541 / 1119
2
ITV and PTV
ITV: Internal variations
Position, size and shape of CTV
•
Tumour shrinkage
•
Organ movement
•
Organ deformation
PTV: External variations
Beam positioning
Patient set-up
If no considerable internal variations are present
Expansion may be performed directly from CTV
to PTV
ITV and PTV margins are not directly “additive”