534-535 / 2239
Derivation of formalism to convert ionisation in plastic to dose to water
Converting ionisation measurement in plastic to dose in water
Phantoms irradiated with
the same MV photon
beam
In water at a reference depth
ref
z
In solid plastic at an equivalent depth
eq
z
( )
( )
( )
s
s
air
eq
air
eq Qs,
eq Qs,
p z
S
N z M z D
=
ρ
(
)
(
)
( )
( )
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
( )
( )
wQ,
w
air
sQ,
s
air
QQ,
Qow, D,
eq Qs,
eq Qs,
0
p
S
p
S
k
N z M z D
⋅
⋅
⋅
⋅
⋅
=
ρ
ρ