Long-term outcomes of skull base chordoma treated with high-dose carbon-ion radiotherapy

Background We evaluated the long-term efficacy and safety of carbon-ion radiotherapy (C-ion RT) for skull base chordoma, a rare neoplasm. Methods Thirty-four patients with skull base chordoma who were treated with C-ion RT were prospectively enrolled and analyzed retrospectively. C-ion RT was delivered with 60.8 Gy (relative biological effectiveness [RBE]) in 16 fractions at four fractions per week. Results The median follow-up period was 108 months. The 5- and 9-year local control rates were 76.9% and 69.2%, respectively. The 5- and 9-year overall survival rates were 93.5% and 77.4%, respectively. Regarding grade 3 or more severe late reactions, one patient developed a grade 3 mucosal ulcer, two developed grade 4 ipsilateral optic nerve injuries, and one developed a grade 5 mucosal ulcer at 9 years and 3 months after C-ion RT. Conclusion C-ion RT with 60.8 Gy (RBE)/16 fractions is a promising treatment option for inoperable skull base chordoma.