A comparison of early prostate-specific antigen decline between prostate brachytherapy and different fractionation of external beam radiation—Impact on biochemical failure

Abstract

PurposeThe aim of this study was to compare early prostate-specific antigen (PSA) decline patterns and PSA nadirs between low-dose-rate seed prostate brachytherapy (LDR-PB) and different fractionations of external beam radiotherapy (EBRT) and their predictive importance for biochemical failure (bF). Methods and MaterialsPatients with D'Amico low- or intermediate-risk prostate cancer who underwent a single-modality treatment without androgen deprivation were included in this study. Three different treatment groups were compared: (1) normofractionation EBRT up to 70.2–79.2 Gy/1.8–2.0 Gy, (2) LDR-PB, and (3) EBRT with hypofractionation 60 Gy/3 Gy daily or 5–7.25 Gy once a week over 9–5 weeks, to a total dose of 45–36.25 Gy, respectively. The log-rank test, Cox regression analysis, and nonparametric tests were used. ResultsWe analyzed 892 patients: the median followup for patients without bF was 84 months (interquartile range 60–102 months), with 12% of patients experiencing bF. The PSA decline within the first 15 months was generally exponential. LDR-PB showed a faster early exponential decline compared with EBRT treatments, but whether decline was fast or slow had no influence on recurrence. The only factors that were positive predictive factors in univariate and multivariate analyses were the time to nadir >48 months (median), PSA nadir <0.5 ng/mL, and <0.2 ng/mL (all p < 0.001). ConclusionsAlthough there are significant differences in early exponential PSA decline between different treatments, only the PSA nadir and longer time to nadir were predictive factors for bF.