Fig. 1

Bladders contours on MRI scans acquired at the beginning and the end of a 1.5 T MR-Linac online adaptive session and rigidly registered. Coronal, transversal and sagittal MRI planes for a representative patient not undergoing (a–c) and undergoing (d–f) the bladder filling control procedure. In red and blue the bladder contoured on the MRI acquired at the beginning and end of the session