title: Accuracy of a dose-area product compared to an absorbed dose to water at a point in a 2 cm diameter field.
abstract: OBJECTIVE
  Graphite calorimeters with a core diameter larger than the beam can be used to establish dosimetric references in small fields. The dose-area product (DAP) measured can theoretically be linked to an absorbed dose at a point by the determination of a profile correction. This study aims at comparing the DAP-based protocol to the usual absorbed dose at a point protocol in a 2 cm diameter field for which both references exist.
  
  
  METHODS
  Two calorimeters were used, respectively, with a sensitive volume of 0.6 cm (for the absorbed dose at a point measurement) and 3 cm diameter (for the DAP measurement). Profile correction was calculated from a 2D dose mapping using three detectors: a PinPoint chamber, a synthetic diamond, and EBT3 films. A specific protocol to read EBT3 films was implemented and the dose-rate and energy dependences were studied to assure a precise measurement, especially in the penumbra and out-of-field regions.
  
  
  RESULTS
  EBT3 films were found independent on dose rates over the range studied but showed a strong under-response (18%) at low energies. Depending on the dosimeter used for calculating the profile correction, a deviation of 0.8% (PinPoint chamber), 0.9% (diamond), or 1.9% (EBT3 films) was observed between the calibration coefficient derived from DAP measurements and the one directly established in terms of absorbed dose to water at a point.
  
  
  CONCLUSIONS
  The DAP method can currently be linked to the classical dosimetric reference system based in an absorbed dose at a point only with a confidence interval of 95% (k = 2). None of the detectors studied can be used to determine an absorbed dose to water at a point from a DAP measurement with an uncertainty smaller than 1.2%.
authors.affiliation: CEA, LIST, Laboratoire National Henri Becquerel (LNE-LNHB), Gif-sur-Yvette F-91191, France.
authors.forename: S
authors.initials: S
authors.lastname: Dufreneix
authors.affiliation: CEA, LIST, Laboratoire National Henri Becquerel (LNE-LNHB), Gif-sur-Yvette F-91191, France.
authors.forename: A
authors.initials: A
authors.lastname: Ostrowsky
authors.affiliation: CEA, LIST, Laboratoire National Henri Becquerel (LNE-LNHB), Gif-sur-Yvette F-91191, France.
authors.forename: B
authors.initials: B
authors.lastname: Rapp
authors.affiliation: CEA, LIST, Laboratoire National Henri Becquerel (LNE-LNHB), Gif-sur-Yvette F-91191, France.
authors.forename: J
authors.initials: J
authors.lastname: Daures
authors.affiliation: CEA, LIST, Laboratoire National Henri Becquerel (LNE-LNHB), Gif-sur-Yvette F-91191, France.
authors.forename: J M
authors.initials: JM
authors.lastname: Bordy
mesh_terms: D002138:Calibration; D002151:Calorimetry / Q000295:instrumentation / Q000379:methods*; D003198:Computer Simulation; D005373:Film Dosimetry / Q000295:instrumentation / Q000379:methods*; D009010:Monte Carlo Method; D014867:Water
chemical_list: D014867:Water