Safety and early outcomes of proton therapy and low-dose rate brachytherapy boost for patients with prostate cancer

PURPOSE: Brachytherapy boost improves biochemical control for patients with prostate cancer. Here, we report the safety and early efficacy of proton therapy (PT) with a low-dose-rate (LDR) brachytherapy boost. METHODS: This retrospective study included patients with intermediate- or high-risk prostate cancer treated with PT followed by LDR boost, with or without androgen deprivation therapy (ADT), from 2010 through 2023. Patient, disease, and treatment characteristics, gastrointestinal (GI) and genitourinary (GU) toxicity, and efficacy outcomes are reported. RESULTS: Ninety-nine patients received PT and LDR boost; median age at diagnosis was 68 years (interquartile range [IQR] 61-72). Most patients ( n = 77) were White, 12 were African American, 5 Asian, and 3 Hispanic. Thirty-five patients had intermediate-risk (4 favorable and 31 unfavorable), 56 had high-risk, and 8 had very high-risk disease. Median PT dose was 44 Gy(RBE) (range 40-50.4) and median LDR dose was 90Gy (range 90-110). Pd-103 seed strands were used for 95 patients and I-125 for 4; 90 had MRI-assisted radiosurgery brachytherapy; 91 received ADT; and 21 had a rectal spacer. At a median follow-up time of 45 months, 5-year biochemical recurrence-free survival was 98%. There was no local recurrence, distant metastasis, or cancer death. Four patients had acute urinary retention after brachytherapy procedure. Eleven patients (11%) had late grade 2 GU toxicity, and 3 (3%) had late grade 2 GI toxicity. One patient had grade 3 urethral stricture requiring dilatation and transurethral resection. CONCLUSIONS: At 45 months' follow-up time, treatment with PT and LDR boost led to high control rates and low toxicity for men with prostate cancer. (c) 2025 American Brachytherapy Society. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.