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Vital Signs

Spring 2011

Patients Should Ask About Radiation Levels for Diagnostic Tests


VS-Spring2011-Radiation LevelsDiagnostic imaging tests — from simple chest X-rays and ultrasound to more sophisticated techniques such as CT, MRI and nuclear-medicine scans — save lives every day by opening a window into the body to detect early signs of disease, investigate the nature of symptoms and determine the course of treatment. But some forms of imaging involve significant levels of radiation. A patient should discuss with his or her physician any potential risks from such exposure prior to proceeding with an imaging test to ensure that the test’s benefits outweigh the risks, says Michael Herbst, M.D., a family medicine physician at UCLA Medical Center, Santa Monica.

“A common X-ray for something like a broken bone involves so little radiation as to be negligible in terms of risk,” Dr. Herbst says. “But certain tests, particularly CT scans, involve as much as 100 times the level of radiation, and over a lifetime there can be a cumulative effect that should be cause for concern. If one of these tests is recommended, it’s reasonable for patients to ask how much radiation they will be exposed to, what is the likelihood of that affecting them and whether there are suitable alternatives.”

“When patients are engaged in decisions about their treatment, they do better,” agrees Edward Zaragoza, M.D., UCLA diagnostic radiologist. “It’s always important to ask whether this is the most appropriate examination under the circumstances — and if it’s determined that it is, to ensure we deliver a dose that is as low as reasonably possible to be effective in obtaining optimal results.”

Everyone is exposed to a certain amount of radiation in the environment, Dr. Zaragoza notes, and this so-called background radiation is nothing to worry about. But large amounts of radiation can damage DNA beyond its ability to repair itself, increasing the risk of cancer. Compared with routine radiographs, CT, fluoroscopy and nuclear-medicine techniques emit relatively higher but medically accepted radiation doses. In some cases there are alternatives, such as MRI and ultrasound, which do not expose patients to radiation. MRI has become a particularly powerful and safe tool for characterizing orthopaedic and neurologic issues, Dr. Zaragoza says.

But for certain types of issues – from heart procedures and tumor detection to visualization of bone anatomy — CT remains the clear choice. “You don’t want to push your doctor to get you a CT scan if you don’t need VS-Spring2011-Radiation Levels Diagnosticsone,” explains Dr. Herbst. “If you’re having headaches that are persisting or increasing in intensity, a CT scan might be the right thing to do, but you wouldn’t want to get one year after year. On the other hand, for patients who are being monitored after having had cancer, we wouldn’t want to risk not diagnosing a recurrence because of the much smaller risk of the radiation causing a new cancer.”

Radiologists are especially careful to limit exposure for children and young adults. “With young people, there is concern that they will have to live with their radiation doses for many years, and there could be cumulative effects with repeated exposures,” Dr. Zaragoza explains. UCLA participates in the Image Gently national campaign to lower radiation dosages in the imaging of children. For young women, he adds, breast tissues are more sensitive to radiation so every effort is made to avoid the thoracic region. But even for these patients, there may be important reasons for having the test. “If your physician recommends a CT scan, a fluoroscopy or a nuclear-medicine study, you want to ask about it and make sure it’s for a good reason,” Dr. Herbst says. “If it’s not necessary or there is an alternative, that should be considered. But in the great majority of cases, the benefits of getting that test will far outweigh the risks.”

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