Using bismuth breast shields to protect women's breasts from radiation during a chest computed tomography exam is more effective than a technique that turns the CT on-and-off as it scans, according to a new study.

In a study shared Wednesday at the American Roentgen Ray Society's annual meeting in Chicago, researchers said women undergoing chest CT exams might get lower doses to both the breast and body using breast shields, rather than having posteriorly centered partial CT scans.

The researchers, led by Dr. Rafel Tappouni, were prompted to the do the study because of the growing use of CT scans and concerns over breast's sensitivity to radiation. For instance, because of worries about breast radiation, about three years ago the International Commission of Radiation Protection doubled the tissue weighting factor for breasts from 0.05 to 0.1.

In chest CT exams, the doctors want information about, say, the lungs, but not the breasts, so protecting them is important.

Posteriorly centered partial CT, also called organ-based dose modulation CT, is a technique in which the CT tube switches on for 232° out of 360° per rotation, according to the researchers' abstract, published online.

While this results in a lowered dose to the breast, it's at the cost of a slightly higher dose to the chest.

"We found that posteriorly centered partial CT does decrease skin entrance radiation dose to the breast by 16 percent, but increases overall radiation dose to the chest by 8 percent," said Dr. Tappouni, with Penn State Hershey Medical Center in Hershey, Pa. "The bismuth breast shields, on the other hand, reduced skin entrance dose to the breast by 38 percent without an increase in overall radiation dose."

In the study, the researchers measured the doses by placing thermoluminescent dosimeters on the front and back of a Fluke Biomedical-made imaging phantom.

First, the dummy got a baseline chest CT with tube current modulation from a 128-slice Siemens MDCT scanner. Then, the dummy was scanned while wearing a bismuth-impregnated synthetic rubber shield, made by F&L Medical Products. The scan was repeated without the shields, but with the posteriorly centered partial CT technique.

The average baseline dose for front and back detectors was 686 and 602 mrad, the researchers said. For breast shield, the average doses were 426 and 606 mrad. And for posteriorly centered partial CT, 590 and 826 mrad.

The average effective mAs and CT dose index were, for the baseline, 88 mAs and 5.99 mGy; for the breast shield, 87 mAs and 5.93 mGy; and for posteriorly centered partial CT, 95 mAs and 6.47 mGy.

The study adds to an already sizable body of research backing up the effectiveness of breast shields.

For example, about two years ago, researchers found bismuth breast shields combined with automatic tube current modulation and a lower peak kilovoltage resulted in up to 55 percent breast dose reductions.

Still, as the study was presented at a conference and has not appeared yet in a peer-reviewed journal, the results should be considered preliminary.

F&L's AttenuRad breast shields can be bought for about $85-$100 online.

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