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