title: Filmless evaluation of the mechanical accuracy of the isocenter in stereotactic radiotherapy.
abstract: OBJECTIVE
  The Winston-Lutz test verifies the mechanical accuracy of the isocenter in stereotactic radiotherapy. A lead ball inside a small beam is exposed to film applying different combinations of the gantry angle and the table angle. The increasing replacement of films by digital images requires alternative imaging methods. The suitability of two different electronic portal imaging systems and of a system based on digital luminescence radiography was investigated.
  
  
  METHODS
  The imaging systems included the portal imaging devices BEAMVIEW PLUS and OPTIVUE1000 (both Siemens Medical Solutions, Erlangen, Germany) and the luminescence system KODAK ACR 2000 RT (Eastman Kodak Comp., Rochester, NY, USA). 6-MV photons from the linear accelerators PRIMUS and ONCOR (both Siemens Medical Solutions) were applied. First, only the small beam covering the lead ball was exposed. Second, an additional bigger open beam part in a certain distance to the small beam was applied.
  
  
  RESULTS
  For all three investigated imaging systems, which are using preprocessing imaging software, only for the beam arrangement with additional open beam parts, the lead ball could be detected inside the small beam. Only for the application of a dosimetric software tool to the luminescence system, the metal ball inside the small beam became visible without an additional open beam part.
  
  
  CONCLUSIONS
  Applying the proposed beam arrangements, the Winston-Lutz test can be done by digital and filmless imaging systems, thereby saving time as well.
authors.affiliation: Department of Radiotherapy and Radiooncolgy, University Hospital, Carl Gustav Carus University of Technology Dresden, Fetscherstrasse 74, 01307, Dresden, Germany. peter.geyer@mailbox.tu-dresden.de
authors.forename: Peter
authors.initials: P
authors.lastname: Geyer
authors.forename: Hilbert
authors.initials: H
authors.lastname: Blank
authors.forename: Carsten
authors.initials: C
authors.lastname: Evers
authors.forename: Thomas
authors.initials: T
authors.lastname: Leichtner
authors.forename: Horst
authors.initials: H
authors.lastname: Alheit
mesh_terms: D019544:Equipment Failure Analysis / Q000295:instrumentation / Q000379:methods; D005858:Germany; D019563:Mechanics; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care / Q000379:methods*; D011874:Radiometry / Q000379:methods* / Q000592:standards; D016634:Radiosurgery / Q000379:methods* / Q000592:standards*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods*; D014962:X-Ray Film