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measurement with an ionisation chamber
fluence perturbation
Challenge: perturbation factors
A
: field size (aperture)
z
ref
: reference depth
( )
(
)
(
)
(
)
(
)
A
A
A
A
p
ρ
S
z AM
zAM
z AD
A,z D
AS
ref
ref
det
w
air
ref
ref
ref
ref
ref
w
ref
w
cp
,
,
,
=
=
Small fields: relative dosimetry - field size factor, S
cp