title: Polarized dosimetry method for Gafchromic EBT3.
abstract: OBJECTIVE
  To analyze the changes in the polarization state of the flatbed scanner light caused by the EBT3 films and to propose a new method for correcting the lateral effects.
  
  
  METHODS
  The polarization changes induced by radiochromic films are analyzed using linear polarizing film. Based on the results, the linear polarizing films are used in the scanning process of the EBT3 films. This method is tested against the conventional EBT3 dosimetry using a series of simple regular beams and 21 cases of IMRT.
  
  
  RESULTS
  The mean results are statically different from the conventional dosimetry with EBT3. Depending on the transmission axis of the polarizing sheet, the results are better or worse compared to conventional dosimetry EBT3 film. When the transmission axis of the polarizing sheet is parallel to the coating direction, the dosimetry results are better and its variability is smaller. However, when the polarizer transmission axis is perpendicular to the coating direction, results are worse as well as its variability.
  
  
  CONCLUSIONS
  Using a polarized film with the polarization axis parallel to the coating direction of the radiochromic film, and preferably above it, significantly improves the dosimetry results and is an easy and inexpensive way to correct the lateral artifacts of the conventional EBT3 dosimetry.
authors.affiliation: Medical Physics Department, Hospital Universitario de Cruces, Plz. Cruces, Barakaldo, Spain. Electronic address: JOSEFERNANDO.PEREZAZORIN@osakidetza.net.
authors.forename: José Fernando
authors.initials: JF
authors.lastname: Pérez Azorin
authors.affiliation: Department of Oncology, Clínica Universidad de Navarra, University of Navarra, Av Pio XII s/n, Pamplona, Navarre, Spain.
authors.forename: Luis Isaac Ramos
authors.initials: LI
authors.lastname: Garcia
authors.affiliation: Department of Applied Mathematics and Physics, Universidad de Navarra, Av Pio XII s/n, Pamplona, Navarre, Spain.
authors.forename: Diego Maza
authors.initials: DM
authors.lastname: Ozcoidi
authors.affiliation: Medical Physics Department, Hospital Universitario Virgen de las Nieves, Av de las Fuerzas Armadas, Granada, Spain.
authors.forename: Julio F
authors.initials: JF
authors.lastname: Almansa
mesh_terms: D016477:Artifacts; D004867:Equipment Design; D005373:Film Dosimetry / Q000295:instrumentation / Q000379:methods*; D013997:Time Factors
keywords: Lateral correction; Light polarization; Radiochromic film dosimetry