I’m still working on my 2009 ACEP Scientific Assembly handout for the LLSA exam test prep session (which were actually due yesterday!). Even though the conference isn’t until mid-October, the handouts are always due a few months earlier. And every year, it sneaks up on me! One of the articles I’m reviewing is about the risks of CT irradiation, published in the New England Journal of Medicine in 2007.

Currently, approximately 62 million CT scans are obtained in the U.S. annually. This is quite a contrast to the only 3 million obtained in 1980. Have you noticed the dramatically increased use of CT imaging in your Emergency Department? As a level-one trauma center, SF General certainly has. We recently upgraded to 64-slice CT scanners and are consistently pan-scanning all our high-mechanism trauma patients. We often find significant occult injuries which are masked by the patient’s depressed mental status and coexistent injuries.

On an individual patient level, CT = good.
On a public health level, however, CT = bad.

The glaring concern for CT irradiation is the long-term risk of cancer caused by the diagnostic imaging tool. Epidemiologic studies of survivors from the 1945 atomic bombs in Japan and various nuclear plants found that these people were exposed to around 20 milliSieverts of radiation. This is equivalent to an organ dose from a single average CT scan for an adult. The studies found that there was a dose-dependent association between irradiation and the incidence of cancer. This is especially true in children. Estimates suggest that 0.4% of all cancers in the U.S. will be caused iatrogenically by CT scans.

The authors provide suggestions to minimize the public health cancer risk:

  • Adjust the automatic exposure-control option to minimize the radiation dose of each scan. Newer generation scanners allow this feature.
  • Consider ultrasonography and MRI as an alternative to CT because they do not have ionizing radiation risks.
  • Decrease the number of CT scans obtained in the population. Truly weigh the risk of cancer with absolute medical necessity.

There is a great online reference on the National Cancer Institute website, specifically addressing CT imaging for pediatric patients. Link

Reference: Brenner DJ, Hall EJ. Computed tomography – An increasing source of radiation exposure. N Engl J Med 2007; 357:2277-84.

Michelle Lin, MD
ALiEM Founder and CEO
Professor and Digital Innovation Lab Director
Department of Emergency Medicine
University of California, San Francisco
Michelle Lin, MD


Professor of Emerg Med at UCSF-Zuckerberg SF General. ALiEM Founder @aliemteam #PostitPearls at https://t.co/50EapJORCa Bio: https://t.co/7v7cgJqNEn
Michelle Lin, MD