Carbon-Ion Radiotherapy for Prostate Cancer in Patients with a History of Surgery for Benign Prostatic Hyperplasia.

Background/Objectives: Carbon-ion radiotherapy (CIRT) offers precise dose distribution and enhanced biological effectiveness in localized prostate cancer. However, the safety of CIRT in patients with a history of surgery for benign prostatic hyperplasia (BPH), such as transurethral resection of the prostate (TURP), remains unclear. This study aimed to evaluate the long-term safety and oncological outcomes of CIRT in this population. Methods: A retrospective analysis was conducted in 74 of 3848 patients with prostate cancer and a history of surgery for BPH who underwent CIRT combined with risk-adapted androgen deprivation therapy between 2007 and 2023. Adverse events were assessed using CTCAE v5.0. Biochemical recurrence-free survival was estimated using the Kaplan-Meier method and risk factors for hematuria with multivariate logistic regression and receiver operation characteristic (ROC) analysis. Results: CIRT was generally well-tolerated. Early Grade 2 genitourinary (GU) adverse events occurred in 5.4% of patients, and late-Grade 2 or higher GU events occurred in 8.1%. The cumulative incidence of Grade 2 ≥ GU events remained 10% at 36 months. Compared to holmium laser enucleation of the prostate, a shorter interval between BPH surgery and CIRT initiation and a history of TURP were independently associated with an increased risk of hematuria. Notably, 5-year bRFS was 100% in low- and intermediate-risk groups and 88.6% in the high-risk group. Conclusions: CIRT demonstrates acceptable oncological outcomes and urinary complication rates in patients with prostate cancer and a history of BPH surgery. These findings suggest that CIRT can be a feasible treatment option in this surgically altered population, but careful patient selection, individualized treatment planning, and long-term follow-up are essential. Given the absence of a non-BPH control group, oncological efficacy should be interpreted with caution.