Predictors of toxicities and oncological outcomes following postoperative ablative radiotherapy (POPART) for biochemical recurrence

Background: Salvage radiotherapy to the prostate bed (PB) is the standard treatment for biochemical recurrence after radical prostatectomy. Emerging evidence supports hypofractionation, including Stereotactic Body Radiation Therapy (SBRT), in this setting. Predictive factors for toxicity, patient-reported outcomes (PROs) and biochemical recurrence following salvage SBRT to the PB are analyzed in this study. Materials and Methods: Patients with histologically confirmed prostate cancer, PSA 0.1–2.0 ng/mL, and no metastases on PSMA PET, received postoperative SBRT to the prostate bed (32.5 Gy in five fractions, every other day). Toxicity was assessed using CTCAE v5.0, while QoL was measured via ICIQ-SF, IIEF 5, and EPIC-CP questionnaires at baseline and follow-up, with MCID defined as changes > 0.5 SD. PSA levels were also measured to assess oncological outcomes. Statistical analyses included ANOVA, logistic and Cox regression models (p < 0.05 significant). Kaplan-Meier analysis estimated biochemical recurrence-free survival (BRFS). Results: Between April 2021 and September 2023, 100 patients (median age: 71) were treated with a median follow-up of 19.6 months (range: 3.5–42.4). Acute toxicity analysis showed no ≥ G2 GU events and 5 % G2 GI toxicity. Late toxicity included 6.4 % G2 GU events, 1.1 % G3 radiation cystitis, and 1.1 % G2 GI toxicity. Larger CTV and higher baseline bowel scores were predictors of acute G2 GI toxicity, while acute urinary incontinence MCID predicted late G2 GU toxicity. Higher bladder wall and penile bulb doses were associated with worse urinary and sexual outcomes. Biochemical recurrence occurred in 18 patients, with a median time of 10 months. ISUP grade was a significant predictor of recurrence, with lower BRFS rates in higher-grade tumors. Conclusions: SBRT to the PB is a feasible and well-tolerated approach with adequate biochemical control outcomes. Acute symptoms anticipated late side effects. Long-term follow-up and comparative trials are needed to strengthen the role of SBRT in this setting.