Monte Carlo simulation of HDR Brachytherapy dosimetric parameters in different mediums

This study aims to investigate the influence of different materials on the dosimetric parameters of the 192Ir microSelectron HDR source using the MCNP5 code. As a preliminary, the MCNP5 code was initially verified with the published data, and the relative differences were calculated. Homogeneous phantoms, filled with lung, bone, air, and steels materials for a common hip prosthesis such as titanium alloy (Ti), stainless steel, and cobalt -chromium-molybdenum (Co-Cr-Mo) are modeled in this study. Using MCNP5 code, a database for 192Ir HDR Brachytherapy in a standard water phantom and other materials as described above was constructed. The data obtained from the simulation were then used for the calculation of the radial dose function, g(r) and anisotropy function F(r,theta). From the finding, g(r) for bone, lung, and air are water equivalent at r < 6 cm. At r> 6 cm, the TPS overestimate from 7.7% to 35.9% for bone and underestimate the lung dose (2.94%-33%) and air (2.81%- 46.4%). For steels, a large relative difference of up to 62.2% is calculated due to the higher density compared to the water. Meanwhile, a greater relative difference for F(r,theta) is observed at the angle parallel to the Nucletron 192Ir microSelectron HDR source. An increase in the density of the medium leads to inconsistencies in the flatness of the F(r,theta). Great attention should be given to the region greater than 6 cm and the presence of any material other than water at the respective distance could lead to significant underestimation or overestimation of the dosimetric parameters.