Comparison of TG-43 dosimetric parameters of brachytherapy sources obtained by three different versions of MCNP codes

Monte Carlo simulations are widely used for calculation of the dosimetric parameters of brachytherapy sources. MCNP4C2, MCNP5, MCNPX, EGS4, EGSnrc, PTRAN, and GEANT4 are among the most commonly used codes in this field. Each of these codes utilizes a cross-sectional library for the purpose of simulating different elements and materials with complex chemical compositions. The accuracies of the final outcomes of these simulations are very sensitive to the accuracies of the cross-sectional libraries. Several investigators have shown that inaccuracies of some of the cross section files have led to errors in ¹²⁵I and ¹⁰³Pd parameters. The purpose of this study is to compare the dosimetric parameters of sample brachytherapy sources, calculated with three different versions of the MCNP code - MCNP4C, MCNP5, and MCNPX. In these simulations for each source type, the source and phantom geometries, as well as the number of the photons, were kept identical, thus eliminating the possible uncertainties. The results of these investigations indicate that for low-energy sources such as ¹²⁵I and ¹⁰³Pd there are discrepancies in g_L(r) values. Discrepancies up to 21.7% and 28% are observed between MCNP4C and other codes at a distance of 6 cm for ¹⁰³Pd and 10 cm for ¹²⁵I from the source, respectively. However, for higher energy sources, the discrepancies in g_L(r) values are less than 1.1% for ¹⁹²Ir and less than 1.2% for ¹³⁷Cs between the three codes.