Cine 4DCT imaging artifacts: Quantification and correlations with scanning parameters and target kinetics

To study temporal resolved computed tomography imaging (4-Dimensional Computed Tomography: 4DCT) artifacts correlations with scanning parameters and target kinetics and to assess uncertainty introduced by 4DCT in radiotherapy treatment planning. In this work we classified 4DCT artifacts as finite gantry rotation speed related (FGS) and finite sampling frequency related (FSF). We studied FGS artifacts using a respiratory phantom and FSF artifacts using a Monte Carlo simulation of acquisition timing. From our analysis FGS localization error is comparable with image resolution determined by voxel dimensions. Remaining FGS artifacts are correlated with gantry rotation time (Trot), target velocity (v) and their interaction. FSF artifacts occurrence is correlated with sampling ratio (SR), i.e. the ratio of patient respiratory period (Tresp) and sampling time (Ts). In the studied velocity range (0-2 cm/s), using a Trot of 0,5s and a SR higher than 15, FGS and FSF artifacts became comparable with other sources of uncertainty. Our considerations are valid for "ideal" breathing pattern only. When variations from periodical breathing, high target velocity (more than 2 cm/s) or high peak to peak amplitude (more than 2 cm) are present, patient specific images artifacts analysis is recommended.