Development and validation of a multi-institutional nomogram of outcomes for PSMA-PET–based salvage radiotherapy in recurrent prostate cancer.

355 Background: We aimed to develop and validate a multi-institutional nomogram of outcomes for PSMA-PET based salvage radiotherapy (sRT) following radical prostatectomy (RP) patients with recurrent or persistent prostate cancer (PCa). Methods: Data from detectable post-RP prostate-specific antigen (PSA) treated sRT without concurrent androgen-deprivation therapy (ADT) were obtained 11 academic institutions 5 countries. All had scan prior distant metastases on PET excluded this analysis. The freedom biochemical failure (FFBF) rate was estimated, predictive generated validated. Biochemical relapse (BR) defined as PSA nadir +0.2 ng/ml after sRT. Results: Overall, 1029 (training set n=821, external validation n=208) median follow-up 33 months included. On PSMA-PET, 427 (42%) 313 (30%) local nodal recurrences, respectively. Elective pelvic lymphatics irradiated in 368 (36%) patients. received the prostatic fossa receiving dose <66 Gy, 66-70 Gy >70 103 (10%), 551 (54%) 375 patients, Androgen deprivation given 325 (32%) multivariable Cox regression analysis, pre-SRT PSA, ISUP grade, pT stage, surgical margins, ADT use, recurrence PSMA associated FFBF. concordance index 0.7 FFBF validation. Conclusions: present an externally validated contemporary which can estimate individual patient guided Positive lymph nodes seem be new risk factor BR