Figure 4. Respiratory motion patterns of skin and tumour: motion patterns of skin markers and tumour (a) in the x-axis (right upper lung fields in the anterior–posterior (AP) view), (b) in the y-axis (right upper lung fields in the AP view) and (c) in the z-axis (lower lung fields in the lateral view). (d) Motion patterns in the y-axis (right upper lung fields in the AP view): when skin makers began to move, a short delay in motion was caused by respiratory tumour motion. (e) Motion patterns in the y-axis (left upper lung fields in the AP view): when distortions were caused by sudden changes in period, amplitude, or phase of respiration, skin and tumour experienced the same distortions, and thus, remained correlated. x-axis, right–left direction of the body; y-axis, superior–inferior direction; z-axis, anterior–posterior direction.