Long-term outcomes of high dose carbon-ion radiation therapy for unresectable upper cervical (C1-2) chordoma

Background Chordoma is a rare, locally invasive neoplasm of the axial skeleton. Complete resection is often difficult, especially for the upper-cervical (C1-2) spine. We evaluated the efficacy and safety of carbon-ion radiotherapy (CIRT) for unresectable C1-2 chordoma. Methods Patients with C1-2 chordoma treated with definitive CIRT (60.8 Gy [RBE] in 16 fractions) were retrospectively analyzed. We evaluated OS, LC, PFS, and toxicity. Results Nineteen eligible patients all completed the planned course of CIRT. With the median follow-up 68 months (range: 29-144), median OS was 126 months (range: 36-NA). Five-year OS, LC, and PFS were 68.4% (95% CI, 42.8%-84.4%), 75.2% (46.1%-90.0%), and 64.1% (36.3%-82.3%), respectively. Regarding acute toxicity of grade >= 3, there was only one grade 3 mucositis. Late toxicity included radiation-induced myelitis (grade 3 in 1 patient; 5.3%), and compression fractures (n = 5; 26.3%). Conclusions High-dose CIRT is a promising treatment option for unresectable upper cervical chordoma.