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Weekly Updates"The increase in CT [scan] use and in the CT-derived radiation dose in the population is occurring just as our understanding of the carcinogenic potential of low doses of x-ray radiation has improved substantially, particularly for children."
The low-dose in this quote is relative to the amount of radiation absorbed by atom-bomb survivors--long the only yardstick available to radiation-safety researchers. It appeared in a 2007 report in The New England Journal of Medicine which states that, contrary to conventional medical wisdom, the doses received by a CT scan carry a small but definitive risk of cancer. The lead author is David J. Brenner, PhD, Center for Radiological Research, Columbia University Medical Center, New York.
The radiation dose from a CT scan is far larger than that of a conventional x-ray because it typically involves 64 "slices" of radiation exposure, compared to one or two views of a standard x-ray. The American Heart Association, not known for warning the public about the negative aspects of medical care, acknowledged recently that the amount of radiation from a heart scan is equivalent to 600 chest x-rays.
Each scan creates an additional lifetime risk of cancer that is somewhere between 1 in 200 and 1 in 5,000, according to Dr. Brenner. Unfortunately, consumers who try to get information about radiation exposure from their doctors are unlikely to get an accurate answer. In a 2004 survey of radiologists and emergency room physicians, 75% of the entire group significantly underestimated the radiation dose from a CT scan. Worse, 53% of radiologists and 91% of the E.R. doctors did not believe that CT scans increased the lifetime risk of cancer.
Massive Increase in Scans
The large amount of radiation that concerns researchers like Dr. Brenner is due to the technology itself, as well as the alarming increase in usage. An estimated 62 million CT scans are now done annually in the U.S., up from 3 million in 1980. Lately, heart scans have become a source of alarm. The installation of cardiac scanning equipment has tripled in the U.S. in the past two years.
A recent international study in the Journal of the American Medical Association is the first to look at the radiation dose from a heart scan, aka cardiac CT angiography, as it is performed in the real world. The 50 study sites included in this research project were 21 university hospitals and 29 community hospitals. The research team led by Jorg Hausleiter, MD, found doses varied widely according to the equipment and the study site. Worst of all, the available strategies for reducing doses were not being used.
One of the obvious recommendations to emerge from this study is: "Low voltage scanning should be considered, especially for patients who are non-obese and at higher risk of radiation-associated cancer, such as children and young women."
No one would deny that CT scans are an excellent diagnostic tool that may well have saved many lives. The problem is the complete lack of information. As often happens in the U.S., enthusiastic reception of a new technology--by doctors and consumers alike--precedes the science that would identify those people for whom the benefits outweighs the risks.
In many cases, the purportedly new, improved scan has never been proven in a large clinical trial to be better than the older, less expensive tests. Our profit-driven medical care "system" encourages the premature introduction and widespread acceptance of a new, costlier procedure. Add to the mix, entrepreneurial physicians who co-own the scanning equipment and have a financial incentive to overuse it.
Screening Uses Questioned
The first place to start questioning CT scans, according to Dr. Brenner, is their use for symptomless people. Healthy people are the ones most likely to harmed because they would incur the risks of a high radiation dose and overdiagnosis to receive an uncertain benefit. None of the following screening scans has been proven to be life-saving.
CT colonography, or "virtual colonoscopy," is often regarded as a less-invasive alternative to the standard colonoscopy. It's unlikely that many people who choose this method of colon cancer screening are informed of the high radiation dose or its penchant for finding abnormalities in nearby organs that lead to other investigations, some quite risky, that often prove to be benign (i.e., overdiagnosis).
CT lung screening for smokers and former smokers: This relatively new technology has become popular, despite the lung scan's ability to find non-lethal cancers that are usually treated. A large ongoing government-sponsored clinical trial that has randomly assigned smokers and former smokers to a spiral CT lung scan or no scan will provide answers to two questions for this select group of individuals: Will regular scanning reduce their death rate? Will it cause more harm than good?
CT whole-body screening: This is a truly awful idea promoted by Oprah Winfrey and advertised directly to the public on the radio, the Internet, and in newspapers. A whole-body scan will extend all the problems cited above to the rest of the body.
Heart Scans may make sense for people with symptoms like shortness of breath and chest pain. They are not useful, however, for predicting a heart attack or stroke in people without symptoms. Constrictions in the coronary arteries that show up in the heart scans of symptom-free people are not where a future heart attack will occur (though interventional cardiologists have been opening these constrictions for years on the now-discredited belief that they are saving the patient's life). A heart attack occurs when bits of plaque break away from the arterial wall and blocks the blood flow to the heart. Scans cannot identify which blockages will rupture.
Maryann Napoli, Center for Medical Consumers [C] 2009
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