Document Type : Original Paper
Authors
1
Department of Radiology, School of Paramedical Sciences, Shiraz University of Medical Sciences, Shiraz, Iran.
2
1-Radiology Department, Faculty of Paramedical Sciences, Shiraz University of Medical Sciences. Shiraz, Iran 2-Ionizing and Non-Ionizing Radiation Protection Research Center (INIRPRC), School of Paramedical Sciences, Shiraz University
3
Ionizing and Non-Ionizing Radiation Protection Research Center (INIRPRC), School of Paramedical Sciences, Shiraz University of Medical Sciences, Shiraz, Iran. † Now at Physics Department, Università degli Studi di Torino, Turin, Italy.
4
Medical imaging research center, Shiraz university of medical sciences, Shiraz, Iran
Abstract
Introduction: Bismuth efficiency in shielding superficial tissues in computed tomography (CT) scans has been challenged due to the imbalance between image quality and dose reduction. The aim of this study is to reduce bismuth in shields and investigate the possibility of substitution with lower atomic materials, namely magnetite and polyvinyl alcohol (PVA).
Material and Methods: Five different compounds, including raw PVA and four other samples containing variable weight fractions of 3%, 5%, 7%, and 10% bismuth oxide, with constant magnetite of 30% were selected. Shielding factors, including linear attenuation coefficient (μ), mass attenuation coefficient (μρ), half-value layer (HVL), electron density (Ne), and effective atomic number (Zeff), were evaluated over a wide range of energy by precise computational methods, XCOM, and Monte Carlo N-Particle (MCNPX) code.
Results: Increasing the bismuth oxide concentration improves the radiation attenuation and absorption process. This effect was observed in the μρ graphs to medium energies (E < 0.356 MeV). The simultaneous evaluation of Ne and Zeff predicts increased absorption due to the increased and dominant photoelectric effect (<0.1 MeV), attenuation as a consequence of the raised Compton effect (0.1 < E < 0.356 MeV; followed by scattering owing to the predominant Compton effect), and formation (E ≈ 1.22 MeV) and dominance of pair production phenomenon (E > 3 MeV).Also, a quantitative analysis of absorption through HVL in several widely used energies in diagnostic radiology (CT scan) and radiotherapy showed the efficacy of these compounds in ionizing radiation absorption.
Conclusions: This study confirms the advantages of reducing bismuth and substituting it with compounds having lower atomic number materials. Therefore, the possibility of alleviating bismuth and replacing it with magnetite in designing radiation shields in CT scans has been confirmed in this study.
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