Unusually high prostate-specific antigen bounce after prostate brachytherapy: Searching for etiologic factors

PURPOSE: Determine whether fat distribution, body mass index, or clinical and dosimetric factors are associated with prostate specific antigen (PSA) bounce (PSAb) of >= 1.6 ng/mL in patients treated with permanent seed I-125 prostate brachytherapy (PB). METHODS AND MATERIALS: We identified 23 patients with a PSAb of >= 1.6 ng/mL. For each patient with a bounce, at least one control with similar age (age +/- 2 years, n = 31) was identified. Control patients had to have no bounce (<= 0.2 ng/mL) and a most recent PSA of <1 ng/mL. CT at Day 30 after PB was used to determine the volume of subcutaneous adipose tissue, visceral adipose tissue, and peri-prostatic fat. Univariate and multivariate logistic models were used to assess the association between PSAb and adipose tissue distribution and clinical and dosimetric factors. RESULTS: Mean patient age was 62.3 +/- 5.3 years. Mean PSAb height was 2.7 +/- 0.8 ng/mL, and mean time to bounce was 9.6 +/- 4 months. More than 90% of the patients reached a PSA nadir before PSAb within 12 months post-PB. Patients showing PSAb were more likely to have a Tic disease vs. T2a (odds ratio = 18.87; 95% confidence interval: 2.32-454.55; p = 0.019) and a lower seed activity per cc of prostate volume (odds ratio = 0.02; 95% confidence interval = 0.42-2.22; p = 0.026). Neither fat distribution nor body mass index was associated with PSAb (p = 0.11-0.597). CONCLUSIONS: Clinical and dosimetric factors play a role in PSAb of >= 1.6 ng/mL. Fat distribution is not associated with a PSAb. There is presently no satisfactory theory to explain the etiology of PSAb. (C) 2013 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.