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Study Warns of Increased Radiation Risk from Excessive CT Scans


  • ✓ Excessive scanning may be responsible for as many as 2 percent of all cancers in the U.S. within several decades, according to a new study. But several radiology experts question the accuracy of the findings.

Excessive and unnecessary CT scans could be exposing millions of adults and children to radiation levels equal to those experienced by survivors living just two miles away from the atomic bombs dropped on Japan, according to a review article in the Nov. 29 issue of The New England Journal of Medicine.

Excessive scanning may be responsible for as many as 2 percent of all cancers in the U.S. within several decades, warned David J. Brenner, PhD, and Eric J. Hall, PhD, of the Center for Radiological Research at the Columbia University Medical Center in New York. Because as many as one-third of all CT scans in the U.S. may be medically unnecessary, the issue is a major public health risk, they said.

“In a sense this is a call to arms,” Dr. Brenner told Neurology Today in a telephone interview. “It's not going to be easy because overuse of CT is now built into the U.S. medical system for defensive medicine against litigation as well as pressure from patients and pressure on emergency rooms to increase throughput.”

The warning itself raised an alarm among emergency physicians and others, including neuroradiologists, who questioned the validity of comparisons with cancers in Hiroshima survivors and cautioned that the report could dissuade people from having what might be lifesaving scans. Nonetheless, they agreed that better monitoring of CT is needed as well as more awareness of lifetime risks.

According to the report, an estimated 62 million CT scans are currently performed each year in the U.S., up from just 3 million in 1980. Average personal radiation exposure has almost doubled, largely due to the increase in CT scans. The rate will further increase as new CT-based screening becomes more popular — notably screening for colon, lung, and heart problems, as well as “whole-body” scans, according to Dr. Brenner.

The authors used data from a 2005 report by the National Academy of Sciences on cancer risk for 10mGy radiation exposure derived from studies of atomic bomb survivors.

“Survivors who were about two miles away from the explosions actually received radiation doses quite similar to those from a CT scan,” they noted. “Sixty years of study of these survivors provides direct evidence that there will be an increased individual cancer risk, though small, for those who have this same dose of radiation from CT scans.”

Of special concern is CT requested for “defensive” medicine, or when scans are unnecessarily repeated as patients pass through different parts of the medical system or different physicians. Likewise, the increased use of unnecessary scans in children, especially for conditions such as appendicitis, needs to be curtailed, they said.

“We want to make the public aware of the issue, not to have them avoid scans but to ask physicians if the recommended scan is necessary and whether there are any alternatives. That alone might make a little dent.”

Emergency Rooms

The report specifically pointed to the rapid rise in routine CT in emergency rooms as a major area of concern. But American College of Emergency Physicians President Linda Lawrence, MD, defended the increase in ERs as being medically necessary.

“We are concerned about the comparisons, generalizations, and gross oversimplifications being made by the study, which could have grave consequence for patients facing emergency care,” she stated in a news release.

The ER usage data cited in the article was based on a limited survey of 45 emergency physicians that was conducted in 2002, and does not accurately reflect national use or address the reasons for the increasing use in ERs, she said.

“CT is done more often in emergency departments for many important reasons,” said Dr. Lawrence. “Emergency patients by definition are more in need of urgent care than other patients, and diagnostic imaging often is critical to determining the course of treatment. In many cases, the risk of not testing is more dangerous than testing.”

ER physicians are properly trained to determine which medical symptoms require imaging and they are fully aware of the risks of exposure, she added.


Dr. David J. Brenner: “In a sense this is a call to arms. Its not going to be easy because overuse of CT is now built into the U.S. medical system for defensive medicine against litigation as well as pressure from patients and pressure on emergency rooms to increase throughput.”

David M. Yousem, MD, director of neuroradiology at Johns Hopkins, disagreed. In a telephone interview with Neurology Today, he blamed emergency room protocols for many unnecessary CT scans today. Dr. Yousem was one of the authors of the 2002 study cited in the report, and defended that paper's findings.

“We evaluated CT use prior to use in ER settings with scans three years afterwards and found that the number of CT scans tripled. So it seems that availability is a major reason for the increase.”

CT in emergency rooms has become an integral part of the medical system, and that has led to overuse and unnecessary scans, he said. “If someone is in a serious auto accident, especially a child, they almost always do a full-body CT as part of the hospital protocol for so-called mechanism injuries. Its automatic Triage nurses send these patients for CT as a matter of policy — it's part of the protocol, and often this is before they are even seen by a physician. It's amazing today that there's so much scanning in ERs that isn't based on symptoms or evaluation, but rather on an algorithm.”

Pediatric Concerns

In pediatric radiology, many of these concerns are already being addressed, commented Anthony James Barkovich, MD, chief of pediatric neuroradiology at the University of California Medical Center in San Francisco.

“Radiation risks from CT have always been included in diagnostic decisions and are limited wherever possible. We've been addressing the issue for years,” he told Neurology Today in a telephone interview. “There needs to be concern about it, but the relationship of CT radiation exposure and cancer later in life still isn't clear.”

In pediatric neurology, ultrasound or MR can take care of most cases, he added. “We rarely do CT of the CNS in kids unless it's an emergency, typically head trauma and children with shunts, and then we use the lowest possible level of radiation. We don't get the most detailed picture, but it answers the clinical question.”

Although the NEJM review raises important concerns, he too questioned the applicability of the Hiroshima data as a predictive measure of future cancer risk in CT patients. “It may be the best data we have, but I don't think it's applicable to this situation, as the authors suggest.”


Dr. Mahadevappa Mahesh: “The authors estimate that up to 2 percent of all cancers in the future will be due to CT scans being done today is speculation — I dont think their methodology is valid.”

Patient ‘Backlash’

Concerns that media reports about the article could dissuade patients from having necessary scans is well-founded, according to Mahadevappa Mahesh, PhD, assistant professor of radiology at the Johns Hopkins University School of Medicine and chief physicist at Johns Hopkins Hospital in Baltimore.

He told Neurology Today that he has taken many phone calls from alarmed patients who learned about the study in news reports. “That's the trouble with studies like this — there's an instant backlash from patients and parents who are frantic. I've had many calls already from patients canceling scheduled scans, and these are necessary CT scans,” he said in a telephone interview.

A member of the National Council on Radiation Protection, Dr. Mahesh said the data used in the study are questionable and overestimates the risk, but that the council will publish a report in 2008 with more accurate figures.

“The authors' estimate that up to 2 percent of all cancers in the future will be due to CT scans being done today is speculation — I don't think their methodology is valid,” he said. He explained that cancer rates in Hiroshima survivors couldn't readily be adopted to estimate potential risk from CT scans.

“In my opinion the risk falls somewhere in the middle ground,” Dr. Mahesh said. “This study places the risk at the highest level. On the other hand, the paper is a start toward a meaningful discussion of the issue on a national level. It needs to be brought into the limelight.”

Typical Effective Dose Values for CT protocols*

The two tables below list CT doses for various procedures. Regarding CT scans with contrast, one needs to pay attention and account for the number of scans done per exam, factoring in the effective dose estimations, said Mahadevappa Mahesh, PhD, chief physicist at Johns Hopkins Hospital and assistant professor of radiology at Johns Hopkins University School of Medicine.


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• Brenner DJ, Hall E. Computed tomography — An increasing source of radiation exposure. N Engl J Med 2007;357:2277–2284.
•Oguz K, Yousem D, Deluca T, et al. Effect of emergency department CT on neuroimaging case volume and positive scan rates. Acad Radiol 2002;9:1018–1024.
•Health risks from exposure to low levels of ionizing radiation — BEIR VII. Washington, D.C.: National Academies Press 2005.
    •Preston DL, Shimizu Y, Mabuchi K, et al. Studies of mortality of atomic bomb survivors. Report 13: Solid cancer and noncancer disease mortality:1950–1997. Radiat Res 2003;160:381–407.
    •Pierce DA, Preston DL. Radiation-related cancer risks at low doses among atomic bomb survivors. Radiat Res 2000;154:178–186.