Patterns of relapse and outcomes following Single-Fraction High-Dose-Rate brachytherapy monotherapy for Intermediate-Risk prostate cancer.

Abstract

High-dose rate brachytherapy (HDRB) monotherapy has proven effective in managing low- and intermediate-risk prostate cancer (IRPC). This study aims to evaluate patterns of relapse, treatment-related toxicity, and tumor control in patients with IRPC treated with a single fraction of HDRB monotherapy. We reviewed IRPC patients treated with HDRB monotherapy delivered as a single 21 Gy fraction between January 2015 and December 2021. Clinical data, treatment parameters, and outcomes were extracted from medical records. Radiological local recurrences diagnosed by a blinded genitourinary radiologist were confirmed by biopsy. We performed dosimetric analysis of recurrent intraprostatic nodules. Toxicities were graded using CTCAE v4. We report 3- and 5-year biochemical relapse-free survival (bRFS), locoregional relapse-free survival (LRRFS), and overall survival (OS). 87 patients were included (median follow-up: 51.1 months). Biochemical failure occurred in 24.1 % of patients, including local relapse in 16.1 %. Using Cox proportional-hazards model, higher baseline PSA and unfavorable intermediate-risk (UIR) category were associated with an increased local relapse risk (HR 1.2 [95 % CI 1.0-1.42], p = 0.013; HR 4.52 [95 % CI 1.4-14.1], p = 0.01, respectively), whereas a greater prostatic volume receiving 100 % of the prescription dose was protective (HR 0.85 [95 % CI 0.75-0.96]). Dosimetric analyses of recurrences (D98% = 21.6 Gy, D90% = 23.7 Gy, Dmean = 30.6 Gy) showed no association with failure. The 5-year bRFS rate for favorable intermediate-risk (FIR) patients was 83.4 %, and for UIR patients 59.3 %. The 5-year LRRFS rate was 82.6 % for FIR and 76.9 % for UIR patients. The 5-year OS was 96.6 %. Acute grade ≥ 3 genitourinary toxicities occurred in 5.7 % of patients, and late grade ≥ 3 toxicity in 1.1 %. No grade ≥ 2 gastrointestinal toxicity was observed. A single 21 Gy fraction of HDR brachytherapy monotherapy for IRPC appears feasible and safe, yielding a 5-year bRFS of 83.4 % for FIR and 59.3 % for UIR patients. Patterns of failure were not attributable to inadequate dosimetric coverage. Higher baseline PSA levels and UIR classification were associated with an increased risk of local failure.