Long-term outcomes of external beam radiotherapy combined with high-dose-rate brachytherapy boost in intermediate- and high-risk prostate cancer

Background

For intermediate- and high-risk prostate cancer, dose escalation is essential to optimize oncological control. While external beam radiotherapy (EBRT) alone can be limited by dose constraints to adjacent organs-at-risk, high-dose-rate (HDR) brachytherapy provides a highly conformal boost option.

Methods

This retrospective single-institution study analyzed 250 patients with localized intermediate- and high-risk prostate cancer treated between 06/2004 and 03/2024 with EBRT plus HDR brachytherapy boost. The EBRT dose averaged 50.4 Gy (range: 45–64 Gy), followed by HDR boost in nearly all patients (98.8%) with two fractions of 9 Gy. Androgen deprivation therapy (ADT) was administered to 39.2% of patients (98/250). Primary outcomes included local control (LC), progression-free survival (PFS), and overall survival (OS).

Results

After a median follow-up of 63.5 months (mean 70.4, range 3–231), oncological outcomes were excellent. LC rates were 99.6% at 3 years, 98.8% at 5 years, and 98.4% at 10 years. PFS was 98%, 96.8%, and 96% at 3, 5, and 10 years, respectively. OS reached 98.4% at 5 years and 96% at 10 years. During the 231-month follow-up, 8.4% of patients developed biochemical recurrence, whereas in-field progression was observed in only 1.6%. Patients receiving ADT achieved 100% LC across all timepoints. Patterns of failure were predominantly distant (lymph nodes and bone). Acute and late toxicity was predominantly mild. No acute Grade ≥3 genitourinary (GU) or gastrointestinal (GI) toxicity was observed. Late Grade ≥3 toxicity was rare (0.8%, limited to GU events), and no late Grade ≥3 GI toxicity occurred.

Conclusions

The combination of EBRT and HDR brachytherapy boost yields outstanding long-term LC, PFS, and OS for intermediate- and high-risk prostate cancer, confirming this regimen as a highly effective treatment strategy. The dominant pattern of failure was distant, underscoring the need for optimized systemic therapy integration in high-risk patients.