Journal of Medical Physics
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Year : 2021  |  Volume : 46  |  Issue : 4  |  Page : 300-307

An investigation of multileaf collimator performance dependence on gantry angle using machine log files

1 School of Physics, Mathematics and Computing, University of Western Australia, Perth, WA; Peter MacCallum Cancer Centre, Melbourne, Melbourne, VIC, Australia
2 School of Physics, Mathematics and Computing, University of Western Australia; Department of Radiation Oncology, Sir Charles Gairdner Hospital, Perth, WA, Australia
3 Northern Ireland Cancer Center, Belfast City Hospital; Centre for Cancer Research and Cell Biology, Queen's University, Belfast, United Kingdom
4 Northern Ireland Cancer Center, Belfast City Hospital, Belfast, United Kingdom
5 School of Physics, Mathematics and Computing, University of Western Australia, Perth, WA, Australia

Correspondence Address:
Pejman Rowshanfarzad
The University of Western Australia, 35 Stirling Highway, Mailbag M013, Crawley, WA 6009
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmp.JMP_44_21

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Background: Quality assurance of linear accelerators (linacs) is an important part of ensuring accurate radiotherapy treatment deliveries. The aim of this study is to investigate the role of gravity on the positional accuracy of multileaf collimator (MLC) leaves during complex radiotherapy treatments on linacs. This investigation is based on the analysis of the machine log files from five different linacs in multiple centers. Materials and Methods: Three main categories of deliveries were considered: Picket fence, volumetric modulated arc therapy (VMAT) (both delivering with continuous gantry rotation), and sliding gap tests delivered at cardinal gantry angles, to determine the error of the MLC in relation to the gantry angle. Results: Analysis of picket fence tests revealed a dependence of the error upon the gantry angle. For the majority of deliveries, the MLC showed greater error at gantry angles 270 and 90. The errors computed for the cardinal angles for sliding gap tests were all statistically different with greatest error arising at gantry angle 270 and least error at gantry 90. For picket fence, sliding gap, and VMAT cases, MLC errors were dependent on the gantry angle. Conclusions: The errors in leaf positioning were found to be dependent on the gantry angle. For sliding gap tests, the error was greater at gantry angle 270° and 90° and less when the leaf motion was perpendicular to the force of gravity.

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