A system for an intensity-modulated proton therapy of a predetermined target volume within an object includes a proton source to generate a proton beam, a number of proton beam forming units and a beam nozzle having an outlet for the proton beam to penetrate the predetermined target volume of the object, thereby defining a cross sectional scanning exit area. The system includes further a beam bending magnet disposed upstream of the nozzle, and an x-ray tube and an x-ray imager. The x-ray tube is associated with an irradiation channel within the beam bending magnet, wherein the irradiation channel is oriented along the prolongation of the nominal proton beam direction thereby delivering the x-ray beam along the proton beam direction.