Clinical Outcomes of Carbon-Ion Radiotherapy for Unresectable Radiation-Induced Secondary Sarcoma

Purpose While carbon-ion radiotherapy (CIRT) is a promising treatment option for unresectable sarcomas, its efficacy and safety for radiation-induced secondary sarcomas (RIS) remains unclear owing to limited evidence. This study aimed to evaluate the feasibility and safety of CIRT for RIS at our center. Patients and Methods Data concerning eight patients who had undergone CIRT for RIS between December 2018 and December 2024 were retrospectively analyzed. Toxicities were evaluated using Common Terminology Criteria for Adverse Events, version 5.0. Local control (LC), progression-free survival (PFS), and overall survival (OS) rates were determined using the Kaplan–Meier method. Results The median follow-up period was 18.5 months (range, 3.1–32.6 months). The primary malignancies included cervical cancer (n = 2), and endometrial cancer, leiomyosarcoma of the uterus, retinoblastoma, prostate cancer, breast cancer, and schwannoma of the auditory nerve (n = 1 each). The CIRT sites were the pelvis (n = 5), head and neck (n = 2), and central nervous system (n = 1). The histopathologic diagnoses comprised malignant peripheral nerve sheath tumor (n = 2) and others (n = 6). The median tumor diameter was 7.7 (range, 1.2–14) cm. The median dose of initial radiotherapy was 44 (range, 25–50.4) Gy, and the median interval between initial radiotherapy and CIRT was 34.2 (range, 6.2–38.9) years. The dose fractionations of CIRT included 70.4 Gy (relative biological effectiveness [RBE])/16 fractions (n = 7) and 55.2 Gy (RBE)/12 fractions (n = 1). One-year LC, PFS, and OS rates were 71.4%, 37.5%, and 75.0%, respectively. The median OS time was 30.2 months. The percentage of patients with Grade ≥3 toxicities (pain, lymphedema, fracture, and cerebrospinal leak) was 25%. No Grade ≥4 toxicities were observed. Conclusion Our findings suggest that CIRT for unresectable RIS is feasible with acceptable short-term toxicities.