Body contour adaptation for weight‐loss and bolus for head and neck radiotherapy on Ethos version 2.0 and HyperSight: Synthetic CT versus direct calculation

Contours in Ethos v1 rely on reference contours and deformable registration algorithms, whereas Ethos v2 does not. Hence, Ethos v2 is preferred for cases involving weight change. A tight-fitted air gap-free bolus is critical for achieving accurate body contours for Ethos v2 Hypersight CBCTs.