Average amount more than five times higher than annual exposure outside hospital, study shows
MONDAY, Nov. 16 (HealthDay News) -- Heart attack patients arriving at the hospital typically receive the radiation equivalent of 725 chest X-rays from medical tests during that single hospital stay, new research shows.
The average exposure was 14.5 millisieverts (mSv), about one-third the annual maximum of 50 mSv allowed radiation workers and more than five times the amount of background radiation Americans get from just going about their business in any given year.
Although the amount may sound alarming, it's not at all clear at this point whether these dosages actually increase health risk, particularly the likelihood of developing cancer, said the Duke University researchers, who plan to present their findings Monday at the American Heart Association's annual meeting, in Orlando, Fla.
"We have to weigh the potential risk of radiation against the risk of not doing anything, and the risk would be very substantial, especially in these patients who were gravely ill," said Dr. Thomas Gerber, a spokesman for the heart association and a professor of medicine and radiation at the Mayo Clinic, in Jacksonville, Fla. "It's important to realize that nobody has ever been able to show scientifically that radiation at the levels used in medical imaging increase the risk of cancer. These are all theoretical concerns that are mathematically extrapolated from what happened in survivors of Hiroshima and Nagasaki who got so much more radiation."
"The actual biological effects of radiation are an ongoing question," added study author Dr. Prashant Kaul, a fellow in cardiovascular medicine at Duke. "The risks of causing cancer at the radiation dose levels we're talking about is actually uncertain."
The findings arrive in the context of several other recent studies that have shown that patients of all kinds are being exposed to large amounts of radiation from medical imaging procedures.
According to background information in this study, radiation exposure from medical imaging procedures exploded more than 700 percent between 1980 and 2006. One-third of these were cardiovascular procedures.
"Up to this point, we've been thinking about radiation as it relates to an individual imaging test. We think it's appropriate to think of radiation dose per episode of care," Kaul said.
More than 64,000 patients treated for heart attacks at one of about 50 university hospitals over a three-and-a-half year period underwent almost 277,000 procedures involving ionizing radiation. This represented an average of just over four imaging studies per person, with average cumulative radiation dose of 14.5 mSv.
Cardiac catheterization, one of the most important procedures used by cardiologists, represented at least half of the radiation exposure from all procedures, which was expected, Kaul said. Three-quarters of patients underwent this procedure, which is consistent with the guidelines.
"Also, about 50 percent of patients got CT scans, which is maybe a little higher than expected," Kaul said. But the researchers don't know why the patients were getting these chest, head or all-body scans so they can't determine if they were necessary or not.
A head CT delivers 2 mSv, a body CT delivers 10 mSv and a chest scan delivers 7 mSv, he said. A diagnostic catheterization gives about 7 mSv and putting a stent into an artery adds another 8 mSv, on average.
"In the absence of definitive data, most authorities still recommend a conservative strategy following the ALARA [as low as reasonable achievable] principle," Kaul stated. "We would like to increase awareness among physicians so when they're ordering tests involving ionizing radiation, they're thinking about this. At the end of the day, we want to be sure we're ordering the right test for the right patient in a given clinical scenario."
"You see, the potential risk of radiation differs in a patient with no symptoms who comes to the doctor for a regular check-up. For them, a stress test probably would not be meaningful but it's also different if you're a 20-year-old woman or an 80-year-old man," Gerber added.
The Occupational Safety and Health Administration has more on ionizing radiation.
SOURCES: Prashant Kaul, M.D., fellow, cardiovascular medicine, Duke University Medical Center, Durham, N.C.; Thomas Gerber, M.D., professor, medicine and radiology, Mayo Clinic, Jacksonville, Fla.; Nov. 16, 2009, presentation, American Heart Association annual meeting, Orlando, Fla.
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