title: Investigation of the mechanical performance of Siemens linacs components during arc: gantry, MLC, and electronic portal imaging device.
abstract: BACKGROUND
  In radiotherapy treatments, it is crucial to monitor the performance of linac components including gantry, collimation system, and electronic portal imaging device (EPID) during arc deliveries. In this study, a simple EPID-based measurement method is suggested in conjunction with an algorithm to investigate the stability of these systems at various gantry angles with the aim of evaluating machine-related errors in treatments.
  
  
  METHODS
  The EPID sag, gantry sag, changes in source-to-detector distance (SDD), EPID and collimator skewness, EPID tilt, and the sag in leaf bank assembly due to linac rotation were separately investigated by acquisition of 37 EPID images of a simple phantom with five ball bearings at various gantry angles. A fast and robust software package was developed for automated analysis of image data. Three Siemens linacs were investigated.
  
  
  RESULTS
  The average EPID sag was within 1 mm for all tested linacs. Two machines showed >1 mm gantry sag. Changes in the SDD values were within 7.5 mm. EPID skewness and tilt values were <1° in all machines. The maximum sag in leaf bank assembly was <1 mm.
  
  
  CONCLUSIONS
  The method and software developed in this study provide a simple tool for effective investigation of the behavior of Siemens linac components with gantry rotation. Such a comprehensive study has been performed for the first time on Siemens machines.
authors.affiliation: School of Physics, The University of Western Australia, Crawley, WA, Australia.
authors.forename: Pejman
authors.initials: P
authors.lastname: Rowshanfarzad
authors.affiliation: German Cancer Research Center (DKFZ), Medical Physics in Radiation Oncology, Heidelberg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Häring
authors.affiliation: Radiofysisk Laboratorium, Odense University Hospital, Odense C, Denmark.
authors.forename: Hans L
authors.initials: HL
authors.lastname: Riis
authors.affiliation: Radiofysisk Laboratorium, Odense University Hospital, Odense C, Denmark.
authors.forename: Sune J
authors.initials: SJ
authors.lastname: Zimmermann
authors.affiliation: School of Physics, The University of Western Australia, Crawley, WA, Australia ; Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Ebert
keywords: EPID; Siemens; arc; gantry; linac; sag