Mayo Clinic: Radiation Doses Dropping in CT Scans

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SCOTTSDALE, Ariz.—Since 2001, a team of diagnostic radiologists and medical physicists at Mayo Clinic have been actively developing and implementing new techniques to lower radiation doses from CT. They have installed new CT scanners and software and implemented new scanning instructions to lower the doses for more than 100 different CT protocols.

Amy Hara, MD, a diagnostic radiologist at Mayo Clinic Arizona said that doses have dropped more than 50 percent for several scan types. Cynthia McCollough, PhD, a medical physicist at Mayo Clinic Rochester, emphasized that their goal is to reduce the radiation dose without compromising the image quality—and advances in technology are making that possible.

In the following Q&A, Drs. Hara and McCollough provide some insight about the radiation dose from CT imaging and what it means for patients.

What are the risks of medical radiation exposure?

At the low radiation doses from medical imaging, the exact magnitude of risk is a controversial topic. This is because below 100 millisieverts of radiation, the risks are too low to be directly measured. In fact, some experts believe that there is no risk at these low doses. To be on the safe side of this debate, we assume that there is some small increase in cancer risk from even low doses of radiation and so try to keep the dose levels as low as reasonably possible, while at the same time making sure that the image quality is sufficient to provide an accurate diagnosis.

To be clear, there is minimal risk associated with a single or even multiple CT scans. Normally, people get about 3 millisieverts of radiation each year from background environmental radiation, such as radon and cosmic rays. In higher elevation areas such as Colorado, the background exposure can be up to 10 millisieverts per year, yet no increased incidence of cancer in higher background radiation locations has been observed. A CT scan can deliver anywhere from 2 to 10 millisieverts of radiation, depending on what type of scan a patient receives. For exams requiring multiple scans, this can add up to 20-30 milliSieverts, but this is still considered a low dose of radiation. For some, scans, such as a head CT, the exposure is very low, about 1 – 2 milliSieverts.

Because children have a longer life expectancy than adults and some of their tissues are more sensitive to radiation that for adults, we are particularly careful to use lower doses in children. For a CT scan of a baby, the amount of radiation that we use is about five times lower than for an adult. In some patients, such as young adults with a chronic condition that will require many CTs over a lifetime or pregnant women, patients may want to ask their doctor about alternative imaging options or low-dose scan techniques. All patients, however, should ask their doctor how the exam will be used to help diagnose or treat their symptoms. For a medically appropriate CT scan, the benefit is always much greater than the small potential risk. But like any medical test, if it’s not needed it should not be performed.

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