Fran Lowry

December 04, 2012

CHICAGO — Scatter radiation to areas of the body near the breast during screening mammography is negligible and likely does not confer an increased risk for cancer, researchers reported here at the Radiological Society of North America 98th Scientific Assembly and Annual Meeting.

Thyroid shields are unnecessary during mammography and could even result in an increased radiation dose to patients, lead author Alison L. Chetlen, DO, from the Penn State Milton S. Hershey Medical Center in Pennsylvania, told Medscape Medical News.

Dr. Alison Chetlen

"Some patients were unnecessarily worried about radiation during screening mammography, especially to their thyroid. I noticed a lot of calls coming in after a daytime talk show, and patients began requesting thyroid shields during their mammograms," Dr. Chetlen said.

The fact is, thyroid shields can get in the way and impede good mammographic quality and are not recommended during the procedure, she said.

During mammography, some x-rays scatter away from the primary beam and spread outward in different directions.

Although the radiation dose to the imaged breast during a standard mammogram is known and regulated, the dose received by other organs of the body during screening mammography has primarily been extrapolated from phantom measurements, Dr. Chetlen noted.

She explained that knowing the doses to other organs "is important information for women of childbearing age, pregnant women, healthcare providers, and the general public undergoing screening mammography."

To better understand the potential impact of scatter radiation, Dr. Chetlen and her team sought to measure the dose received by the thyroid gland, salivary gland, sternum, lens of the eye, and uterus during digital mammography.

The 207 women in the study group wore radiation dosimeters — devices used to measure the absorbed dose of ionizing radiation — at these sites during a routine screening mammogram.

A medical physicist analyzed the radiation detectors immediately after the exam and found that the doses to the various areas outside of the breast ranged from negligible to very low.

The average estimated dose to the thyroid gland and to the salivary gland was 0.05 mGy. Measured radiation doses to the umbilicus and to the lens of the eye were negligible, indicating no teratogenic risks in early pregnancy and no risk to patients with cataracts.

"We found that radiation doses to the thyroid gland, salivary gland, eyes, and uterus were less than 2% of the annual natural background radiation — the radiation people are exposed to just from living on the planet," Dr. Chetlen said.

The radiation dose decreased slightly with increasing breast density, whereas the scatter radiation dose increased with increasing body mass index and with increased breast compression thickness.

Nevertheless, the radiation dose to all of the organs studied was less than 4% of the average glandular dose to the breast during mammography, Dr. Chetlen reported.

"Getting a mammogram doesn't increase the risk of cancer to these organs," she said. "If a woman asks if she should be concerned that mammography will increase her risk of thyroid cancer and wants to wear a thyroid shield, the physician should explain that the thyroid gland is not exposed to the direct x-ray beam used to image the breast and receives only a tiny amount of scattered x-rays," Dr. Chetlen said.

Dr. Gary Whitman

"She should also be told that wearing a thyroid shield during a mammogram can be detrimental; it gets in the way of the exam and could interfere with optimal positioning and result in artifacts. The potential artifacts from the thyroid collar could necessitate repeating the exam, thus increasing the radiation dose," she explained

Gary Whitman, MD, professor of radiology at the University of Texas M.D. Anderson Cancer Center in Houston, agrees that these results should alleviate some of the patient anxiety. "This study indicates that...scatter radiation from screening mammography is negligible. I think that [the researchers] showed that with various measurements at various sites. These findings should be quite reassuring to patients," he said.

Dr. Chetlen and Dr. Whitman have disclosed no relevant financial relationships.

Radiological Society of North America (RSNA) 98th Scientific Assembly and Annual Meeting: Abstract SSG02 Presented November 27, 2012.