Five-year outcomes in carbon-ion radiotherapy for postoperative pelvic recurrence of rectal cancer: A prospective clinical trial (GUNMA 0801).

Introduction: Carbon-ion radiotherapy (C-ion RT) is associated with favorable clinical outcomes for the pelvic recurrence of rectal cancer. However, few long-term follow-up studies after C-ion RT have been conducted. Hence, we performed an updated analysis of a prospective clinical trial of C-ion RT for the postoperative pelvic recurrence of rectal cancer. Materials and methods: The study included 28 patients. Inclusion criteria were patients with confirmed pelvic recurrence of rectal cancer without distant metastasis; those who underwent curative resection of their primary disease and regional lymph nodes without gross or microscopic residual disease; and those who had radiographically measurable tumors. The total dose of C-ion RT for all the patients was 73.6 Gy (relative biological effectiveness) administered in 16 fractions. Results: The median follow-up duration in all patients and those who survived were 51.2 and 69.2 months, respectively. The follow-up rate at the time of analysis was 96.4%. The 5-year overall survival and local control rates were 50% and 83%, respectively. Four patients had local recurrence, and 17 died of rectal cancer. Regarding late toxicities, two patients developed grade 3 pelvic infection, and nine developed grade 2 peripheral neuropathy. Conclusion: Our updated analysis of a prospective clinical trial of C-ion RT for postoperative pelvic recurrence of rectal cancer confirmed its long-term efficacy and safety. These results suggest that C-ion RT may be a safe and effective treatment option for the postoperative pelvic recurrence of rectal cancer.