This thesis studies nuclear fragmentation induced by protons, 4He and 12C ions in the energy range used for radiotherapy through two different experimental setups. A comprehensive understanding of these nuclear reactions is essential for accurate dose calculation in patients and for verification of the treatment via positron emission tomography (PET). In the first experiment, conducted at the Heidelberger Ionenstrahl-Therapiezentrum, charge- and mass-changing cross sections were measured for the colliding systems 4He +1 H, 4He +12 C, 4He +16 O and 4He +28 Si in the energy range of 70 - 220 MeV/u. The cross sections were obtained via the attenuation method where a DeltaE - E scintillator telescope was used for particle identification. These data will have particular relevance for future applications of 4He ions in ion beam radiotherapy as this technique relies on precise nuclear reaction models for an accurate dose calculation. The widely used parametrization for the total reaction cross section delta R by Tripathi et al. under-predicts the new experimental cross sections for 4He ions in the therapeutic energy range by up to 30%, which can lead to considerable dose calculation uncertainties. Therefore, the parameters in the Tripathi model were optimized and the FLUKA nuclear reaction model was adjusted accordingly. The new models were validated by comparing radiation transport calculations against available 4He depth dose measurements. The impact of the nuclear model changes for 4He ions on their relative biological effectiveness was studied through radiobiological calculations based on the local effect model.In the second experiment, conducted at the Marburger Ionenstrahl-Therapiezentrum, cross sections were measured for the production of 10C, 11C and 15O by protons (40 - 220 MeV) and 12C ions (65 - 430 MeV/u) on C and O targets. The cross sections were obtained via activation measurements of irradiated graphite and BeO targets using a set of three scintillators coupled by a coincidence logic. The measured cross sections are relevant for the particle range verification method by PET where accurate predictions of the beta+-emitter distribution produced by therapeutic beams in the patient tissue are required. This dataset will be useful for validation and optimization of proton-nucleus and nucleus-nucleus reaction models within radiation transport codes. For protons there is a good agreement between a radiation transport calculation using the measured cross sections and a thick target PET measurement from the literature. For 12C-induced nuclear reactions the novel cross sections are a good basis for further model developments.
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