title: [A preliminary study for starshot analysis during quality control of medical linacs].
abstract: OBJECTIVE
  This study was to discuss the influencing factors of Starshot analysis during the quality control of medical linacs.
  
  
  METHODS
  During the quality control of a Siemens medical linac, Starshot analysis were carried out using FilmQA software and KODAK low sensitive films. The influence of setting to the results of Starshot analysis were explored, including Jaw width, shit of gantry angles, center shifts of Jaws, Beam energy and scan resolution.
  
  
  RESULTS
  The offset of Jaws's center had effect on the analysis result and the center offset was linearly related to the result. The influence of Beam energy and scan resolution was much smaller, and the maximum deviation was less than 0.2mm. The deviation for gantry angle at 4 degree was a little larger than 2 degree which deviation was less than 0.1mm.The Jaw width had greater effort on the analysis result, and two trends were found in 2 tests.
  
  
  CONCLUSIONS
  In clinic, if the result of Starshot analysis was out of tolerance, a careful check to multi factors should be made before the last determination.
authors.affiliation: Radiotherapy Department, Zhongshan Hospital affiliated to Fudan University, Shanghai 200032. shzjy@126.com
authors.forename: Jianying
authors.initials: J
authors.lastname: Zhang
authors.forename: Tao
authors.initials: T
authors.lastname: Jiang
mesh_terms: D010315:Particle Accelerators; D011786:Quality Control