenous84. M. Mchta. J. Masc_pin[o. K. Bastin. el al., "Glioblastoma treated with external beam malformations of the brain using a standard linear acceleralor: rallt.mle and lechnique,"

radiotherapy and slereotactic radiosurgery boost," Int. J. Radiat. Oncol. Biol. Phys. 27, Int. J. Radlat. OncoL Biol. Phys, 15, 441 (1998).152 (suppl.) 0993). 107. C. B. Saw, K. Ayyangar, N. Sumharalhlgam, "Cooldhlalc ira._tu..aliu._ ..,d

85. J. Milan and R. E. Bentley. "The storage and manipularioa of radiation dose dala in a calculation ol the angular a._l deplh parameters for a sleLeotactic system," Mud rl,_small digital computer," hr..I. RadioL 47, 115 (1974). 14. 1042 (1997).

86. L.A. Nedzi. H Kooy, E. A exander , eal., "Dose volume consideration in field 108. L. R. Schad. H. Ehricke, B, Wowra, el .1., "Cul_ccfion uf sp.nlal O;_Lo_li,s. i. m.,g.c,_c

shaping for stereotactic radiosurgery using a linear accelerator," Radlosurgcry updalc, resonance angiography for [adiosurgieal tfcallnea[ pianulug of cerebral anetloyclLu_lsPine Manor College, Chestnut Hill, MA, June. 1990. malformations," Magaelic Resonance imaging. 10, 9 (1992).

$7. L.A. Nedzi. H. Kooy, E. Alexander Ill, el al., "Variables associated with the 109. M. C. Schell and H. Kooy, "Stercolacrice radiosurgery quality improvement:development of comphcahons from radiosurgery of intracranlal tumors" Int. J. Radiat. interdepartmental collaboration." Int. J. Radial OncoL Biol. Phys. 28, 551 (I 994),OncoL Biol. Phys. 21.591 (1991). 110. M. C. Scbell, L H. Evans, M. g. Marlel, et aL, "A methodology for the analysis of

88. L.A. Nedzi, H. Kooy. E. Alexander IlL et al., "Dynamic field shaping for stereotacfic stereotacfic radiosurgery beam dala," Submiued to Mud. Phys.. 1994.

radiosurgery: a modeling study," In1..I. Radlal. Oncol. Biol. Phys. 25, 859 (1993). 11 I, M. C. Sche[I. V. Smith, D. A. Larson, et al.. "Evaluation of radiosurgery techniques wilh89. P.F.J. New, R. G. Ojemann, K. R. Davis, el at., "MR and CT of occult vascular cumulative dose volume histograms in linac-based stereotactic external beam

" -malformations of the brain," Am. J. Radiology. 147. 985 (1986). irradiation." Int. J. Radial. OncoL Biol. Phys. 20, i325 O99l ).90. A. N_emierko and M, Goitein, "The influence of the size of the grid used for dose 112. J. G. Schwade, P. V. Houdek, H. J. Laady, el o1., "Small-field sierra, tactic cxtet ,a[ bc:_m

calculation on the accuracy of dose estimation," Mcd. Phys. 16, 239 (1989). radiation therapy of iutracranlal lesions: lracliUaaled IrcalmeiLI with a I_xcd-halo91 A. Olivicr, A. de Lotbinlere, T. Peters, el al., "Combined use of digital subtraction immohilization device," Radiology. 176, 563 (I 990)

angiography and MRI for radiosurgery and sterec_ncephalography," Appl. I 13. C, F. Serago, P. V. Houdek, G. II. |tarhna.n, et .L, '"fissu¢ ._h_.i,..m rafiu_ _a,Lo.,.,c_Neurophysiol. 50, 92 (1987). paramctcrs_ uf sllmB circular 4. b, 10. 15 a,ill 2q MV x lay bea.L_ Iut ludb_.,.rg¢ly,"

92. L. E. Olsson. J. Arndi, A. Fransson, et al.. "Three-dimensional dose mapping from Phys, Mcd. Biol. 37, 1943 (It_92)• • in

gamma knife reatment us,ng a doslme er gel and MR- ag g, Radiotherapy and i 14. C. F, Serago, A. A. Lewla, P. V. |{uudek, el t_l, "'ll*_{llOVCd h.i_ du:_¢d_.tL,b.a$$vl*t.I,JlOncology. 24, 82 (1992). radiosurgery with irregularly slmped Ii¢[ds," I.l J. Radial. Oncol Biol. Phys. 19, 134

93. S. Otto-O¢lschlager, W. Schlegel. W. Lorenz, "Different collimators in convergent beam (1990) (abstract).irradiation of irregularly shaped inlracranlal largel voiunms," Radiotherapy and I 15. C. F. Scrago, A. A. Lewin, P. V. Houdck, et ul., "Stercotactic radiosurgcry: dose volume

Ontology. 30. 175 (1994). analysis of linear accelerator lechniques," Mud. Phys. 19. 181 (1992).

94. T. M. Peters, J. Clark. B. Pike, et al., "Stereolactic surgical planning with magnetic l 116. C. F. Serago. A. A, Lewin, P. V. Houdck, el .I., "Stcreotactic target point vcrifica_iou ofresonance imaging, digital subtraction angiography and computed tomography." Appl. _ an x-ray and CT Idealizer." lnl. J. Radial. Oncoh Biol. Phys. 20, 517 (1991).Neurophysiol. 50. 33 (1987). 117. E. Shaw, R. Kline. M. Gillin. et at., "Radialion therapy oncology group: radiosurgery' I

95. M.H. Phillips, K. A. Frankel, J. T. Lyman, et al., "Comparison ofdiffetenl radiation qua _ty assura ce gu de ncs, n.J. gad_a. Ch_col. B o. Phys. 27, 1231 (1993)types and irradiatton geometries in slereolac0c radiosurgery.' Int. J. Radial. Oncol. Biol. I 18. R. L. Siddon and N. H. Barth, "Stereoiaxlc localization of iutracru_ia[ targets," ha[ JPhys. 18. 211 (1990). Radial, Oncol. Biol. Phys. 13, 1241 (1997).

96. M.H. PhiOips, K.A. FrankeI. L T. Lyinan, etal.,"Heavycharged-paaiclestereotactic 119. K.E. SixclaadR. Podgorsak."Builduprcgiouofhigh-e.cigy x i;_yhcu.,_ ;,,radiosurgery: cerebral anglography and CT in the treatment of intracranial vascular radiosurgcry," Mud. Phys. 20, 761 (1993)malformalions," Int. J. Radiat. Oncol. Biol. Phys. 17. 419 (1989). 120. K. E. Sixcl, "Physical parameters of narrow photo, beams in _adi_.._g¢_,," iVl S.-

97. B. Pike, T. M. Peters, E. B. Podgorsak. el al., "Ster¢otaclic external bean) calculations for thesis, McGill University, Molureal, Canada. 1990.

radiosurgical treatment of brain lesions." Appl. Neurophysiol. 50, 269 (1987). 121. V. Smdh, M" C, Schelt, and D, A. Larsuu, "'The role of letliLt_y eoil,.alio. 1,,i h.ac9g. B. Pike, E. B. Podgorsak, T. M. Peters, el al., "Dose distributions in dynamic stereotactic based radiosurgery," Alnerican Association of Vhysiclsts in McdJci.¢ An_ual IVieut[.g.

radiosurgery." Mud. Phys. 14, 7g0 (1987). 1989.99. E. B. Podgorsak, ' Physics for radmsurgery w_ h linear accelerators, ' Neurosurgery 122. A. Sofat, G. Kralimenos, and D. G. Thomas, "Early expe*icnce with the Gill-ThoJnas

Clinics of North America. 3.9 (1992), ediled by L.D. Lunsford, "Ster¢otacllc : Locator for computed tomography-directed slereot actic biopsy of intracrauial lesions."Neurosurgery 31,972 (1992).

Radiosurgery." _ 123. L. Souhami, A, Olivicr, E. B, Podgorsak, et al., "Radiosurgery of cerebral arleriovcnous

86 87

V

malformations with thedynamic stereolaciic irradialion." Int. J. Radial• OncoL Biol.Phys.19,775 (1990).

124. L, Steiner, Radiasurgery in cerebral arterlovenous malformation._. Textbook of AAPM REPORT SERIES ($10.00 Each)cerebrovascular surgery, edited by Flare and Pein, (Springer Verlag, New York, 1986). No. 4 "'Basic Quality Control in Diagnostic Radiology," AAPM Task

125. V. Sturm, B. Koher, K. H. Hover, et al., "SlereolaeBc percutaneous single dose Force on Quality Assurance Protocol (1977)in'adiation of brain metastases with a linear aceeleralor," Int. J. Radiat. Oncoh Biol.

Phys. 13, 279 0987). No. 6 "Scintillation Camera Acceptance Testing & Perlormauce

126. T. S. Sumanaweera, J. R. Adler, S. Napel, el al., "Characterization of apatial distortion Evaluation," AAPM Nuclear Medicine Committee (1980)in magne Jc _sonance imaging and n s mplnca _ons for s ereo acc surgery,Neurosurgery 35, 696 (1994). No. 7 "Protocol for Neutron Beam Dosimetry," AAPM Task Group

127. G. K. Svensson, "Physical aspects ofquafity _surance," For the comm ee on qua y #18 (1980) (FREE)assurance in radiation oneology. American College of Radiology, 1990.

128. J. T_i, B. A. Buck, G. K. Svensson. et al., "Qualily assurance n s eteo ace No. 8 "Pulse Echo Ultrasound hnaging Systenls: Perlormancc Tests &

radiosurgery using a standard linear accelerator," Int. J. Radiat. Oncol. Biol. Phys. 21, Criteria," P. Carson & J. Zagzebski (1980)737 (1991).

29. J. Van Dyk, R. B. Barnett, J. E. Cygler, et al., "Commissioning and quality assurance of No. 9 "Computer-Aided Scintillation Camera Acceptance Testing."trealment planning computers," Int. J. Radial. Oneol. Biol. Phys. 26, 261 (1993). AAPM Task Group of the Nuclear Medicine Committee (1982)

130. K. E. Wallner, J. H. Galieich, M. G. Malkin. et al., "Inability of eompuled tomography

appearance of recun'ent malignant aslroeyloma to predict survival following NO. 10 "A Standard Format for Digital Image Exchange," Baxlerreoperafion," J. Clin. Oncology 7, 1492 (1989l. et al. (1982)

131. K. E. Wafiner, J. B. Galicich, M. G. Malkin, el al., "Paoerns of failure followingtreatment for glioblasloma multlforme and anaplastie aslrocytoma," Int. J. Radial. No. 11 "A Guide to the Teachiz_g of Cliuical Radlological Physlc_ to

Oncol. Biol. Phys. 16, 1405 (1989). Residents in Radiology," tKAPM Comudttee on the 'l'laiJtiug ul132. L. Walton, C. K. Bomford, and D. Ramsden, "The Sheffield slereotactic radiosurgery Radiologists (1982)

unit: physical characteristics and principles of operation," Br. L Radiol. 60, 897 (1987).133. R. R. Wilson, "Radiological use of fast protons," Radiology 40, 487 (1946). No. 12 "Evaluation of Radiatiu, Exposui¢ Lcvcl_ io Utile Cald_a,.134. K. R. Winston and W. Lulz, "Linear aeceleralor as a neurosurglcal Iool for slereotaellC Catheter za on Labora or es, AAPM CI )e la_k l_ort.e of the

radiosurgery," Neurosurge_ 22, 454 (1988). Diagnoslic Radiology Committee (1984)135. A. Wu, A. H. Malta, A. M. Kalend, el al., "Physics of gamma knife approach on

convergent beams in stereolactlc radlosurgery,".lnt. J. Radial. OncoL Biol. Phys. 18, No. 13 "Physical Aspects of Quality Assurance iJ Rad'a "o [ he apy,941 (1990). AAPM Radiation Therapy Commitlee TG #24, with contribuliou

136. D. Yeung, J. Paha, J. Fontanesl, et al., "Systematic analysis of errors in target by TG #22 (1984)i

oea nza ion and rea men delnvery n s ereo acc rad osurgery (SRS), Int. J. Rad at. No. 15 "Performance Evaluation and Quality Assurance in Digital

Oneol. Biol. Phys. 28, 493 (1994). Subtraction Angiography," AAPM Digilal

Radiography/Fluorography Task Gloup (1985)

No. 16 "Protocol for lteavy Charged-Partlcle 'ffiezap) lJcaJ,

Dosimetry," AAPM TG #20 of the Radlatitm "l hCrap) ko_,_,,_tt¢¢(1986)

NO. 17 "The Physi_:td A_;pe_l_ oI 'l_tal aLld It,all 15od_ t'hut,n_Irradiation," AAPM TG #29 ol the Radiation Therapy L'_,mmdtee

(1986)

No. 18 "A Primer on Low-Level Ionizing Radialion alld its Biological

Effects," AAP Biological Effects Committee (1986)

No. 19 "Neutron Measurements Around High Energy X-Ray

Radiotherapy Machines," AAPM RadlatioI; Therapy TG _27(1987)

No. 20 "Site Plauning for Maguetic Rc_,o a Ice 1 ag g Sy_tc sAAPM NMR TG _2 (1987)

No. 21 "Specilicallon of Brachytherapy Soulce _ilc_l_th," AAI'_Vl

Radiation Therapy TG //32 (1987)

88

V

No. 39 "Specification and Acceptance Testing of ComputedNo. 22 "Rotation Scintillation Camera Spect Acceptance Testing and Tomography Scanners," Diagnostic X-Ray Imaging Comminee

QualityControl,"Task Groupof the NuclearMedicine TG #2 (1993)Committee (1987)

• No. 40 "Radiolabeled Antibody Tun]or Dos me ry, ' AAPM NuclearNo. 23 "Total Skin Electron Therapy: Technique and Dosimetry," Medicine Committee TG #2 (1993)

AAPM Radiation Therapy TG #30 (1988)No. 41 Remote Afterloadmg T_ch Lology, Remote Alterloadi_, 6

No. 24 "Radiotherapy Portal Imaging Quality," AAPM Radiation . Technology TG #41 (1993)

Therapy TG #28 (1988) _ No. 42 "The Role of the Clinical Medical Physicist i_JDiag.,_s6cNo. 25 "Protocols for the Radiation Safety Surveys of Diagnostic f Radiology," AAPM Professional Information and Clinical

Radiological Equipment," AAPM Diagnostic X-Ray Imaging _ Relations Committee TG #2 (1993)CommitteeTG#1(1988)

No. 43 "Quality Assessment and Improvement of Dose ResponseNo. 26 "Performance Evaluation of Hyperthermia Equipment," AAPM Models," $25, (1993). Published by Medical Physics Publishing.

HypeithermiaTG #1 (1989) Theycanbecontactedat (800)442-5778or fax(608)265-

No. 27 "Hyperthermia Treatment Planning," AAPM Hyperthermia 2121Committee TG #2 (1989) No. 44 "Academic Program for Master of Scieuce Degree in Medical

Physics," AAPM Education and Tlaining of Medical PhysicistsNo. 28 "'Quality Assurance Methods and Phantoms for MagneticResonanceImaging," AAPM Nuclear Magnetic Resonance _ Committee (1993)

Committee TG #1 (1990) No. 45 "Manageulent of l(adiatiou L)ncology Pati¢.ts _,ith lllJFla_Jtcd

No. 29 "Equipment Requirements and Quality Control for Curd'at Pace akers," AAPM Task G #up #4 _,1994)Mammography," AAPM Diagnostic X-Ray Imaging Committee _ No. 46 "Comprehensive QA 'or Rad a on Ontology," AAPIVITG#7(1990) RadiationTherapyCommitteeTG#40(1994)

.No. 30 "E-mail and Academic Computer Networks," AAPM Computer No. 47 "AAPM Code of Practice for Radiotherapy AcceleratoJs,"Committee TG #1 (1990) _ AAPM Radiation Therapy TG #45 (1994)

No. 31 "Standardized Methods for Measuring Diagnostic X-Ray No. 48 "The Calibration and Use of Plane-Parallel Ionization ChambersExposures," AAPM Diagnostic X-Ray Imaging Committee TG for Dosimetry of Electron Beams," AAPM Radiation Therapy

#8(1991) ConmfineeTG#39(1994)

No. 32 "Clinical Electron-Beam Dosimetry," Radiation Therapy No. 49 "Dosimetry of Auger-Electro. Emitti.g l(z_dJ,)iuacl_d¢a/' ._kikl'lVlCommittee TG #25 (1991) Nuclear Medicine TG #t_ (1995)

No. 33 "Staffing Levels and Responsibilities in Diagnostic Radiology" No, 50 "Fetal Dose flora l).aaiuthe_apy ¢,itlt t'n.JLo. Dc.,m_ " ,_._rlwDiagnostic X-Ray Imaging Committee TG 05 (1991) Radialton Therapy Committee 'IG 036 (19_)5)

No. 34 "Acceptance Testing of Magnetic Resonance Imaging Systems" No. 51 "Dosimetry ot lnlerstitial Brachytherapy Sou,cos," A/_PlVlAAPM Nuclear Magnetic Resonance TG #6 (1992) _ Radiation Therapy Comminee TG #43 (1995)

i

No. 35 "Recommendations on Performance Characteristics of No. 52 "Quantitation of SPECT Performance," AAPM NuclemDiagnostic Exposure Meters" AAPM Diagnostic X-Ray Imaging _ Medicine Comminee TG #4 (1995)

TG #6 (1992) No. 53 "Radiation Information for llospital Persounel," AAPMNo. 36 "'Essentials and Guidelines for Hospital Based Medical Physics Radiation Safety Committee (1995)

Residency Training Programs," AAPM Presidential Ad HocCommittee (1992) No. 54 "Stere#tactic Radlosurgery," Radiation Thelapy Commioec TG

#42 (1995)No. 37 "Auger Electron Dosimetry" AAPM Nuclear Medicine

Committee TG #6 (1993)

No. 38 "'The Role of the Physicist in Radiation Oncology," ProfessionalInformation and Clinical Relation Committee TG #1 (1993)

!i:

V

Return to: American Institute of Physics Name:c/o AIDCE O. Box 20 Address:Williston, VT 05495-0020(800) 809-2247 phone(802) 864-7626 FAX

copies of @ __ Prepayment requiredU.S. check or International

copies of @ Money Order

copies of @ Amount enclosed __

¢m