ESTRO 2024 - Abstract Book

S4143

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

Andrew R Bromiley, John McLellan, Julie Fox, Adam El Qmache, Polly Darby, Catriona Burnett, Nicola Miller, Gillian McIntosh, Rachel Adam, Amy Hamilton, Richard Cheyne, Kirsten Laws, Rafael Moleron

NHS Grampian, Radiotherapy, Aberdeen, United Kingdom

Purpose/Objective:

The aim of this work was to (1) establish a streamlined workflow for delivering online adaptive radiotherapy (oART) using Ethos for head and neck (H&N) cancer patients and (2) to provide an analysis of the early treatment dosimetric results and service impact. We investigated the possibility of performing daily CBCT guided oART for head and neck cancers within a workable time slot for daily treatment in a public healthcare radiotherapy treatment facility. The workflow was created to allow for treatment with oART without the requirement for the clinician to be present at each treatment session. We examine the results of more than 120 fractions of head and neck treatment for: (1) total time, broken down into the time for each step in the online adaptive process; (2) the choice of plan, adaptive versus scheduled; (3) the total treatment actually received versus the expected treatment. The ability to deliver routine adaptive treatment quickly and the improvement in treatment for the patient is key to rolling out this technique across radiotherapy. Aberdeen Royal Infirmary has 2 Ethos machines (Varian Medical Systems Inc. Palo Alto, California) with which we can deliver CBCT guided online adaptive treatment. The Ethos treatment unit comes with an in-built record and verify system with which the treatment can be evaluated and independent dose calculation software, Mobius. Data was sent to the Eclipse treatment planning system to allow further comparisons of summed DVH data for the patients. Additional data was also pulled from the Mobius system to independently evaluate dose volume metrics. Four patients, comprising 3 oropharynx and 1 postoperative oral cavity reirradiation, underwent a combined total of 123 consecutive adaptive sessions. The patients were treated using the adaptive workflow for the entire course of treatment. For all cases the treatment is planned using the Ethos planning system using a tested RT Intent (Ref 1): 100216.); this is referred to as the reference plan. The scheduled plan is the reference plan positioned for best match of the adapted target volumes to the planned target volumes. The treatment process is broken into several steps: evaluation of the CBCT; review of the major organs at risk (influencers); review of the adapted CTV and margins; review of the scheduled and adapted plans against the reference plan; independent MU check of the chosen treatment; and delivery of the treatment. We collected data on how quickly each of these steps was completed to assess where the process may be made more efficient. Material/Methods:

Across the whole treatment course, the target and OAR doses in the scheduled and adapted plans were compared using a paired t-test. These doses were assessed alongside the planned dose.

Results: