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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)