AAPM REPORT No.82 2003 调强放射治疗的指导文件交付、治疗计划和临床实施

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Guidance document on delivery, treatment planning, and clinical

implementation of IMRT: Report of the IMRT subcommittee

of the AAPM radiation therapy committee

Gary A. Ezzell

Mayo Clinic, Scottsdale, Arizona 85259

James M. Galvin

Thomas Jefferson University Hospital, Philadelphia, Pennsylvania 19019

Daniel Low

Mallinckrodt Institute of Radiology, St. Louis, Missouri 63101

Jatinder R. Paltaa)

University of Florida, Gainesville, Florida 32610

Isaac Rosen

UT M.D. Anderson Cancer Center, Houston, Texas 77001

Michael B. Sharpe

Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada

Ping Xia

University of California at San Francisco, San Francisco, California 94101

Ying Xiao

Thomas Jefferson University Hospital, Philadelphia, Pennsylvania 19019

Lei Xing

Stanford University School of Medicine, Stanford, California 94305

Cedric X. Yu

University of Maryland School of Medicine, Baltimore, Maryland 21201

共Received 27 August 2002; accepted for publication 21 March 2003; published 24 July 2003兲

Intensity-modulated radiation therapy 共IMRT兲represents one of the most signiﬁcant technical ad-

vances in radiation therapy since the advent of the medical linear accelerator. It allows the clinical

implementation of highly conformal nonconvex dose distributions. This complex but promising

treatment modality is rapidly proliferating in both academic and community practice settings.

However, these advances do not come without a risk. IMRT is not just an add-on to the current

radiation therapy process; it represents a new paradigm that requires the knowledge of multimo-

dality imaging, setup uncertainties and internal organ motion, tumor control probabilities, normal

tissue complication probabilities, three-dimensional 共3-D兲dose calculation and optimization, and

dynamic beam delivery of nonuniform beam intensities. Therefore, the purpose of this report is to

guide and assist the clinical medical physicist in developing and implementing a viable and safe

IMRT program. The scope of the IMRT program is quite broad, encompassing multileaf-collimator-

based IMRT delivery systems, goal-based inverse treatment planning, and clinical implementation

of IMRT with patient-speciﬁc quality assurance. This report, while not prescribing speciﬁc proce-

dures, provides the framework and guidance to allow clinical radiation oncology physicists to make

American Association of Physicists in Medicine. 关DOI: 10.1118/1.1591194兴

Key words: 3-D conformal radiotherapy, intensity-modulated radiation therapy, inverse planning,

plan optimization, quality assurance

TABLE OF CONTENTS

I. INTRODUCTION............................ 2090

A. Relation of intensity-modulated radiation

therapy 共IMRT兲, three-dimensional

conformal radiation therapy 共3DCRT兲, and

traditional practice........................ 2090

B. Objectives for this document. ............... 2090

C. Organization of this document............... 2091

II. DELIVERY SYSTEMS FOR IMRT............ 2091

A. General issues of IMRT delivered with MLC. . 2091

1. MLC leaf positional accuracy. . . . ........ 2091

2. Linac performance

for small MU delivery.................. 2093

3. MLC control issues.................... 2093

4. MLC physical characteristics............. 2093

B. Additional issues with dynamic IMRT with

MLC................................... 2094

1. MLC leaf positional and leaf speed

accuracy. ............................ 2094

2. Other dynamic MLC issues.............. 2095

C. IMRT with physical attenuators.............. 2095

D. IMRT with rotating fan beams 共tomotherapy兲. . 2095

1. Peacock positional accuracy............. 2095

2. Peacock dosimetric measurements......... 2096

3. Helical tomotherapy.................... 2096

E. IMRT with rotating cone beams

共intensity-modulated arc therapy兲............ 2096

F. Leaf sequencing for segmental and dynamic

IMRT with MLCs. ........................ 2096

1. Sliding window algorithms.............. 2096

2. Areal or reducing algorithms............. 2097

III. TREATMENT PLANNING FOR IMRT........ 2098

A. Differences between IMRT and conventional

treatment planning: dose calculations and

beam modeling........................... 2098

1. Modeling head scatter, penumbra, and

transmission.......................... 2098

2. Leaf sequencing and deliverability........ 2098

3. Heterogeneity corrections. ............... 2098

B. Differences between IMRT and conventional

treatment planning: Planning algorithms....... 2099

C. Differences between IMRT and conventional

treatment planning: Speciﬁc planning issues. . . 2100

1. Dose uniformity vs dose shaping......... 2100

2. Target and structure delineation. . ......... 2100

3. Dose grid............................ 2101

4. Buildup region........................ 2101

5. Flash and mobile targets................ 2101

6. Margins.............................. 2101

7. Radiobiologic issues. ................... 2102

8. Plan evaluation. . ...................... 2102

D. Learning how to use the inverse planning

system.................................. 2103

E. Commissioning an IMRT planning system for

dosimetric accuracy....................... 2103

F. QA of individual treatment plans............ 2105

1. Independent calculation methods.......... 2105

2. Veriﬁcation measurements. . . ............ 2105

3. Other plan checks. ..................... 2106

IV. CLINICAL IMPLEMENTATION OF IMRT. .... 2106

A. Overview. . .............................. 2106

B. Equipment and space requirements........... 2107

1. Shielding. . . . . . . . . . . . . . . . . . . . . . . ...... 2107

2. Space planning........................ 2107

3. Equipment............................ 2107

C. Time and personnel requirements............ 2107

D. Changes in treatment planning and treatment

delivery process.......................... 2107

1. General considerations.................. 2107

2. Immobilization........................ 2107

3. Image acquisition...................... 2107

4. Structure segmentation.................. 2108

5. IMRT treatment planning................ 2108

6. File transfer and management. . . . ........ 2108

7. Plan validation........................ 2109

8. Position veriﬁcation.................... 2109

9. IMRT treatment delivery................ 2109

E. QA of equipment and individual patient

treatments............................... 2110

F. Staff training and patient education. .......... 2110

1. Radiation oncologists................... 2110

2. Radiation oncology physicists............ 2110

3. Dosimetrists.......................... 2111

4. Radiation therapists.................... 2111

5. Service engineers...................... 2111

6. Patient education...................... 2111

G. Patient scheduling, billing, and charting. ...... 2112

H. Overall integration........................ 2112

V. SUMMARY................................ 2112

I. INTRODUCTION

A. Relation of intensity-modulated radiation therapy

„IMRT…, three-dimensional conformal radiation

therapy „3DCRT…, and traditional practice

IMRT is an extension of 3DCRT that uses nonuniform

radiation beam intensities that have been determined by vari-

ous computer-based optimization techniques. Three-

dimensional conformal therapy is a change from traditional

practice in that it uses targets and normal structures identiﬁed

on multiple transverse images, ﬁeld design based on beam’s

eye view projections, volumetric dose calculations, and volu-

metric plan evaluation tools such as dose–volume histo-

grams 共DVHs兲. IMRT uses all the tools of 3DCRT and adds

other novel features. IMRT seeks to further shape dose dis-

tributions by modulating the intensity of each ﬁeld. Thus,

new capabilities of linear accelerators 共linacs兲and collima-

tors must be installed, commissioned, and maintained. Also,

computing the needed intensity patterns and machine instruc-

tions to create them complicates the treatment planning pro-

cess signiﬁcantly. The computer algorithms associated with

IMRT planning must be commissioned for dosimetric accu-

racy. Users must learn how to use inverse planning systems

to produce and evaluate high quality plans. These are new

tasks that physicists and other radiation oncology staff must

accomplish. Many physicists and their colleagues are now

struggling with the question of ‘‘what do I need to know and

do to implement IMRT safely and effectively?’’

B. Objectives for this document

The objectives for this document are

共a兲to describe in general terms how IMRT differs from

3DCRT with respect to treatment delivery, treatment plan-

ning, and clinical implementation and give references so

readers can get more details if desired;

共b兲to describe how these differences impact commission-

ing of the treatment planning and delivery systems, and pro-

vide guidance on the commissioning process;

共c兲to describe the impact on ongoing quality assurance

共QA兲and provide guidance on QA practice; and

2090 Ezzell

et al.

: Clinical implementation of IMRT 2090

Medical Physics, Vol. 30, No. 8, August 2003

共d兲to describe how these processes ﬁt together with each

other and provide guidance on the clinical implementation of

IMRT.

Because of the emerging and rapidly changing nature of

IMRT, this document cannot be deﬁnitive or prescriptive.

Task group reports and Codes of Practice will eventually

emerge as the ﬁeld matures. Our intention in this document

is to provide guidance during this introductory period. We

have tried to avoid being overly repetitive of other docu-

ments, such as the recent report of the IMRT Collaborative

Working Group 共CWG兲1and special issues of Medical

Dosimetry,2,3 with which readers should also be familiar. We

have also consulted with ASTRO representatives who are

developing recommendations for the clinical use of IMRT. It

should be recognized that the development of IMRT is still in

its infancy and is rapidly evolving. Therefore, many speciﬁc

statements made within this document are likely to be out-

dated as the new generation of planning and delivery systems

become available.

C. Organization of this document

After this introductory section, this presentation follows

with a description in Sec. II of delivery methods used for

IMRT and associated commissioning and QA. An under-

standing of delivery mechanisms is necessary to appreciate

some of the factors that impact IMRT treatment planning.

Section III on treatment planning follows. That section cov-

ers commissioning a planning system for dosimetric accu-

racy, which is inherently related to the delivery mechanism.

It also covers learning how to effectively use an inverse plan-

ning system. These two sections address objectives 共a兲-共c兲;

that is, they explain the differences from 3DCRT and provide

guidance on commissioning and QA of treatment planning

and delivery systems. Finally, in Sec. IV on clinical imple-

mentation we outline the issues that have to be addressed by

the physicist and other team members in order to bring IMRT

online, and so we address objective 共d兲.

II. DELIVERY SYSTEMS FOR IMRT

The difference between 3DCRT and IMRT with respect to

treatment delivery is implied in the phrase intensity modula-

tion. Three-dimensional conformal therapy uses blocks or

multileaf collimators 共MLCs兲to deﬁne ﬁxed ﬁeld bound-

aries. Modulators such as wedges or tissue compensators are

often employed to improve dose homogeneity within the tar-

get. IMRT extends the complexity of the intensity modula-

tion to achieve more complex dosimetric aims, such as cre-

ating dose distributions with concavities. Many methods of

achieving this modulation have been proposed and applied to

clinical practice. One class of techniques holds the beam

direction constant during irradiation and indexes the collima-

tor shape to a fraction of the total prescribed MU for that

direction, thus subjecting any given point in the patient to a

desired proportion of ‘‘open’’ and ‘‘blocked’’ beam. Another

technique uses ﬁxed gantry angles and physical attenuators

to achieve the modulation. Yet another class of techniques

moves the gantry during the irradiation, indexing the colli-

mator shape and gantry angle to the delivered dose. Each

delivery technique has its own unique features that give rise

to different commissioning and QA considerations.

In this section we will emphasize those techniques that

have been implemented commercially using MLCs since

they are the most common and of widest interest to practic-

ing medical physicists. It provides guidance for commission-

ing and QA for these. Other techniques are described brieﬂy.

Although IMRT planning and delivery are intimately re-

lated, in this section we suggest tests of the IMRT delivery

system using MLC control ﬁles that have been developed

independently from the IMRT planning system. In this fash-

ion, the causes of dose deviations can be isolated to the de-

livery or planning system.

In Secs. II A and II B we describe IMRT delivery systems

that use ﬁxed gantry angles and MLCs. In Sec. II C we de-

scribe IMRT delivery systems that make use of ﬁxed gantry

angles and physical attenuators. In Secs. II D and II E we

describe IMRT delivery systems that make use of gantry ro-

tations and MLC. In Sec. II F we provide background infor-

mation on the leaf sequencing algorithms that are used in the

segmental and dynamic IMRT techniques described in Secs.

II A and II B.

A. General issues of IMRT delivered with MLC

The CWG recommends the term segmental IMRT

共SMLC-IMRT兲when the collimator shape is constant during

irradiation and changes between irradiations. Synonymous

terms are step-and-shoot and stop-and-shoot. The gantry

does not move during irradiation. Each collimator shape thus

is a subﬁeld 共or a segment兲. The desired intensity pattern is

obtained by the fractional weighted summation of the inten-

sity pattern from all subﬁelds.

1. MLC leaf positional accuracy

In conventional 3DCRT, the MLC deﬁnes the outer aper-

ture of the beam shape. An uncertainty of 1 to 2 mm in leaf

location may be inconsequential to the output and, in gen-

eral, to clinical outcome, since the uncertainty is small com-

pared with the aperture size. Segmental IMRT builds up a

ﬂuence pattern by adding together many segments, some of

which may be quite narrow. Several investigators have

shown that, for beam widths of 1 cm, uncertainties of a few

tenths of a millimeter in leaf position can cause dose uncer-

tainties of several percent.4,5 Furthermore, the beam edges

move to many locations within the treated area, so their lo-

cations must be known to high precision so that their contri-

butions sum accurately. For these reasons, the accuracy of

relative MLC leaf position must be maintained to a precision

of better than a millimeter. Conventional QA tests for static

MLCs are not sufﬁciently sensitive for this purpose.

A key point for IMRT is that the location of the radiation

ﬁeld edge must be well established with respect to the nomi-

nal location of the MLC leaf end. For MLCs with rounded

leaf ends, there is an offset between the beam edge as deﬁned

by the light ﬁeld and that deﬁned by the 50% decrement line

of the radiation ﬁeld.6This is typically 0.4 to 1.1 mm de-

2091 Ezzell

et al.

: Clinical implementation of IMRT 2091

Medical Physics, Vol. 30, No. 8, August 2003

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摘要：

本文深入解读了AAPM REPORT No.82（2003年发布的调强放射治疗指导文件），系统阐述了调强放射治疗（IMRT）在交付系统、治疗计划设计以及临床实施过程中的核心原则与技术规范。该报告由美国医学物理学家协会（AAPM）发布，旨在为放射肿瘤科医生、医学物理师和剂量师提供一套标准化的操作指南，涵盖多叶准直器校准、剂量验证方法、逆向计划优化策略以及患者特定质量保证流程。通过分析该文献，读者可全面了解IMRT技术的物理基础、治疗精度控制要点及临床常见问题的解决方案，对于提升放疗安全性、优化靶区

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