Multicenter study of carbon-ion radiation therapy for nonsquamous cell carcinomas of the oral cavity

Background: The aim of this study was to evaluate the efficacy and safety of carbon-ion radiation therapy for nonsquamous cell carcinomas of the oral cavity in a multicenter study. Methods: Retrospective analysis of the clinicopathological features and outcomes of 76 patients with oral nonsquamous cell carcinomas with N0-1 M0 status and were treated with carbon-ion radiation therapy at four institutions in Japan between November 2003 and December 2014 was performed. Results: Salivary gland carcinoma, mucosal melanoma, and three other carcinomas were found in 46, 27, and 3 patients, respectively. T1-3, T4a, and T4b disease was diagnosed in 27, 18, and 31 patients, respectively. Median follow-up period was 31.1 months (range, 3-118 months). Three-year local control, progression-free survival, and overall survival of all patients were 86.8%, 63.1%, and 78.4%, respectively. Multivariate analysis showed T classification (T4) to be a significant independent poor prognostic factor for local control. Acute grade 3 mucositis was observed in 38 patients. Grades 3 and 4 late morbidities were observed in 9 and 4 patients, respectively. No grade 5 late toxicity was observed. Conclusions: Oral nonsquamous cell carcinomas could be treated effectively, with acceptable toxicity, by carbon-ion radiation therapy.