1089 - Treatment Outcomes and Prognostic Factors of Carbon Ion Radiation Therapy for Localized Prostate Cancer: A Single-Institution Retrospective Study of over 7000 Patients

Purpose/Objective(s): Carbon ion radiation therapy (CIRT) is characterized by its excellent dose concentration and high biological effectiveness. In localized prostate cancer, CIRT is expected to provide high local control rates and reduce adverse events. This study retrospectively analyzed the treatment outcomes and prognostic factors of CIRT for prostate cancer at our institution.

Materials/Methods: Patients who underwent CIRT for localized prostate cancer between August 2013 and July 2024 were included in the study. The total dose administered was 51.6 Gy (RBE) in 12 fractions over 3 weeks. The endpoints evaluated included biochemical recurrence-free survival (bRFS), overall survival (OS), cancer-specific survival (CSS), local control rate (LC), and acute and late adverse events. Prognostic factor analysis was conducted for age, sex, performance status (PS), and disease stage, and other clinical parameters.

Results: A total of 7,054 patients with histologically confirmed localized prostate cancer underwent CIRT between August 2013 and July 2024. The median age was 71 years (range: 40–92 years). The distribution of T-stage classification was as follows: T1a/1b/1c/2a/2b/2c/3a/3b/4=8/10/2158/2124/692/1062/696/269/35. The Gleason score distribution was as follows: 4/5/6/7/8/9/10/ unclassifiable = 1/4/1208/3204/1613/918/104/2 cases. The median PSA level was 8.05 ng/mL (range: 0.008–640 ng/mL). According to the D'Amico classification, 755 patients were classified as low-risk, 2,631 as intermediate-risk, and 3,668 as high-risk. The median follow-up period was 43 months (longest: 136 months). The 5-year bRFS, OS, CSS, and LC rates for the entire cohort were 92.0%, 96.3%, 99.8%, and 98.2%, respectively. According to risk classification, the 5-year bRFS, OS, CSS and LC rates were 92.0%/98.4%/100%/96.5%, 94.0%/97.6%/99.9%/98.1%, and 90.4%/94.8%/99.6%/98.8% for low/intermediate/high-risk patients, respectively. A total of 18 cases with Grade 3 or higher adverse events were observed. Among acute adverse events, three cases of Grade 3 dysuria were observed. Among late adverse events, six cases of Grade 3 rectal hemorrhage and eight cases of Grade 3 hematuria were observed. No Grade 4 or higher adverse events were reported. Multivariate analysis identified age, D'Amico classification, Gleason score, duration of androgen deprivation therapy (ADT), and diabetes mellitus status as significant prognostic factors for overall survival.

Conclusion: This study indicates CIRT is an effective treatment for localized prostate cancer with a low incidence of severe adverse events. Age, D'Amico classification, Gleason score, ADT duration, and diabetes mellitus status were identified as potential prognostic factors.