Abstract

Introduction: Hip prostheses (HP) are used in hip augmentation to replace diseased hip joints. However, high-Z inserts cause dose perturbations during radiotherapy, resulting in unacceptable dose distributions in the target and in regions surrounding the prosthesis. This study evaluates the dosimetric effect of HP during prostate radiotherapy using Monte Carlo (MC) simulations. Materials and Methods: BEAMnrc MC user-code was used to model an Elekta Precise linac head. Simulations were performed on a 16-core Linux platform. DOSXYZnrc was used to calculate dose distributions in a mathematical Rando phantom with and without HP. The 3D dose files from DOSXYZnrc were analysed by MCSHOW software for extracting PDD data. Stainless steel, titanium and ultra-high-molecular-weight polyethylene HP were used. Prosthetic models were drawn into the phantom CT dataset using MCSHOW and then converted into the desired HP material using an IDL code. Various photon beam configurations of 6, 10, 15 and 20MVwere used. Results: Dose attenuation along the prosthesis ranged between 32% and 64%. Maximum dose attenuation occurred at the head/proximal shaft where the width is thickest; minimum attenuation was at the tip. Higher attenuation occurred at a lower beam energy. The shadowing effect is densitydependent, and its maximum effect is caused by stainless steel prostheses. Conclusion: The dose within/beyond prostheses drops significantly due to attenuation by the prostheses. For bilateral HP, the PTV dose reduction can reach over 60%. MCSHOW allowed the addition of HP in the phantom from CT dataset of a patient without HP, thus eliminating streak artefacts from CT scan in the presence of HP. Results highlight the importance of beam position on the dose distribution.

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