532-533 / 2239
Derivation of formalism to convert ionisation in plastic to dose to water
Converting dose in plastic to dose in water
Phantoms irradiated with
the same MV photon
beam
In water at a reference depth
In solid plastic at an equivalent depth
eq
z
s
Ψ
ref
z
w
Ψ
( )
( )
w
w
en
ref
w
ref
Qw,
β
ρ
µ
Ψ=
z
z D
( )
( )
s
s
en
eq s
eq
Qs,
β
ρ
µ
Ψ=
z
z D
(
)
(
)
( )
( )
w
s
w
s
ref
sp,
eq sp,
2
ref
ref
eq
ref
ref
eq Qs,
ref
ref
Qw,
,
,
β
ρ
µ
+
+
=
en
r S
r S
z
SSD
z
SSD
r z D r z D