Suboptimal results of deformable image registration. The contours of the macroscopic primary tumor in the planning CT and the follow-up CT are shown in red and arrows point to artefacts after deformable image registration. Patient #5: deformation artefacts of the hilar bronchi (which were included into the GTV). The rather large amount of normal tissue within the GTV is probably responsible for this poor performance of DR. Patient #4: deformation artefacts after tumor shrinkage with a decay of the GTV.