International Journal of Radiation Oncology*Biology*Physics
Clinical InvestigationConsensus Guidelines for Delineation of Clinical Target Volume for Intensity-Modulated Pelvic Radiotherapy in Postoperative Treatment of Endometrial and Cervical Cancer
Introduction
Intensity-modulated radiotherapy (IMRT) enables the delivery of complex RT plans that previously could not be accomplished with conventional techniques, including the most sophisticated three-dimensional (3D) conformal RT (3D-CRT). Conventional 3D-CRT is accomplished with a set of fixed radiation beams that are shaped using the projection of the target volume and normally have a uniform intensity across the field. When appropriate, conventional fields can be modified by simple devices such as compensating filters or wedges. IMRT delivers optimized, nonuniform, radiation beam intensities to deliver highly conformal therapies, especially to targets that have complex shapes and/or concave regions.
The advantage IMRT has over 3D-CRT is also the greatest challenge facing the radiation oncology community—that is, defining the targets that need to be irradiated to accomplish the goals of therapy. This is particularly challenging in whole pelvic RT for gynecologic malignancies. Traditional conformal postoperative RT has delivered RT in a “four-field box” technique. The anteroposterior–posteroanterior portions of the field's lateral extents tend to be defined by the bony pelvis. The lateral fields often include the presacral space posteriorly, especially in cervical cancer; anteriorly, the field is defined by the external iliac lymph nodes. This traditional treatment volume has provided excellent tumor control with what is traditionally considered acceptable toxicity. However, these techniques, based on generic bony landmarks as surrogates for the clinical target volume (CTV), do not lend themselves to customized treatment planning using an individual patient's CTV and results in substantial irradiation of normal organs such as the small bowel, rectum, and bone marrow.
The use of IMRT provides the ability to confine the high-dose portions of the radiation fields to nontraditional shapes. It is generally considered that the CTV to be irradiated postoperatively for endometrial cancer and cervical cancer includes the draining lymphatics, parametrium, and upper vagina. The middle of the pelvis, in the postoperative situation, is often occupied by relatively radiosensitive small intestine. In addition, the rectum and bone marrow are not thought to be at risk of recurrence and hence are unnecessary to irradiate. IMRT has been shown to reduce normal tissue irradiation 1, 2, 3, 4, 5, 6 and has been associated with reduced acute 7, 8 and chronic (9) toxicity compared with conventional 3D-CRT.
Critical to the use of IMRT as a standard option for postoperative therapy for endometrial and cervical cancer is a clear understanding of the CTV definitions. In preparation for a prospective clinical trial (Radiation Therapy Oncology Group [RTOG] trial 0418), the RTOG led an international collaboration to define an atlas of target definitions for postoperative pelvic RT for endometrial and cervical cancer. This report provides the conclusions of this collaboration.
Section snippets
Methods and Materials
The RTOG elected to proceed with a prospective trial evaluating the role of IMRT in postoperative RT for endometrial and cervical cancer (RTOG 0418). The primary objective of the trial was to determine the transportability of IMRT to a multi-institutional setting. Secondary objectives included toxicity and disease control endpoints. In preparation for the activation of the trial, it was believed that an atlas would improve the ability to obtain the trial's primary objective. The RTOG
Results
The committee achieved a consensus CTV definition. The CTV should include the common, external, and internal iliac lymph node regions (Table 1). The upper 3.0 cm of the vagina and paravaginal soft tissue lateral to the vagina should also be included. For patients with cervical cancer, or endometrial cancer with cervical stromal invasion, it was also recommended that the CTV include the presacral lymph node region. Specific recommendations have been given for a bladder integrated target volume
Discussion
The use of IMRT for gynecologic malignancies has increased significantly in recent years (29). Interest in the application of IMRT for gynecologic cancer has been increasingly supported by retrospective analyses reporting favorable toxicity rates 7, 8, 9, 16, 17, 18 compared with conventional techniques. Moreover, the use of IMRT has not apparently compromised target coverage or the therapeutic results, because outcome data from several institutional series have been favorable 7, 9, 16, 17, 18,
Conclusion
Intensity-modulated RT is a promising development in RT, with a significant body of published data supporting its utility for gynecologic and other cancers. Additional careful study of this technique is warranted. The consensus guidelines presented in this report have standardized an important aspect of IMRT planning for postoperative treatment of cervical and endometrial cancer. It is imperative that new technology be investigated as carefully as any new therapy in oncology. The results of the
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Conflict of interest: none.