Mammogram radiation risk is lower than thought

According to the World Health Organization, breast cancer kills more than 500 000 women worldwide every year, and mammography is the only breast cancer screening method that has proved to be effective in organized programs. But recommendations for mammography must weigh the benefits of an early diagnosis against the risks of x-ray radiation damage. Standard dosimetry recognizes that of the three breast tissues—skin, fatty, and fibroglandular—the last is the one truly at risk for damage from x rays. Models for simulating radiation dose in mammography routinely use a homogeneous mixture of fibroglandular and fatty tissue, covered by a layer of skin. But real breast anatomy is heterogeneous, with glandular tissue preferentially located near the breast’s center. A large study at the University of California, Davis, has now accounted for that heterogeneity. PhD candidate Andrew Hernandez told a gathering at the July meeting of the American Association of Physicists in Medicine that he and his colleagues used three-dimensional imaging data of 219 women of different ages, ethnicities, and breast densities and sizes to create realistic models. Then, employing Monte Carlo simulations, they obtained the mean glandular dose (DgN)—the currently accepted metric—for both the homogeneous and the more realistic heterogeneous tissue distributions. The results for the homogeneous case agreed with earlier work of other researchers and validated the study. For the heterogeneous case, the team found that DgN values on average were about 30% lower, which strongly suggests that for the past three decades, mammography radiation dose levels, and risks, have been overestimated by about that amount. (A. M. Hernandez, J. M. Boone, J. A. Seibert, AAPM Abstract 27307 , 2015; also Med. Phys. 42, 3548, 2015, doi:10.1118/1.4925275 .)