An Investigation of Multileaf Collimator Performance Dependence on Gantry Angle Using Machine Log Files

Jeremy L Hughes, Martin A Ebert, Conor K McGarry, Christina E Agnew, Mahsheed Sabet, Pejman Rowshanfarzad

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Abstract

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.

Original languageEnglish
Pages (from-to)300-307
Number of pages8
JournalJournal of Medical Physics
Volume46
Issue number4
Early online date31 Dec 2021
DOIs
Publication statusPublished - 10 Mar 2022

Bibliographical note

Funding Information:
J. H. gratefully acknowledges the award of the Attraction Scholarship in Radiation Oncology Medical Physics from the WA Department of Health. This work was partly supported by the WA Department of Health Merit Award.

Publisher Copyright:
© 2021 Wolters Kluwer Medknow Publications. All rights reserved.

Keywords

  • DynaLog
  • linac
  • log files
  • multileaf collimator
  • Varian

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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