512 / 1542
6/3/2017
MV beam
MU efficiency and leakage
75
ESTRO physics course 2017
Jaws
MLC leaf
Zone I
Zone II
Zone II
Zone III
Zone III
Zone I: Primary beam
“
Wanted
dose” to target
“
Unwanted
dose” to healthy
tissue and OAR in the beam path
Zone II: MLC/Collimator Leakage
+ scatter
“
Unwanted
dose”
Zone III: Linac head leakage
+ scatter
“
Unwanted
dose”
Head/Jaw leakage 0.1%
MLC leakage 0.5% to 3%
Exposure outside beam aperture
MV beam
MV beam
Jaws
Jaws
MLC leaf
Open beam: 140 MU
Sliding window (1 cm): 680 MU
MLC leaf
Remark: For this particular MLC device average leakage < 1%
MU efficiency and leakage
76
ESTRO physics course 2017