The dose distribution close to an 192Ir wire source: EGS4 Monte Carlo calculations

Dosimetric investigation of LDR brachytherapy ¹⁹²Ir wires by Monte Carlo and TPS calculations

PURPOSE

The aim of this study was to investigate the dose rate distribution around (192)Ir wires used as radioactive sources in low-dose-rate brachytherapy applications.

MATERIALS AND METHODS

Monte Carlo modeling of a 0.3-mm diameter source and its surrounding water medium was performed for five different wire lengths (1-5 cm) using the MCNP software package.

RESULTS

The computed dose rates per unit of air kerma at distances from 0.1 up to 10 cm away from the source were first verified with literature data sets. Then, the simulation results were compared with the calculations from the XiO CMS commercial treatment planning system.

CONCLUSION

The study results were found to be in concordance with the treatment planning system calculations except for the shorter wires at close distances.

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

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.