ESTRO 2025 - Abstract Book

S3174

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

3407

Digital Poster Feasibility of daily CBCT guided online adaptive treatment for all head and neck tumours Julie A Fox, Andrew R Bromiley, John McLellan, Polly Darby, David J Carnegie, Catriona Burnett, Nicola Miller, Gillian Mcintosh, Rachel Adam, Amy Hamilton, Megan Fraser-Bell, Martin Rudge, Kirsten Laws, Rafael Moleron Radiotherapy Aberdeen, NHS Grampian, Aberdeen, United Kingdom Purpose/Objective: The aim of this work was to show the feasibility of delivering online adaptive radiotherapy using Ethos for head and neck cancer patients across the full spectrum of primary treatment sites and tumour stage. The adaptive treatment delivery is a radiographer-led process, and we have identified possible efficiencies in the treatment allowing delivery within a standard time slot on the Ethos treatment unit. Material/Methods: The radiographers received training in head and neck voluming, plan dose assessment, and they initially performed the adaptive process under supervision of a clinician. We used the Ethos emulator software to evaluate changes to the defined CTV and PTV to assess whether changes to the organ at risk (OAR) “influencers” have a significant impact on the CTVs and PTVs. The patients were treated using the adaptive workflow for the entire course of treatment. CTV coverage was compared in the adaptive and scheduled plans with the reference plan of each patient. Across the whole treatment course, the target and OAR doses in the scheduled and adapted plans were compared for a range of treatments in 16 patients, 288 delivered fractions. Results: Treatments included oropharynx, larynx, hypopharynx, nasopharynx, parotid, post-operative and recurrence. Similar experience is found for all types and sizes of tumour of the head and neck and radiographers did not require further training for expansion of the tumour site from oropharynx to different levels of the head and neck. The Emulator studies showed that there is no need to alter the brainstem, spinal canal or mandible influencers as the outcome will not be significantly affected. In all cases the CTV coverage in the adapted plan was either closer to the reference plan than the scheduled plan or improved over the reference plan. All adaptive plans were better than the scheduled plan for parotid where this can be spared in a clinically significant range 20-26Gy, and this does not lead to compromise of the PTV. The adapted plan was appropriate for treatment in all fractions but not used initially when staff were in training. Conclusion: CBCT guided online adaptive head and neck radiotherapy treatments are feasible on Ethos for all types of head and neck tumour and staging and is on the way to becoming standard of care in Aberdeen. These results are supporting evidence for safe reduction of CTV to PTV margins in appropriate clinical trials.

Keywords: Head, Neck, Adaptive