Incidence of, and risk factors for, mandibular osteoradionecrosis in patients with oral cavity and oropharynx cancers

•Mandibular osteoradionecrosis developed in 5.5% of head and neck cancer patients.•Smoking at the time of RT and pre-RT tooth extraction were clinical risk factors.•The use of 3D-conformal RT vs intensity-modulated RT was an additional risk factor.•Modifiable risk factors should be minimized. To evaluate the incidence of, and risk factors associated with, mandibular osteoradionecrosis (MORN) following radiation therapy (RT) for oral cavity and oropharyngeal cancers. Patient and treatment records of 252 consecutive patients with oral cavity or oropharynx cancers treated with RT by a single radiation oncologist at a high volume academic institution from August 2009 to December 2015 were retrospectively reviewed. A Cox regression model was used to assess factors associated with the development of MORN. RT dosimetry was compared between patients with MORN and a matched cohort of patients without MORN. MORN developed in 14 patients (5.5%), occurring 3–40 (median 8) months post-RT. Factors associated with MORN on univariable analysis included primary diagnosis of oral cavity vs oropharynx cancer (hazard ratio [HR]: 3.0, p=0.04), smoking at the time of RT (HR: 3.1, p=0.04), mandibular invasion of the primary (HR: 3.7, p=0.04), pre-RT tooth extraction (HR: 4.52, p=0.01), and treatment with 3D-conformal RT vs intensity-modulated RT (HR: 5.1, p=0.003). On multivariable analysis, pre-RT tooth extractions and RT technique remained significant. A dosimetric comparison between patients with and without MORN showed no significant differences. The incidence of MORN is low in the modern era at a high volume academic center. Modifiable risk factors including pre-RT tooth extractions, smoking, and RT technique are associated with MORN, and the risk should be minimized with appropriate dental evaluation and treatment, smoking cessation efforts, and the use of intensity-modulated RT.