Presenter(s)
A. Sasse1, S. Lakshmi Narayanan Akila2, A. Liu1, Z. Chalmers3, J. Cowan4, B. Raizenne5, W. S. Chen1, E. Pan6, I. Kouchkovsky6, E. Maldonado6, X. Zhu7, R. Bose6, J. C. Hong2, P. Carroll8, and S. N. Seyedin2; 1UCSF Department of Radiation Oncology, San Francisco, CA, 2University of California, San Francisco, Department of Radiation Oncology, San Francisco, CA, 3UCSF Bakar Precision Medicine Cancer Center, San Francisco, CA, United States, 4University of California San Francisco, Department of Urology, San Francisco, CA, 5University of California, San Francisco, Department of Urology, San Francisco, CA, 6UCSF Department of Genitourinary Medical Oncology, San Francisco, CA, 7University of California, San Francisco, Division of Hematology/Oncology, Department of Medicine, San Francisco, CA, 8Department of Urology, University of California San Francisco, San Francisco, CA
Purpose/Objective(s): Men with biochemical recurrence (BCR) after radical prostatectomy (RP) commonly receive salvage radiotherapy (SRT) with concurrent androgen deprivation therapy (ADT). Prior randomized trials evaluating SRT dose escalation did not incorporate ADT, and it remains unclear whether higher prostate bed doses improve outcomes when delivered with concurrent ADT. We hypothesized that SRT dose escalation does not significantly reduce post-radiation failure in patients treated with ADT.
Materials/Methods: We retrospectively identified 193 men with pT2–3N0/X, non-metastatic prostate cancer who developed BCR (PSA >0.2 ng/mL) after RP and received SRT with concurrent ADT from 2000–2023. Patients with <3 months follow-up, prior adjuvant RT, or radiographic recurrence at the time of SRT were excluded. Patients were stratified by prostate bed dose: low dose (<70 Gy, n=80) versus high dose (=70 Gy, n=113). Covariates included time from RP to SRT, ADT type and duration, and pelvic nodal irradiation. The primary endpoint was progression, defined as biochemical failure (PSA =0.4 ng/mL) and/or imaging-confirmed recurrence after SRT. Outcomes were estimated using Kaplan–Meier methods with log-rank testing and multivariable Cox regression. Subgroup analysis was performed by PORTOS genomic classifier.
Results: With a median follow-up of 107 months, 193 patients were evaluable. Most had Grade Group 2 disease (40%), pT3a stage (53%), and positive margins (36%), with a median age of 63 years. At SRT, the median interval from RP was 51 months, median PSA was 0.25 ng/mL, and mean ADT duration was 6.3 months. Median prostate bed dose was 70 Gy (range, 60–80.3 Gy). The 7-year cumulative incidence of post-SRT failure was 33.5%. Progression at 7 years did not significantly differ between dose groups (42% low dose vs 28% high dose, p=0.16). On multivariable analysis, radiation dose was not associated with progression (HR 1.47, 95% CI 0.84–2.59; p=0.18). Among patients with imaging-confirmed recurrence, only five developed isolated prostate bed failure, three of whom received <70 Gy. Patterns of localized (10% vs 5%, p = 0.48), pelvic nodal (19% vs 21%, p = 0.86), non-regional nodal (10% vs 11%, p =0.91) and distant relapse (26% vs 34%, p=0.45) were similar between (low vs high dose) cohorts. Stratification by PORTOS (low n=71; high n=25) and dose did not demonstrate differences in progression (p=0.95).
Conclusion: Among men receiving SRT with concurrent ADT, prostate bed doses <70 Gy were not associated with inferior progression or increased gross local recurrence. PORTOS did not identify a subgroup benefiting from dose escalation, though analyses were limited by small numbers of high PORTOS patients. Future studies will aim to evaluate alternative dose thresholds.