774-775 / 2239
Modelling geometric penumbra
( )
r
eA
e
zr
p
ra
z
r
z
p
z
z
eff
−
σ
−
⊗
πσ
=
ρ
2
2
2
1
,
( )
r
eB
r
eA
zr
p
rb
z
ra
z
z
z
−
−
+
=
ρ
,
coll
z
A Ahnesjö et al (1992)
Med Phys
19, 263-273
Gaussian source
distribution
coll
coll
z
z
z z
−
⋅σ=σ
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.