title: Effect of photon energy spectrum on dosimetric parameters of brachytherapy sources.
abstract: OBJECTIVE
  The aim of this study is to quantify the influence of the photon energy spectrum of brachytherapy sources on task group No. 43 (TG-43) dosimetric parameters.
  
  
  BACKGROUND
  Different photon spectra are used for a specific radionuclide in Monte Carlo simulations of brachytherapy sources.
  
  
  METHODS
  MCNPX code was used to simulate 125I, 103Pd, 169Yb, and 192Ir brachytherapy sources. Air kerma strength per activity, dose rate constant, radial dose function, and two dimensional (2D) anisotropy functions were calculated and isodose curves were plotted for three different photon energy spectra. The references for photon energy spectra were: published papers, Lawrence Berkeley National Laboratory (LBNL), and National Nuclear Data Center (NNDC). The data calculated by these photon energy spectra were compared.
  
  
  RESULTS
  Dose rate constant values showed a maximum difference of 24.07% for 103Pd source with different photon energy spectra. Radial dose function values based on different spectra were relatively the same. 2D anisotropy function values showed minor differences in most of distances and angles. There was not any detectable difference between the isodose contours.
  
  
  CONCLUSIONS
  Dosimetric parameters obtained with different photon spectra were relatively the same, however it is suggested that more accurate and updated photon energy spectra be used in Monte Carlo simulations. This would allow for calculation of reliable dosimetric data for source modeling and calculation in brachytherapy treatment planning systems.
authors.affiliation: Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.
authors.forename: Mahdi
authors.initials: M
authors.lastname: Ghorbani
authors.affiliation: Bioinformatics Research Center, Sabzevar University of Medical Sciences, Sabzevar, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Mehrpouyan
authors.affiliation: Comprehensive Cancer Centers of Nevada, Las Vegas, Nevada, USA.
authors.forename: David
authors.initials: D
authors.lastname: Davenport
authors.affiliation: Department of Basic Medical Sciences, Neyshabur University of Medical Sciences, Neyshabur, Iran.
authors.forename: Toktam
authors.initials: T
authors.lastname: Ahmadi Moghaddas
keywords: TG-43 dosimetric parameters; brachytherapy; dose distribution; photon energy spectrum