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Salvage radiotherapy guided by functional imaging for macroscopic local recurrence following radical prostatectomy: A multicentric retrospective study.

251 Background: For prostate cancer (Pca), salvage radiotherapy (sRT) with or without androgen deprivation therapy (ADT) is currently the only curative treatment option in case of post-radical prostatectomy (RP) biochemical relapse (BR). Functional imaging techniques have shown that macroscopic recurrence (MR) in the prostate bed (PB) are frequent. In this study, we aimed to assess efficacy and safety of sRT in patients with MR inside the PB proven by functional imaging. Methods: A multicenter retrospective study was conducted in 16 European centers. Patients were included if they displayed BR after RP for Pca, with MR only in the PB proven by functional imaging. All patients had to be eligible for sRT. The overall population was divided along 4 groups according to the delivered treatment: dose escalation on MR (A), dose escalation on PB (B), double dose escalation MR+PB (C), no dose escalation (D). The primary endpoint was progression-free survival (PFS). Secondary outcomes included the metastasis-free survival (MFS), biochemical PFS (bPFS) and overall survival (OS). Grade ≥2 genito-urinary (GU) and gastro-intestinal (GI) acute and late toxicities were collected. Results: Between January 2000 and December 2019, 363 patients with isolated MR after RP for Pca were treated by sRT. The median pre-sRT PSA level was 0.63ng/mL (range, 0.2-23.6). At the time of BR, 266 (73%) patients presented MR in the PB proven by magnetic resonance imaging, and 110 (30%) by positron emission tomography. The median follow-up was 53.6 months (range, 47.52; 58.32). The 5-year PFS and MFS were 70% (95%CI [63.8-75.4]) and 83.7% (95%CI [78.4-87.8]), respectively. Grade ≥2 GU and GI late toxicities were found in 43 (12%) and 11 (3%) patients, respectively. A 5-year PFS benefit was highlighted for groups A, B and C (313 patients) when the MR dose was ≥72Gy: 72,8% (95%CI 64.6-79.4) versus 60.3% (95%CI 48,4-70,3), p = 0.03. Conclusions: In a modern series integrating functional imaging data, we confirmed that sRT is effective in the event of MR inside the PB, with an acceptable toxicity profile. Prospective data should further investigate the correlation between MR-targeted dose escalation and PFS.