Dose Course 2018_Flipping book

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 D

open field (beamlet) dose derived from the dose per MU factor-based formalism

open mm



dC

=

m

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)