On-line compensation of dose changes caused by tumor motion

Treating tumors that are subject to intrafractional motion (e.g. lung tumors) with scanned particle beams leads to deterioration of the deposited dose distributions. One possible technique to mitigate motion effects is beam tracking [1]. In case of rotational motion the beam path and thereby the dose deposition in the plateau region proximal of the Bragg peak position changes despite adaptation of the Bragg peak position by tracking (see Figure 1). Adequate on-line compensation of these effects will be required for tumors that rotate remarkably during respiration. [2].