The present invention relates to a system and method for assisting radiotherapy planning. A data storage is provided comprising a patient support device library, the patient support device library comprising patient support device data for a plurality of patient support devices. A source medical image of a patient on a scanning couch is analysed to determine a reference plane. A patient support device is selected from the patient support device library, to select patient support device data for the selected patient support device. A modified medical image, based on the source medical image, wherein generating the modified medical image comprises positioning a representation of the patient support device relative to the reference plane.