Warning: Radiation risks from medical imaging

Ever since the Fukushima nuclear reactor disaster in Japan in March, there has been a lot of interest in the media about the health effects of exposure to radiation  including those from medical imaging such as X-rays and CT (computed tomography) scans. Many patients want to know if radiation from mammograms, bone density tests, nuclear imaging, PET scans, and so forth will increase their risk of developing cancer.

The ability to peer inside the body is nothing short of miraculous and has saved countless lives since X-rays were discovered more than a century ago. Today, the array of imaging tests available is bewildering, the technology intimidating, and circumstances and possible outcomes (Is it cancer? A stroke? A heriniated disc?) often terrifying. For most people, there’s very little risk from routine X-rays such as chest X-rays or dental X-rays. But experts have become increasingly concerned about the overuse of many types of scans, not only because of the huge and growing expense, but even more of the potential risk posed by the cumulative exposure to radiation. They are used to diagnose diseases, trauma, and abnormalities, as well as to guide and monitor treatment.

The radiation you get from X-ray, CT, and nuclear imaging is ionizing radiation — high-energy wavelengths or particles that penetrate tissue to reveal the body’s internal organs and structures. Ionizing radiation can damage DNA, and although your cells repair most of the damage, they sometimes do the job imperfectly, leaving small areas of “misrepair.” The result is DNA mutations that may contribute to cancer years down the road.

Exposure to ionizing radiation from natural or background sources hasn’t changed for the past 30 years, but in many industrialized countries, total per capita radiation has nearly doubled, and experts believe the main reason is increased exposure that comes from medical sources which has grown from 15 percent in the early 1980s to 50 percent today. CT alone accounts for 24 percent of all radiation exposures.

Most of what we know about the risks of ionizing radiation comes from long-term studies of people who survived the 1945 atomic bomb blasts at Hiroshima and Nagasaki. These studies show a slightly but significantly increased risk of cancer in those exposed to the blasts, including a group of 25,000 Hiroshima survivors who received less than 50 mSv of radiation  an amount you might get from two or three CT scans.


Because they’re so commonly used today, CT scans are the biggest source of radiation of all imaging technologies. A special type of X-ray that produces cross-sectional images, or “slices,” of the body, CT scans are used to diagnose everything, from heart diseases and cancer to brain tumors, kidney stones, and injuries. Abdominal CT scans tend to produce the most radiation — averaging about 500 times more radiation than a simple chest X-ray, and 1,000 times more than a dental X-ray or bone mineral density test (DEXA). Other types of imaging that use radiation include nuclear diagnostic tests, such as PET scans, as well as fluoroscopy. MRI and ultrasound, in contrast, do not use radiation.

The risk from a single CT scan, when appropriately done, is miniscule, but radiation exposures add up over a lifetime. A study in the Archives of Internal Medicine in 2009 estimated that 72 million scans were done in the US in 2007. After excluding scans done following a diagnosis of cancer and those performed during the last five years of a person’s life, the researchers projected that CT scans in the US would cause about 29,000 extra cases of cancer in the future and about 14,5000 deaths. That’s about two percent of all annual cancers.