Purpose: To investigate the biochemical control rates and survival for Gleason score 7-10 prostate cancer patients undergoing permanent prostate brachytherapy as a function of the biologic effective dose (BED).
Methods and materials: Six centers provided data on 5,889 permanent prostate brachytherapy patients, of whom 1,078 had Gleason score 7 (n = 845) or Gleason score 8-10 (n = 233) prostate cancer and postimplant dosimetry results available. The median prostate-specific antigen level was 7.5 ng/mL (range, 0.4-300). The median follow-up for censored patients was 46 months (range, 5-130). Short-term hormonal therapy (median duration, 3.9 months) was used in 666 patients (61.8%) and supplemental external beam radiotherapy (EBRT) in 620 (57.5%). The patients were stratified into three BED groups: <200 Gy (n = 645), 200-220 Gy (n = 199), and >220 Gy (n = 234). Biochemical freedom from failure (bFFF) was determined using the Phoenix definition.
Results: The 5-year bFFF rate was 80%. The bFFF rate stratified by the three BED groups was 76.4%, 83.5%, and 88.3% (p < 0.001), respectively. Cox regression analysis revealed Gleason score, prostate-specific antigen level, use of hormonal therapy, EBRT, and BED were associated with bFFF (p < 0.001). Freedom from metastasis improved from 92% to 99% with the greatest doses. The overall survival rate at 5 years for the three BED groups for Gleason score 8-10 cancer was 86.6%, 89.4%, and 94.6%, respectively (p = 0.048).
Conclusion: These data suggest that permanent prostate brachytherapy combined with EBRT and hormonal therapy yields excellent bFFF and survival results in Gleason score 7-10 patients when the delivered BEDs are >220 Gy. These doses can be achieved by a combination of 45-Gy EBRT with a minimal dose received by 90% of the target volume of 120 Gy of (103)Pd or 130 Gy of (125)I.