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Dose per MU formalisms:

factor-based dose calculations

Intensity modulated fields (IMRT)

For IMRT techniques (Segmental-MLC or Dynamic-MLC), the

general approach

for the calculation of dose per MU from a

modulated field is:

1. Split the modulated field into K segments

2. Sub-divide each segment into a number of beamlets, M

3. Calculate the dose per MU for each beamlet as an open field

based on the factor-based formalism

4. Sum up the doses from each beamlet, with a weight proportional

to the contribution of the segment to total dose, and accounting for

the effect of MLC leakage and transmission.

M

m

open

mm

dC

M

D

open field (beamlet) dose derived

from the dose per MU factor-based

formalism

Beamlet weight depending on how it contributes to the dose from the

segment. This weight is also adjusted dosimetric properties of the

MLC (leakage and transmission)