Body Fat Distribution, Waist Circumference and Body Mass Index in Permanent Seed Prostate Brachytherapy

Abstract

Purpose: Recent studies have shown that obesity is associated with more aggressive prostate cancer variants and a higher prostate specific antigen (PSA) recurrence following prostatectomy. The aim of this study is to analyze the influence of body mass index (BMI) and the distribution of adipose tissue on clinical pretreatment variables and PSA evolution post 125I prostate brachytherapy. Materials and Methods: We studied 59 men with low risk or ‘low tier” intermediate risk (maximum one intermediate risk feature) prostate cancer who had undergone 125I radioactive seed implantation as monotherapy. Inclusion criteria were an absence of hormonal therapy or external beam radiotherapy, a minimum of 8 months of followup and at least 3 followup PSA values. We calculated the BMI (kg/m2), waist circumference and the quotient between visceral and subcutaneous fat (VF/SF) measured on computed tomography at the iliac crest level. To analyze the influence of anthropometric measures on post-brachytherapy PSA evolution, we divided the patients into 2 groups: 1) rapid PSA descent post-brachytherapy to <0.5 ng/mL in the first 12 months following brachytherapy (n = 28); 2) slow PSA descent post-brachytherapy to <0.50 ng/mL and a followup of ≥24 months (n = 23) or a PSA bounce of ≥0.50 ng/mL (n = 6). The influence of those anthropometric measures on pretreatment PSA, prostate volume and number of positive biopsies were calculated using Spearman correlation coefficient. Differences between the 3? post-brachytherapy outcome groups were analyzed using the Pearson chi-square and Fisher's exact test. Relative risk estimate was calculated to measure of the strength of the association between the presence of a factor and the occurrence of an event. All tests were two-tailed. Results: There was an influence of the different anthropometric measures on pretreatment characteristics; there was a positive correlation between VF/SF and the PSA before treatment (r = 0.282, p = 0.029); and waist circumference with the number of positive biopsies (r = 0.374, p = 0.004). VS/SF, BMI and waist circumference were not different between both post-brachytherapy PSA-outcome groups (p≥0.439). The following factors were associated with being in the slow descent group: younger patients (less than the median age of 65 years), p = 0.003, relative risk (RR) 2.256 (95% confidence interval (CI), 1.249-4.073) and prostates smaller than the median 41 cc, p = 0.034, RR 0.550 (95%CI, 0.320-0.944). All patients with a waist circumference of >100 cm were in the rapid descent group. Among the patients with a VF/SF >0.9, 83% were in the slow descent group. Conclusions: In this small pilot study, waist circumference and VF/SF were weakly correlated to pretreatment characteristics. There seems to be a tendency that an increase in visceral fat and waist circumference has an influence on the type of PSA response. Larger studies are needed to determine if anthropomorphic measures have a direct influence on post-brachytherapy PSA response.