PROSTATE BED DELINEATION GUIDELINES FOR POSTOPERATIVE RADIOTHERAPY, ON BEHALF OF THE GFRU (FRANCOPHONE GROUP OF UROLOGICAL RADIOTHERAPY)

ABSTRACT Purpose Prostate bed (PB) irradiation is considered the standard post-operative treatment after radical prostatectomy (RP) for tumors with high-risk features and/or persistant PSA, or for salvage treatment in case of biological relapse. Four consensus guidelines have been published to standardize practices and reduce the inter-observer variability in PB delineation, however with discordant recommendations. In order to improve the reproducibility in the PB delineation, the Francophone Group of Urological Radiotherapy (GFRU – Groupe Francophone de Radiotherapie Urologique) worked to propose a new and more reproducible consensus guideline for PB clinical target volume (CTV) definition. Methods and Materials A four-step procedure was used. First, a group of 10 GFRU prostate experts evaluated the four existing delineation guidelines for post-operative radiotherapy (EORTC, FROGG, RTOG, and PMH) in order to identify divergent issues. Second, datasets of 50 magnetic resonance imaging (MRI) studies (25 after RP and 25 with an intact prostate gland) were analyzed to identify the relevant anatomical boundaries of the PB. Third, a literature review of surgical, anatomical, histological, and imaging data was performed to identify the relevant PB boundaries. Fourth, a final consensus on PB-CTV definition was reached among experts. Results Definitive limits of the PB-CTV delineation were defined, using easily visible landmarks on computed tomography scans (CT). The purpose was to ensure a better reproducibility of PB definition for any radiation oncologist even without experience in post-operative radiotherapy. Conclusions New recommendations for PB delineation based on simple anatomical boundaries and available as a CT image atlas are proposed by the GFRU. Improvement in uniformity in PB-CTV definition and treatment homogeneity in the context of clinical trials are expected.