Figure 4

Simulation of a phantom irradiation. Simulation of a phantom irradiation to illustrate the steps of dose calculation in the presence of motion using tracking. 4DCT data were modelled static, with exception of the target (white contour) which moves up and down. Shown are overlays of relative dose distributions on the CT motion phases. a) Reference motion phase with reference dose distribution for the stationary target. b) The resulting dose distribution for tracking which is comparable to a). Small differences distal of the sharp CT gradient occur due to the finite pencil beam width (see text for details). The effective dose distribution is the weighted sum of transformed sub-dose distributions at all motion phases. Sub-dose distributions at extreme target positions are shown in c) and e) and transformed to the reference motion phase in d) and f).