370-371 / 1726
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 (e.g. uncertainties when setting up
according to skin marks)
If no considerable internal variations are present
Expansion may be performed directly from CTV
to PTV
ITV and PTV margins are not directly “additive”