Development and validation of contouring guidelines for post-cystectomy adjuvant radiation of bladder cancer.

Abstract

409 Background: Several organizations are developing clinical trials to evaluate adjuvant radiotherapy (RT) for bladder cancer patients at elevated risk of locoregional failure (LF). However, the clinical target volumes (CTVs) & organs at risk (OARs) for this treatment have not been defined in detail. Our purpose was to define multi-institutional consensus CTVs & OARs for male & female bladder cancer patients undergoing adjuvant RT in clinical trials. Methods: We convened a multi-disciplinary group of bladder cancer specialists from 9 centers in 3 countries. 5 radiation oncologists (ROs) & 7 urologists participated in the development of the proposed contours. The group proposed initial language for the CTVs & OARs and contoured them on CT scans of a male & female cystectomy patient with input from ≥ 1 urologist at each center. Using the binomial maximum-likelihood estimates method, we generated 95% level initial contours. We evaluated the contours for level of agreement using the Landis & Koch interpretation of the K statistic. Based on the initial contouring, the group updated its descriptions of the CTVs & OARs. To determine if the revised language produced consistent contours, the cystectomy bed (CB) contour was redrawn on the CT sets by an additional 5 ROs. Results: The group proposed that patients at elevated risk for LF with R0 resections should be treated to the pelvic nodes alone (internal/external iliac, distal common iliac & presacral) whereas patients with ≥ R1 resections should be treated to the pelvic nodes & CB. The group proposed the rectum, bowel space, bone marrow & urinary diversion as OARs. The level of agreement for the initial CTVs & OARs from the group varied substantially (Table). Consensus language to describe CTV & OAR structures where the initial contours varied was successfully developed. Contours & feedback from the validation group are being analyzed. Conclusions: Initial descriptions of CTVs & OARs have been successfully developed. External validation & feedback are pending. The results will be applicable to clinical trials of adjuvant RT in bladder cancer. [Table: see text]