NRG Oncology/RTOG Consensus Guidelines for Delineation of Clinical Target Volume for Intensity Modulated Pelvic Radiation Therapy in Postoperative Treatment of Endometrial and Cervical Cancer: An Update

Abstract

Purpose: Accurate target definition is critical for the appropriate application of radiation therapy. In 2008, the Radiation Therapy Oncology Group (RTOG) published an international collaborative atlas to define the clinical target volume (CTV) for intensity modulated pelvic radiation therapy in the postoperative treatment of endometrial and cervical cancer. The current project is an updated consensus of CTV definitions, with removal of all references to bony landmarks and inclusion of the para-aortic and inferior obturator nodal regions.

Methods and materials: An international consensus guideline working group discussed modifications of the current atlas and areas of controversy. A document was prepared to assist in contouring definitions. A sample case abdominopelvic computed tomographic image was made available, on which experts contoured targets. Targets were analyzed for consistency of delineation using an expectation-maximization algorithm for simultaneous truth and performance level estimation with kappa statistics as a measure of agreement between observers.

Results: Sixteen participants provided 13 sets of contours. Participants were asked to provide separate contours of the following areas: vaginal cuff, obturator, internal iliac, external iliac, presacral, common iliac, and para-aortic regions. There was substantial agreement for the common iliac region (sensitivity 0.71, specificity 0.981, kappa 0.64), moderate agreement in the external iliac, para-aortic, internal iliac and vaginal cuff regions (sensitivity 0.66, 0.74, 0.62, 0.59; specificity 0.989, 0.966, 0.986, 0.976; kappa 0.60, 0.58, 0.52, 0.47, respectively), and fair agreement in the presacral and obturator regions (sensitivity 0.55, 0.35; specificity 0.986, 0.988; kappa 0.36, 0.21, respectively). A 95% agreement contour was smoothed and a final contour atlas was produced according to consensus.

Conclusions: Agreement among the participants was most consistent in the common iliac region and least in the presacral and obturator nodal regions. The consensus volumes formed the basis of the updated NRG/RTOG Oncology postoperative atlas. Continued patterns of recurrence research are encouraged to refine these volumes.

Fig. 1.

Individual contour overlay and the 95% confidence interval contour for the pre-sacral region.

Fig. 2.

Para-aortic and common iliac nodal clinical target volumes (CTVs). (a) The superior portion of para-aortic nodal CTV (cyan) begins at or 1 to 1.5 cm above the left renal vessels. At this level, the inferior vena cava (IVC) is distended on the IV contrast scan (white arrow). The contour extends laterally abutting the psoas muscles (black arrowhead). (b) The distended IVC (white arrow) on the intravenous (IV) contrast scan is gradually included into the volume inferiorly. (c) There should not be a concavity to the contour in the space between the aorta and IVC in this region to assure coverage of the inter-aortocaval nodes. (d) The common iliac node CTV (blue) at the midportion of the chain should extend approximately 1 cm anterolateral to the common iliac artery (black arrow), along the iliopsoas muscle (asterisks). Also pictured is the presacral nodal CTV (magenta).

Fig. 3.

Para-aortic nodal clinical target volume (CTV) on intravenous (IV) contrast scan versus non–contrast scan. The superior para-aortic nodal CTVon (a) an IV contrast scan and (b) non–contrast scan. Inferior para-aortic nodal CTVon (c) an IV contrast scan and (d) a non–contrast scan. Note the difference in IVC distention on the contrast scan that requires a gradual inclusion of the IVC with margin compared with recommended expansions off the nondistended IVC and aorta on the contrast scan.

Fig. 4.

Presacral, internal and external iliac nodal clinical target volumes (CTVs). (a) The presacral nodal CTV (magenta) sits anterior to S1/S2 vertebral bodies and should be 1 to 1.5 cm wide, and it may encompass adjacent bowel if present, to account for motion of the bowel. (b) The insertion of the piriformis muscle (white arrows) on the sacrum marks the inferior extent of the presacral nodes. (c) The inferior extent of the external iliac nodal CTV (cyan) is seen either where the circumflex vessels originate from the external iliac vessels (blue arrow) or where external iliac vessels turn laterally to become the inguinofemoral vessels. (d) Similarly, the inferior extent of the internal iliac nodal CTV (yellow) should stop as the internal iliac vessels turn laterally to leave the pelvis. (e) Inferior to the external iliac CTV lays the circumflex node (black arrow), which is often enlarged, but it is rarely malignant, thus is not typically included. (f) The obturator vessels leave the pelvis through the obturator notch (black arrowheads), which marks the inferior extent of the obturator nodal CTV (green).

Fig. 5.

Use of internal target volume (ITVs). The vaginal ITV (blue) accounts for motion of the vaginal CTV (pink) in various states of bladder and rectal filling as show in in the upper, mid, and lower vagina (Fig. 5a-c) and on sagittal CT (Fig 5d). (a) The obturator nodal CTV (green) is carved out of bladder; however, an obturator nodal ITV (magenta) should also be considered, accounting for changes in bladder filling. (d) A sagittal view showing vaginal CTV and ITV. If ITVs are not used, then one should use a larger PTV to account for bladder and rectal filling.

Fig. 6.

Vaginal clinical target volume (CTV). (a-d) The vaginal CTV (pink) includes the proximal vagina and any remaining parametrial tissue, and it should extend laterally to the obturator CTV (green) or (b) to the medial aspect of the obturator internus muscle. (c) On coronal view, one can appreciate the lateral “ears” of the vaginal cuff that should be included and can extend superior to the vaginal apex (white arrow). (d) For routine cases, the urethra (yellow) is not at risk and can be carved out of the inferior, anterior extent of the vaginal CTV.