Does the option to rotate the Elekta Beam Modulator MLC during VMAT IMRT delivery confer advantage?—a study of ‘parked gaps’

摘要: When delivering intensity-modulated radiation therapy (IMRT) using the volumetric modulated arc (VMAT) technique on an Elekta accelerator equipped with Beam Modulator multileaf collimator (MLC), orientation of MLC, relative to head, is generally fixed during delivery. However, it has ability rotate about its axis as gantry simultaneously rotates. This note shows that this can confer a potential advantage when planning and IMRT via VMAT. A computer model been built in which MLC rotation angle could be varied each control point (gantry location) within constraints specified speed time available for rotation. The was used optimize trajectory such way minimize number parked gaps between leaves are needed some orientations but not others (and cannot reach shielding safety surrounding jaws available). presented work started simple situation collimating gantry-successive single convex shapes. As broad statement 40% reduction achieved. study then extended investigate optimized trajectories multiple separate concave shapes with, once again, saving unwanted or over-irradiation.