Oligorecurrent nodal prostate cancer: Radiotherapy quality assurance of the randomized PEACE V-STORM phase II trial

PURPOSE: Aim of this study is to report the results of the radiotherapy quality assurance program of the PEACE V-STORM randomized phase II trial for pelvic nodal oligorecurrent prostate cancer (PCa). MATERIAL AND METHODS: A benchmark case (BC) consisting of a postoperative case with 2 nodal recurrences was used for both stereotactic body radiotherapy (SBRT, 30 Gy/3 fx) and whole pelvic radiotherapy (WPRT, 45 Gy/25 fx + SIB boost to 65 Gy). RESULTS: BC of 24 centers were analyzed. The overall grading for delineation variation of the 1st BC was rated as 'UV' (Unacceptable Variation) or 'AV' (Acceptable Variation) for 1 and 7 centers for SBRT (33%), and 3 and 8 centers for WPRT (46%), respectively. An inadequate upper limit of the WPRT CTV (n = 2), a missing delineation of the prostate bed (n = 1), and a missing nodal target volume (n = 1 for SBRT and WPRT) constituted the observed 'UV'. With the 2nd BC (n = 11), the overall delineation review showed 2 and 8 'AV' for SBRT and WPRT, respectively, with no 'UV'. For the plan review of the 2nd BC, all treatment plans were per protocol for WPRT. SBRT plans showed variability in dose normalization (Median D90% = 30.1 Gy, range 22.9-33.2 Gy and 30.6 Gy, range 26.8-34.2 Gy for nodes 1 and 2 respectively). CONCLUSIONS: Up to 46% of protocol deviations were observed in delineation of WPRT for nodal oligorecurrent PCa, while dosimetric results of SBRT showed the greatest disparities between centers. Repeated BC resulted in an improved adherence to the protocol, translating in an overall acceptable contouring and planning compliance rate among participating centers.