Facing a CT Scan? Think About Radiation

The evidence continues to mount that we might be getting too much.

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How much radiation you've been exposed to may be the last thing on your mind on the way to the emergency room. But with the increasing use of computed tomography, or CT scans, and nuclear medicine screenings as highly accurate first-line tools in diagnosing illnesses and injuries, a new study suggests such concerns should be front and center.

The study, presented this week at the annual conference of the Society for Academic Emergency Medicine, confirms what many doctors have believed: that people may be receiving doses of radiation, sometimes unnecessarily, that put them at a heightened risk of cancer. Researchers found that a typical patient who visited the emergency room received a cumulative radiation dose of 40 millisieverts over a five-year period. Ten percent of patients ended up with a staggering 100 or more millisieverts. Both levels are well above the safety threshold for lifetime radiation exposure. Exposures above the threshold leave patients vulnerable to increased long-term risk of cancer. As a point of comparison, one chest CT is around 10 millisieverts of radiation and a traditional chest X-ray only 0.02 millisieverts.

The findings come just months after a New England Journal of Medicine report suggested that about one third of all CT scans are unnecessary and that overuse of these tests may be a significant factor in raising the total public risk of cancer deaths in the coming decades. The Columbia University researchers noted that while the individual risks of cancer from CT scans remain low, the increased incidence of cancer may be considerable. To balance image quality with these safety concerns, radiologists use a protocol known as the ALARA principle, short for As Low as Reasonably Achievable. It's meant to ensure that "CT dose factors are kept to a point where risk is minimized for maximum diagnostic benefit," says Arl Moore, president of the American College of Radiology.

Both studies raise the question of when CT and other diagnostic exams are necessary. "There are times when performing a scan is very valuable and absolutely worth the risk," says Timothy Bullard, lead author of the current study and chief medical officer at Orlando Regional Medical Center. In the case of diagnosing acute appendicitis, for example, CT scans have become an almost indispensable tool, reducing the chances of removing a healthy appendix from 24 percent down to just 3 percent. Similarly, with life-threatening or potentially debilitating problems from head trauma, "the obvious risks from radiation are outweighed by the benefit of the test," says Lynn Massingale, an emergency physician from Knoxville, Tenn., and CEO of Team Health, a company that provides ER doctors to more than 260 emergency departments nationwide.

There are times, however, "when we need to ask if it's worth exposing someone to this radiation and if doing so will actually give us the medical information we seek," says Bullard.

Hanging over every decision, according to many ER physicians, is the threat of legal liability. If, for example, a doctor misses a subdural hematoma because a CT scan wasn't ordered, malpractice suits are not an uncommon response. Another problem, according to Linda Lawrence, president of the American College of Emergency Physicians, is that emergency room doctors often have no way of knowing how much prior exposure a patient has had. Absent a reason not to, physicians often go straight to the test that provides the most information—the CT scan.

The fix, Bullard and others say, is for emergency departments nationwide to adopt portable electronic medical records that would store the number and type of exams as well as the estimated cumulative radiation exposure for each patient. Until that happens, though, experts recommend that patients keep track of all of their X-ray and CT scans and make sure that any medical personnel who might order diagnostic tests know the tally.

It's also entirely appropriate for patients to ask their doctors if another diagnostic exam could be used instead of a CT scan. Ultrasound and MRI, for example, do not emit the same sort of harmful radiation.Manufacturers have added adjustable dosage settings on the CT scanning equipment that take into account a patient's size and weight. Patients should inquire if technicians operating the machines are trained to minimize radiation exposure while still providing accurate images. Gregory Morrison, chief knowledge officer of the American Society of Radiologic Technologists, says patients should also ask if radiation could be reduced by performing one scan instead of several.