title: Absolute calibration of the Gamma Knife® Perfexion™ and delivered dose verification using EPR/alanine dosimetry.
abstract: OBJECTIVE
  Elekta Leksell Gamma Knife(®) (LGK) is a radiotherapy beam machine whose features are not compliant with the international calibration protocols for radiotherapy. In this scope, the Laboratoire National Henri Becquerel and the Pitié-Salpêtrière Hospital decided to conceive a new LKG dose calibration method and to compare it with the currently used one. Furthermore, the accuracy of the dose delivered by the LGK machine was checked using an "end-to-end" test. This study also aims to compare doses delivered by the two latest software versions of the Gammaplan treatment planning system (TPS).
  
  
  METHODS
  The dosimetric method chosen is the electron paramagnetic resonance (EPR) of alanine. Dose rate (calibration) verification was done without TPS using a spherical phantom. Absolute calibration was done with factors calculated by Monte Carlo simulation (MCNP-X). For "end-to-end" test, irradiations in an anthropomorphic head phantom, close to real treatment conditions, are done using the TPS in order to verify the delivered dose.
  
  
  RESULTS
  The comparison of the currently used calibration method with the new one revealed a deviation of +0.8% between the dose rates measured by ion chamber and EPR/alanine. For simple fields configuration (less than 16 mm diameter), the "end-to-end" tests showed out average deviations of -1.7% and -0.9% between the measured dose and the calculated dose by Gammaplan v9 and v10, respectively.
  
  
  CONCLUSIONS
  This paper shows there is a good agreement between the new calibration method and the currently used one. There is also a good agreement between the calculated and delivered doses especially for Gammaplan v10.
authors.affiliation: CEA, LIST, Laboratoire National Henri Becquerel, 91191 Gif-sur-Yvette Cedex, France.
authors.forename: Amaury
authors.initials: A
authors.lastname: Hornbeck
authors.affiliation: CEA, LIST, Laboratoire National Henri Becquerel, 91191 Gif-sur-Yvette Cedex, France.
authors.forename: Tristan
authors.initials: T
authors.lastname: Garcia
authors.affiliation: Radiotherapy Department, Medical Physics Unit, University Hospital Pitié-Salpêtrière, 75013 Paris, France.
authors.forename: Marguerite
authors.initials: M
authors.lastname: Cuttat
authors.affiliation: Radiotherapy Department, Medical Physics Unit, University Hospital Pitié-Salpêtrière, 75013 Paris, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Jenny
mesh_terms: D000409:Alanine; D000465:Algorithms; D001932:Brain Neoplasms / Q000601:surgery; D002138:Calibration; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006257:Head / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008954:Models, Biological; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011874:Radiometry / Q000379:methods*; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods*; D011879:Radiotherapy Dosage; D012984:Software; D014057:Tomography, X-Ray Computed; D014867:Water
chemical_list: D014867:Water; D000409:Alanine