Outcomes and Prediction Models for Exclusive Prostate Bed Salvage Radiotherapy among Patients with Biochemical Recurrence after Radical Prostatectomy

SIMPLE SUMMARY: Exclusive prostate bed salvage radiotherapy (SRT) without androgen deprivation therapy provides excellent treatment outcomes for selected patients with an increasing PSA after radical prostatectomy. We found that two risk factors, pre-SRT PSA and PSA-doubling time (PSA-DT), were shown to be predictive for clinical progression. According to the risk classification system proposed in the present study, men with a pre-SRT PSA < 0.45 ng/mL and PSA-DT > 8 months for post-prostatectomy biochemical recurrence (BCR) could be classified as “low risk” for recurrence or metastasis following SRT alone. Further prospective, multicenter studies are needed to validate these definitions. Nevertheless, individualized treatment decisions could be tailored based on these prediction models. ABSTRACT: Background: The addition of androgen-deprivation therapy (ADT) or pelvic radiation to prostate bed salvage radiotherapy (SRT) has been debated for prostate cancer patients with biochemical recurrence (BCR) after radical prostatectomy. This study aimed to assess the outcomes and propose prediction models for exclusive prostate bed SRT. Methods: This is a prospective observational cohort study with patients who underwent SRT with a pre-SRT PSA < 1.5 ng/mL after radical prostatectomy. Patients were treated with 70-Gy SRT to the prostate bed exclusively. Kaplan–Meier survival analyses and Cox regression analyses were applied for depicting and predicting BCR-free survival, ADT-free survival, and metastasis-free survival (MFS). Regression-based coefficients were used to develop nomograms. Results: A total of 105 patients were included and 91 patients were eligible. The median follow-up period was 39 months. The 5-year BCR-free survival, ADT-free survival, and MFS were 37%, 50%, and 66%, respectively. Multivariable analysis showed that a pre-SRT PSA < 0.45 ng/mL was the only independent factor associated with longer BCR-free survival (p = 0.034), while a PSA-DT > 8 months had better ADT-free survival (p = 0.008). Patients with a PSA-DT > 8 months showed a 100% MFS and a 43% 5-year absolute benefit in MFS than a PSA-DT ≤ 8 months. All patients with a pre-SRT PSA < 0.45 ng/mL and PSA-DT > 8 months were free from subsequent ADT and any metastasis. Conclusions: In patients with a PSA < 0.45 ng/mL and PSA-DT > 8 months for post-prostatectomy BCR, prostate bed SRT provided excellent outcomes without the need for concomitant ADT or pelvic radiotherapy.