317 / 1456
Keeping things in perspective
• Margin recipe assumptions
– Perfectly conformal dose distribution
– Large and smooth (compared to penumbra size) CTV
– Translational errors only
– Large number of fractions (for the 0.7 part)
• Real life
– Not conformal, i.e. margin will depend on shape of dose distr.
– Not smooth
– Lots of changes
translations, rotations, shape changes,
delineation errors…
– Any number of fractions (or very few!)