A CT scan can mean the difference between an accurate and a wrong diagnosis, timely and delayed treatment and, in some cases, life and death. But because CT scans and other tests that use X-ray technology expose the body to often large doses of radiation, their unnecessary, repeated and excessive use may increase cancer risk, especially in children.
Radiologists from Johns Hopkins Children's Center and elsewhere are sounding the alarm and urging judicious use of radiation-based imaging in children. Some 7 million CT scans are performed in children every year in the United States, many of them avoidable, the doctors say.
"CT scans save lives and have revolutionized medical diagnostics, but as physicians, we should remind ourselves that every CT scan we order now stays with a child for a lifetime," said pediatric radiologist Melissa Spevak, M.D., during a recent presentation at Hopkins, the first of several she is giving to help educate fellow physicians, nurses and radiology technicians about ways to reduce radiation exposure in children. Her efforts are inspired by the "Image Gently" campaign of the Society for Pediatric Radiology and the Alliance for Safety in Pediatric Imaging.
Not only are children's growing tissues and rapidly dividing cells more vulnerable to the effects of radiation, but exposure to radiation at an earlier age gives cancerous mutations that much more time to develop into full-blown disease, Spevak says. And because of the difference in body size, a single CT scan can deliver a much higher dose of radiation to a child than to an adult.
Before ordering a CT scan, Spevak says doctors should ask the following critical questions: "Is this the right test for this condition?" and "Can I obtain the answer in another way?" If the answer to the first question is yes and the answer to the second question is no, the next question should be, "What is the minimum dose that will give me the answer?"
Parents should ask the same questions of their doctors and should consider carrying a list with the types and dates of all imaging tests their child has had. Conversely, doctors should ask parents about previous imaging tests and estimate the child's cumulative dose.
To minimize radiation, doctors suggest the use of alternative imaging technologies like MRI and ultrasound whenever possible, imaging only the indicated body area, avoiding multiple scans, and using the lowest amount of radiation based on the child's size or age.
The safe threshold for radiation exposure has not been defined, but cancer risk is cumulative, rising in proportion to the dose received, with each subsequent exposure increasing that risk, according to a 2005 landmark report by the National Academy of Sciences.
Exactly how likely one is to develop cancer from medical imaging remains the subject of debate, but a 2007 study in the New England Journal of Medicine estimated that up to 2 percent of all cancers in the United States may stem from medical radiation. Epidemiological studies have shown increased cancer among people exposed to nonmedical radiation at doses ranging from 5 to 150 millisieverts (a unit of radiation exposure). The natural environmental radiation people absorb per year is between 3 and 3.5 mSv. An abdominal CT scan in an adult person delivers anywhere between 1 and 30 mSv or up to nine years worth of natural environmental radiation in a single dose. But an abdominal scan in a newborn may result in a much higher dose if the CT scanner settings are not adjusted to the infant's smaller size. By comparison, a set of dental X-rays delivers 0.005 mSv, a chest X-ray delivers 0.01 mSv, and a mammogram delivers around 3 mSv.
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