Dose Course 2018_Flipping book

Example 2: Modelling the MLC in Philips Pinnacle 3 Physics Reference Guide v9.10

Transmission and Tongue & Groove effect

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

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

position of the leaf used for dose calculations

the position of the leaf tip projected to the plane of the isocentre

• 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) 24

Young et al, J App Clin Med Phys, 17(6), 2016