Volume Conformal Irradiation of Moving Target Volumes with Scanned Ion Beams

The intensity modulated raster scanning technique enables an extremely precise irradiation of tumours, which can be fixed in position and do not move. This thesis investigates how to extend raster scanning to moving target volumes, like in the thorax. Two different strategies were studied: A rescanning of the volume which is not correlated to the target motion and an active realignment of the beam in all three dimensions during the irradiation (online motion compensation). The simulations and experiments concerning rescanning showed that the dose distribution can be improved in a limited part of the irradiation field, but the border area of the field remains strongly inhomogeneous. To improve the homogeneity over the whole target volume an extension of the irradiation field would be required, sacrificing volume conformity and increasing the dose contribution to the normal tissue in the tumour bed. The approach of active realignment of the beam during the irradiation avoids smearing of the dose distribution. In simulations the effect of different motion parameters on the dose homogeneity was calculated. Based on these calculations, a prototype for online motion compensation was constructed. In this setup the compensation of lateral motion components was realised with the scanning magnets. Longitudinal motion compensation was achieved with a fast, passive wedge system driven by linear motors. Both systems enabled an online realignment of the beam position with sub-millimetre precision. This prototype setup allowed the delivery of static dose distributions to targets, which were subject to respiration-like motion, with a precision of 1-2%.