Prostate Bed Delineation Guidelines for Postoperative Radiation Therapy: On Behalf Of The Francophone Group of Urological Radiation Therapy

Abstract

Prostate bed (PB) irradiation is considered the standard postoperative treatment after radical prostatectomy (RP) for tumors with high-risk features or persistent prostate-specific antigen, or for salvage treatment in case of biological relapse. Four consensus guidelines have been published to standardize practices and reduce the interobserver variability in PB delineation but with discordant recommendations. To improve the reproducibility in the PB delineation, the Francophone Group of Urological Radiotherapy (Groupe Francophone de Radiothérapie Urologique [GFRU]) worked to propose a new and more reproducible consensus guideline for PB clinical target volume (CTV) definition. A 4-step procedure was used. First, a group of 10 GFRU prostate experts evaluated the 4 existing delineation guidelines for postoperative radiation therapy (European Organization for Research and Treatment of Cancer; the Faculty of Radiation Oncology Genito-Urinary Group; the Radiation Therapy Oncology Group; and the Princess Margaret Hospital) to identify divergent issues. Second, data sets of 50 magnetic resonance imaging studies (25 after RP and 25 with an intact prostate gland) were analyzed to identify the relevant anatomic boundaries of the PB. Third, a literature review of surgical, anatomic, histologic, and imaging data was performed to identify the relevant PB boundaries. Fourth, a final consensus on PB CTV definition was reached among experts. 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 postoperative radiation therapy. New recommendations for PB delineation based on simple anatomic 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.