Influence of pretreatment and treatment factors on intermediate to long-term outcome after prostate brachytherapy

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.

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 (125)I, 221 (10.4%) received (103)Pd and 719 (34.1%) received supplemental external beam irradiation combined with (103)Pd. 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.

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).

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.