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Factor-based dose calculations: basic dosimetric quantities
In-air output ratio or output factor in air, Sc
d
ref
c
ref
Is the ratio of
primary collision water kerma in free-space K
p
per
monitor unit (MU) between an arbitrary collimator setting c and the
reference collimator setting c
ref
at the same location on the beam’s
central axis:
( )
(
)
(
)
M
;
M ;
ref
ref
p
ref
p
d cK
dc
K
cS
c
=
Also known as:
Mini-phantom output ratio
Collimator scatter factor
Head scatter factor
Sc quantifies fluence variations with collimator settings that can
be used in beam modelling and dose calculations.
Usually d
ref
= 10cm and c
ref
=10cm
E
K
d
spectrum
primary
en
E
p
=
Report pf AAPM TG106: Accelerator beam data commissioning, Med Phys, 35(9), 2008
AAPM TG 74 report, Med Phys 36 (11), 2009