Apparatus for radiation therapy combines a patient table, an MRI and a radiation treatment apparatus mounted in a common treatment room with the MR magnet movable from a position outside a radiation shielded door to an imaging position. An RF-shielded door is movable between a position, separating part of the treatment apparatus from the magnet and an open position allowing access of the patient to the treatment apparatus. In one configuration there is a row of treatment rooms and the magnet is mounted to move along a passageway outside the row of radiation shielded doors of the rooms.