title: New methods for optical distance indicator and gantry angle quality control tests in medical linear accelerators: image processing by using a 3D phantom.
abstract: OBJECTIVE
  In order to keep the acceptable level of the radiation oncology linear accelerators, it is necessary to apply a reliable quality assurance (QA) program.
  
  
  METHODS
  The QA protocols, published by authoritative organizations, such as the American Association of Physicists in Medicine (AAPM), determine the quality control (QC) tests which should be performed on the medical linear accelerators and the threshold levels for each test. The purpose of this study is to increase the accuracy and precision of the selected QC tests in order to increase the quality of treatment and also increase the speed of the tests to convince the crowded centers to start a reliable QA program. A new method has been developed for two of the QC tests; optical distance indicator (ODI) QC test as a daily test and gantry angle QC test as a monthly test. This method uses an image processing approach utilizing the snapshots taken by the CCD camera to measure the source to surface distance (SSD) and gantry angle.
  
  
  RESULTS
  The new method of ODI QC test has an accuracy of 99.95% with a standard deviation of 0.061 cm and the new method for gantry angle QC has a precision of 0.43°. The automated proposed method which is used for both ODI and gantry angle QC tests, contains highly accurate and precise results which are objective and the human-caused errors have no effect on the results.
  
  
  CONCLUSIONS
  The results show that they are in the acceptable range for both of the QC tests, according to AAPM task group 142.
authors: Department of Biomedical Engineering, College of Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran.
authors: Mahdi Heravian
authors: MH
authors: Shandiz
authors: Department of Radiologic Technology, School of Paramedical Science, Mashhad University of Medical Science, Mashhad, Iran.
authors: Ghorban Safaeian
authors: GS
authors: Layen
authors: Cancer Research Center, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
authors: Kazem
authors: K
authors: Anvari
authors: Department of Biomedical Engineering, College of Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran.
authors: Mohammadmahdi
authors: M
authors: Khalilzadeh
keywords: Gantry angle; Linear accelerator; Optical distance indicator (ODI); Quality control; Source to surface distance (SSD)