title: High throughput film dosimetry in homogeneous and heterogeneous media for a small animal irradiator.
abstract: OBJECTIVE
  We have established a high-throughput Gafchromic film dosimetry protocol for narrow kilovoltage beams in homogeneous and heterogeneous media for small-animal radiotherapy applications. The kV beam characterization is based on extensive Gafchromic film dosimetry data acquired in homogeneous and heterogeneous media. An empirical model is used for parameterization of depth and off-axis dependence of measured data.
  
  
  METHODS
  We have modified previously published methods of film dosimetry to suit the specific tasks of the study. Unlike film protocols used in previous studies, our protocol employs simultaneous multi-channel scanning and analysis of up to nine Gafchromic films per scan. A scanner and background correction were implemented to improve accuracy of the measurements. Measurements were taken in homogeneous and inhomogeneous phantoms at 220 kVp and a field size of 5 × 5 mm(2). The results were compared against Monte Carlo simulations.
  
  
  RESULTS
  Dose differences caused by variations in background signal were effectively removed by the corrections applied. Measurements in homogeneous phantoms were used to empirically characterize beam data in homogeneous and heterogeneous media. Film measurements in inhomogeneous phantoms and their empirical parameterization differed by about 2%-3%. The model differed from MC by about 1% (water, lung) to 7% (bone). Good agreement was found for measured and modelled off-axis ratios.
  
  
  CONCLUSIONS
  EBT2 films are a valuable tool for characterization of narrow kV beams, though care must be taken to eliminate disturbances caused by varying background signals. The usefulness of the empirical beam model in interpretation and parameterization of film data was demonstrated.
authors.affiliation: Department of Radiation Oncology, Brigham & Women's Hospital, Boston, MA, USA; Department of Experimental Radiation Oncology, University Medical Center, Mannheim, Germany. Electronic address: linda-jacqueline.wack@med.uni-tuebingen.de.
authors.forename: L
authors.initials: L
authors.lastname: Wack
authors.affiliation: Department of Radiation Oncology, Brigham & Women's Hospital, Boston, MA, USA.
authors.forename: W
authors.initials: W
authors.lastname: Ngwa
authors.affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, John Hopkins University, Baltimore, USA.
authors.forename: E
authors.initials: E
authors.lastname: Tryggestad
authors.affiliation: Department of Radiation Oncology, Brigham & Women's Hospital, Boston, MA, USA.
authors.forename: P
authors.initials: P
authors.lastname: Tsiamas
authors.affiliation: Department of Radiation Oncology, Brigham & Women's Hospital, Boston, MA, USA.
authors.forename: R
authors.initials: R
authors.lastname: Berbeco
authors.affiliation: Department of Radiation Oncology, Brigham & Women's Hospital, Boston, MA, USA.
authors.forename: S K
authors.initials: SK
authors.lastname: Ng
authors.affiliation: Department of Experimental Radiation Oncology, University Medical Center, Mannheim, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Hesser
authors.affiliation: Department of Radiation Oncology, Brigham & Women's Hospital, Boston, MA, USA. Electronic address: pzygmanski@lroc.harvard.edu.
authors.forename: P
authors.initials: P
authors.lastname: Zygmanski
mesh_terms: D000818:Animals; D005373:Film Dosimetry / Q000379:methods*; D008962:Models, Theoretical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D013997:Time Factors; D014867:Water
chemical_list: D014867:Water
keywords: Empirical beam model; Film dosimetry; Small animal radiotherapy; kV irradiator