Abstract: The invention concerns a device and a process for adjusting the range of an ion beam, in particular for irradiation in tumor therapy. For this purpose, first the reference position of a target volume to be irradiated is determined. Subsequently, the range of an ion beam is configured such that said beam is adjusted to the reference position of the target volume, in such a manner that the Bragg peak, i.e. the maximal energy loss and thereby the maximal damage occurs in the region of the target volume which is to be destroyed. In the case that it has been determined that the reference position has been altered by a movement of the target volume, the ion beam is then deflected from the beam axis such that the ion beam is directed to various regions of a range modulator, in order that the ion beam experience a correspondingly adjusted energy loss in passing through the range modulator.