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Dose calculation – AAPM-TG43: The Dose Rate Constant
Λ
The dose rate constant, Λ, is defined as the dose rate to water in water at the reference
point, namely at a distance of r
0
= 1 cm on the transverse axis (θ
0
= 90
0
), per unit air
kerma strength, S
K
:
0 0
)θ,r(D
&
=
(r
0
,
θ
0
)= (1cm, 90
0
)
r
0
= 1cm
Λ is expressed in units of cGy.h
-1
.U
-1
and
1U = 1 µGy.m².h
-1
= 1
cGy.cm².h
-1
K
S
Λ