High-dose-rate brachytherapy (HDR-BT) is a potential treatment for localized prostate cancer. However, high-quality evidence or literature on HDR-BT in older patients is limited. Therefore, we aimed to evaluate HDR-BT treatment outcomes by comparing results between older and younger patients.

We included 973 patients with primary prostate cancer who were treated with radiation therapy (external beam radiotherapy + HDR-BT) at our institution between November 1997 and December 2021. Propensity score matching was used. The biochemical freedom from failure (bFFF), prostate cancer-specific survival (PCSS), and adverse events were compared between the two groups. The groups comprised 196 matched patients aged ≥ 75 years and 196 patients aged < 75 years. Multivariate analysis was conducted for bFFF.

The median follow-up period after matching was 79.5 and 107.5 months for patients aged ≥ 75 and < 75 years, respectively. Matched 7-year bFFF was 82.9 and 83.1% in those aged ≥ 75 and < 75 years, respectively. However, 7-year PCSS was 100% and 99.3%, respectively, with no significant differences (p = 0.690 and 0.641, respectively). Age was not associated with bFFF in the multivariate analysis (Hazard ratio = 0.976, 95% Confidence interval: 0.674–1.414, p = 0.898). Conversely, low-grade T classification and, Gleason score, low initial prostate-specific antigen levels, hormone therapy, and higher doses (Biologically Effective Dose [BED] ≥ 243.0 Gy) were significantly associated with higher bFFF. The matched 7-year cumulative incidence rate of grade ≥ 2 genitourinary adverse events was 13.5 and 20.4% for those aged ≥ 75 years and < 75 years, respectively. The gastrointestinal toxicity rate was 5.3 and 4.4%, respectively, with no significant differences observed (p = 0.754 and 0.675, respectively).

Compared with the younger group (< 75 years), Moreover, high BED irradiation resulted in better bFFF.