ABSTRACT Background Sinonasal malignancies (SNM) are rare, heterogeneous tumors with poor prognosis. There is an unmet need to improve treatment outcomes. Despite advances in imaging and molecular classification, optimal curative radiotherapy (RT) strategies remain undefined. We analyzed the pattern of failure after RT, focusing in depth on local recurrence. Methods This retrospective cohort study included 104 SNM patients treated with curative‐intent RT (either primary or after endoscopic surgery) at a tertiary center between 2010 and 2022. Local recurrences were delineated on follow‐up imaging and registered to pretreatment plans. Recurrence location was classified as in‐field, marginal, or out‐of‐field based on dose at the center of mass. Results Local recurrence rate was 25%. Most local recurrences (81%) occurred in‐field in the high‐dose region (> 95% of prescribed dose), with a median dose of 65 Gy. Perineural spread accounted for most out‐of‐field failures. Local recurrence significantly impaired disease‐specific survival. Conclusions Local failures after RT for SNM predominantly arise in‐field within adequately irradiated volumes, suggesting biological radioresistance. These findings support the need for histology‐driven, biologically tailored treatment strategies.
Ridder et al. (2026) studied this question.