Will getting two or three CT scans of the abdomen expose a person to the same amount of radiation as people who lived near the atomic blast that ravaged Hiroshima in 1945 but survived?
Will they increase a person's lifetime cancer risk?
If you answered "yes" to both questions, you're spot on. You're also better informed than many patients at inner-city emergency departments, according to a new survey from Cooper University Hospital in Camden, New Jersey.
Researchers there asked more than 1,100 patients who came in with stomach pain to rate statements similar to the questions above. Half said they had very little faith in the comparison between Hiroshima survivors and patients who had CT scans, rating their agreement at 13 on a scale from 0 to a perfect 100.
The majority of patients also tended to disagree that the scans would increase their cancer risk. And three-quarters underestimated the x-ray radiation from a CT scan compared with traditional chest x-rays, which are at least 100 times weaker.
"The point of the paper was not to create mass hysteria," said Dr. Brigitte Baumann, an emergency physician at Cooper, whose findings appeared online December 14th in the Annals of Emergency Medicine.
"The concern is patients who keep coming back to their physicians and get a lot of scans," she told Reuters Health. Some patients—like the ones who come in with chest pain coughing up blood—obviously need a CT scan, she said, but in general "the whole topic is just a big shade of gray."
In recent decades, the number of Americans having computed tomography scans has soared, reaching 72 million in 2007, and some doctors now worry that they may be overused.
According to one government study, CT scans done in 2007 alone will cause about 29,000 cancers and kill nearly 15,000 Americans.
From a single patient's perspective, the risk seems less daunting: It would take 1000 "average" scans to produce one extra case of cancer in 50-year-olds, the National Cancer Institute's Amy Berrington told Reuters Health in November.
By comparison, about one in three Americans will develop some type of cancer, so the extra risk may be a small price to pay if the consequence is better treatment.
The radiation dosage from one scan typically ranges from a few millisieverts—comparable to the yearly background radiation from natural sources—to tens of millisieverts.
Hiroshima survivors living a couple miles from the blast often received between five and 100 millisieverts, according to Dr. David J. Brenner, who heads the Center for Radiological Research at Columbia University in New York and was not involved in the new study.
He said there is little difference between the x-rays beamed at patients in hospitals and the mix of x-rays and gamma radiation produced by a nuclear explosion.
"The biggest difference is that the atomic bomb survivors got whole-body radiation, whereas CT is very directed exposure," he said.
Dr. Baumann and colleagues also tapped into the medical records of their patients, finding that half had gotten scans at the hospital in the past five years.
"We have people who have gotten as many as 57 scans," she said. "That is a huge number."
The U.S. Food and Drug Administration has recently started pushing for doctors to curb unnecessary radiation from medical imaging. But patients may need a push, too, Dr. Baumann's survey shows.
Patients told the researchers tests such as blood work and CT scans would boost their confidence in their medical evaluation.
"When they go to the emergency department, they're not really happy if all you do is speak to them; they want more," Dr. Baumann said.
She now takes extra pains to explain the risks and benefits of CT scans to patients. And it seems to have an effect. Just this week, for instance, one of her patients who was determined to get a scan for kidney stones chose to wait and see if the pain would disappear on its own.
"I think we should take a couple minutes to discuss radiation," Dr. Baumann said, noting that the findings probably apply to other inner-city hospitals as well.
"We probably overestimate how much patients understand and underestimate how much we should tell them," she said.
Ann Emerg Med. Posted online December 14, 2010. Abstract
Frederik Joelving • Reuters Health Information © 2011