Fig. 4

The projection area of the ellipsoid CTV and the general PTV in the XOY plane and YOZ plane are shown in a, c. The CTV (thick black line) is margined isotropically with m (gray area) in three directions to PTV (thin black line). The projection areas of the ellipsoid CTV and BSPTV of beam 0° in the XOY plane and YOZ plane are shown in b, d. The margin area (gray area) of BSPTV of beam 0° is smaller than that of the general PTV. The projection areas of the ellipsoid CTV and BSPTV of beam 90° in the XOY plane and YOZ plane are shown in c, e. The margin area (gray area) of BSPTV of beam 90° is smaller than that of both the general PTV and BSPTV of beam 0°