1. Med Phys. 2010 Oct;37(10):5448-55.

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.

Kolbun N, Levêque P, Abboud F, Bol A, Vynckier S, Gallez B.

Biomedical Magnetic Resonance Unit, Louvain Drug Research Institute, Université
catholique de Louvain, Avenue Mounier 73.40, B-1200 Brussels, Belgium.

PURPOSE: 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.


PMID: 21089781 [PubMed - indexed for MEDLINE]