Evaluation of hypothetical Gd source for use in brachytherapy

Abstract

Aim

The purpose of this work is to evaluate the dosimetric parameters of a hypothetical ¹⁵³Gd source for use in brachytherapy and comparison of the dosimetric parameters with those of ¹⁹²Ir and ¹²⁵I sources.

Materials and methods

Dose rate constant, the radial dose function and the two dimensional (2D) anisotropy function data for the hypothetical ¹⁵³Gd source were obtained by simulation of the source using MCNPX code and then were compared with the corresponding data reported by Enger et al. A comprehensive comparison between this hypothetical source and a ¹⁹²Ir source with similar geometry and a ¹²⁵I source was performed as well.

Results

Excellent agreement was shown between the results of the two studies. Dose rate constant values for the hypothetical ¹⁵³Gd, ¹⁹²Ir, ¹²⁵I sources are 1.173[[ce:hsp sp="0.25"/]]cGyh⁻¹[[ce:hsp sp="0.25"/]]U⁻¹, 1.044[[ce:hsp sp="0.25"/]]cGyh⁻¹[[ce:hsp sp="0.25"/]]U⁻¹, 0.925[[ce:hsp sp="0.25"/]]cGyh⁻¹[[ce:hsp sp="0.25"/]]U⁻¹, respectively. Radial dose function for the hypothetical ¹⁵³Gd source has an increasing trend, while ¹⁹²Ir has more uniform and ¹²⁵I has more rapidly falling off radial dose functions. 2D anisotropy functions for these three sources indicate that, except at 0.5[[ce:hsp sp="0.25"/]]cm distance, ¹⁹²Ir and ¹²⁵I have more isotropic trends as compared to the ¹⁵³Gd source.

Conclusion

A more uniform radial dose function, and 2D anisotropy functions with more isotropy, a much higher specific activity are advantages of ¹⁹²Ir source over ¹⁵³Gd. However, a longer half-life of ¹⁵³Gd source compared to the other two sources, and lower energy of the source with respect to ¹⁹²Ir are advantages of using ¹⁵³Gd in brachytherapy versus ¹⁹²Ir source.