Fig. 4

Comparison of sum dose profiles through a matching area for TH&TH (a) and TH&TD (b). The sum dose profiles were obtained along the superior-inferior axis at the level of the isocenter (Line A-B in Fig. 1d). To assess the effect of longitudinal setup errors, the FFP plans (lower PTV plans) were shifted superiorly (positive: overlapped) and inferiorly (negative: separated); no positional shift (black), + 0.5 cm (pink), + 1.0 cm (orange), + 1.5 cm (green), + 2.0 cm (red), − 0.5 cm (blue), − 1.0 cm (brown), − 1.5 cm (sky blue), and − 2.0 cm (purple). Solid and dashed lines are the sum dose profile for VGMT using 5-GVs and 7-GVs