Fig 3. Landmarks used to compute registration and distance metrics.

Center of mass (COM) are calculated for fiducial markers, gross tumor volume (GTV) and liver. GTV and liver volumes are estimated in all phases via contour propagation based on DIR from the mid-ventilation phase. Estimated fiducial markers’ positions are computed with the transformation φ found by registration. The registration error (r_error) from Eq (1) is illustrated here as the euclidean distance of estimated fiducial markers’ position versus measured fiducial markers’ position.