Risks of Radiation

Weighing the Radiation Risks of CT, X-ray and Other Imaging

When X-ray radiation is absorbed within our bodies, it can damage molecular structures and potentially cause harm. Very high doses of radiation can cause damage to human cells, as evidenced by skin burns, loss of hair, and increased incidence of cancer that have occurred in atomic bomb survivors. Because high doses of radiation can cause cancer, investigations have been performed into the risks of cancer from lower radiation doses.  

At the present time all studies of the risk of cancer from low doses of radiation have limitations. Among other published material on the subject, the Radiologic Society of North America and the American Association of Physicists in Medicine issued a well-respected position statement updated in 2023 that states:

There is a greater concern regarding the risks of radiation in pediatric patients, highlighting the need for prudent use of medical radiation in pediatric patients.  At UCSF we are aware of these concerns and when a CT is determined to be the best exam to address the clinical question in pediatric patients, we utilize ALARA principles and the latest technology to minimize radiation dose.

References:

• AAPM Position Statement on Radiation Risks from Medical Imaging Procedures. Policy date 11/16/23. 
• Wei-Hao, W., Chia-Yu, S., Shih-Chung, W., & Yu-Hsuan Joni, S. (2023). Risks of leukemia, intracranial tumours and lymphomas in childhood and early adulthood after pediatric radiation exposure from computed tomography. Canadian Medical Association Journal, 195(16), E575. doi:10.1503/cmaj.221303

Risks of Radiation vs. Benefits of Radiation

Generally speaking, all medical procedures and tests carry both risks and benefits, and any consideration of radiation risk must be balanced against the benefits. Media reports generally focus on the risks of radiation, but there are substantial benefits to these tests that must be considered in any balanced discussion of risk versus benefit. Another way of thinking about risk is to focus on the likelihood that something will not happen, rather than the odds that it will happen. For example, a one in 2,000 risk of cancer means a 99.95 percent chance of not getting cancer.

Risks in Context

In addition to the benefits, the small risk from medical imaging radiation should be considered in the context of other risks. The risk of death from smoking, for example, kills 440,000 Americans every year, a much greater and easily reversible proven death toll from a man-made product that produces no medical benefit.

To put the estimated risk of developing cancer from an imaging study in context, keep in mind that:

• The annual dose of radiation we all receive from background radiation is from 3 to 5 mSv.
• Flying from New York to Los Angeles two or three times exposes an individual to a gamma ray dose that is equivalent to the radiation dose received from a chest X-ray.
• Spending nine to 50 days in Denver, Colorado exposes an individual to soil radioactivity dose that is equivalent to the radiation dose received from a mammogram.

Risk Comparisons

The amount of radiation during a typical adult body CT scan (10 mSv) is about the same as the radiation we get every two years from background sources, and the presumed risk of getting a fatal cancer from this amount of radiation is about one in 2,000. The table and graph below put this risk in the context of other occurrences that are of similar magnitude. For example, a patient who has never smoked is more than twice as likely to die from lung cancer as from a cancer caused by a typical CT scan.

Risk of Death from Common Occurrences

Relative Risk