A system includes exactly one rotary frame for holding at least one x-ray tube, and one radiation detector that is situated opposite, the x-ray tube being equipped with a diaphragm that can be dynamically adjusted. The system includes a first operating mode for imaging in which the x-ray tube radiate a ray fan of constant fan angle onto the oppositely situated detector, and CT image data records are calculated from the measured data of the detector. It includes a second operating mode for irradiation in which by using at least one imaging x-ray tube used in the first operating mode radiates an x-ray fan that varies with reference to alignment during the rotation of the rotary frame, is narrower perpendicular to the system axis, and remains aligned with the site of at least one tumor in the patient independently of the angular position of the rotary frame.