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The widening of the pencil is limited
❑
The pencil-beam width (
MCS
)
as a function of depth agrees
well with experiment at small
and moderate depths.
❑
Then it continues to increase,
whereas in reality it goes
through a maximum and
finally decreases.
❑
This is managed by the
g(x)
function or has to be managed
in other ways in some systems
❑
This is due to the reduction or
loss of the number of electrons
in the beam at large depths
due to range straggling
Dublin 2018
10
From Handbook of Radiotherapy Physics
Ed Mayles, Nahum and Rosenwald