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Dose per MU formalisms:
factor-based dose calculations
Irregular fields shaped with MLCs
• MLC design and position in linac head
o
Lower jaw replacement
o
Upper jaw replacement
o
Add-on (3
rd
level) configuration
• Depending on the MLC design, its influence
on Sc and Sp needs to be considered
separately:
• Upper or lower jaw replacement MLC
(e.g. Elekta, Siemens linacs)
➢
The equivalent square from a sector
intergration of the MLC aperture is
used for both Sc and Sp
• Add-on (3
rd
level) configuration (eg Varian
linacs)
➢
Sc
eq. Sq. of secondary jaws
➢
Sp
eq. Sq. from MLC aperture
0.920
0.940
0.960
0.980
1.000
1.020
1.040
1.060
1.080
0
5
10
15
20
25
30
35
40
45
SQUARE FIELD SIZE [cm]
OUTPUT RATIO IN AIR
Primus
GE 43
SL 25
MM 50
Cl 2300 CD
Klein et al 1995 IJROBP
Boyer 1992 MP
Palta et al 1995 MP
Das et al 1999 MP
Georg et al 1999 PMB