Dose Course 2018_Flipping book
Handling the beam spectrum – depth changes
Instead of integrating over energy, the collision kerma and scerma distributions can be calculated directly by raytracing with parameterized exponentials. Effect of spectral changing with depth, i.e. depth hardening is described by means of the hardening coefficients P and S
e.g. Pinnacle, Raystation
e.g. Oncentra
parameters
( )
n
P z
parameterization
P
P
( )
(
) z z
E
E z
−
1 − −
0
(
)
0
E
=
e
=
e
,
P P ,
i
i
P
P
i
en
i
=
1
0
0
0
0
( )
S
n
S z
parametrization
S
0
( )
( S S 1 − −
) z z
E
E z
−
(
)
,
S S ,
( ) i E
( ) i E
0
=
−
e
=
e
i
i
en
0
i
=
1
0
0
0
The parameters derived using a (depth dose effective) spectrum. Only P and P are directly measurable quantities.
Heterogeneities considered by using different sets of parameters for each tissue type, mapped by using lookup tables from the Hounsfield numbers!
11
Made with FlippingBook HTML5