Dosimetric Studies for Rescanning in scanned particle therapy*

Treatment of moving targets can result in local over and under dosage due to interference effects of the beam application and the motion of the target, so called interplay. Rescanning is one option to mitigate effects of tumor motion in scanned particle therapy [1, 2]. Rescanning is based on statistical methods that show that the dosimetric effect of interplay will average and lead to a homogeneous coverage of the clinical target volume if a sufficiently high number of rescans and margins that cover for the motion extent are used. [3]. Beam application in the rescan-mode sets new demands on deflecting magnets, energy variation, and dosimetry because ideally the treatment time is conserved when reirradiating each point by the number of rescans with proportionally reduced irradiation time and dose per run. Therefore we performed dosimetric studies with the rescan implementation at the carbon therapy cave of GSI to investigate if the dose can be delivered as prescribed.