Laird Harrison

May 12, 2014

SAN DIEGO — Many people overestimate their exposure to ionizing radiation from mammography, a new study shows.

Asked to compare the radiation dose from a mammogram to five other benchmarks, a sample of 1350 people (including 2 men) ranked mammography above its accurate place on the list.

"It shows that there needs to be some education," Jacqueline Hollada, a researcher at the University of California, Los Angeles, told Medscape Medical News.

Hollada presented the study here at the American Roentgen Ray Society (ARRS) 2014 Annual Meeting.

Study participants, who had reported to the university breast imaging center for mammography, were asked to compare the radiation from mammography to the radiation from 2 days in Denver, Colorado; a flight from Los Angeles to New York; the annual dose from food; the annual background dose; and the annual limit for a radiation worker.

The participants checked boxes indicating whether mammography exposed them to significantly less, slightly less, about the same, slightly more, or significantly more radiation compared with each of these benchmarks.

To interpret the participants' scores, Hollada and her colleagues ranked the benchmarks, including mammography, from highest to lowest radiation dose, with 1 equal to the most radiation and 6 equal to the least radiation.

Mammography exposes people to 0.4 mSv, while the extra dose from spending 2 days in Denver is 0.006 mSv, the dose from the airplane flight is 0.04 mSv, the average annual dose from food is 0.3 mSv, the average yearly background dose is 3.1mSv, and the limit for a radiation worker per year is 50 mSv.

Mammography should rank 3.5 in this order because it is between the dose from food and the annual background dose. But the average of the participants' choices produced a score of 2.9.

The difference between 3.5 and 2.9 on this scale is greater than it seems because the scale is logarithmic, said Hollada.

Because people coming for mammography already overestimate their risk, it seems likely that other people are not getting mammography because they fear radiation, she said.

Asked to comment, R. Edward Hendrick, PhD, a clinical professor of physics at the University of Colorado in Denver, said it was hard to draw any conclusions from these results.

"I don't think if you gave this test to radiologists or referring physicians they would do any better," he told Medscape Medical News. "I'm considered an expert on radiation and its effects, and I wouldn't have any idea of how ingested food compares to mammography."

He was more interested in another portion of the questionnaire filled out by the participants. Asked which imaging modalities use radiation, 40% included MRI and only 64% included x-ray. Only 18% included angiography, even though it involves one of the highest doses.

Among the survey's other findings were the following:

  • Forty-two percent of participants said they received no explanation or insufficient explanation of the risks and benefits of mammography.

  • Twenty-eight percent were unsure about or disagreed with the statement that mammography's benefits outweigh its risks.

  • Fifty-eight percent were willing to accept more radiation in exchange for higher diagnostic accuracy.

The question of risk from radiation exposure is not a simple one, Dr. Hendrick pointed out, because no one has found a way to pinpoint what tumors, if any, were caused by imaging.

Estimates of risk depend on linear extrapolations from much higher doses, such as those from the nuclear weapons used at Hiroshima and Nagasaki.

By using data such as that, he said, the risk of dying from cancer because of mammography in a woman aged 40 years is 1/70,000; the risk declines rapidly with age.

Dr. Hendrick and his colleagues have developed an easy reference card that physicians can use to explain to their patients the risks of radiation from imaging.

Ms. Hollada and Dr. Hendrick have disclosed no relevant financial relationships.

American Roenten Ray Society (AARS) 2014 Annual Meeting. Abstract 017. Presented May 5, 2014.

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