The ovelapping of targets between simulation CT and CBCT scans of a right upper lung NSCLC. The pink circle represents the GTV and green circle represents the PTV contours in planning CT. From left to right: transverse, sagital and coronal. A: precorrection, shows shifts of the target position from planning contours. B: Post-correction with online correction, shows satisfactory overlapping of the contours between simulation and CBCT images. C: Post-treatment, the targets in CBCT still overlaps well with the contours in planning CT.