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The problem …
Energ
CSDA range
1
For brachytherapy photons:
d
ll l i
h
y
[keV]
-
electrons [g/cm
2
]
[cm]
30
1.8E-03
2.5
100
1.2E-02
5.6
350
1 1E 01
8 9
•
secon ary e- ranges are sma re at ve to p oton
m.f.p.
•
e- radiative energy loss is negligible
. -
.
1000
4.4E-01
14
•
CPE can be assumed to exist at all points (except
close to a source or high Z materials)
Dose to a point can be approximated by collision KERMA throughout a geometry
of mm sized voxel elements
In short, to know the dose distribution one needs to know the energy distribution
of fluence Φ at all points of a geometry:
,
Ε
,
Table from: Venselaar, Baltas, Meigooni, Hoskin (Eds), Comprehensive Brachytehrapy: physical and
clinical aspects. CRC Press, Taylor & Francis, © 2013