Dose 2016

Modelling geometric penumbra

ra

rb

r eA z −

r eB z −

p

( ) ,

z

z

zr

=

+

ρ

2

p

r eA z −

ra

1

r

−

2

( ) ,

p

eff

σ

=

⊗

zr

e

z

z

2

ρ

πσ

z

z

coll

Gaussian source distribution

As z coll varies for different collimators the additional part of the kernel, describing the geometric penumbra, should vary between different calculation points ⇒ Problems for fast convolutions.

coll z z − ⋅σ=σ

z

z

coll

A Ahnesjö et al (1992) Med Phys 19, 263-273