Shielding performance of multi-metal nanoparticle composites for diagnostic radiology: an MCNPX and Geant4 study

Lead-free polymer composite shields are used in diagnostic radiology to protect patients from unnecessary radiation exposure. This study aimed to examine and introduce the radiation-shielding properties of single- and multi-metal nanoparticle (NP)-based composites containing Bi, W, and Sn using Geant4, MCNPX, and XCom for radiological applications. The mass attenuation coefficients and effective atomic numbers of single- and multi-metal NP-loaded polymer composites were calculated using the Geant4 and MCNPX simulation codes for X-ray energies of 20-140 keV. The nano-sized fillers inside the polydimethylsiloxane (PDMS:C₂H₆SiO) matrix included W (K = 69.5 keV), Bi (K = 90.5 keV), and Sn (K = 29.20 keV). For single-metal shields, one filler was used, while in multi-metal shields, two fillers were required. The MCNPX and Geant4 simulation results were compared with the XCom results. The multi-metal NP composites exhibited higher attenuation over a larger energy range owing to their attenuation windows. In addition, Bi₂O₃ + WO₃ NPs showed a 39% higher attenuation at 100-140 keV, and that of Bi₂O₃ + SnO₂ NPs was higher at 40-60 keV. Meanwhile, the WO₃ + SnO₂ NPs exhibited lower attenuation. The difference between the results obtained using Geant4 and XCom was less than 2%, because these codes have similar simulation structures. The results show that the shielding performance of the Bi₂O₃ + WO₃ filler is better than that of the other single- and multi-metal fillers. In addition, it was found that the Geant4 code was more accurate for simulating radiation composites.

Trade-off between breast dose and image quality using composite bismuth shields in computed tomography: A phantom study

INTRODUCTION

Many researchers have suggested that bismuth composite shields (BCS) reduce breast dose remarkably; however, the level of this reduction and its impact on image quality has not been assessed. This study aimed to evaluate the efficiency of nano- and micro- BCS in reducing the dose and image quality during chest computed tomography (CT) scans.

MATERIALS AND METHODS

Bismuth shields composed of 15 weighting percentage (wt%) and 20 wt% bismuth oxide (Bi₂O₃) nano- and micro-particles mixed in silicon rubber polymer were constructed in 1 and 1.5 mm thicknesses. The physical properties of nanoparticles were assessed using a scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX). Breast radiation doses were measured experimentally during chest CT using PMMA standard dosimetry phantom (body phantom, 76-419-4150, Fluke Biomedical) in the presence of the shields. The image quality was assessed by calculating signal and noise values in different regions.

RESULTS

The SEM images showed that the average size of Bi₂O₃ nano- and micro-particles was about 70 nm and 150 μm, respectively. The breast doses were reduced by increasing the shield thickness/bismuth weight percentage. The maximum dose reduction was related to the 20% weight of Bi₂O₃ nano-particles and a thickness of 1.5 mm. The minimum dose reduction was related to the 15% weight of Bi₂O₃ micro-particles with a thickness of 1 mm. The mean noise was higher in nano-particle bismuth shields than in micro-particles.

CONCLUSION

Composite shields containing bismuth nano- and micro-particles can reduce the breast dose during chest CT examinations while negatively impacting diagnostic image quality. Several critical factors, such as bismuth concentration, particle size, and shield thickness, directly affect the efficiency.