Answer to Question #4505 Submitted to "Ask the Experts"

I had a paranasal sinus CT scan today. I had a scan lying on my tummy with a chin support and then another one lying on my back. Before the procedure, I asked the technician if I would be wearing a lead apron/shield during the procedure. The technician said there's no need for that, since there is a new theory/study showing that no shielding allows scatter to exit the body. Is this true and safe?

No, this is not true. The shielding in question would be shielding placed over the reproductive organs to minimize exposure from the direct x-ray beam or scattered radiation from an x-ray beam that is close to the reproductive organs, i.e., within a few inches. Since your study was of the sinuses, the direct x-ray beam was a considerable distance from the reproductive organs. One study (Dietrich et al. 2005) has shown that the scattered radiation dose to tissue that is eight inches out of the direct CT beam is only about 1% of the exposure received by tissue in the beam. In your case of a sinus study, the reproductive organs were much farther than eight inches from the direct beam. The scattered radiation to the reproductive organs was insignificant and not requiring of any shielding.

Kenneth L. Miller, CHP, CMHP

Reference
Dietrich M, Miller K, King S. Determination of potential uterine (conceptus) doses from axial and helical CT. Operational Radiation Safety (Supplement to Health Phys) 88(2):S10-S13; 2005.