Therapy system (100) for irradiating a target volume (2) of a patient (1) with a charged particle beam (6), including a beam generator (3), a beam transport system (4), and a nozzle (5) for distributing the beam to the target volume (2), the nozzle (5) being, when in operation, under vacuum. The therapy system comprises an X-ray device (10) which is rotatably mounted inside the nozzle (5) between a first position and a second position. In the first position, an X-Ray source (12) within the X-Ray device is able to emit X-Rays along a charged particle beam path for generating an X-Ray image on a corresponding X-Ray receiving device (11) arranged opposite to the patient (1), said X-Ray image serving to determine a correct position of the target volume (2) with regard to the charged particle beam (6). In the second position, the X-Ray device (10) is set outside of a charged particle beam treatment path envelope (23), so that the charged particle beam (6) can reach and irradiate the target volume (2).