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How to get the dose distribution?
❑
To get a depth dependence one has to correct the planar fluence of electrons
❑
The weighting factor
g
(
z
) is determined such that the dose as a function of
depth on the central axis for a given field size exactly equals the measured
central axis depth dose
o
Corrected to infinite SSD
o
Bremsstrahlung dose, is subtracted (assumed constant at all depths less
than
R
p
❑
In practice,
g
(
z
) must be determined for a range of field sizes for a beam of a
particular energy as the model can only predict the change over a small
range of field sizes
Dublin 2018
7
From Handbook of Radiotherapy Physics
Ed Mayles, Nahum and Rosenwald
D
(
r
,
z
)
=
d
p
(
r
,
z
)
×
g
(
z
)
D
measured
,
electrons
_
only
,
SSD
=¥
(0,0,
z
)