Mammography Scatter Radiation Presents No Cancer Risk

CHICAGO - Mammograms are a fact of life for many women in America. Unfortunately, so are daytime talk shows. When one show suggested that errant radiation from mammograms may cause cancer in other parts of the body, women blanched and doctors cringed.

But a new study presented Tuesday at RSNA 2012 found that radiation received by other organs during a mammogram is very low and does not present an increased cancer risk.

“The risk of cancer to nearby organs is indistinguishable from incidence of cancer due to other sources. The benefits of screening mammography greatly outweigh the scatter radiation to these organs,” said Alison L. Chetlen, DO, who led the study.

Chetlen and colleagues at Penn State Hershey Medical Center set out to study the radiation received by the thyroid, salivary gland, lenses of the eyes, sternum and uterus during a typical mammography and compare it to background radiation that all humans receive simply from living on Earth.

During a mammogram, some X-rays in fact do “scatter” from the beam directed at the breast, she said. While this radiation is weakened, some women became concerned that radiosensitive areas like the thyroid might absorb these extraneous rays and cause cancer later in life. They prefer to wear collars to shield them from the radiation.

As part of the study, 207 women were fitted with six tiny radiation detectors called dosimeters. Smaller than the size of the penny, these detectors measured the amount of ionizing radiation present on the skin while undergoing a two-view mammography screening. The detectors were evaluated by a health physicist and organ dose was calculated based on the skin dose and the average tissue thickness between the skin and the organ.

Researchers found that the average dose received during a screening is miniscule, less than 2 percent than the amount received annually through background radiation.

The absorbed radiation measurements were taken in milligray, mGy. The uterus, for instance, received .002 mGy of radiation during the screening. By comparison, the annual natural background dose is 3.1 millisieverts, mSv, equivalent in this study to mGy. Therefore, “screening mammography can be performed during pregnancy with no increased risk to the fetus,” Chetlen advised.

As for the thyroid, Chetlen posits that thyroid shields are unnecessary and perhaps even detrimental to the mammography process. “The thyroid gland is not radiosensitive in the age group undergoing screening mammography,” she pointed out. “We know that the thyroid collar can get in the way, so much so that if, depending on the heaviness of the patient, it can override the upper inner breast which could obscure significant findings of breast cancer. It could reduce the quality of the image, it may get in the way of the image, causing a shadow or artifact, and we'd have to retake the view.”

Chetlen noted that these are not exact measurements, but more a guideline to be considered by physicians concerning mammography radiation levels.