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Dose per MU formalisms:
factor-based dose calculations
Calculations at points off-axis (asymmetric fields)
(
)
(
)
( ) (
)
(
)
( )
2
eqsq d,
eqsq d,
eqsq
ref
ref
d
,
,
,
; , ,
+
⋅
⋅
⋅
⋅
⋅
=
d SSD
SAD
xd OAR d s TPR
sS cS
M
d cD
M
SSD xdsD
p
c
For off-axis positions up to 5cm
no significant variation from the values CAX
On-axis data used
Off-Axis Ratio: representing
off-axis variations of
primary fluence; different
approaches to determine
1.06
1.08
18 MV OPEN BEAM
(Varian 2100)
measured in mini-phantom at 10 cm depth
this experimentally
0.98
1.00
1.02
1.04
0
2
4
6
8
10
12
14
16
OAR
OFF-AXIS DISTANCE [cm]
6%