Target Volume Determination 2015

Keeping things in perspective

• Margin recipe assumptions

– Perfectly conformal dose distribution – Large and smooth (compared to penumbra size) CTV – Translational errors only – Homogeneous dose distribution – Large number of fractions (for the 0.7 part)

Beware of assumptions!!

• Real life – Not conformal, i.e. margin will depend on shape of dose distribution – Not smooth – Lots of changes  translations, rotations, shape changes…

– Inhomogeneous dose distributions – Any number of fractions (or very few!)