The raster-scanning method for carbon beams developed at GSI for cancer treatment provides excellent dose gradients, with effective sparing of critical structures close to the tumor mass.

Compared to conventional photon radiotherapy, dose delivery to moving (4D) targets, such as lung, liver or kidney is more complex mainly due to two factors: (1) interference between target and beam motion (interplay) and (2) the changing range to the target due to its motion.

Interplay leads to highly variable over- and underdoses, which prevent the simple use of margin concepts for motion compensation as used in photon radiotherapy. The finite range of ion beams in matter is a major advantage, but also require precise knowledge of the radiological pathlength to the target tissue. As this pathlength changes with motion especially in the lung, dedicated mitigation strategies are necessary.

The Medical Physics group has developed and investigated efficient motion mitigation techniques including beam gating, rescanning, beam tracking, and 4D-optimization strategies. All techniques were implemented and experimentally validated at GSI’s Cave M with a number of in-house developed motion platforms and phantoms. The primary aim of these studies is to achieve conformal dose coverage with maximum sparing of healthy tissue.

The in-house developed treatment planning software TRiP4D permits large-scale simulation studies both for cancer and non-cancer targets, for example the non-invasive treatment of cardiac arrhythmia.