AAPM REPORT No.148-TG148 2010 Tomo的QA

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QA for helical tomotherapy: Report of the AAPM Task Group 148a…

Katja M. Langenb兲

Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, Orlando, Florida 32806

Niko Papanikolaou

Department of Radiation Oncology, Cancer Therapy and Research Center, University of Texas Health

Science Center at San Antonio, San Antonio, Texas 78229

John Balog

Mohawk Valley Medical Physics, Rome, New York 13440

Richard Crilly

Department of Radiation Medicine, Oregon Health and Science University, Portland, Oregon 97239

David Followill

Section of Outreach Physics, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030

S. Murty Goddu

Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri 63110

Walter Grant III

Department of Radiology/Section of Radiation Oncology, Baylor College of Medicine, Methodist Hospital,

Houston, Texas 77030

Gustavo Olivera

TomoTherapy, Inc., Madison, Wisconsin 53717 and Department of Medical Physics,

University of Wisconsin, Madison, Wisconsin 53706

Chester R. Ramsey

Thompson Cancer Survival Center, Knoxville, Tennessee 37916

Chengyu Shi

Department of Radiation Oncology, Cancer Therapy and Research Center, University of Texas Health

Science Center at San Antonio, San Antonio, Texas 78229

共Received 9 February 2010; revised 27 April 2010; accepted for publication 15 June 2010;

published 20 August 2010兲

Helical tomotherapy is a relatively new modality with integrated treatment planning and delivery

hardware for radiation therapy treatments. In view of the uniqueness of the hardware design of the

helical tomotherapy unit and its implications in routine quality assurance, the Therapy Physics

Committee of the American Association of Physicists in Medicine commissioned Task Group 148

to review this modality and make recommendations for quality assurance related methodologies.

The speciﬁc objectives of this Task Group are: 共a兲To discuss quality assurance techniques, fre-

quencies, and tolerances and 共b兲discuss dosimetric veriﬁcation techniques applicable to this unit.

This report summarizes the ﬁndings of the Task Group and aims to provide the practicing clinical

medical physicist with the insight into the technology that is necessary to establish an independent

and comprehensive quality assurance program for a helical tomotherapy unit. The emphasis of the

report is to describe the rationale for the proposed QA program and to provide example tests that

can be performed, drawing from the collective experience of the task group members and the

published literature. It is expected that as technology continues to evolve, so will the test procedures

that may be used in the future to perform comprehensive quality assurance for helical tomotherapy

Key words: helical tomotherapy, quality assurance

We dedicate this task group report to the memory of Sam Jeswani. Sam was a great enthusiast of

the tomotherapy technology and a tireless customer champion. Sam was the Director of Customer

Relations at TomoTherapy, Inc. and a friend to many of us. Sam died during the terrorist attacks in

Mumbai in November 2008.

TABLE OF CONTENTS

I. INTRODUCTION............................ 4818

II. GLOSSARY AND ABBREVIATIONS. . ......... 4819

III. SYSTEM OVERVIEW....................... 4820

IV. SYSTEM SPECIFIC ACCEPTANCE AND

COMMISSIONING ASPECTS................ 4821

V. TREATMENT DELIVERY FOR HELICAL

TOMOTHERAPY........................... 4822

V.A. Introduction............................ 4822

V.A.1. Unique aspects of helical tomotherapy

treatment delivery.................... 4822

V.B. Periodic quality assurance................ 4823

V.B.1. Mechanical alignments................ 4823

V.B.2. Beam parameters..................... 4826

V.B.3. Synchrony tests...................... 4830

V.B.4. Miscellaneous aspects................. 4830

V.B.5. Calibration.......................... 4831

VI. TREATMENT IMAGING FOR HELICAL

TOMOTHERAPY.......................... 4834

VI.A. Introduction............................ 4834

VI.A.1. Unique aspects of megavoltage CT

imaging............................. 4835

VI.B. Periodic quality assurance................ 4835

VI.B.1. Spatial/geometry tests................. 4835

VI.B.2. Image quality tests.................... 4837

VI.B.3. MVCT dosimetry..................... 4838

VI.B.4. Image export for analysis.............. 4839

VII. TREATMENT PLANNING FOR HELICAL

TOMOTHERAPY.......................... 4839

VII.A. Introduction............................ 4839

VII.A.1. Unique aspects of helical tomotherapy

treatment planning.................... 4839

VII.B. Periodic quality assurance................ 4840

VII.B.1. Geometric validation tests.............. 4840

VII.B.2. Dosimetric validation tests............. 4841

VII.B.3. Clinical treatment plan QA............. 4841

VII.C. MVCT-based treatment planning........... 4845

VIII. SUMMARY AND RECOMMENDATIONS.... 4845

VIII.A. Daily................................. 4845

VIII.B. Monthly............................... 4845

VIII.C. Quarterly.............................. 4845

VIII.D. Annual................................ 4845

VIII.E. Major component replacement............. 4845

APPENDIX A: WORKSHEET A: HELICAL

TOMOTHERAPY PHOTON BEAM

CALIBRATION............................... 4851

APPENDIX B: NOTE ON CONTROL XML FILES

AND CONTROL SINOGRAMS.................. 4851

APPENDIX C: RADIATION SAFETY............. 4851

APPENDIX D: EXAMPLE OF DAILY TEST

PROCEDURES................................ 4851

APPENDIX E: PATIENT ARCHIVES............. 4851

APPENDIX F: TREATMENT PLANNING TIPS.... 4851

I. INTRODUCTION

Task Group Report 40 outlines a comprehensive quality as-

surance 共QA兲program in radiation oncology that applies to

any external beam radiation therapy equipment.1A code of

practice speciﬁc to radiotherapy accelerators is provided by

Task Group Report 45.2Both reports are comprehensive in

nature and supply fundamental guidelines to the medical

physics community.

With the introduction of new technology into the ﬁeld of

radiation oncology, a need arises to provide guidelines that

are tailored to these newer treatment modalities. The quality

assurance of newer technologies is addressed in Task Group

Report 142.3While TG-142 provides the foundation for QA

guidelines of newer technologies, there are several commer-

cially available technologies that are sufﬁciently different

from C-arm type accelerators and require a unique set of QA

recommendations. One such technology is helical tomo-

therapy. It is therefore the intent of this Task Group Report to

provide QA guidelines for helical tomotherapy that, while

based on TG-142 guidelines, are speciﬁcally adapted to this

technology.

There are a fair number of the TG-142 QA recommenda-

tions that can be directly applied to helical tomotherapy 共e.g.,

output constancy兲. Whenever possible, guidelines from TG-

142 and other relevant task group reports have been adopted

in this report. However, several traditional QA recommenda-

tions are not applicable 共e.g., light ﬁeld tests兲to helical to-

motherapy. On the other hand, important aspects of the to-

motherapy treatment modality are not tested with traditional

QA tests. This Task Group Report provides a comprehensive

set of recommendations on all aspects of the helical tomo-

therapy system that should be tested and the respective rec-

ommended test frequencies. References to existing Task

Group Reports are made throughout this report where appro-

priate. General QA guidelines such as the establishment of a

departmental comprehensive QA program, as described in

TG-40 are not discussed in this report.

Helical tomotherapy is an intensity modulated radiation

therapy 共IMRT兲delivery technique that was developed at the

University of Wisconsin-Madison and was later commercial-

ized by TomoTherapy, Inc. of Madison, Wisconsin.4Tomo-

Therapy, Inc. is the only vendor that markets and manufac-

tures treatment units that use this delivery process.

Procedures and recommendations discussed in this report are

therefore speciﬁc to TomoTherapy’s treatment units. Tomo-

Therapy units combine IMRT treatment delivery and mega-

voltage computed tomography 共MVCT兲imaging capabili-

ties. The units were introduced into clinical routine in 2003.

Currently, more than 280 units have been installed world-

wide. It is anticipated that additional Tomotherapy-speciﬁc

treatment techniques will be developed in the future. Static

gantry angle and dynamic y-jaw modes are currently under

development. These techniques are not considered in this

report. Quality assurance procedures speciﬁc to these tech-

niques will have to be developed once those techniques be-

come commercially available.

In this Task Group Report, an overview of the Tomo-

4818 Langen et al.: TG-148 4818

Medical Physics, Vol. 37, No. 9, September 2010

Therapy system and its unique aspects is provided. Delivery,

imaging, and treatment planning quality assurance are dis-

cussed in three chapters of this report. Quality assurance as-

pects are summarized according to their recommended fre-

quency in Sec. VIII. The Appendix contains a collection of

useful discussions that we hope will be of interest to the

practicing medical physicist.

II. GLOSSARY AND ABBREVIATIONS

Virtual Water™phantom: A cylindrical Virtual Water™

phantom that is supplied by TomoTherapy, Inc. Tomotherapy

users commonly refer to this phantom as the “cheese” phan-

tom. This phantom can be used for various quality assurance

procedures. The phantom comes apart in two hemicylinders

and has holes for placing ion chambers as well as plugs for

CT density tests. It has a diameter of 30 cm and a length of

18 cm. Figure 1shows diagrams and pictures of this phan-

tom.

TomoTherapy coordinate system convention: Tomo-

Therapy uses the following machine coordinate system nam-

ing convention: When the patient is positioned head-ﬁrst-

supine on the couch, +x points toward patient’s left side, +y

points toward the patient’s head, and +z points toward the

patient’s anterior side. This coordinate system is ﬁxed, i.e., it

does not rotate with the gantry. Figure 2shows a picture of

the treatment unit with the coordinate system superimposed.

DQA: Delivery quality assurance. This procedure is inte-

grated in the TomoTherapy planning system. The patient

plan is recalculated in a new CT anatomy. This new CT

anatomy is typically a phantom. The DQA plan can then be

delivered and the measured dose in the phantom can be com-

pared to the calculated dose for quality assurance.

Field width/slice width: The longitudinal extent 共i.e., in

y-direction兲of the fan beam is frequently referred to as ﬁeld

width in the literature. In this document, we follow the nor-

mal diagnostic radiology convention and use the term “slice

width” to refer to the longitudinal extent of the treatment

ﬁeld.

Helical tomotherapy: The speciﬁc delivery technique.

Modulation factor: Longest leaf opening time in a plan

divided by the average opening time of all nonzero leaf

opening times.

MVCT: Megavoltage computed tomography.

Output: The TomoTherapy plans are based on time rather

than on monitor units. The output of the machine is therefore

measured in dose per unit time. Throughout this Task Group,

the term output is used in this sense.

Pitch: The pitch is deﬁned as the ratio of the couch travel

per gantry rotation divided by the treatment slice width.

Sinogram: A binary ﬁle that contains data for each projec-

tion. There are several types of sinograms, such as imaging

sinograms derived from detector data or control sinograms

that contain ﬂuence or MLC data for each projection or

pulse.

Treatment plane: This plane marks the area that is deﬁned

by the center of the radiation ﬁeld in the longitudinal 共y兲

direction. In the x- and z-directions, this plane is parallel to

the rotating fan beam.

TomoTherapy: Company that produces and markets a sys-

tem that is based on a helical tomotherapy delivery tech-

nique.

Virtual isocenter: The treatment plane is located inside the

bore and for convenient patient setup a virtual isocenter is

deﬁned 70 cm from the treatment isocenter in the negative

y-direction. As with CT simulation, the virtual isocenter is

located outside the bore and is localized via laser projections.

XML ﬁle: An XML ﬁle is generated at the end of the

FIG. 1. Top row: Drawing and picture of a front view of the vendor supplied

Virtual Water™phantom. Each of the black circles 共e.g., arrow 1兲contains a

Virtual Water™plug that can be removed 共arrow 2兲for ion chamber inser-

tion. The picture of the front view shows the phantom with a ﬁlm inserted in

the coronal plane and an ion chamber located above the ﬁlm plane. Lower

row: Drawing and picture of the back view of the phantom. There are 20

holes for insertion of test plugs. All holes can be ﬁlled with Virtual Water™

plugs or with a set of density calibration plugs as shown in the photo.

Resolution and ion chamber plugs are also available.

FIG. 2. The coordinate system used by TomoTherapy.

4819 Langen et al.: TG-148 4819

Medical Physics, Vol. 37, No. 9, September 2010

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摘要：

本文介绍AAPM REPORT No.148（TG148报告）2010年版中针对螺旋断层放疗系统（TomoTherapy）的质量保证（QA）标准与操作规范。该报告由美国医学物理学家协会（AAPM）发布，旨在为临床物理师提供一套系统化的QA流程，涵盖射束剂量验证、MVCT图像配准精度、治疗床移动准确性、多叶准直器叶片位置稳定性及治疗计划系统独立核对等关键环节。TG148首次明确了Tomotherapy特有组件的测试频率（如每日、每月、年度检查），并强调针对IMRT和VMAT模式的端到端验证方法。对

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