Dose reduction in CT using bismuth shielding: measurements and Monte Carlo simulations

Area of Science:

• Medical Physics
• Radiological Imaging
• Radiation Protection

Background:

• Computed tomography (CT) scans involve significant patient radiation exposure.
• Shielding techniques are crucial for minimizing radiation dose to patients during CT procedures.
• Bismuth shielding has emerged as a potential method for dose reduction in medical imaging.

Purpose of the Study:

• To evaluate the potential dose reduction offered by bismuth shielding in computed tomography (CT).
• To assess the impact of bismuth shielding on image quality and identify optimal placement for critical organ protection.
• To compare the efficacy of bismuth shielding with lead shielding and evaluate simulation accuracy using different phantom models.

Main Methods:

• Direct dose measurements using an ionization chamber in a polymethylmethacrylate (PMMA) phantom.
• Monte Carlo simulations using the MCNPX code for dose calculation.
• Comparison of experimental and simulation results, and validation with a voxelized phantom (KTMAN-2).

Main Results:

• Bismuth shielding achieved dose reductions ranging from 1.2% to 55%, varying with measurement points, voltage, and shielding type.
• Significant dose reduction (34-55% on average) was observed for positions covered by shielding, with negligible impact on peripheral sites.
• Image artifacts were minimal when shielding was placed >1 cm from organs; bismuth and lead shielding showed comparable dose reduction (<2-3% difference).

Conclusions:

• Bismuth shielding is effective in reducing patient radiation dose during CT scans.
• Selective placement of bismuth shielding is recommended to protect critical organs like the eye lens, thyroid, and breast.
• Bismuth shielding presents a comparable alternative to lead shielding for dose reduction in CT imaging.