The role of carbon ion radiotherapy for unresectable locally recurrent rectal cancer: a single institutional experience

Background Treatment for locally recurrent rectal cancer after surgery is still a challenge. With the physical and biological advantages, carbon-ion radiotherapy (CIRT) could be a choice for these patients. The purpose of this study was to investigate the efficacy and safety of CIRT for unresectable locally recurrent rectal cancer in Chinese patients. Methods Date from 25 patients with unresectable locally recurrent rectal cancer treated by CIRT from July 2015 to April 2019 were analyzed retrospectively. The endpoints of this study were overall survival (OS), local control (LC) and acute and late toxicity. Results With the median follow-up of 19.6 (range 5.1–52.5) months, data of all 25 patients were collected. Median prescribed dose for tumor was 72 Gy (relative biologic efficacy (RBE)) (range 48-75.6 Gy (RBE)). The LC rates at 1 and 2 years were 90.4% and 71.8%. Overall LC at 1- and 2-year were 76.2% and 30.5% for 9 patients whose prescribed tumor doses of CIRT < 66 Gy (RBE), 100% and 100% for 16 patients whose prescribed doses of CIRT ≥ 66 Gy (RBE). Patients received ≥ 66 Gy (RBE) had obviously better LC rates than those received < 66 Gy (RBE) (P = 0.001). The OS rates at 1 and 2 years were 82.9% and 65.1%, respectively. No acute toxicity over grade 2 was observed, grade 3 late toxicity were observed in 3 patients: gastrointestinal toxicity (n = 1), neuropathy (n = 1), pelvic infection (n = 1). No Grade 4 or higher toxicity was observed. Conclusion Our study shows that CIRT is effective for unresectable locally recurrent rectal cancer patients with acceptable toxicity.