M R Bayatiani - Ph.D of Medical Physics. Assistant professor, Department of Medical Physics and Radiotherapy, Arak university of Medical Sciences and Khansari hospital, Arak, Iran
F Seif - Ph.D of Medical Physics. Assistant professor, Department of Medical Physics and Radiotherapy, Arak university of Medical Sciences and Khansari hospital, Arak, Iran
S Hamidi - Ph.D of Physics. Associate professor, Department of Physics, Arak University, Arak, Iran
S Bagheri - Ms.c of Physics, Department of Physics, Arak University, Arak, Iran

Introduction: Metal prostheses in patients affect the radiotherapy dose distribution. Metal prostheses with high density and atomic number cause major changes in scattering and attenuation of radiation. The present study aims to assess the impact of metal knee prosthesis with various dimensions and materials on radiotherapy dose distribution. Material and Methods: In this research, the Varian Linac and water phantom were simulated using the MCNPX code. Dose distribution of photon beam in a water phantom, with and without the presence of knee prostheses made of cobalt-chromium-molybdenum alloy, steel, titanium, and titanium alloy used in men and women was investigated using the Monte Carlo simulation.Results: The prosthesis led to an increase in dose in comparison with cases that there was used no prosthesis. According to values of the depth dose percentage, the maximum dose increase was found to be ۶.۸%, ۶.۱%, ۴%, and ۴.۲۹%, and dose reduction ۴۱.۱۸%, ۴۰.۶۶%, ۳۷.۷۶%, and ۳۷.۵۱% for prosthetics with men’s knee dimensions made of cobalt-chromium-molybdenum alloy, steel, titanium alloy, and titanium, respectively. Above all, does increasing to ۶.۴%, ۵.۹%, ۳.۸%, and ۳.۹۴% and doses reducing to ۴۰.۸۷%, ۴۰.۳۶%, ۳۶.۹۴%, and ۳۶.۶۹ were observed in prosthetics for women. The highest amount of dose reduction for men’s prostheses made of mentioned materials was found to be ۴۸.۷۵%, ۴۷.۷%, ۴۵%, and ۴۵.۸%, respectively. In addition, it was ۴۶.۳۶%, ۴۵.۸%, ۴۳.۸%, and ۴۳.۹۵% for women’s prostheses, respectively.Conclusion: Material will have a significant impact if a part of the knee bone places behind the prosthesis. According to the obtained values, it is recommended to utilize prostheses made of titanium and titanium alloys for knee arthroplasty. The prosthesis can either increase or decrease dose in tumor or lead to increase dose at organs at risk.

Dose Distribution, Knee Prosthesis, Monte Carlo Simulation, Treatment planning