A therapeutic apparatus comprising: a magnetic resonance imaging system adapted for acquiring a set of magnetic resonance imaging data in an imaging zone, wherein the magnetic resonance imaging system comprises a means for generating a magnetic field, a guiding means adapted for guiding a beam of charged particles to a target zone within a subject such that the beam encloses an angle with the magnetic field lines of the magnetic field within the imaging zone, the angle being between 0 degrees and 30 degrees, wherein the imaging zone comprises the target zone, a zone determination means for determining the location of the target zone within the subject using the set of magnetic resonance imaging data.