Postoperative radiotherapy and external carotid artery diameter: is there a link to osseous free flap osteoradionecrosis risk?

OBJECTIVES: Postoperative radiotherapy (PORT) is a cornerstone in the multimodal treatment of head and neck malignancies but may lead to osteoradionecrosis (ORN) inside healthy osseous free flaps. This study analyzes the role of external carotid artery (ECA) narrowing as a potential contributor to flap ORN, as prior evidence in this regard remains unclear. MATERIALS AND METHODS: This retrospective study analyzed 89 patients who received osseous free flaps and PORT between April 2017 and December 2024. ECA diameters were measured on pre- and post-radiotherapy computed tomographies. Applied radiation doses to the ECA and flaps were extracted from treatment plans. A Cox-proportional-hazard model was developed to identify free flap ORN predictors. RESULTS: PORT led to a significant reduction in ECA diameter (-1.06 ± 1.05 mm, p < 0.001). No significant difference in ECA narrowing between patients with and without free flap ORN was found (p = 0.41). Multivariate analysis confirmed nicotine abuse (hazard ratio (HR) 6.66 [1.95;22.78], p = 0.003) as an independent free flap ORN predictor. Conversely, no significant association was found between ECA dose, flap dose, ECA narrowing, or plate exposure and ORN occurrence. CONCLUSIONS: Although PORT results in measurable ECA narrowing, this vascular change does not significantly influence free flap ORN risk. Future prevention strategies should instead prioritize known modifiable risk factors and further. aim to consider osseous free flaps as structures at risk during radiotherapy planning.  CLINICAL RELEVANCE: While ECA irradiation leads to arterial narrowing, it was not identified as a predictor for free flap ORN formation.