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Qw, s,
k
Calculated; using basic (tabulated) interaction coefficient data;
and: stopping power ratio data and chamber perturbation factors
generated by Monte Carlo methods
Directly measured
( )
( )
MUs
equal
eq Qs,
ref
Qw,
Qw, s,
z M
z M
k
=
Derivation of formalism to convert ionisation in plastic to dose to water
Phantom dose conversion factor
Example: at 5cm PWDT, 6MV (TPR20,10=0.668), PTW30013 cylindrical chamber
983 .0
PWDT
=
c
(
)
(
)
004 .1
SSD ,09.5
SSD ,5
MUs
equal
Q PWDT,
Qw,
Qw,
PWDT,
=
=
M
M
k