Influence of Pretreatment and Treatment Factors on Intermediate to Long-Term Outcome After Prostate Brachytherapy

Purpose: We describe how treatment factors influence biochemical freedom from failure, local control, freedom from metastasis and cause specific survival in patients treated with prostate brachytherapy. Materials and Methods: We followed 2,111 men who underwent brachytherapy a median of 6 years (range 2 to 17). Median prostate specific antigen was 7 ng/ml. Of the men 1,455 (68.9%) had clinical stage T2a or less and 1,428 (67.6%) had Gleason score less than 7. A total of 1,171 patients (55.5%) received I-125, 221 (10.4%) received Pd-103 and 719 (34.1%) received supplemental external beam irradiation combined with Pd-103. Post-implant dosimetry was done 30 days after implantation with doses converted to the biologically effective dose. Prostate biopsy was done 2 years after permanent prostate brachytherapy in 586 men (27.8%). Survival functions were determined by the Kaplan-Meier method and Cox regression with proportions tested by the log rank test. Results: The 12-year biochemical freedom from failure rate was 78.6%, and stage, Gleason score, prostate specific antigen and biologically effective dose were significant predictors (p = 0.007, <0.001, 0.005 and <0.001, respectively). In 964 patients at low risk the biochemical freedom from failure rate was 88.1% and significant predictors were hormonal therapy (p = 0.030), prostate specific antigen (p = 0.026) and biologically effective dose (p = 0.003). In 499 patients at intermediate risk the biochemical freedom from failure rate was 79.2% with biologically effective dose a significant predictor (p < 0.001). In 648 men at high risk the biochemical freedom from failure rate was 67% and significant predictors were hormonal therapy, Gleason score and biologically effective dose (p = 0.036, <0.001 and 0.012, respectively). The local failure rate was 7.3% with biologically effective dose a significant predictor (p <0.001). Prostate biopsy was positive in 21 of 121 cases (21.5%) for a biologically effective dose of 150 Gy2 or less, in 14 of 248 (5.6%) for greater than 150 to 200 Gy2 and in 3 of 193 (1.6%) for greater than 200 Gy2 (p <0.001). The 12-year freedom from metastasis rate was 95.2% with Gleason score a significant predictor (p <0.001). Cause specific survival at 12 years was 94.5% with Gleason score and biologically effective dose significant predictors (p <0.001 and 0.027, respectively). Conclusions: Permanent prostate brachytherapy yields excellent long-term oncologic outcomes. High biologically effective dose may need to be delivered to achieve successful biochemical freedom from failure, local control and cause specific survival.