Relationship between percent positive biopsies and biochemical outcome after permanent interstitial brachytherapy for clinically organ-confined carcinoma of the prostate gland.

PURPOSE: Recently, the percentage of positive prostate biopsies has been reported to be statistically significant in predicting the biochemical outcome after either radical prostatectomy or 3-dimensional conformal external beam radiotherapy. In this study, we evaluated the impact of the percentage of positive prostate biopsies in predicting the 5-year biochemical outcome for patients with clinically organ-confined prostate cancer undergoing permanent interstitial brachytherapy. METHODS AND MATERIALS: Two hundred sixty-two hormone naive patients underwent transperineal ultrasound-guided permanent prostate brachytherapy with generous periprostatic margins, using either 103Pd or 125I for clinical T1b/T2b NXM0 (1997 AJCC) adenocarcinoma of the prostate gland from April 1995 to October 1999. No patient was lost to follow-up. The actual percentage of positive biopsies (number of positive biopsies/total number of biopsies) was determinable for 255 of the 262 patients. Of the evaluated cases, 133 patients were implanted with 103Pd and 122 patients with 125I. The median patient age was 68 years (range 48-81). The median follow-up was 38.6 months (range 6-73). Follow-up was calculated from the day of implantation. Patients were stratified by the percentage of positive biopsies into the following groups: <34%, 34-50%, and >50%. Additional clinical parameters evaluated included patient age, clinical T-stage, Gleason score, pretreatment prostate specific antigen (PSA), risk group, and prostate volume. Low-risk patients were staged as clinical T1c/T2a, Gleason score < or =6, and pretreatment PSA < or =10 ng/mL, intermediate-risk patients presented with one unfavorable prognostic parameter, and high-risk patients presented with two or more unfavorable prognostic parameters (clinical stage T2b, PSA >10 ng/mL, Gleason score > or =7). Treatment parameters included the use of supplemental external beam radiation and choice of isotope. Biochemical disease-free survival was defined by the American Society of Therapeutic Radiation and Oncology consensus definition.
RESULTS: For the 255 evaluated patients, the 5-year actuarial biochemical no evidence of disease survival rate was 92.5%. For patients with low, intermediate, and high-risk disease, 95.8%, 98.1%, and 79.4% of patients were free of biochemical failure, respectively. When each risk group was stratified into the percent positive biopsy categories of <34%, 34-50%, and >50%, no statistical difference was found in biochemical outcome for the biopsy subgroups. In multivariate analysis, none of the clinical or treatment parameters predicted for failure in the low-risk group; only Gleason score was predictive for intermediate-risk patients and only PSA for high-risk patients. In the overall population, PSA and Gleason score were both found to be predictors of biochemical failure, but not risk group, clinical stage, or percentage of positive biopsies. There was no significant dependence between the percent positive biopsy group and the Kaplan-Meier biochemical survival rates for any of the various subgroups of clinical and treatment parameters, except for clinical stage T1c-T2a (p = 0.006). The median postimplant PSA was 0.2 ng/mL for patients with either low-risk disease or <34% positive biopsies and 0.1 ng/mL for all other risk groups or percent positive biopsy subgroups.
CONCLUSION: Although a significant trend was found for biochemical failure with increasing percent positive biopsies in the overall population, our results suggest that the percentage of positive biopsies is not statistically significant in predicting the 5-year biochemical disease-free outcome for patients with low, intermediate, and high-risk disease undergoing permanent prostate brachytherapy. Only the Gleason score in intermediate-risk patients and the pretreatment PSA level in high-risk patients was predictive of biochemical failure. We believe this relative lack of significance for the percentage of positive biopsies is a result of dose escalation far exceeding other radiotherapy modalities and the ability to aggressively treat the periprostatic region compared with radical prostatectomy by way of the accurate placement of periprostatic seeds.