ESTRO 2025 - Abstract Book

S959

Clinical – Head & neck

ESTRO 2025

Conclusion: The 20 fraction HYDRA treatment delivers a focal boost to the tumor center without compromising organs at risk. The pre-defined interim analysis of the first 10 HYDRA-photon patients showed acceptable toxicity and local control. The immune effects of HYDRA are still to be evaluated.

Keywords: hypofractionation, focal boost, proton therapy

References: 1. Elbers JB, Gunsch PA, Debets R, Keereweer S, van Meerten E, Zindler J, et al. HYpofractionated, dose-redistributed RAdiotherapy with protons and photons to combat radiation-induced immunosuppression in head and neck squamous cell carcinoma: study protocol of the phase I HYDRA trial. BMC cancer. 2023;23(1):541.

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Mini-Oral Involved neck only versus mucosal radiotherapy for HNSCCUP: a national multicentre review of primary emergence, failure patterns and toxicity rates WY Poon 1,2 , AL Peters 1,2 , S Walters 2 , Z Iyizoba-Ebozue 2 , C Hannon 2 , S Kingdon 2 , K Yogalingam 2 , L Kennedy 2 , J Peck 1,2 , K Cavanagh 1,2 , R Fernandes 2 , Y Wang 2 , S Thomas 2 , M Rowe 2 , K Grellier 2 , K Mactier 2 , M Baxter 2 , S Growcott 2 , A Muse 2 , R Kitson 2 , O Gbenebichie 2 , K Laws 2 , J Hardman 3 , C Wilson 1,2 , C Paterson 1,2 1 Clinical Oncology, Beatson West of Scotland Cancer Centre, Glasgow, United Kingdom. 2 NOTCH, National Oncology Trainees Collaborate for Healthcare (NOTCH) Collaborative Group, NOTCH, United Kingdom. 3 ENT INTEGRATE, The UK ENT Trainee Research Network (ENT INTEGRATE), ENT INTEGRATE, United Kingdom Purpose/Objective: Squamous cell carcinoma of unknown primary in the head and neck (HNSCCUP) is rare and practice is informed by retrospective single centre studies. For unilateral disease, radical non-surgical treatment approaches are to irradiate the involved neck only (INO), or to include prophylactic mucosal and contralateral neck irradiation (MUC). There is a paucity of contemporary evidence to favour either strategy. The aim of this work is to report on one of the largest multicentre datasets in HNSCCUP to allow meaningful comparisons between the two approaches with regards to disease control and toxicity. Material/Methods: This is a retrospective UK multicentre cohort study conducted via NOTCH (the National Oncology Trainees Collaborate for Healthcare). Patients diagnosed with HNSCCUP from 2016-2023, who had unilateral neck disease and received radical radiotherapy, were eligible for inclusion. All underwent FDG PET-CT during diagnostic work up. Results: 196 patients treated with volumetric modulated arc therapy (VMAT) for HNSCCUP from 13 UK centres were included. Table 1 includes demographics, and Table 2 displays toxicity, dosimetry and survival data. 74 patients (38%) received INO radiotherapy (RT) and 122 (62%) received MUC RT. 116 patients were treated with primary RT and 80 with adjuvant RT. Median duration of follow up was 57 months (IQR 40-70). 3 patients had primary emergence (2 in the INO group and 1 in the MUC group), all receiving salvage surgery. No patient with primary emergence had died at time of data analysis. The INO group had a higher nodal stage with 15% N3b vs 3% in MUC group, whereas stage N3a was more frequent in the MUC group (1% vs 10%). Contralateral recurrence was 5.4% for INO and 0.8% for MUC (p=0.10), with all but one having salvage surgery. OS at 5 years was 80% for INO and 81% for MUC (p=0.87). MUC had a higher rate of acute (11% vs 34%, p<0.001) and long term feeding tube requirement (0 vs 5.7%, p<0.05). The mean dose to the contralateral parotid, and maximum dose to the spinal cord/brainstem were significantly higher in the MUC group (p<0.001).