Salvage Radiotherapy for Rising Prostate-Specific Antigen Levels After Radical Prostatectomy for Prostate Cancer: Dose-Response Analysis

Purpose: To investigate the association between external beam radiotherapy (EBRT) dose and biochemical failure (BcF) of prostate cancer in patients who received salvage prostate bed EBRT for a rising prostate-specific antigen (PSA) level after radical prostatectomy. Methods and Materials: We evaluated patients with a rising PSA level after prostatectomy who received salvage EBRT between July 1987 and October 2007. Patients receiving pre-EBRT androgen suppression were excluded. Cox proportional hazards models were used to investigate the association between EBRT dose and BcF. Dose was considered as a numeric variable and as a categoric variable (low, <64.8 Gy; moderate, 64.8-66.6 Gy; high, >66.6 Gy). Results: A total of 364 men met study selection criteria and were followed up for a median of 6.0 years (range, 0.1-19.3 years). Median pre-EBRT PSA level was 0.6 ng/mL. The estimated cumulative rate of BcF at 5 years after EBRT was 50% overall and 57%, 46%, and 39% for the low-, moderate-, and high-dose groups, respectively. In multivariable analysis adjusting for potentially confounding variables, there was evidence of a linear trend between dose and BcF, with risk of BcF decreasing as dose increased (relative risk [RR], 0.77 [5.0-Gy increase]; p = 0.05). Compared with the low-dose group, there was evidence of a decreased risk of BcF for the high-dose group (RR, 0.60; p = 0.04), but no difference for the moderate-dose group (RR, 0.85; p = 0.41). Conclusions: Our results suggest a dose response for salvage EBRT. Doses higher than 66.6 Gy result in decreased risk of BcF.