Biologically effective dose values for prostate brachytherapy: effects on PSA failure and posttreatment biopsy results.

To analyze the effect of biologically effective dose (BED) values on prostate-specific antigen (PSA) failure and posttreatment biopsy. From 1990 to 2003, 1,377 patients had prostate brachytherapy alone (I-125 or Pd-103) (571), hormonal and brachytherapy (371), and trimodality therapy (hormonal, implant, and external beam) (435). Dose was defined as the D90 (dose delivered to 90% of the gland from the dose-volume histogram). Freedom from PSA failure (FFPF) at 10 years was 87%. The 10-year FFPF for BED<100, >100-120, >120-140, >140-160, <160-180, >180-200, and >200 were 46%, 68%, 81%, 85.5%, 90%, 90%, and 92%, respectively (p<0.0001). BED and Gleason score had the greatest effect, with p values of p<0.0001 in multivariate analysis. Posttreatment positive biopsy rate was 7% (31/446). The positive biopsy rates for BED100-120, >120-140, >140-160, >160-180, >180-200, and >200 were 24% (8/33), 15% (3/20), 6% (2/33), 6% (3/52), 7% (6/82), 1% (1/72), and 3% (4/131), respectively (p<0.0001). BED was the most significant predictor of biopsy outcome in multivariate analysis (p=0.006). Biologically effective dose equations provide a method of comparing different isotopes and combined therapies in the brachytherapy management of prostate cancer. The effects of BED on FFPF and posttreatment biopsy demonstrate a strong dose-response relationship.