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• 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.
( )
(
)
0
0
( ) 1
b
M M M A b A M
= +
= +
M
0
M
b
Monitor chamber
Dose per MU formalisms:
model-based dose calculations
Fraction of the total signal of the monitor chamber
which is attributed to particles that have backscattered
into the monitor chamber
o
= 1 +
−1
or