Upgrade of the therapy control system for on-line dose compensation

Beam tracking is the potentially most conformal motion mitigation technique in scanned ion beam therapy. For translational motion, beam tracking has been shown to be feasible precisely [1]. If rotational or even deformable motion is present, dose deposition changes even if beam tracking is applied because beam tracking adapts the Bragg peak position only. Dose deposition to other regions, mainly the plateau region of the depth dose profile, might be subject to changes due to the changed beam path [2]. A dedicated method is needed for compensation of these dose changes. Due to the variability in tumor motion and scanning progress these dose changes can only be compensated online, i.e. during treatment, based on measured target motion and scanning progress. The principle feasibility of on-line adaptation of individual voxel doses has been shown previously [3]. In this work the full implementation in an upgraded version of the therapy control system (TCS) is described and results of dedicated experiments are reported.