Background Hypofractionated proton therapy for localized prostate cancer has the advantage that it is easier for patients to receive treatment and allows the treatment facility to treat more patients by shortening the overall treatment period. Objective We evaluated the acute genitourinary toxicities in particular, and discussed the clinical feasibility of hypofractionated proton therapy. Method Hypofractionated proton therapy was delivered using a spot-scan technique with two opposing lateral fields, one per day, four times per week, through 3 weeks in 12 fractions for a total dose of 51.6 GyE. All patients underwent gold marker placement and spacer insertion before treatment. Patients were risk-grouped according to the National Comprehensive Cancer Network (NCCN) guidelines, with intermediate-risk patients receiving neoadjuvant androgen deprivation therapy (ADT) and high-risk patients receiving both neoadjuvant and adjuvant ADT. Acute normal tissue toxicity was assessed according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0, and the maximum response within 3 months after the start of treatment was evaluated. Result From March 2121 to June 2025, 150 cases of prostate cancer were treated with hypofractionated proton beam therapy. Patients' ages ranged from 43 to 89 years, with a median age of 71 years. The NCCN risk classification consisted of 38 low-risk cases, 66 intermediate-risk cases, and 46 high-risk cases. The CTV ranged from 13cc to 116cc, with a median of 36.5cc. The overall treatment period ranged from 16 to 32 days, with a mean of 18 days and a median of 17 days. The number of urinations before treatment ranged from 3 to 20 times, with a median of 8 times. The maximum number of urinations after the start of treatment improved in 21 cases (14%) and increased in 129 cases (86%), of which 9 cases (6%) recorded more than twice the number of urinations before treatment (CTCAE Grade 2). No grade ≥3 acute urinary frequency toxicities were observed. No grade ≥2 acute urinary retention, urinary pain, urinary urgency or hematuria toxicities were observed. No GI toxicity of grade 1 or higher was observed. Conclusion Hypofractionated proton therapy for prostate cancer is a dose fractionation method to be applied clinically in terms of acute normal tissue toxicity, and although the observation period is short, with a maximum of 51 months and an average of 16 months, there have been no cases of recurrence, including PSA recurrence, and its clinical feasibility is highly regarded.

Hypofractionated Proton Therapy, Prostate Cancer, Acute Genitourinary Toxicities