Dose-volume histogram analysis of brainstem necrosis in head and neck tumors treated using carbon-ion radiotherapy

We aimed to evaluate the relationship between brainstem necrosis and dose-volume histograms in patients with head and neck tumors after carbon-ion radiotherapy.

We evaluated 85 patients with head and neck tumors who underwent carbon-ion radiotherapy and were followed-up for ≥12months. Brainstem necrosis was evaluated using the Common Terminology Criteria for Adverse Events (version 4.0).

The median follow-up was 24months, and four patients developed grade 1 brainstem necrosis, with 2-year and 3-year cumulative rates of 2.8% and 6.5%, respectively. Receiver operating characteristic curve analysis revealed the following significant cut-off values: a maximum brainstem dose of 48Gy (relative biological effectiveness [RBE]), D1cm³ of 27Gy (RBE), V40Gy (RBE) of 0.1cm³, V30Gy (RBE) of 0.7cm³, and V20Gy (RBE) of 1.4cm³. Multivariate analysis revealed that V30Gy (RBE) was most significantly associated with brainstem necrosis. The 2-year cumulative rates were 33% and 0% for V30Gy (RBE) of ≥0.7cm³ and <0.7cm³, respectively (p<0.001).

The present study indicated that the dose constraints might help minimize brainstem necrosis after carbon-ion radiotherapy.