Screening mammography is safer than previously thought, suggests a large study that determined women receive about 30 percent less radiation during the test than assumed. The research is being presented at the 57th Annual Meeting of the American Association of Physicists in Medicine (AAPM).
"Our findings suggest that the harms of screening mammography are smaller than perceived by a significant amount and its efficacy therefore is that much greater," said Andrew Hernandez, BS, a PhD candidate in biomedical engineering at the University of California Davis. "Our large study confirms smaller studies that found the levels of radiation women receive during screening mammography are overestimated."
The breast is composed of skin, fat and glandular tissue. Because the latter is at greatest risk of being damaged by radiation, current methods in mammography focus on the radiation dose deposited only to the glandular tissue. But these methods assume that the breast is composed of a uniform mixture of glandular and fat tissue. Previous studies (one based on computer models and one based on 20 patients) found the glandular tissue is not distributed uniformly throughout the breast, leading to an overestimation of the radiation dose to the breast.
The new study used a comprehensive model of breast anatomy based upon computed tomography (CT) exams of 219 women representing a large population average over a range of breast density, age, ethnicity, and size to determine how the glandular tissue is distributed throughout the breast. The study concluded that the radiation dose is overestimated by 25-35 percent.
Because the amount and distribution of glandular tissue varies from breast to breast, some women could receive 20 percent less radiation than thought, while others could receive 40 percent less, said Hernandez.
Currently, there is disagreement regarding when mammography screening for breast cancer should begin in women at average risk for the disease, and how often it should occur. While the American Cancer Society recommends yearly screening beginning at age 40, the U.S. Preventive Services Task Force recommends waiting until age 50, and then screening every other year. Both groups recommend earlier screening in women at increased risk for breast cancer.
"The decision to screen is a computation based both on benefit and risk. We know what the benefits are, and our research now suggests that the risk of developing cancer from screening mammography is 30 percent lower than previously thought," said Hernandez. "The next step is to update the radiation dose methods relevant to mammography to reflect the real distribution of glandular tissue."
In addition to Hernandez, collaborators on the study being presented at AAPM are: J.M. Boone, and J.A. Seibert.