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Relative dose: output factors (field size factor), S
cp
( )
(
)
(
)
ref
ref
w
ref
w
cp
,
z AD
A,z D
AS
=
(
)
(
)
[ ]
A
A
A
A
p
ρ
S
z AM
zAM
ref
det
w
air
ref
ref
ref
,
,
=
Determination of dose in small fields
=
det
water
air
air
air
water
p
ρ
S
m
1
e
W
M D
A
: field size (aperture)
z
ref
: reference depth
ref
•
volume effect
•
energy dependence
•
perturbation
Challenges in the determination of S
cp