Figure 6. Prediction of internal tumour location from external skin markers, and the uncertainties of tumour position due to movement during breathing before prediction (actual tumour motion) and after prediction (corrected tumour motion, which were the difference between actual tumour motion and predicted motion): motions (a) in the y-axis (right lower lung fields in the anterior–posterior (AP) view) and (b) in the y-axis (lower lung fields in the lateral view) were predicted by an amplitude fitting, and motions (c) in the y-axis (right lower lung fields in the AP view) by a phase-corrected fitting. (d) Prediction with remote skin markers: from skin motion in the z-axis in the lateral view, tumour motion in the y-axis in the AP view was predicted (lower lung fields in the lateral view). The uncertainties of tumour position were reduced (a) from 2.26 cm to 0.92 cm, (b) from 2.26 cm to 1.05 cm, (c) from 1.78 cm to 0.77 cm, and (d) 1.74 cm to 0.72 cm. x-axis, right–left direction of the body; y-axis, superior–inferior direction; z-axis, anterior–posterior direction.