A medical device includes a moving gantry, on which a radiation source is arranged, and a collision-protection apparatus for preventing a patient from colliding with the moving gantry. The gantry is operable to be moved around a patient-positioning apparatus. The collision-protection apparatus can be configured as a mechanical collision-protection apparatus that is operable to be positioned between the patient and the moving gantry. The collision-protection apparatus can also be configured as a collision-monitoring apparatus that detects the crossing of a predefined volume by an object, the collision-monitoring apparatus having a control apparatus that controls the motion of the gantry as a function of whether a crossing of the volume has or has not been detected.
