Optimized Prostate Brachytherapy Minimizes the Prognostic Impact of Percent of Biopsy Cores Involved With Adenocarcinoma

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Abstract
A higher percent of positive biopsy cores predicts poor biochemical failure-free survival. The highest dose covering at least 90% of the prostate is a standard method of measuring implant quality. We tested the hypothesis that the percentage of positive biopsy cores loses its adverse prognostic impact in patients who receive implants with a highest dose covering at least 90% of the prostate of 100% or greater of the prescription dose. A total of 568 patients with intermediate to high risk adenocarcinoma of the prostate who were previously treated with brachytherapy in a prospective, randomized study were evaluated. The relationship between the percentage of positive biopsy cores, the highest dose covering at least 90% of the prostate and biochemical failure was examined. At a median followup of 50 months the rate of 5-year biochemical failure-free survival was 87% for the entire group and 92% vs 81% for patients with less than 50% vs 50% or greater positive biopsy cores (log rank p = 0.009). The mean highest dose covering at least 90% of the prostate was statistically lower in failing vs nonfailing cases (p = 0.03). Gleason score, prostate specific antigen, 50% or greater positive biopsy cores and the highest dose covering at least 90% of the prostate were the only statistically significant predictive factors for biochemical failure-free survival on multivariate Cox regression analysis. When regression analysis was restricted to the 237 patients who received implants with a highest dose covering at least 90% of the prostate of 100% or greater, 50% or greater positive biopsy cores lost predictive value but prostate specific antigen and Gleason score remained independent prognostic factors. A total of 50% or greater positive biopsy cores is an independent predictor of poor biochemical failure-free survival in patients treated with brachytherapy. High quality prostate brachytherapy, defined by a highest dose covering at least 90% of the prostate of 100% or greater, minimize the adverse effect of 50% or greater positive biopsy cores on time to biochemical failure.

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