Objectives: To investigate the significance of the percentage of positive biopsy cores (PPBCs) in predicting the biochemical outcome in patients with low-risk prostate cancer undergoing brachytherapy or three-dimensional conformal external beam radiotherapy (3D-CRT). Methods: We retrospectively reviewed 360 patients with low-risk prostate cancer who had undergone low dose-rate brachytherapy (125I) or 3D-CRT from 1993 to 2006. Of the 360 patients, 189 had undergone 3D-CRT and 171 had undergone brachytherapy. The patients were stratified according to treatment modality and PPBCs (<34%, 34%-50%, >50%). Biochemical failure was defined by the 2006 Radiation Therapy Oncology Group-American Society for Therapeutic Radiology and Oncology, Phoenix Consensus Conference definition. Results: The median follow-up in the 3D-CRT and brachytherapy groups was 51 and 37 months, respectively. The number of patients who had a PPBCs of <34%, 34%-50%, and >50% in the 3D-CRT and brachytherapy cohorts was 154, 26, and 9 and 133, 25, and 15, respectively. The 5-year freedom from biochemical failure rate for 3D-CRT and brachytherapy was 95% and 96%, respectively; the corresponding median prostate-specific antigen nadirs were 0.7 and 0.3 ng/mL (P < .001). No significant differences were found in age, stage, Gleason score, or PPBCs between the 2 cohorts. Cox regression analysis showed that the pretreatment prostate-specific antigen level, stage, PPBCs, and treatment modality did not predict for the time to biochemical failure. When stratified by PPBCs, no significant difference in FFBF for either modality was seen. Conclusions: In patients with low-risk prostate cancer, brachytherapy and 3D-CRT remain excellent treatment choices, regardless of the tumor volume as estimated by the PPBCs. Longer follow-up and the recruitment of men with a greater volume of disease (>50% PPBCs) are needed to confirm these preliminary findings.
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