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Head scatter: equivalent square of a rectangular field
Empirical approach
to account for different
influence of collimator layers
primary collimator
S
Linac head
wedge
monitor chamber
upper Y-jaws
lower X-jaws
flattening filter
MLC leaf
f
S
U
S
L
(
)
yxG
yx1G
y)(x,
c
e
+ ⋅
⋅ ⋅ +
=
x
lower jaw
y
upper jaw
G weighting factor
Vadash P and Bjärngard B E (1993) Med. Phys. 20, 733-734.
depends on:
treatment head design
beam energy
beam modifiers