Clinical Investigation
Consensus Guidelines for Delineation of Clinical Target Volume for Intensity-Modulated Pelvic Radiotherapy for the Definitive Treatment of Cervix Cancer

https://doi.org/10.1016/j.ijrobp.2009.10.075Get rights and content

Purpose

Accurate target definition is vitally important for definitive treatment of cervix cancer with intensity-modulated radiotherapy (IMRT), yet a definition of clinical target volume (CTV) remains variable within the literature. The aim of this study was to develop a consensus CTV definition in preparation for a Phase 2 clinical trial being planned by the Radiation Therapy Oncology Group.

Methods and Materials

A guidelines consensus working group meeting was convened in June 2008 for the purposes of developing target definition guidelines for IMRT for the intact cervix. A draft document of recommendations for CTV definition was created and used to aid in contouring a clinical case. The clinical case was then analyzed for consistency and clarity of target delineation using an expectation maximization algorithm for simultaneous truth and performance level estimation (STAPLE), with kappa statistics as a measure of agreement between participants.

Results

Nineteen experts in gynecological radiation oncology generated contours on axial magnetic resonance images of the pelvis. Substantial STAPLE agreement sensitivity and specificity values were seen for gross tumor volume (GTV) delineation (0.84 and 0.96, respectively) with a kappa statistic of 0.68 (p < 0.0001). Agreement for delineation of cervix, uterus, vagina, and parametria was moderate.

Conclusions

This report provides guidelines for CTV definition in the definitive cervix cancer setting for the purposes of IMRT, building on previously published guidelines for IMRT in the postoperative setting.

Introduction

Intensity-modulated radiotherapy (IMRT) is being increasingly explored as a means to reduce normal tissue toxicity in cervix cancer with or without treatment intensification (such as extended-field radiotherapy or concomitant boost) 1, 2, 3, 4, 5, 6. Reductions in acute and late toxicities with the use of IMRT have been reported in conjunction with low rates of in-field failures2, 3, 7. Accurate target definition is vitally important to ensure the target is not under-treated and to limit the dose to surrounding normal tissues. There are published guidelines on clinical target volume (CTV) definitions for a number of tumor sites including the postoperative gynecological and prostatectomy setting 8, 9. However, CTV definitions for IMRT for the radical treatment of cervix cancer remain variable within the literature2, 3, 5, 6, 10. The amount of organ motion, tumor regression, and deformation that cervix cancer patients demonstrate is more substantial than in prostate cancer 11, 12, 13, 14, 15, 16, 17, 18. These complex intrapelvic organ dynamics imply greater caution when highly conformal radiotherapy (such as IMRT) is used for this site than for prostate cancer. In order for IMRT to be delivered safely, adequate planning tumor volume (PTV) margins are necessary to account for CTV motion.

The aim of this report is to provide consensus guidelines for defining CTV for the intact cervix in order to achieve safe clinical IMRT practice in preparation for a planned Radiation Therapy Oncology Group (RTOG) Phase 2 clinical trial. These guidelines would supplement currently published consensus guidelines on postoperative IMRT for endometrial and cervix cancer (9).

Section snippets

Methods and Materials

A proposal for a prospective RTOG trial evaluating the role of IMRT in the definitive cervix cancer setting was the impetus behind the development of these guidelines. Representatives from the following groups participated in the Gyn IMRT Consortium: RTOG; National Cancer Institute of Canada; Japan Clinical Oncology Group; and European Society of Therapeutic Radiology and Oncology.

An electronic survey among Consortium members was undertaken prior to the June 2008 RTOG meeting to determine

Results

A total of 16 members from the Consortium were surveyed, with a response rate of 75% (12/16). There was general consensus on the structures to be included in the CTV (such as GTV, cervix, uterus, parametria, vagina, and regional lymph nodes) but less agreement regarding the definition of these structures for the purposes of contouring. All respondents agreed that the lateral boundary of parametria should be at the pelvic sidewall and that the medial boundary of parametria should abut the GTV,

Discussion

Traditional whole-pelvis radiotherapy fields based on bony landmarks encompasses targets within the pelvis with little sparing of OAR. The benefit of these large treatment volumes is that geographical miss is minimized. In the era of more conformal treatment, where target delineation becomes critical, one of the major difficulties with pelvic IMRT for the radical treatment of cervix cancer lies in the definition of the CTV components. While there is general agreement on what constitutes the

Conclusions

This is the first consensus document attempting to clarify target definitions for whole-pelvis IMRT for the intact cervix. It was felt that clear target definition guidelines would be useful in achieving consistency across different treatment centers. This report does not attempt to address issues of minimizing organ motion or adaptation to organ motion or tumor regression. The value of this document lies in providing groundwork for safe practice, building on previously published guidelines for

Acknowledgment

The names of the radiation oncologists who contributed to this work as members of the Gyn IMRT Consortium are listed in the Addendum to this article.

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