Outcomes {12}
Primary outcome:Treatment accuracy: the specific measurement made will be the average chest wall position extracted from the EPID images captured at each treatment fraction. The metric used for analysis will be the ‘displacement’ or difference between this measured position on each captured image frame and the planned average chest wall position from the digitally reconstructed radiograph (DRR). The average per fraction displacements will be compared across the two arms of the trial.Secondary outcomes:Setup time: The appointment duration will be measured as the time recorded in the ARIA patient management system between patient check-in and appointment end for each treatment fraction, and aggregated for each arm of the trial.Patient comfort and user friendliness. A patient survey (see Technology assessment: A staff survey (see To develop — offline — the use of the electronic portal imaging device (EPID) for real-time MLC tracking during monitoring the chest wall position in breast radiotherapy. This work will be reported as future research outputs.Estimated dose delivered. Measured chest wall displacement relative to planned position (taken from the EPID images captured at treatment time, see the primary outcome) will be used to apply an isocentre shift in the treatment planning system, following the approach of Doebrich et al. [