Comparing X-ray dose reduction capability of silicon-bismuth micro- and nanocomposite shields using chest CT test

Comparison of radiation shields of different thicknesses and structures (especially different particle sizes of their constituents) is helpful to select an appropriate shield for patient protection in medical imaging tests particularly CT-scan. In this study micro- and nano-powders of bismuth were mixed with silicone matrix to make composite radiation shields for breast. The shields were provided in dimensions of 20×20 cm, thickness of 1 mm, and bismuth weight ratio of 10%. The chest CT test (TOSHIBA 16 multi-slice device) was performed on a female phantom with normal breast size in 100 kVp and 50 mA with slice thickness of 0.5 mm and pitch of 1 mm. To avoid image artifacts, a foam layer of 1 cm was wrapped around the phantom under the shields. Measurement of dose in the surface (equivalent to skin) and forth layer (equivalent to glandular tissue) of phantom breast was done using thermoluminescence dosimeter. Results showed that dose on the surface of phantom breast declined up to 12% and 18.4% in the presence of silicon-bismuth micro- and nanocomposite shields, respectively, and both composites reduced the breast dose significantly (p<0.5). Also, the nanocomposite shields reduced radiation dose more than the microcomposite shields. Additionally, less noise variation was observed in CT images acquired with the nanocomposite shields.