ESTRO 2025 - Abstract Book

S380

Brachytherapy - Urology

ESTRO 2025

1710

Digital Poster Long-Term Outcomes of High-Dose-Rate Brachytherapy Combined with Hypofractionated External Beam Radiotherapy for High-Risk Prostate Cancer Kenta Ohmatsu 1 , Yaichiro Hashimoto 1 , Miki Tsujii 1 , Sawa Kono 1 , Takayuki Kanai 1 , Shigehiko Kuribayashi 1 , Junpei Iizuka 2 1 Radiation Oncology, Tokyo Women’s Medical University, Tokyo, Japan. 2 Urology, Tokyo Women’s Medical University, Tokyo, Japan Purpose/Objectives: Prostate cancer is characterized by a low alpha-beta ratio (approximately 1.5 Gy) compared to adjacent normal tissues, such as the rectum, which has a higher ratio (around 5 Gy). This radiobiological feature suggests that high dose-rate brachytherapy (HDR-BT), combined with hypofractionated external beam radiotherapy (EBRT), could enhance therapeutic efficacy, particularly in high-risk patients. This study aims to evaluate the long-term clinical outcomes of this combined approach in patients with high-risk localized prostate cancer. We retrospectively analyzed 110 patients with high-risk prostate cancer (T1-3N0M0) as classified by the D’Amico criteria. All patients received EBRT (45 Gy in 15 fractions over five weeks, on alternate weekdays) followed by HDR BT (18 Gy in 2 fractions delivered on a single day) at our institution between August 2005 and June 2011. Androgen deprivation therapy (ADT) was administered, including 3–6 months of neoadjuvant ADT during radiotherapy, followed by an additional 6 months of adjuvant ADT post-radiotherapy. Biochemical failure was defined according to the Phoenix criteria as PSA nadir plus 2.0 ng/mL. Biochemical recurrence-free survival (bRFS) and overall survival (OS) were analyzed, and prognostic factors were assessed using Cox proportional hazards models. Results: The median age of the patients was 66.5 years (50–79 years). The median follow-up period was 127 months (29–215 months). The 5-year and 10-year bRFS rates were 82.3% and 74.0%, respectively, while the OS rates were 98.0% and 92.7%. Material/Methods: