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CHICAGO -- A female teenager who undergoes repeat chest or cardiac CT studies may see her 10-year risk for breast cancer double, researchers said here.

After retrospectively reviewing the records of about 250,000 women enrolled in a large healthcare delivery system, researchers found that an increase in CT use between 2000 and 2010 may result in an increase in the risk of breast cancer for some women, including younger patients and those who undergo multiple radiation-based imaging studies, reported Rebecca Smith-Bindman, MD, from the University of California San Francisco, and colleagues at the Radiological Society of North America (RSNA) meeting.

"Until now, the impact of this increased use of imaging on radiation exposure to breast tissue and the subsequent risk of breast cancer has not been known," Smith-Bindman said in a written statement. "Our goal was to quantify imaging utilization and radiation exposure to the breast among women...and to use these data to determine the imaging-related risk of breast cancer from those studies."

The group collected CT dose parameters on 1,656 patients and used a newly developed, automated Monte Carlo computational method to estimate breast and effective doses.

For nuclear medicine scans, data were abstracted on the volume of injected radiopharmaceutical for 5,507 exams and were used to estimate breast doses.

The breast-specific absorbed doses and the Preston 2002 pooled model for radiation-effects on breast cancer risk were used to estimate women's 10-year risk of developing breast cancer based on age at exposure to CT.

Using NCI Breast Cancer Surveillance Consortium data, they estimated women's 10-year risk of breast cancer, based on the Gail model and Surveillance Epidemiology and End Results (SEER) age-specific cancer incidence data, and compared the imaging-related risk to the underlying Gail risk.

They found increases in CT utilization from 2000 to 2010 of 99.8 CT scans per 1,000 women in 2000 to 192.4 CT scans per 1,000 women in 2010 for a 6.8% annual increase.

Furthermore, in 2010, 46% of those CT studies exposed the breast to radiation.

Radiation doses to the breast from CT scans were variable, but the highest breast doses were delivered by multiple-phase cardiac (median 51.6 mGy, IQR 21.2, 73.1) and chest CT (median 34 mGy, IQR 16, 74).

"A child or young adult who underwent two cardiac or chest CTs before the age of 23 has a higher 10-year risk of developing breast cancer from these exams than her underlying risk of developing breast cancer in the same period," the authors wrote.

Lead author Ginger Merry, MD, from Prentice Women's Hospital -- Northwestern Memorial Hospital in Chicago, emphasized that "the breast tissue is radiosensitive and CT of the chest, heart, and spine deliver significant doses. Younger women are at the highest risk due to increase radiosensitivity of the breast at younger ages, and longer life span to see cancer."

While nuclear medicine imaging decreased from 39.3 scans per 1,000 women in 2000 to 27.5 scans per 1,000 women in 2010, for a 3.5% annual decline, 84% percent of nuclear medicine studies done in 2010 exposed the breast to radiation.

Smith-Bindman also noted that the additive risk of radiation exposure might be even more problematic for women at high risk for breast cancer, with that risk increasing to 37 per 100,000 women from 32 per 100,000 women.

"Thus imaging should be used only when appropriate and when it will improve outcomes," she said. "Imaging providers need to assess the doses associated with each exam, limit multiphase protocols, and optimize the dose to minimize exposures and risk."

Richard Morin, PhD, from the Mayo Clinic in Jacksonville, Fla., told 名媛直播 that the results should be interpreted with caution.

"The time period for this study is over 10 years, and CT technology over that period has changed substantially. The person in 2000 most likely did not get the same [radiation] dose as a person in 2010. Lumping together [time periods] like this creates a great deal of confusion," warned Morin, who is also a member of the RSNA Public Information Advisory Network.

But he agreed that the important take-home message from the study is for radiologists to "image wisely. As long as the imaging study is ordered properly, the benefit to that patient will far outweigh any potential risk."

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