Factors associated with late local failure and its influence on survival in men undergoing prostate brachytherapy

To determine the factors associated with a positive post-treatment prostate biopsy (PB) and the effects of local failure on biochemical control and cause-specific survival (CSS) in men receiving prostate brachytherapy.

Of 545 men with post-implant PB, 484 were routine (median 24 months) while 61 (median 55 months) were for cause. 114 had a repeat PB for rising PSA. Initial mean PSA was 10.5 ng/ml (±13.9) while 244 (44.8%), 202 (37.1%) and 99 (18.2%) had low, intermediate or high-risk disease. Treatments were implant only in 287 (52.7%), and implant with androgen deprivation therapy (ADT) ± external beam in 258. Radiation doses were converted to the biologically equivalent dose (BED). Final biopsy results were the last biopsy performed on that patient. Associations for the first and final biopsies with PSA, clinical stage (CS), Gleason grade group, time on hormone therapy (ADT) and BED were determined by ANOVA, chi-square and binary linear regression. Freedom from Phoenix failure (FFPF) and cause-specific survival were estimated by Kaplan Meier method and Cox proportions hazards.

After a median of 11.4 years the first and final biopsy were positive in 10.8% and 8.8%, respectively. Significant linear regression associations with first positive PB were ADT (p = 0.005), CS (p = 0.044) and BED (p = 0.030) while only BED (p < 0.001) was significant for the final PB. Positive biopsy occurred in 21/112 (18.8%), 16/230 (7.0%) and 3/182 (1.6%) for BED ≤150, >150-200 and >200 Gy (p < 0.001), and in 29/261 (11.1%) for BED (median) ≤185 Gy vs. 5/263 (1.9%) for > 185 Gy (OR 4.2, p < 0.001). 15-year FFPF was 75.6 vs. 17.5% and cause-specific survival was 94.2 vs. 75.5% for negative vs. positive biopsy.

Higher radiation doses are associated with 1.9% late local failure following prostate brachytherapy. A negative post-implant PB is associated with superior FFPF and decreased prostate cancer mortality.