title: Monte Carlo study of the energy and angular dependence of the response of plastic scintillation detectors in photon beams.
abstract: OBJECTIVE
  By using Monte Carlo simulations, the authors investigated the energy and angular dependence of the response of plastic scintillation detectors (PSDs) in photon beams.
  
  
  METHODS
  Three PSDs were modeled in this study: A plastic scintillator (BC-400) and a scintillating fiber (BCF-12), both attached by a plastic-core optical fiber stem, and a plastic scintillator (BC-400) attached by an air-core optical fiber stem with a silica tube coated with silver. The authors then calculated, with low statistical uncertainty, the energy and angular dependences of the PSDs' responses in a water phantom. For energy dependence, the response of the detectors is calculated as the detector dose per unit water dose. The perturbation caused by the optical fiber stem connected to the PSD to guide the optical light to a photodetector was studied in simulations using different optical fiber materials.
  
  
  RESULTS
  For the energy dependence of the PSDs in photon beams, the PSDs with plastic-core fiber have excellent energy independence within about 0.5% at photon energies ranging from 300 keV (monoenergetic) to 18 MV (linac beam). The PSD with an air-core optical fiber with a silica tube also has good energy independence within 1% in the same photon energy range. For the angular dependence, the relative response of all the three modeled PSDs is within 2% for all the angles in a 6 MV photon beam. This is also true in a 300 keV monoenergetic photon beam for PSDs with plastic-core fiber. For the PSD with an air-core fiber with a silica tube in the 300 keV beam, the relative response varies within 1% for most of the angles, except in the case when the fiber stem is pointing right to the radiation source in which case the PSD may over-response by more than 10%.
  
  
  CONCLUSIONS
  At +/- 1% level, no beam energy correction is necessary for the response of all three PSDs modeled in this study in the photon energy ranges from 200 keV (monoenergetic) to 18 MV (linac beam). The PSD would be even closer to water equivalent if there is a silica tube around the sensitive volume. The angular dependence of the response of the three PSDs in a 6 MV photon beam is not of concern at 2% level.
authors.affiliation: Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Lilie L W
authors.initials: LL
authors.lastname: Wang
authors.forename: David
authors.initials: D
authors.lastname: Klein
authors.forename: A Sam
authors.initials: AS
authors.lastname: Beddar
mesh_terms: D055592:Biophysical Phenomena; D006801:Humans; D015233:Models, Statistical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use*; D010969:Plastics; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy / Q000706:statistics & numerical data; D012588:Scintillation Counting / Q000706:statistics & numerical data*
chemical_list: D010969:Plastics