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Dose per MU formalisms:

factor-based dose calculations

Modulation with physical wedges

• Physical wedges introduce changes in the beam spectrum, which are dependent on wedge material and influence dosimetric parameters

that vary with depth (TPR, RDD) as well as phantom scatter, Sp

• The position of the wedge, whether internal (motorised) or external (manually inserted) affects Sc

• Dosimetric parameters for wedged beams should not be confused with open beam data

• Irregular wedged beams need some special considerations for MU calculation / verification

Additional correction factors needed in the dose per MU formalism

0,90

0,95

1,00

1,05

1,10

1,15

0 5 10 15 20 25 30 35 40

EQUIV. FS [cm]

OUTPUT RATIO IN AIR

X 6 - op

X 10 - op

X 25 - op

X 6 - we

X 10 - we

X 25 - we

Example: Elekta Precise, 60

°

internal wedge

Variation open vs wedged fields:

With FS

~ 10% open

~ 20% wedge

Wedge angle

Energy

Linac specific