Dose Course 2018_Flipping book
Criteria depending on position in photon beam
8
1.8
Measured Calculated
1.6
δ
Points along the central axis of the beam beyond the depth of dose maximum: low dose gradient area . Points on and off the central axis in the build-up and penumbra region. This region includes also points in the proximity of interfaces: high dose gradient area . Points inside the beam ( e.g ., inside 80% of the geometrical beam) but off the central axis: low dose gradient area . Points outside the geometrical beam or below shielding blocks, jaws, MLC, etc … where the dose is lower than, for instance, 7% of the central axis dose at the same depth: low dose gradient area .
1
δ
1.4
2
1.2
1.0
δ
1
0.8
Dose
0.6
0.4
0.2
0.0
0
25
50
75
100
125
150
175
200
Depth (mm)
120
δ
3
100
80
60
RW
50
Dose
40
Calculated Measured
20
δ
2
δ
4
0
-150
-100
-50
0
50
100
150
Position (mm)
Adopted from Venselaar, 2001
Dublin 2018
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