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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