title: Experimental determination of the radial dose distribution in high gradient regions around 192Ir wires: comparison of electron paramagnetic resonance imaging, films, and Monte Carlo simulations.
abstract: OBJECTIVE
  The experimental determination of doses at proximal distances from radioactive sources is difficult because of the steepness of the dose gradient. The goal of this study was to determine the relative radial dose distribution for a low dose rate 192Ir wire source using electron paramagnetic resonance imaging (EPRI) and to compare the results to those obtained using Gafchromic EBT film dosimetry and Monte Carlo (MC) simulations.
  
  
  METHODS
  Lithium formate and ammonium formate were chosen as the EPR dosimetric materials and were used to form cylindrical phantoms. The dose distribution of the stable radiation-induced free radicals in the lithium formate and ammonium formate phantoms was assessed by EPRI. EBT films were also inserted inside in ammonium formate phantoms for comparison. MC simulation was performed using the MCNP4C2 software code.
  
  
  RESULTS
  The radical signal in irradiated ammonium formate is contained in a single narrow EPR line, with an EPR peak-to-peak linewidth narrower than that of lithium formate (approximately 0.64 and 1.4 mT, respectively). The spatial resolution of EPR images was enhanced by a factor of 2.3 using ammonium formate compared to lithium formate because its linewidth is about 0.75 mT narrower than that of lithium formate. The EPRI results were consistent to within 1% with those of Gafchromic EBT films and MC simulations at distances from 1.0 to 2.9 mm. The radial dose values obtained by EPRI were about 4% lower at distances from 2.9 to 4.0 mm than those determined by MC simulation and EBT film dosimetry.
  
  
  CONCLUSIONS
  Ammonium formate is a suitable material under certain conditions for use in brachytherapy dosimetry using EPRI. In this study, the authors demonstrated that the EPRI technique allows the estimation of the relative radial dose distribution at short distances for a 192Ir wire source.
authors.affiliation: Biomedical Magnetic Resonance Unit, Louvain Drug Research Institute, Université catholique de Louvain, Avenue Mounier 73.40, B-1200 Brussels, Belgium.
authors.forename: N
authors.initials: N
authors.lastname: Kolbun
authors.forename: Ph
authors.initials: P
authors.lastname: Levêque
authors.forename: F
authors.initials: F
authors.lastname: Abboud
authors.forename: A
authors.initials: A
authors.lastname: Bol
authors.forename: S
authors.initials: S
authors.lastname: Vynckier
authors.forename: B
authors.initials: B
authors.lastname: Gallez
mesh_terms: D055592:Biophysical Phenomena; D001918:Brachytherapy / Q000706:statistics & numerical data*; D004578:Electron Spin Resonance Spectroscopy / Q000706:statistics & numerical data; D005373:Film Dosimetry / Q000706:statistics & numerical data; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000706:statistics & numerical data; D007496:Iridium Radioisotopes / Q000008:administration & dosage / Q000627:therapeutic use*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000706:statistics & numerical data
chemical_list: D007496:Iridium Radioisotopes