title: Automating linear accelerator quality assurance.
abstract: OBJECTIVE
  The purpose of this study was 2-fold. One purpose was to develop an automated, streamlined quality assurance (QA) program for use by multiple centers. The second purpose was to evaluate machine performance over time for multiple centers using linear accelerator (Linac) log files and electronic portal images. The authors sought to evaluate variations in Linac performance to establish as a reference for other centers.
  
  
  METHODS
  The authors developed analytical software tools for a QA program using both log files and electronic portal imaging device (EPID) measurements. The first tool is a general analysis tool which can read and visually represent data in the log file. This tool, which can be used to automatically analyze patient treatment or QA log files, examines the files for Linac deviations which exceed thresholds. The second set of tools consists of a test suite of QA fields, a standard phantom, and software to collect information from the log files on deviations from the expected values. The test suite was designed to focus on the mechanical tests of the Linac to include jaw, MLC, and collimator positions during static, IMRT, and volumetric modulated arc therapy delivery. A consortium of eight institutions delivered the test suite at monthly or weekly intervals on each Linac using a standard phantom. The behavior of various components was analyzed for eight TrueBeam Linacs.
  
  
  RESULTS
  For the EPID and trajectory log file analysis, all observed deviations which exceeded established thresholds for Linac behavior resulted in a beam hold off. In the absence of an interlock-triggering event, the maximum observed log file deviations between the expected and actual component positions (such as MLC leaves) varied from less than 1% to 26% of published tolerance thresholds. The maximum and standard deviations of the variations due to gantry sag, collimator angle, jaw position, and MLC positions are presented. Gantry sag among Linacs was 0.336 ± 0.072 mm. The standard deviation in MLC position, as determined by EPID measurements, across the consortium was 0.33 mm for IMRT fields. With respect to the log files, the deviations between expected and actual positions for parameters were small (<0.12 mm) for all Linacs. Considering both log files and EPID measurements, all parameters were well within published tolerance values. Variations in collimator angle, MLC position, and gantry sag were also evaluated for all Linacs.
  
  
  CONCLUSIONS
  The performance of the TrueBeam Linac model was shown to be consistent based on automated analysis of trajectory log files and EPID images acquired during delivery of a standardized test suite. The results can be compared directly to tolerance thresholds. In addition, sharing of results from standard tests across institutions can facilitate the identification of QA process and Linac changes. These reference values are presented along with the standard deviation for common tests so that the test suite can be used by other centers to evaluate their Linac performance against those in this consortium.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109-5010.
authors.forename: Tobias
authors.initials: T
authors.lastname: Eckhause
authors.affiliation: Department of Radiation Oncology and Cellular Oncology, The University of Chicago, Chicago, Illinois 60637.
authors.forename: Hania
authors.initials: H
authors.lastname: Al-Hallaq
authors.affiliation: Ann Arbor VA Medical Center, Ann Arbor, Michigan 48109.
authors.forename: Timothy
authors.initials: T
authors.lastname: Ritter
authors.affiliation: Department of Radiation Oncology, Cedars-Sinai Medical Center, Los Angeles, California, 90048.
authors.forename: John
authors.initials: J
authors.lastname: DeMarco
authors.affiliation: Department of Radiation Oncology and Cellular Oncology, The University of Chicago, Chicago, Illinois 60637.
authors.forename: Karl
authors.initials: K
authors.lastname: Farrey
authors.affiliation: UCSD Medical Center, La Jolla, California 92093.
authors.forename: Todd
authors.initials: T
authors.lastname: Pawlicki
authors.affiliation: UCSD Medical Center, La Jolla, California 92093.
authors.forename: Gwe-Ya
authors.initials: GY
authors.lastname: Kim
authors.affiliation: Department of Radiation Oncology, University of Alabama Birmingham, Birmingham, Alabama 35249.
authors.forename: Richard
authors.initials: R
authors.lastname: Popple
authors.affiliation: Karmanos Cancer Institute, McLaren-Flint, Flint, Michigan 48532.
authors.forename: Vijeshwar
authors.initials: V
authors.lastname: Sharma
authors.affiliation: Royal North Shore Hospital, Sydney, NSW 2065, Australia.
authors.forename: Mario
authors.initials: M
authors.lastname: Perez
authors.affiliation: Karmanos Cancer Institute, McLaren-Flint, Flint, Michigan 48532.
authors.forename: SungYong
authors.initials: S
authors.lastname: Park
authors.affiliation: Royal North Shore Hospital, Sydney, NSW 2065, Australia.
authors.forename: Jeremy T
authors.initials: JT
authors.lastname: Booth
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109-5010.
authors.forename: Ryan
authors.initials: R
authors.lastname: Thorwarth
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan 48109-5010.
authors.forename: Jean M
authors.initials: JM
authors.lastname: Moran
mesh_terms: D001331:Automation; D055615:Electrical Equipment and Supplies; D010315:Particle Accelerators / Q000592:standards*; D019047:Phantoms, Imaging; D011786:Quality Control; D012984:Software