ASMR

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