Figure 4.

PTV dose $({\mathrm{D}}_{\text{PTV}})$ and air cavity PTV $({\mathrm{D}}_{\text{PTV‐ac}})$ dose differences and inverse square factor results with various air cavity sizes (in radius) in different balloon sizes. The y‐axis is calculated by $({\mathit{D}}_{\text{PTV‐ac}}-{\mathrm{D}}_{\text{PTV}})/{\mathrm{D}}_{\text{PTV}}(\%)$.