820 / 1245
0
20
40
60
80
100
120
-150
-100
-50
0
50
100
150
Position (mm)
Dose
Calculated
Measured
RW
50
δ
3
δ
2
δ
4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0
25
50
75
100
125
150
175
200
Depth (mm)
Dose
Measured
Calculated
δ
1
δ
2
δ
1
Criteria depending on position in photon beam
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
.
Adopted from Venselaar, 2001
Warsaw 2017
7