Shield Reduces Breast Radiation Exposure by Up to 73% During Chest CT

Yael Waknine

May 18, 2005

May 18, 2005 -- Use of a custom-designed lightweight tungsten-antimony shield during chest computed tomography (CT) examination reduces the radiation dose delivered to female breasts by 43% to 73%, without compromising diagnostic information or image quality, according to the results of a study presented here at the annual meeting of the American Roentgen Ray Society 105th Annual Meeting in New Orleans, Louisiana.

"For the last several years, there has been a virtual explosion in the number of CT examinations that are being done worldwide -- in the U.S. alone, there are now more than 35 million CT scans done per year -- and we are noticing that a larger percentage of younger patients are undergoing these examinations as well," Mark Parker, MD, lead investigator, told Medscape.

Dr. Parker is an associate professor of radiology in the VCU Health System at the Medical College of Virginia Hospitals and Physicians in Richmond.

"Patients are getting not only just one CT examination, but multiple repeat follow-up examinations," noted Dr. Parker, pointing out that each diagnostic chest CT or CT angiography imparts a radiation dose of 20 to 50 mGy to a woman's breasts, the equivalent of 10 to 25 two-view mammograms and as many as 100 to 400 chest x-rays.

"The radiation dose absorbed by a patient for the course of these studies or for a lifetime has potentially deleterious effects on sensitive tissues such as the eyes, thyroid, reproductive organs, and female breasts," Dr. Parker said. "The younger the patient is the more sensitive their tissues would be to these effects."

In the study, investigators designed a 6.0-cm thick breast shield of tungsten-antimony composite (0.250 lead equivalents), with a 2.0-cm woven quilted pad buffer layer to reduce image noise. The shield's efficacy in reducing radiation exposure was tested on a model (referred to as a "phantom") constructed of tissues comparable to that of a human thorax, including mediastinum, chest wall, and breast (50% adipose/50% glandular).

Readings from thermoluminescent dosimeters positioned in five locations on the breast phantom showed that use of the shield effectively reduced the radiation dose by 43% to 73% (55% at the 12:00 plane, 57% at the 6:00 plane, 73% in the axilla equivalent, 43% at the nipple level, and 55% at the chest wall). The images obtained were diagnostically acceptable, with minimal artifacts.

"The shield is a means of reducing radiation dose exposure in patients without compromising diagnostic information or image quality," said Dr. Parker, noting that scan parameter manipulations, typically used by radiologists in an effort to reduce exposure of women and young patients, often result in a loss of diagnostic information.

Following the completion of a study to confirm that the shield does not interfere with the visualization of nodules 5- to 7-mm in size placed within the phantom, a submission will be made to the institutional review board for clinical trial approval.

"Based on the results of our studies on our phantom study, I am not anticipating that there is going to be any association with significant degradation of image quality," noted Dr. Parker. "We hope to have the shield commercially available within the next several months."

"Radiologists as well as the clinical physicians that order chest CT examinations need to be cognizant of the fact that the examination is associated with a high radiation dose to patients and should seek alternative ways of evaluating that clinical question," Dr. Parker concluded. "We hope to have the shield available on the market soon, so that it can go into clinical practice as a means of reducing radiation dose exposure when a chest CT or CT angiography is indeed necessary."

The study was funded in part by Worldwide Innovations and Technologies, future maker of the breast shield.

AARS 105th Annual Meeting. Abstract 8. Presented May 16, 2005.

Reviewed by Gary D. Vogin, MD

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