Increased CT use may boost breast cancer risk

Increased use of CT may boost breast cancer risk in certain women, such as younger patients and those who receive repeat exams, according to research presented at the RSNA 2012 meeting. Nuclear medicine exams may also raise the risk of breast cancer.

Dr. Ginger Merry, from Prentice Women's Hospital/Northwestern Memorial Hospital in Chicago, and colleagues evaluated imaging and associated radiation exposure among female members enrolled in a large integrated healthcare system between 2000 and 2010, including more than 250,000 enrollees each year.

"When a woman undergoes CT or nuclear medicine imaging of her chest, abdomen, or spine, her breast tissue will absorb some radiation," senior author Dr. Rebecca Smith-Bindman, of the University of California, San Francisco, said in a statement. "Breast tissue is one of the tissues in the body known to be sensitive to developing cancer as a result of radiation exposure."

The group collected CT dose parameters on 1,656 patients and used a Monte Carlo computational method to estimate breast and effective doses. Merry and colleagues also abstracted nuclear medicine data on the volume of injected radiopharmaceutical for 5,507 exams.The researchers then estimated the women's imaging-related risk of breast cancer, and compared it to their underlying risk of developing breast cancer (which was estimated based on data collected by the Breast Cancer Surveillance Consortium).

CT utilization increased from 99.8 scans per 1,000 women in 2000 to 192.4 scans per 1,000 women in 2010 (an annual increase of 6.8%), according to the researchers. The group also found that in 2010, 46% of those CT examinations exposed the breast to radiation. Nuclear medicine imaging decreased from 39.3 scans per 1,000 women in 2000 to 27.5 scans per 1,000 women in 2010 (a 3.5% annual decline); however, in 2010, 84% of nuclear medicine studies still exposed the breast to radiation.

A child or young adult who undergoes two or more chest or cardiac CT exams before the age of 23 more than doubles her 10-year risk of breast cancer, according to Merry and colleagues.

"If imaging is truly indicated, then the risk of developing cancer is small and should not dissuade women from getting the test they need," Smith-Bindman said. "On the other hand, a lot of patients are undergoing repeat chest and cardiac CT, many of which aren't necessary. Women, and particularly young women, should understand there is a small but real potential risk of breast cancer associated with cardiac and chest CT, and the risk increases with the number of scans."

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