318 / 1456
Keeping things in perspective
• GTV
PTV margin
– No underdosage allowed
– Use margin prescription
• CTV
PTV margin
– In the CTV there is a probability of tumor cells
– Not clear what PTV margin to use
probabilistic approach
– Margin prescription probably too large
– CTV sometimes based on ‘anatomical’ borders (e.g. bone)
Margin prescription does not apply, or applies to the border