Clinicopathologic Predictors of PSMA-PET Detection, Recurrence Pattern, and Biochemical Outcome Following Salvage Radiotherapy After Radical Prostatectomy

Purpose: Biochemical recurrence (BCR) after radical prostatectomy (RP) presents heterogeneous recurrence patterns and variable outcomes following salvage radiotherapy (sRT). We evaluated clinicopathologic determinants of PSMA-PET/CT detection, anatomical recurrence distribution, and biochemical disease-free survival (bDFS) following PSMA-PET-guided sRT. Methods: This retrospective single-institution study included 140 patients with BCR after RP who underwent Ga-PSMA-PET/CT prior to sRT with or without androgen deprivation therapy. PSMA-PET-positive findings were categorized as prostate bed only (PBO) or pelvic nodal involvement with or without the prostate bed (PLNI). Receiver operating characteristic (ROC) analysis, logistic regression, and Cox proportional hazards models were employed. Results: PSMA-PET detected locoregional recurrence in 77/140 patients (55%). On multivariable analysis, PSA at recurrence (OR=2.07; p=0.003) and age (OR=1.07; p=0.016) were the sole independent predictors of PSMA-PET positivity. ROC analysis yielded AUC=0.74 (optimal threshold of 0.58 ng/mL). Among PSMA-positive patients, PBO was associated with a longer time to BCR (tBCR) (37.5 versus 15 months; p=0.006). Seminal vesicle invasion (SVI) and pT-stage predicted PLNI on univariable analysis. Among 124 of 140 evaluable patients (median follow-up 31 months), estimated bDFS at 24, 36, and 60 months was 89.7%, 80.2%, and 54.1%, respectively. SVI (HR=2.39; p=0.031), EPE (HR=2.82; p=0.012), pT-stage (HR=1.64; p=0.021), and pN-stage (HR=1.83; p=0.045) were associated with increased failure on univariable Cox regression, though none retained independent significance. Conclusion: PSA burden and age independently predicted PSMA-PET detection. Recurrence patterns reflected disease behavior, as PBO was associated with longer tBCR. Adverse pathologic features were associated with pelvic nodal disease and reduced biochemical control; none remained independently predictive.