530-531 / 2239
Derivation of formalism to convert ionisation in plastic to dose to water
Scaling photon energy fluence
In water at a reference depth
In solid plastic at an equivalent depth
Phantoms irradiated with
the same MV photon
beam
ref
z
w
Ψ
eq
z
s
Ψ
Simplification: by keeping SSD and
field size ( r ) the same for the
irradiation in solid phantom:
(
)
(
)
( )
( )
ref
sp,
eq sp,
2
ref
ref
eq
ref
ref
eq
ref
ref
,
,
r S
r S
z
SSD
z
SSD
r z
r z
s
w
+
+
=
Ψ
Ψ
Phantom
scatter factors
in solid
phantom
Seuntjens et al, 2005, Med.Phys. 32 pp2945-