RadiationIconBottom Line 1

Interpret this data how you will: Exposure to 2-3 CT scans of the head will triple the risk of brain tumors; 5-10 head CT scans will triple the risk of leukemia. In absolute terms, this translates into approximately 1 excess case of leukemia and 1 excess brain tumor per 10,000 patients.

Why It’s Important for Emergency Medicine 

The ED is fast becoming the biggest culprit of unnecessary radiation exposure. But does this exposure actually increase the risk of cancer? Previous studies have estimated risk from projection models based on studies of the atomic bombs in Japan. This is the first cohort study to assess the risk of cancer after CT. It reviews 178,604 children over a 27 year span, estimates the radiation dose to individual organs, and identifies subsequent cancers using the National Health Service Central Registry. This is the most robust study yet to not only associate, but quantify, the real (albeit small) risk of cancer and CT scans.

Major Points

  • Estimated radiation dose to bone marrow from 5-10 head CT scans was 50 mGy (1mGy = 1mSv).
  • Estimated radiation dose to the brain from 2-3 head CT scans was 60 mGy.
  • RR of leukemia in children receiving >30 mGy was 3.18.
  • RR of brain tumor in children receiving >50 mGy was 2.82.
  • These risks are remarkably close to the risks estimated by the Life Span Study of Japanese atomic bomb survivors.


  • Retrospective observation cohort study using data collected from the National Health Service (NHS) of Great Britain.
  • Cancer incidence was identified by using the NHS Central Registry (NHSCR) which stores health information for most residents of Great Britain
  • Data was analyzed for the years 1985-2002 and study participants were < 22 years of age.


  • CT scanners continue to change.
  • The authors estimate that the cumulative absolute risk of being diagnosed with a brain tumor or leukemia 10 years after the first CT scan is 0.01%… not exactly clinically significant enough to change management decisions.

Reviewed by P. Mello

MIA 2012 = Most Interesting Articles series of 2012

Pearce M, Salotti J, Little M, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet. 2012;380(9840):499-505. [PubMed]
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