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Example 2: Modelling the MLC in Philips Pinnacle
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Physics Reference Guide v9.10
Leaf Ends
•
Leaf-end shape is modelled
rounded
•
Leaf end radius of curvature
: an adjustable(‘global’) parameter
•
Leaf Offset:
an adjustable (‘global’) parameter (an estimate of
the increase in transmission through the leaf end relative to the
transmission from the full MLC thickness
the position of the
leaf tip projected
to the plane of the
isocentre
position of
the leaf used
for dose
calculations
Transmission and Tongue & Groove effect
Young et al, J App Clin Med Phys, 17(6), 2016
Typical values
:
Leaf-end curvature: 8 – 15 cm
MLC leaf offset: 0.1cm
Tongue & groove width: 0.1cm
MLC intra-transmission: 1.5-2%, interleaf trans: 5%
Williams et al PMB, 51 (2006) N65-N78
Young et al, J App Clin Med Phys, 17(6), 2016
•
MLC leaf ends are modelled rounded
•
No explicit ray-tracing through leaf ends
•
The difference between nominal leaf end and radiation field
(one HVL of beam attenuation) is approximated by an off-set
parameter and the leaf end curvature (‘leaf off-set table’)
•
T&G modelled using an adjustable parameter (no ray tracing)
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