estimation of dose perturbation due to the presence of metal hip prostheses in radiotherapy with electron and photon beams: a monte carlo study

Purpose: the impact of various hip prosthesis materials on the amount of dose perturbation generated by 9 mev electron and 18 mv photon beams during pelvic radiation therapy is analyzed in this research.materials and methods: the varian 2100 c/d linac head for the electron (9 mev) and photon (18 mv) modes and a water phantom with a realistic hip prosthesis were modeled using the monte carlo (mc) code; mcnpx (ver. 2.6.0) and were benchmarked for measurement. four different materials, including cobalt–chromium–molybdenum-alloy (ccm), stainless steel (ss), titanium, and titanium-alloy (ti-alloy) were evaluated. the changes in electron and photon fluences and dose perturbations due to the presence of the hip prostheses were investigated.results: an increased dose of 13.29%, 13.77%, 6.16%, and 5.93% for 9 mev and 30.43%, 33.05%, 10.89%, and 11.27% for 18 mv was calculated for ti-alloy, ti, ccm, and ss prosthesis, respectively. at 0.5 mm distance from the prosthesis, the electron backscatter factor (ebf) of 1.31, 1.33, 1.15, and 1.14 for 9 mev and 1.32, 1.34, 1.11, and 1.12 for 18 mv was calculated for ti-alloy, ti, ccm, and ss prosthesis, respectively. dose perturbation is higher at a near distance from the prosthesis; by reducing the distance from the ti-alloy prosthesis (1.5 to 0.5 mm), an increased dose of 7.70% and 5.54% resulted in 18 mv and 9 mev, respectively. the dose decreases of up to 21% behind the hip prosthesis were calculated for 18 mv.conclusion: it is essential to consider the dose perturbation due to the presence of a hip prosthesis to achieve the optimal treatment planning in radiotherapy.