Rescanning to mitigate the impact of motion in scanned particle therapy

Treatment of targets that move during the irradiation with a scanned particle beam leads to deterioration of the dose distribution [1]. This dose deterioration results from interference of target motion and scanned beam, so called interplay. Apart from beam tracking [2] and gating [3] rescanning [4] can be used to mitigate the impact of motion. Rescanning mitigates interplay effects by multiple reirradiations of the target with proportionally less dose during a single scan and margins that cover the motion extent. In principle, local mis-dosage averages out over several reirradiations. Rescanning was implemented at GSI, initial results are presented.