Incidence and Site‐Specific Risk Factors of Jaw Osteoradionecrosis for Head and Neck Patients in the <scp>IMRT</scp> / <scp>VMAT</scp> Era: Evidence From a Large, Hospital‐Based Cohort

PURPOSE: Osteoradionecrosis (ORN) of the jaw remains a serious late complication of head and neck cancer (HNC) radiotherapy. Although intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc radiotherapy (VMAT) are expected to reduce ORN risk, large real-world data in the modern era are limited. This study evaluated the incidence, latency, and risk factors of ORN across radiotherapy modalities in a large hospital-based cohort. MATERIALS AND METHODS: We retrospectively analyzed 6199 patients with HNC treated with curative radiotherapy between 2006 and 2020. ORN was defined as exposed necrotic jaw bone persisting for > 3 months without tumor recurrence. ORN incidence was compared between conventional 2D/3D radiotherapy and IMRT/VMAT. Latency to ORN onset was assessed using Kaplan-Meier analysis, and independent predictors were identified using multivariate Cox regression for demographic, tumor-related, treatment-related, and patient-related variables. RESULTS: Overall, 278 patients (4.5%) developed ORN. The incidence was 5.5% after 2D/3D radiotherapy and 4.4% after IMRT/VMAT, without a significant overall difference. However, IMRT/VMAT significantly reduced ORN risk in nasopharyngeal carcinoma (NPC) (1.6% vs. 5.4%, p = 0.006). ORN incidence was highest in oral cavity cancers (7.9%), particularly gingival and floor-of-mouth subsites. Median latency to ORN onset was 24 months (interquartile range 12-44) and was longer after IMRT/VMAT than after 2D/3D radiotherapy (26 vs. 18 months, p = 0.021). Multivariate analysis identified non-NPC diagnosis (adjusted hazard ratio [aHR] 2.71), advanced clinical stage (aHR 1.66), dental extraction (aHR 3.21), adverse oral habits (aHR 1.45), and abnormal body mass index (aHR 1.45) as independent predictors of ORN (all p < 0.05). CONCLUSION: In this large contemporary cohort, ORN occurred in 4.5% of HNC patients after radiotherapy. IMRT/VMAT reduced ORN risk and delayed onset, particularly in NPC. Tumor site, disease stage, dental extraction, oral habits, and nutritional status remain key determinants, underscoring the importance of individualized risk stratification and preventive dental care in the IMRT/VMAT era.