The patients eligible for the study are those treated by radiotherapy on Linac MRI for a mobile cancerous lesion (pancreas, liver, kidneys, adrenals, lung, adenopathy above or below the diaphragm ...). After signing the consent form, each patient will be randomized to one of two treatment arms: * Standard arm : Radiotherapy treatment with Linac MRI without non-magnetic shielding * Experimental arm : radiotherapy treatment with Linac MRI with non-magnetic screen The aim is to evaluate the effect of using a non-magnetic screen visible to the patient in the bunker during radiotherapy sessions delivered by Linac MRI on decreasing the ratio between the actual treatment time and the treatment time predicted by the machine.