Dose Course 2018_Flipping book

Dose per MU formalisms: model-based dose calculations

• The signal from the monitor chamber has a component that originates from particles which have backscattered from the upper part of the jaws into the chamber.

• The fraction of this signal depends on the aperture defined by the upper jaws and increases as this decreases.

Fraction of the total signal of the monitor chamber which is attributed to particles that have backscattered into the monitor chamber

(

)

( ) b M M M A b A M = + = + 0 ( ) 1

M

b

0

Monitor chamber

M 0

or

−1

o = 1 +