Proton therapy for head and neck adenoid cystic carcinoma: Initial clinical outcomes

Background. The purpose of this study was to report outcomes of proton therapy in head and neck adenoid cystic carcinoma. Methods. We conducted a retrospective analysis of 26 patients treated between 2004 and 2012. Twenty patients (77%) had base of skull involvement; 19 (73%) were treated for initial disease and 7 (27%) for recurrent disease. Twenty patients were treated postoperatively, 6 after biopsy alone and 24 had positive margins or gross residual disease. Median dose delivered was 72 Gy (relative biological effectiveness [RBE]). Results. Median follow-up was 25 months (range, 7-50 months). The 2-year overall survival was 93% for initial disease course and 57% for recurrent disease (p5.19). The 2-year local control was 95% for initial disease and 86% for recurrent disease (p5.48). The 2-year distant metastatic rate was 25%. Late toxicity of grade 0 or 1 was seen in 17 patients, grade 2 in 5, grade 3 in 2, grade 4 in 1, and grade 5 in 1. Conclusion. Initial outcomes of proton therapy are encouraging. Longer follow-up is required.