Fran Lowry

November 28, 2012

CHICAGO, Illinois — Computed tomography (CT) scans, particularly to the chest, might increase a woman's risk for breast cancer, and the risk increases with the number of scans, researchers reported in a poster session here at the Radiological Society of North America (RSNA) 98th Scientific Assembly and Annual Meeting.

Dr. Rebecca Smith-Bindman

"There is a small but real increased risk of breast cancer associated with CT scans that include the chest in the field of view, such as pulmonary embolism and cardiac studies. This risk is higher for young women who receive multiple CT scans," senior author Rebecca Smith-Bindman, MD, professor of radiology and biomedical imaging at the University of California, San Francisco, told Medscape Medical News.

However, some experts, such as Richard L. Morin, PhD, from the Department of Radiology at the Mayo Clinic in Jacksonville, Florida, caution that such scans can save lives and should not be eschewed because of misplaced fears about hypothetical cancers that might or might not occur at some point in the future. Dr. Morin was not involved in the study.

Background

The use of chest and cardiac CT has grown rapidly; over the past decade, the use of CT imaging has increased 6.8% per year. The impact of the radiation that accompanies these scans on breast tissue and the subsequent risk for breast cancer is largely unknown, Dr. Smith-Bindman explained.

In this study, "we were interested in breast cancer risks, the cumulative radiation dose that women are receiving, the impact of those doses on risks, and the short-term risks that occur 10 to 20 years after an imaging test is done," she said. "Longer-term risks are a little harder to understand," she added.

Dr. Ginger Merry

The researchers, led by Ginger Merry, MD, MPH, a breast imaging fellow from Prentiss Women's Hospital of Northwestern Memorial Hospital in Chicago, Illinois, retrospectively analyzed information on CT dose from 1656 women enrolled in a large integrated healthcare system who underwent CT examinations that exposed the breast to radiation from 2000 to 2010.

They obtained 124 CT and 42 nuclear medicine exams per 1000 female enrollees per year.

The researchers used an automated computational method to estimate the effective radiation dose and the amount of radiation absorbed by the breast. They used this information to estimate the patients' risk of developing breast cancer starting 10 years after exposure.

Results

Doses of radiation to the breast from CT were variable, with the highest doses delivered by multiple-phase cardiac CT (median, 51.6 mGy; interquartile range [IQR], 21.2 - 73.1) and chest CT (median, 34 mGy; IQR, 16 - 74).

According to the researchers, a person who underwent 2 or more cardiac or chest CTs before the age of 23 would double her 10-year risk of developing breast cancer from the radiation of these exams, compared with her natural risk of developing breast cancer.

For instance, if a 15-year-old girl who is otherwise at low risk for breast cancer (not a carrier of the BRCA mutation) undergoes a CT scan and gets breast cancer 10 years later, it is more likely to have come from the CT radiation than from her underlying risk, Dr. Smith-Bindman explained. "The risks of cancer are small but real."

Although the reason for the CT scan was not tracked in the study, Dr. Smith-Bindman explained that women undergo chest CT and cardiac scans for many reasons, including chest pain and suspected pulmonary embolism.

Technology and Research Methods Questioned

Dr. Richard Morin

Dr. Morin, speaking as a member of the RSNA Public Information Advisory Network, noted that the estimated risk seen in this study might not be statistically significant.

He also pointed out that CT technology has changed considerably since 2000.

"The time period of the study was over 10 years, but CT technology over [that time course] changed substantially," Dr. Morin noted. There would have been a difference in radiation dose between a CT performed in 2000 and that performed in 2010. Combining these creates confusion when trying to draw a specific conclusion from such a study, he added.

He also called into question the methods used by the researchers to obtain the radiation doses they cite.

"The fact that they used payment data, payer's data, and [information] like that does not mean they got the radiation doses." In fact, he said, they might not have even gotten exposure data.

Optimizing Radiation Dose

Such criticisms aside, Dr. Morin agrees that the most important message is that using the optimal amount of radiation is crucial.

"That is the message of Image Wisely. For an individual patient, as long as the exam is ordered appropriately, the benefit to that patient far outweighs any risk of a hypothetical cancer that could ever occur in the future. That's the most important message, particularly for referring physicians and for the general public," he said.

Dr. Morin insisted that if he had a 15-year-old daughter, he would let her have a CT scan "if she had the appropriate symptoms. There's no question about it. Because whatever that CT scan is going to answer affects her today, right now, not something that is hypothetical. You heard the word hypothetical here quite a few times. This is cancer by statistics. It doesn't mean that an individual patient is going to get cancer," he explained.

Study Could "Send the Wrong Message"

Some of the recent literature has frightened people away from appropriately ordered CT scans, Dr. Morin added.

"We have had concrete examples of physicians who have not ordered a CT scan for a patient who subsequently had a bad effect," he said.

"I think a very large number of us in the medical physics and scientific community are concerned that studies like this might send the wrong message. We have examples of parents who had young children involved in an accident who did not get a CT scan and died of a subdural hematoma."

The appropriate use of medical imaging is important; so is patient counseling, Dr. Morin added.

"I counsel patients who don't want a CT scan all the time. Patients should feel empowered to ask their physician what he or she expects to see on the CT exam. If the answer is not satisfactory, then they should consider another type of exam. Similarly, if there are multiple exams, the question to be asked is, 'What do you hope to get out of this exam that you didn't get out of the previous...scans?' We are all for using this technology judiciously. It can be lifesaving."

Dr. Smith-Bindman, Dr. Merry, and Dr. Morin have disclosed no relevant financial relationships.

Radiological Society of North America (RSNA) 98th Scientific Assembly and Annual Meeting: Abstract LL-HPS-TU3A. Presented November 27, 2012.

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