S558
Clinical – Head & neck
ESTRO 2026
hypothyroidism risk in HNC patients. References: 1) Chow JCH, Cheung KM, Cheung GTC, et al. Dose- volume predictors of post-radiation primary hypothyroidism in head and neck cancer: A systematic review. Clin Transl Radiat Oncol. 2022;33:83-922) Lertbutsayanukul C, Kitpanit S, Prayongrat A, et al. Validation of previously reported predictors for radiation-induced hypothyroidism in nasopharyngeal cancer patients treated with intensity-modulated radiation therapy, a post hoc analysis from a Phase III randomized trial. J Radiat Res. 2018;59(4):446-553) Chow JCH, Lui JCF, Cheung KM, et al. Post-radiation primary hypothyroidism in patients with head and neck cancer: External validation of thyroid gland dose- volume constraints with long-term endocrine outcomes. Radiother Oncol. 2022;177:105-10 Keywords: head and neck cancer, hypothyroidism, NTCP
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Quantitative CT Bone Density Patterns in Mandibular Osteoradionecrosis Inform Surveillance Strategies
Zaphanlene Kaffey 1 , Mai Badawy 1 , Lina Shbita 1 , Anthony Minsuk Kang 1 , Omar Mohammad 1 , Sarah Mirbahaeddin 1 , Samuel Mulder 1 , Cem Dede 1 , Mohamed Naser 1 , Laia Humbert-Vidan 2 , Stephen Lai 3 , Clifton Fuller 1 1 Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, USA. 2 Department of Radiation Oncology, Vall d’Hebron Institute of Oncology (VHIO), Barcelona, Spain. 3 Department of Head and Neck Surgery, Division of Surgery, The University of Texas MD Anderson Cancer Center, Houston, USA Purpose/Objective: Current dose-volume models predict patient-level osteoradionecrosis (ORN) risk but cannot identify which specific mandibular regions require targeted surveillance or prophylaxis. We investigated the spatial and temporal radiographic characteristics of mandibular ORN to determine optimal imaging surveillance strategies. Material/Methods: We analyzed 47 head and neck cancer patients who developed mandibular ORN, each with three CT timepoints: baseline (pre-RT), intermediate follow-up (temporal midpoint between RT completion and ORN diagnosis, ±3 months), and ORN diagnosis. Deep learning auto-segmentation using IMPACT (Image- based Mandibular and maxillary Parcellation and Annotation using Computer Tomography) subdivided the mandible into six anatomical subregions (alveolar,
Figure 2
Conclusion: This multicenter study represents the largest external validation of prediction models for radiation-induced hypothyroidism to date. Current NTCP models may underestimate the long-term risk of hypothyroidism, particularly in low-risk patients. Incorporating surrogates of thyroid reserve, especially baseline TSH level, enhances predictive accuracy. The best- performing model offers potential for guiding personalized radiotherapy planning to reduce
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