The present disclosure relates to a medical apparatus. In one implementation, the medical apparatus includes a hadron therapy device adapted for directing a hadron beam having an initial beam energy along a beam path to a target spot located inside a subject of interest an MRI for acquiring a magnetic resonance (MR) image within an imaging volume having the target spot a prompt-γ system adapted for acquiring a signal generated by the hadron beam and a controller configured for computing an actual position of the Bragg peak of the hadron beam, based on the signal acquired by the PG system, and locating the actual position of the Bragg peak on the MR image.
