Figure 1.

Schematic diagram of a target volume on pCT and rCT scans. TV was manually delineated on pCT [TV_{_pCT} (gray + blue)] and rCT [V_{_rCT} (pink + blue)] scans; common [V_{_common} (blue)] and union [V_{_union} (gray + blue + pink)] volumes are shown from a single rCT axial slice. The OI of V_{_rCT} on rCT scan was calculated by V_{_common}/V_{_pCT}, which presented the ratio of common volume and the volume of the targets in pCT. Dice similarity coefficients were calculated as 2× V_{_common}/(V_{_rCT} + V_{_pCT}). pCT, planning CT; rCT, repeat CT; TV, target volume; OI, overlapping index; V_rCT, the volume in the rCT; V_{_common}, common volume; V_{_pCT}, volume in pCT.