In this single-arm prospective BREAST-ART study breast cancer patients with an indication for postoperative radiotherapy will be treated according to the Dutch and institutional guidelines. Target volumes will be the whole breast, chest wall, axillary levels, tumor bed boost and partial breast irradiation on the right side and left side with a deep inspiration breath hold technique. Robust templates are developed for offline and online treatment planning with an IMRT tangential multiple-beam setup. A simulation of the online adaptive workflow is performed in breast cancer patients already treated on the Ethos-linac with the standard offline adaptive workflow. Patients will be treated following the online adaptive workflow delivered on the Ethos-Linac. Patient experience will be evaluated using an in-house developed questionnaires after the first and last fraction, scoring treatment satisfaction on a 4-point Likert scale. Furthermore, all dosimetric data, volume details, DICOM images and the time spend on all parts of the online adaptive workflow will be evaluated.
