Dosimetric effects of different hip prosthesis materials during pelvic radiotherapy using high energy photons

Abstract

This study investigates the effects of different hip prosthesis materials on the secondary neutron and electron contamination produced by high energy, i.e. 18 MV, photon beams during pelvic irradiation. Three different materials, including Titanium-alloy (Ti-alloy), Stainless Steel (SST), and Cobalt–Chromium–Molybdenum-alloy (Co–Cr–Mo), were evaluated in a Monte Carlo (MC) study. The Varian 2100 C/D linac head and an ICRP reference adult male voxel phantom with a realistic hip prosthesis were simulated using the MCNPX (ver. 2.6) MC code. As expected, results showed that secondary electron and neutron generation mainly depends on the shape and material type of the prosthesis. The mean dose increase factor (DIF) for electron contamination is 1.72, 1.53, and 1.35 for Co–Cr–Mo, SST, and Ti-alloy, respectively, at the tissue-prosthesis interface. Electron contamination also depends on the prosthesis thickness and it is increased by increasing the thickness. The maximum DIF for neutrons occurs at the center of the prosthesis stem and its mean DIF is 2.91, 2.49, and 2.34 underneath Co–Cr–Mo, SST, and Ti-alloy prostheses, respectively. The amount of neutron DIF is slightly reduced above prostheses. Furthermore, the results indicate that the most significant change in the electron dose distribution is observed at the tissue-prosthesis interface. The neutron dose equivalent is increased from 76% to 200% in the presence of the different materials of the prosthesis. Hip prostheses made of Ti-alloy can significantly decrease the dose due to neutron and electron contamination, compared to the other materials considered in the simulations.