Predictive factors of oral mucositis in patients with locally recurrent inoperable head and neck cancer treated with boron neutron capture therapy.

Background and purpose: The prognosis of recurrent head and neck (HN) cancer is poor. High response rates have been achieved with boron neutron capture therapy (BNCT) in the treatment of locally recurrent HN cancer. Radiation-induced oral mucositis (OM) is a common adverse effect of BNCT. We evaluated the factors associated with severe OM in patients treated with BNCT. Patient/material and methods: Ninety two patients with locally recurrent inoperable HN cancer were treated with nuclear reactor-based BNCT in 1-2 fractions. The association between grade 3 OM, patient clinical parameters and maximum weighted oral mucosa dose was evaluated. Mucosal dose was calculated using the skin nitrogen concentration of 4.2%. A sigmoidal normal tissue complication probability (NTCP) model was created by dividing patients into four equal sized groups based on increasing dose levels.

Results: Grade 3 OM was observed in 42% of patients after the first BNCT treatment. The prevalence of OM increased with higher maximum oral mucosa doses. From the NTCP curve, we estimated the dose corresponding to a 50% probability (D50) for grade 3 OM to be 13.5 Gy(W). Older age was the only patient- related factor significantly associated with increased grade 3 OM risk.

Interpretation: Higher maximum oral mucosa doses increased the risk of grade 3 OM. Older age was the only other factor related to severe OM.