Course book Advanced Treatment Planning 2018

2.5 S + 0.7 s is a simplification

• Dose gradients (‘penumbra’ = s p

) very shallow in

lung → smaller margins for random errors

s ) ( 64.1 5.2 2 2 s

M

+S =

s − + 64 .1

p

p

• Number of fractions is small in hypofractionation

• Residual mean of random error gives systematic error • Beam on time long → respiration causes dose blurring

• If dose prescription is at 80% instead of 95%:

p 2

2

M

=

+S

s ( 84.0 5.2 +

s

)

−

.0

84

s

p

( van Herk et al, IJROBP 47: 1121-1135, 2000)