Eligibility criteria according to EAU/ESTRO/SIOG guidelines for exclusive iodine-125 brachytherapy for intermediate-risk prostate adenocarcinoma patients: impact on relapse-free survival

Introduction
Iodine-125 (125I) brachytherapy (BT) alone for intermediate-risk (IR) prostate adenocarcinoma (PCA) is controversial. The purpose of the study was to investigate potential predictive factors in selected IR-PCA patients treated with BT.

Material and methods
Among 547 patients treated with 125I BT between 2003 and 2013, 149 IR-PCA cases were selected according to NCCN classification after an additional exclusion of patients with prostate specific antigen (PSA) > 15 ng/ml and ISUP group 3. A relapse was defined as a biochemical failure, using ASTRO Phoenix definition, or a relapse identified on imaging. Survival curves were estimated with Kaplan-Meier method. Potential prognostic variables including EAU/ESTRO/SIOG guidelines eligibility criteria were analyzed using univariate and Cox’s proportional hazards regression analysis.

Results
Of the 149 IR patients, 112 were classified as favorable, with 69 cases eligible to BT according to EAU/ESTRO/SIOG guidelines, and 37 patients were identified as unfavorable as per NCCN. Androgen deprivation therapy (ADT) was applied in 6 patients only. Percentage of positive biopsy cores were ≤ 33% and  50% for 119 and 11 patients, respectively. With a median follow-up of 8.5 years, 30 patients experienced a relapse. 10-year overall survival, progression-free survival (PFS), and relapse-free survival (RFS) were 84% (95% CI: 75-90%), 66% (95% CI: 56-75%), and 77% (95% CI: 67-84%), respectively. Failure to meet EAU/ESTRO/SIOG criteria was significantly associated with a lower RFS (p = 0.0267, HR = 2.37 [95% CI: 1.10-5.08%]).

Conclusions
Brachytherapy is an effective treatment for selected IR-PCA cases. Patients who were not eligible according to EAU/ESTRO/SIOG guidelines demonstrated a lower RFS.