MEDICAL PHYSICS COMMITTEE Medical Physics ...

Int. J. Radiation Oncology Biol. Phys., Vol. 51, No. 3, Supplement 2, pp. 96 –102, 2001 Copyright © 2001 Radiation Therapy Oncology Group Printed in the USA. All rights reserved 0360-3016/01/$–see front matter

PII S0360-3016(01)01789-8

MEDICAL PHYSICS COMMITTEE Medical Physics Committee Key Members: Michael T. Gillin, Ph.D., Chair (1990), Stereotactic Radiosurgery and Prostate Brachytherapy; James Galvin, D.Sc., Co-Chair, Head and Neck and Gastrointestinal Cancer; Ivan A. Brezovich, Ph.D.; James Chu, Ph.D.; Indra Das, Ph.D.; Nicholas A. Detorie, Ph.D.; Doracy Fontenla, Ph.D.; William Hanson, Ph.D., Radiologic Physics Center and Gynecologic Cancer; William B. Harms, Sr, Three-Dimensional Conformal Radiotherapy; M. Saiful Huq, Ph.D., RTOG Headquarters; Robert Kline, Ph.D., Brain Tumors and Genitourinary Cancer; Colin Orton, Ph.D.; Ervin B. Podgorsak, Ph.D., Brain Tumors; James Purdy, Ph.D., Image-Guided Radiotherapy and Lung Cancer; Isaac Rosen, Ph.D.; Michael Schell, Ph.D., Stereotactic Radiosurgery; N. Suntharalingam, Ph.D., Consultant; Kathryn A. Winter, M.S., Statistical Center; and J. Keith De Wyngaert, Ph.D. INTRODUCTION

dentialing efforts is to ensure that patients who are entered in these protocols are treated in a manner specified in the protocols, so that high-quality data are available for analysis. 3. The Medical Physics Committee, together with the 3D QA Center in St. Louis, has successfully defined an RTOG external beam communications protocol, which has been implemented by five different commercial software companies. These standards have resulted in the central review of the dosimetry of patients entered into RTOG 3D-CRT protocols. 4. IMRT is an exciting new treatment approach. The Medical Physics Committee is in the initial phase of establishing a credentialing process that will include both a treatment verification component and a data transfer central review component. Substantial efforts have been expended to ensure that the dosimetric specifications are complete, consistent, and obtainable with the current technology. In addition, the Medical Physics Committee is performing initial data exchange, dosimetry evaluation, and educational activities. During the next grant period, the Medical Physics Committee will increase its efforts on IMRT protocols, prostate brachytherapy protocols, and 3D-CRT protocols. It can be expected that all commercial planning systems will incorporate Digital Imaging and Communication in Medicine (DICOM) RT, so that an even larger number of institutions can participate in the 3D-CRT protocols. The dosimetry associated with prostate brachytherapy protocols will be reviewed using a digital approach, as opposed to the nondigital approach used in RTOG 98-05. The IMRT dose specifications and treatment delivery approaches will be refined.

The Medical Physics Committee is a core resource to the RTOG that provides medical physics and dosimetry quality management services, as well as intellectual input into clinical trial design and analysis from the medical physics leadership. The RTOG seeks to determine the appropriate role for the many new technologies currently available in radiation oncology. The Medical Physics Committee has been especially active in the quality assurance aspects of protocols that use state-of-the-art treatment planning and treatment delivery techniques, including stereotactic radiosurgery (SRS), three-dimensional (3D) conformal radiotherapy (CRT), prostate brachytherapy, and now intensity-modulated radiotherapy (IMRT). The successful testing of these technologies within the cooperative group setting requires a common vocabulary, a set of minimal technical capabilities demonstrated through a credentialing process, appropriate dosimetric specifications that focus on the critical clinical question, and a comprehensive central review. The RTOG has been successful in establishing mechanisms that address each of these requirements. 1. The RTOG Medical Physics Committee, either acting alone or in coordination with the Radiologic Physics Center and/or the 3D Quality Assurance (QA) Center, has adopted and popularized a common vocabulary so that concepts such as clinical target volume and planning target volume (PTV) are now commonly integrated into protocols. 2. The Medical Physics Committee has credentialed ⬎90 institutions to participate in RTOG SRS protocols. The 3D QA Center has credentialed 41 institutions to participate in RTOG 94-06, the 3D prostate cancer protocol; 19 institutions to participate in RTOG 93-11, the 3D lung cancer protocol; and 15 institutions to participate in RTOG 98-03, the 3D brain tumor protocol. The Radiologic Physics Center (RPC) has credentialed 41 institutions to participate in RTOG 98-05, the first permanent prostate implant protocol, and subsequent prostate implant protocols. The importance of these substantial cre-

ENCOMPASSING VISION Major research questions The major hypotheses being investigated by the RTOG that have a significant medical physics element include the following: 96

Medical Physics Committee

1. Increased RT dose delivered in a conformal fashion will result in increased local tumor control for selected malignancies. 2. Improved conformal treatments will maintain or improve local tumor control and decrease treatment morbidity for selected site malignancies. 3. SRS, which can be delivered by either a gamma knife or a linear accelerator-based system, together with other modalities, can improve the quality of life for patients with brain metastases. 4. Fractionated, stereotactic-based RT treatments can increase tumor control for malignant glioma patients. 5. Dosimetric criteria for evaluating the adequacy of a permanent prostate implant, either as monotherapy or in combination with external beam RT, can be established. 6. IMRT will maintain or increase local control for selected head and neck cancer and other malignancies, while decreasing the morbidity of these treatments. 3D conformal RT The RTOG dosimetric terms for 3D-CRT protocols have been based on the International Commission on Radiation Units and Measurement (ICRU) Report 50, published in 1993. Many RTOG protocols now routinely use the concepts of a clinical target volume and PTV. Recently, the ICRU published a supplement to the ICRU Report 50, ICRU Report 62. Among other contributions, ICRU Report 62 refines the concept of a PTV to differentiate between internal margins to account for variations in size, shape, and position of the clinical target volume and the setup margin to account for all uncertainties in patient– beam positioning. ICRU Report 62 introduces the concept of a planningorgan-at-risk volume and conformity index, the quotient of the treated volume to the PTV. The concepts defined and modified in this new ICRU Report are very timely and will be incorporated into future RTOG protocols, especially those involving IMRT. The RTOG will continue its substantial efforts using 3D-CRT with new protocols that use a conformal doseescalation approach or a conformal avoidance approach, or a combination of these approaches. The Medical Physics Committee will contribute to these efforts by working with the individual Disease Site Committees in the areas of dosimetric specifications during the protocol development process, education of the clinical community during the patient acquisition phase, and dosimetry data review during the analysis phase. The Committee works closely with the Image-Guided Radiotherapy Committee to achieve these goals. Stereotactic radiosurgery. The RTOG will continue its substantial efforts in testing the modality of SRS in the treatment of metastatic or primary brain tumors. The Medical Physics Committee will continue to credential institutions to participate in these protocols. After DICOM RT is adopted, the RTOG will change its credentialing approach and re-credential each institution using a digital data transfer, similar to the approach used in the 3D-CRT protocols.

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The RTOG has developed its first protocol, RTOG B-0023, a Phase II trial of accelerated RT using weekly stereotactic conformal boosts for supratentorial glioblastoma multiforme, which combines the precision of its stereotactic protocols with the conformality of its 3D-CRT protocols. This protocol requires conformal treatment apertures using multiple coplanar/noncoplanar static conformal beams. It does not permit arc-based circular collimator treatment approaches. The Medical Physics Committee is working closely with the principal investigator in developing appropriate dosimetric and treatment delivery specifications for this important, new, hybrid treatment approach. Prostate brachytherapy. RTOG 98-05 was the first cooperative group protocol evaluating brachytherapy in the management of prostate cancer. This protocol was designed for the most favorable patients, namely patients whose prostatespecific antigen level was ⬍10 ng/mL and whose Gleason score was ⬍7. Its objectives included an evaluation of the effectiveness of transrectal ultrasound-guided permanent 125 I seed implantation of the prostate compared with historical data within the cooperative group setting and the establishment of appropriate QA standards based on data from multiple institutions. This protocol defined the evaluation target volume as the post-implant CT definition of the prostate. This protocol defined the minimal target dose, high-dose volumes, and low-dose volumes. The evaluation target volume has been independently defined by a diagnostic radiologist at the central review. The doses to the prostate and surrounding tissues are recalculated on the basis of this definition. The dosimetry submitted by the participating institution is compared with the dosimetry generated during the central review. The Report of the American Association of Physicists in Medicine (AAPM) Task Group 64 on permanent prostate seed implant brachytherapy was published after RTOG 98-05 was established. The report recommends documentation of the dose levels that cover 100%, 90%, and 80% of the target volume for postimplant evaluation (i.e., D100, D90, and D80) and the fractional volume receiving 200%, 100%, 90%, and 80% of the prescribed dose (i.e., V200, V100, V90, and V80). The RTOG is posed to make a major contribution to prostate implant evaluation by the central review of RTOG 98-05. The number of patients that any one institution can contribute was deliberately limited. Thus, the analysis should define what is actually being delivered to the prostate and will compare the central dose distribution to the institution’s analysis. The initial analysis of the first 30 patients entered in RTOG 98-05 shows an inconsistent approach by some institutions in relating their postimplant CT-based prostate definition to their preimplant transrectal ultrasound-based prostate definition, and poor correlation between the volume as defined by the institution and the volume as defined in the central review, with the volume as defined by the institution substantially smaller. This results in larger institutional dose values for D100, D90, and D80. The parameter that displayed the highest correlation between the institutional calculation and the central review calculation was the V80. In

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I. J. Radiation Oncology

● Biology ● Physics

general, the base and anterior sections of the prostate received less than the prescription dose. The experience obtained in the review of the dosimetric data for this protocol indicates the need for a central dosimetric review. This experience also indicates the need for the education of participating institutions relative to the definition of the postimplant prostate as imaged on CT. It is anticipated that eventually postimplant CT images will be posted on a Web site to serve as a guide in defining the prostate. The next RTOG prostate implant protocol will permit either a digital review for those institutions capable of meeting the data transmission requirements or an analog review for those institutions unable to able to meet those requirements. The RTOG anticipates that by the time its Phase III protocol is ready, all participating institutions will be able to participate in a digital central review. Intensity-modulated RT Radiation oncology treatment planning and treatment delivery systems continue to evolve at a rapid rate. Conventional 3D-CRT treatments are based on the definition of the PTV from digital imaging (CT or MRI), with the patient in the treatment position, utilizing beam’s eye view beam placement and dose–volume histogram analysis. IMRT can be viewed as a newer and more generalized version of 3D-CRT. The inverse-planned IMRT treatment approach alters the RT intensity in proportion to the amount of the PTV encompassed by a particular beam (i.e., the beam intensity is increased when the PTV is large and decreased when the PTV is small). The basic problem addressed by IMRT is to calculate a physically deliverable modulated beam fluence profile that will produce an acceptable dose distribution for the PTV and the surrounding organs at risk. Currently, at least four different approaches to treatment delivery with IMRT are available: 1. Tomotherapy using either a specially designed multileaf collimator system or a specially designed linear accelerator. 2. A static, segmental approach using a conventional multileaf collimator (MLC). 3. An approach that uses an X-ray compensating filter. 4. An approach that uses a scanning RT beam. No single method has emerged as the more appropriate treatment technique for a specific disease site with a specific treatment goal. In conjunction with the Image-Guided RT and Disease Site Committees, the Medical Physics Committee is addressing the challenging dosimetric questions of implementing IMRT within the cooperative group setting. Multiple delivery systems will be used by the RTOG member institutions. Older dosimetric concepts, such as specifying the dose to a point (isocenter), are no longer valid with IMRT. The specification of the dose when it is being delivered through multiple segmented dynamic or static fields is a challenge. The RTOG stereotactic experience in which the dose is specified to an isodose surface, which ranges from

Volume 51, Number 3, Supplement 2, 2001

approximately 80% for a linear accelerator stereotactic system to 50% for gamma knife treatment, will be a reasonable starting position. The RTOG also has substantial experience in delivering high doses to the PTV in the various 3D-CRT protocols. The confirmation of the delivered dose, given the multiple delivery systems, is another challenge. With IMRT, it will be important to focus on the important clinical questions and to avoid having protocols become planning system and delivery system dependent. The Medical Physics Committee will help the developers of individual protocols define the essential dosimetric elements for each IMRT protocol to ensure that the clinical question being asked by the protocol is appropriately addressed. The first RTOG protocol that uses IMRT, RTOG H-0022, addresses a quality-of-life issue for patients with oropharyngeal cancer. The objectives of this study include the following: 1. Assessment of the feasibility of adequate target coverage and major salivary gland sparing in patients with oropharyngeal cancer treated with IMRT techniques. 2. Determination of whether improvement in quality-of-life scores may be achieved compared with similar patients treated with standard RT. 3. Determination of the nature and prevalence of acute and late side effects and their relation to the dose and volume of normal tissue irradiated. 4. Determination of the rate and pattern of locoregional tumor recurrence and dose–volume and tumor control relationships. A major issue posed by this protocol is the adequacy of the target definition and organs at risk in the planning process in the group setting. The highly conformal dose distributions increase the potential of missing volumes containing subclinical disease compared with standard RT techniques. This situation makes the QA and verification steps in the delivery process particularly important for IMRT. RTOG H-0022 contains definitions for both the target and critical normal structures. The treatment will aim to deliver the RT dose to the PTVs with the exclusion of the noninvolved tissue, as feasible. The planning method is not restricted to the use of inverse planning techniques. Any method for generating plans that meet the dose prescription can be used. Dose–volume histogram analysis of the PTV and the critical structures will be used to demonstrate the adequacy of each plan relative to the dose prescription. The dose specification will include the percentage of the PTV that will be permitted to receive a minimal dose and the percentages of the PTV that can receive varying doses greater than the prescribed dose. The planning priorities are as follows: 1. Critical normal structure constraints (e.g., maximal doses to brainstem, spinal cord). 2. Prescription goals (e.g., dose to the PTVs). This protocol has three PTVs, namely, gross tumor and lymph node metastasis, subclinical PTV at high risk (first echelon


nodes or dissected neck area containing lymph node metastases), and subclinical disease. 3. Dose constraint goals (e.g., dose and volume constraints for the parotid glands). Treatment verification will depend on the treatment technique implemented. For static, segmented treatments with an MLC, port films will be taken for each field at the beginning of treatment, consisting of a series of exposures of each MLC segment at two monitor units per segment, superimposed on an open field image of the patient. For dynamic intensity modulation methods, verification of the calculated dose will be accomplished by placing an ion chamber and films in a special phantom for which the patient plans have been recalculated. After all the issues are resolved for the head and neck IMRT study, a breast study will be opened. In early invasive breast cancer, a Phase II study addressed the timing and volume of breast to be treated. In contrast to the traditional 6-week treatment regimen of whole-breast RT, RTOG 95-17 administered brachytherapy delivered in 1 week or less. This scheme allowed the RT to be completed shortly after recovery from surgery and avoided the delay in administering RT after chemotherapy. The study demonstrated that the technique was feasible, and the early results have been excellent. This protocol will be followed by a similar study using IMRT to treat the same quadrant breast volume in a similarly short time. If IMRT is as successful as the breast brachytherapy study, the Committee plans to develop a Phase III trial comparing traditional whole-breast RT to a short-term quadrant RT technique, using either brachytherapy or IMRT. Patients would receive chemotherapy after the short-course quadrant treatment, in contrast to those randomized to the traditional 6-week RT course, who would receive their chemotherapy first. This study has received support from patient advocates for increasing access of breast conservation to those who live far from a medical center, minimizing the issues of “sequencing” needed for systemic chemotherapy and breast RT, decreasing the overall treatment time, and largely avoiding exit RT to the heart and lung regions. The Medical Physics Committee will explore using the RTOG Web site as an educational tool for these challenging IMRT studies. The Medical Physics Committee is working closely with the 3D QA Center in St. Louis to generate guidelines and procedures for the IMRT protocol QA and treatment verification. The Medical Physics Committee will also work with the 3D QA Center to develop reporting mechanisms for all RTOG IMRT protocols. At this point, treatment verification for IMRT is a difficult and labor-intensive process. Intensity patterns are often extremely complex and nonintuitive. This situation has given rise to the use of film dosimetry techniques that map the 3D dose distribution as one or more two-dimensional displays. This verification technique is usually combined with one or more point measurements using a small ioniza-

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tion chamber in a phantom. A final verification measure uses a standard port film to demonstrate the position of the isocenter used for treatment. The Medical Physics Committee will use this procedure at the start of protocol H-0022 but will also work to develop methods that are more manageable. This could involve the elimination of some of the steps described above after the successful accrual of a specified number of cases by a particular institution. Another possible simplifying approach includes the method of placing a transmission film at the position of the block tray to register the intensity pattern for each position of the gantry. The Medical Physics Committee will make recommendations on the adoption of new verification methods as they become available. QA will be conducted by the RTOG 3D QA Center. The 3D QA Center will recalculate the dose–volume histograms for the PTVs, designated critical structures, and unspecified tissues. Definitions have been created for minor variation and major deviations of the treatment plans for the prescription criteria. The RTOG will refine their experience from this protocol for future IMRT protocols. Response to problems The previous review noted that the RTOG faced a resource allocation question, namely to choose between developing, implementing, and monitoring protocols with very specific hypotheses and assessing, reviewing, and proposing general standards for conformal modalities, some of which are still in the process of evolution. The primary purpose of the RTOG is to conduct multi-institutional prospective, randomized trials. To accomplish this purpose, the RTOG must adopt general standards to ensure that all participating institutions are delivering similar types of treatment to patients entered in RTOG protocols. The RTOG has been very successful in adopting the ICRU recommendations for dose specification for its protocols, especially for its conformal protocols. The RTOG has also adopted the recommendations of the AAPM with respect to the calibration of RT devices and RT sources. The RTOG does not propose its own general standards. The previous review also noted that the previous “proposal does not provide concrete descriptions of how they will determine the scope of their work nor how they will accomplish the tasks that they select. Although it is admittedly difficult to map a strategy related to emerging technologies, a lack of clear planning will delay or inhibit a direct and unequivocal approach to solutions, which may compromise RTOG’s ability to implement protocols. Given the resources requested for medical physics research in this proposal, it may be difficult to achieve both the specific and more general aims.” The priorities of the RTOG are developed by the Research Strategy Committee and denote the clinical nature of the RTOG. Emerging technologies are important only to the extent that they provide a better approach to answer a specific scientific question. It is the responsibility of the Medical Physics Committee to ensure that the clinical protocols incorporate the most current ver-

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sion of generally accepted dosimetric principles and treatment planning concepts. It is certainly true that the RTOG must make cautious and prudent decisions, owing both to the limited resources and to the nature of the group. One example of a cautious and prudent, yet contemporary, series of decisions involves the RTOG activities with permanent prostate implants. Because of concerns relating to the calibration of 103Pd seeds, the RTOG has yet to consider a protocol using them. The first RTOG protocol, RTOG 98-05, only permitted the use of 125I seeds whose calibration was directly traceable to the National Institute of Standards and Technology (NIST). Multiple seed vendors have contacted the RTOG and requested that their seeds be permitted to be used in RTOG protocols. These vendors have been informed that their seeds must meet the AAPM criteria [Medical Physics 25 (12), December, 1998], namely NIST traceable calibration and two peer reviewed publications, before the seed will be acceptable for RTOG protocols. The next RTOG prostate implant protocol will permit all seeds that meet this standard to be used. The first RTOG prostate seed protocol was based on the techniques developed in Seattle in an effort to determine the capability of the group to use this approach. It was the judgment of the RTOG that this approach was the most commonly used one in the United States. The RTOG, with the help of Dr. Blasko, specified the preplanning volume. The RTOG differed from the Seattle experience in the timing of the postimplant CT study in an effort to minimize the effect of the swelling of the prostate after the trauma of implantation. The RTOG did not propose its own standards for this conformal modality. Another example of the RTOG’s efforts in balancing between its limited resources and the desire to use emerging technologies is its investigations of intensity modulation. The first RTOG protocol will involve a head and neck site. This protocol will not limit either the treatment planning approach or the treatment delivery approach. Both forward planning and inverse planning approaches will be permitted. The intensity modulation can be achieved by any of the currently available static or dynamic treatment delivery approaches. The Medical Physics Committee has worked with the Head and Neck Committee on the dosimetry specification aspects of this protocol. The Medical Physics Committee is pursuing a two-element demonstration project to support this protocol. This demonstration project will initially involve three different institutions with two different planning systems, namely Corvus from the NOMOS Corporation (Sewickley, PA) and Focus from Computerized Medical Systems, Inc. (St. Louis, MO). These three institutions have three different treatment delivery approaches: a dynamic special MLC system, a standard static MLC system, and a tissue compensator system. This demonstration project should help identify some of the challenges of using the IMRT technology within the group setting. SRS serves as a final example involving the use of emerging technologies within the RTOG. The RTOG used its collective experience gained from its first stereotactic


protocol to define the dosimetric criteria for future RTOG protocols. These criteria reflected the diverse treatment delivery options found within the RTOG. These options ranged from accelerator-based systems to gamma knives. Subsequent protocols used this technology to address specific clinical questions. This experience, which was built on the individual institutional experiences with this new technology, serves as a model to guide the RTOG in dealing with emerging technologies. The Medical Physics Committee serves to aid communication among the RTOG Headquarters Dosimetry Staff, the RPC, and the 3D QA Center through the use of regular conference calls, e-mails, and the semiannual RTOG meetings. The Medical Physics Committee and the RPC mutually agree on the services that the RPC will provide to the RTOG. The RPC provides the RTOG with a calibration review service through its thermoluminescent dosimetry (TLD) program, credentialing for several brachytherapy protocols (e.g., the breast protocol RTOG 95-17 and the prostate protocol, RTOG 98-05), and the development of various phantoms and dosimetric analysis of the treatment of these phantoms. The Medical Physics Committee and the 3D QA Center mutually agree on the services that the 3D QA Center will provide to the RTOG. The 3D QA Center currently provides the RTOG with a mechanism for central digital review for specific external beam protocols (e.g., RTOG 93-11, 94-06, and 98-03). The clinical review of patients entered in RTOG protocols is the responsibility of the primary investigators for each specific RTOG protocol. The Medical Physics Committee interacts with the RTOG Headquarters Dosimetry Staff to aid the staff in addressing specific dosimetric issues. It is the RTOG Headquarters Staff that receives the vast majority of the inquiries regarding the details of specific RTOG protocols. The Medical Physics Committee serves as a resource to the RTOG Dosimetry Staff in addressing certain issues. The Medical Physics Committee reviews the semiannual QA report and inquires about problems with either the initial review or the final review. In the present grant period, the development and implementation of an electronic protocol review program has been successful. This permits the primary investigator and others to review plans, beam films, and treatment records from their offices instead of physically traveling to the data, resulting in greater efficiency in the entire review process without diminishing the QA aspect of the program. The RTOG, in its efforts both in Philadelphia and in St. Louis, has taken major strides to accomplish this objective. One goal for the next grant period is to involve more primary investigators in this electronic review process. Future directions Encourage adoption of TG 51 at RTOG institutions. The AAPM has introduced a new protocol (TG 51) for the calibration of megavoltage photon and electron beams [Medical Physics 26 (9), September 1999]. This new protocol will most likely result in a patient receiving 0 –2%


more RT than patients are currently receiving when treated with beams calibrated under the old calibration protocol, TG 21. The Medical Physics Committee will encourage RTOG member institutions to adopt this new calibration protocol within the next 2 years. The Medical Physics Committee will recommend to the various primary investigators for RTOG protocols that they do not to change their dose prescriptions. In conjunction with the RPC, the Medical Physics Committee will review the changes in calibration made by the RTOG institutions. Continue development of disease site guidelines for 3DCRT. In the next 5 years, the RTOG will have 3D-CRT protocols for each major disease site. These protocols will emphasize either dose escalation or structure avoidance. The current protocols and future protocols will define the disease sites that will benefit from this technology. The RTOG will have set guidelines for the radiation oncology community for the appropriate use of 3D-CRT. Develop QA guidelines for image fusion treatment planning. In the next 5 years, the RTOG will develop protocols that will involve continuous refinement in the definition of the target volume. The fusion of various types of images (e.g., the choline image from MR spectroscopy to define active regions of brain metabolism with the standard MR or CT axial data set) will become increasingly important for the treatment of brain, lung, prostate, and other sites. The Medical Physics Committee will need to establish QA guidelines relative to image fusion activities. The fusion of images will most likely be based on DICOM standards and will include images that are not currently in routine use for treatment planning purposes (e.g., MR spectroscopy and positron emission tomography). The continued refinement of PTVs and the identification of organs at risk will lead to the refinement of the RTOG’s 3D-CRT protocols for both dose escalation and structure avoidance. Develop guidelines for structure avoidance protocols. In the next 5 years, the RTOG will develop protocols involving gated treatment technology. This technology will be consistent with the RTOG’s structure avoidance protocols, especially for lung, breast, and upper abdomen treatment sites. The fractionated conformal, high-precision stereo-like protocol, which is currently under development, represents an important evolutionary step in using stereo principles to treat patients with primary brain tumors. This should be viewed as part of the RTOG’s structure avoidance program. Implement data transmission through DICOM RT planning systems. One major QA advance in SRS in the next 5 years will be the adoption of DICOM RT by the radiation oncology community. Presently, the stereotactic protocols are being reviewed by the protocol’s primary investigator and a physicist, using film and hard copies of patient dosimetry data. The RTOG will then be able to request that its members require that SRS commercial software vendors provide DICOM RT in their planning systems for data transmission. Once this has been incorporated into the SRS planning systems, the RTOG will institute a digital central review of its SRS protocols.

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Continue the work of the Prostate Brachytherapy QA Center. The RTOG has established a permanent Prostate Brachytherapy QA Center, in conjunction with its 3D-CRT Quality Assurance Center. The Prostate Brachytherapy QA Center will ensure the scientific soundness of future protocols by (1) individual and institutional credentialing; (2) establishment of procedural standards; (3) case submissions; and (4) centralized QA review. The procedural standards will include a written protocol outlining the normal conduct of the implant procedure at the institution; a method of preplanning, which can be based either on an individually performed plan for a specific patient on a planning system or a standard, published set of rules; a method of postimplant dosimetry; a method of assaying a representative sample of seeds for their activity; and a method of independently checking the results of the treatment plan. The centralized QA review will generate a report to be issued to the submitting institution within 30 days of the receipt of all required materials and data. The report will contain the following: 1. An analytical evaluation of the delineation of the gross target volume, clinical target volume, urethra, and rectum. 2. Isodose displays. 3. A dose–volume histogram of the prostate, a dose–surface histogram of the rectum and urethra, and a dose profile or trace along the center of the urethra. The following quantifiers associated with the dose–volume histogram will also be provided: 1. The volume of the prostate included within the surface defined by various reference doses (i.e., V200, V150, V100, and V80). 2. The dose, which defines a surface within the prostate that encompasses various percentages of the prostate volume (i.e., D100, D90, and D80). 3. The maximal dose to the urethra and rectal surface (i.e., the surface area of the urethra that receives ⬎250 Gy and the surface area of the rectum that receives ⬎100 Gy. 4. The target–volume ratio of the dose distribution (i.e., the volume encompassed by the reference isodose surface divided by the volume of the prostate). 5. A comparative evaluation of the implant with all other implants in the database in terms of the above quantifiers. RTOG P-0019 is the next RTOG protocol that involves a permanent implant in the prostate. This protocol combines external beam RT (i.e., 45 Gy to the regional lymphatics) and an 125I implant with a dose of 108 Gy (TG 43). To be eligible for this protocol, patients must have prostate-specific antigen values ⬍20 ng/mL and Gleason scores of 7 or lower. The QA for patients entered in this and subsequent prostate brachytherapy protocols will be performed by the RTOG Permanent Prostate Implant QA Center. The RTOG is currently attempting to convince all commercial suppliers of prostate brachytherapy software to meet its data transmission standards. Through its protocols for permanent

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prostate implants, the RTOG is establishing national guidelines of practice for this procedure. Develop IMRT standards. The RTOG will devote substantial resources toward meeting the challenges of developing IMRT as a tool to be used in the cooperative group setting. This may be the most important contribution that the RTOG will make in the next 5 years. IMRT has the potential of being a quantum leap forward in the use of ionizing RT for many disease sites. It contains the capabilities of both dose escalation without elongation of the period during which the treatment is delivered and structure avoidance. The RTOG can define the standards of clinical practice for this technology. IMRT technology will continue to develop and mature in the next 5 years in both treatment planning and treatment delivery. The Medical Physics Com-


mittee has taken several steps to begin to meet this challenge. The most important medical physics activity is the close interaction with the oncologists in defining the dose specification for IMRT. The definition, review, testing, and refinement process for IMRT dose specifications, which the RTOG has been doing for the past 9 months, will continue and will evolve to reflect developments in this technology. Generic specifications, which are independent of specific commercial systems, for institutions to participate in RTOG IMRT protocols will be developed, using the experience with 3D-CRT. IMRT protocols will be developed for treatment sites other than the head and neck. It is important that high clinical and dosimetric standards be established for IMRT to ensure that this technology can meet its substantial promise.