The use of breast shielding for dose reduction in pediatric CT: arguments against the proposition

Excerpt

Selective organ shielding was introduced in 1997 [1]; it involves sheets placed over the tissue for protection against the incoming primary X-ray beam. Breast shielding is achieved by applying commercially available latex sheets over the breasts. The sheets contain bismuth, which provides effective attenuation of X-rays in the energy range used in CT. The thin and flexible breast shields are designed to cover both breasts. They attenuate the X-ray beam by about 50%, depending on tube voltage and filtration. The use of bismuth shields has a negligible effect on the mean energy of the beam, or the proportion of low-energy photons in the beam, because modern CT scanners use pre-filtered beam spectra with typical half-value-layers ranging from 7- to 10-mm aluminum. The bismuth merely provides a decrease in overall beam intensity, the same as would occur with a reduced tube current (Fig. 1). Because bismuth shields are placed within the scan volume, their effects on both radiation dose and image quality must be considered.

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