According to Dr. Atul Gawandea, surgeon at the Brigham and Women’s Hospital in the Dana-Farber Cancer Institute, "We know that doing 62 million scans every year for a population of 300 million is not just unnecessary and wasteful, but it’s dangerous. It’s producing tens of thousands of cancers" (NPR’s "Morning Edition," September 3, 2009).
Medical CT and PET scanners expose at least four million North Americans to high doses of radiation each year, a new study shows. Around 400,000 of them get very high doses, higher than the maximum annual doses allowed for nuclear reactor or nuclear weapon site workers or anyone working with radioactive materials, according to an August 27 article in the New England Journal of Medicine, "Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures."
PET stands for "positron emission tomography" and CT refers to "computed tomography." A positron is a subatomic particle like an electron, except it has a positive charge. PET scans start with injecting a patient with radioactive tracer isotopes that then accumulate in the tissues being examined. The radioactive elements typically used in the scans are:
- Carbon-11
- Nitrogen-13
- Oxygen-15
- Fluorine-18
The new study did not estimate how many cancers radioactive CT and PET scans might cause over time. Dr. Rita Redberg, a cardiologist and researcher at the University of California at San Francisco, told the New York Times on August 27 that "tens of thousands" of additional cancers would probably result from such treatments. In addition, an often-cited 2001 study by D.J. Brenner published in the American Journal of Roentgenology ("Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT") concluded that, "In the U.S., of approximately 600,000 abdominal and head CT examinations annually performed in children under the age of 15 years, a rough estimate is that 500 of these individuals might ultimately die from cancer attributable to the CT radiation."
"It’s certain that there are increased rates of cancer at low levels of radiation and as you increase the levels of radiation, you increase cancer," Redberg said. In 2007, the Health & Human Services Department reported that the number of CT scans ordered for Medicare patients nearly quadrupled between 1995 and 2005. The number of PET scans rose even faster. "Federal rules allow physicians to profit from the use of machines they own or lease," the Times reported. Dr. Reza Fazel, the new study’s chief author, said the use of the scans seems to have increased between 2005 and 2007 as well.
Radiation doses to patients are measured in millisieverts. The average U.S. resident gets about three millisieverts per year from radioactive pollution and the radioactivity found in nature. The new study found that about 4 million U.S. patients receive cumulative doses of over 20 millisieverts, or 7 times the annual average from other sources. Of that group, 10 percent, or 40,000, received at least 50 millisieverts, "more than the annual maximum that nuclear regulators allow," the Times reported.
Gawande, during his appearance on "Morning Edition," told reporter Ari Shapiro that, "Rational care would be to recognize [that] we are doing head scans for people with ordinary headaches, that we already have good evidence and guidelines indicating that it’s not smart to do that scan."
In an editorial accompanying the August New England Journal article, Dr. Michael Lauer wrote, "We have to think and talk explicitly about the elements of danger in exposing our patients to radiation."
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John LaForge is co-director of Nukewatch and edits its quarterly. He lives on Anathoth Community Farm in Luck, Wisconsin.
