Your toddler fell while running and struck his head on the tiled kitchen floor. He cried immediately and then took his usual nap.  When he woke up an hour later, he seemed uncomfortable and vomited a few times. You are advised to bring your child to the Emergency Room after calling your primary physician.  Your child is alert and still seems more tired than usual, but he has not vomited again.  The ER physician is recommending a brain CT scan to make sure your child does not have a serious brain injury.

You are equally, if not more anxious for reassurance, but have heard about the harmful effects of radiation.  Is obtaining a brain CT scan the right choice?  You wonder, how much radiation will your child get from the CT scan and how is this going to affect him?

A CT scan is a valuable, widely available, and rapid imaging technique which can provide important, even life-saving information.  As with any medical test, the value of the information gained from the test should outweigh the risk associated with the test.  In this scenario, the very small risk of radiation exposure from this test is much less than the risk of missing a significant brain injury from his fall.

For other clinical situations, alternative imaging techniques which do not require radiation exposure such as ultrasonography and MRI, may be more appropriate.  Sometimes, observation and monitoring of the patient may be a reasonable alternative to immediate imaging. You should have this discussion with the physician ordering the test. You should also inquire if the facility where the CT is being done is utilizing the lowest radiation dose possible to adequately perform the test.

How much radiation is used in a CT scan and regular x-rays?

We are all exposed to small amounts of naturally occurring background radiation from air, water, soil, rocks, building materials, and cosmic radiation.  It is helpful to compare radiation used in x-rays and CT scans to our daily background radiation exposure.

Radiation source  
Days of background radiation
1 day
Chest x-ray 1 day
Brain or head CT scan 
up to 8 months
Abdominal CT scan up to 20 months

As seen above, radiation exposure from regular x-rays are minimal. X-rays are the standard tests performed to diagnose common conditions such as pneumonia or broken bones.

Although there is no conclusive evidence that radiation from medical x-rays causes cancer, some studies of populations exposed to similar low levels of radiation have shown slight increases in cancer risk, particularly in children.  There is a 20-25 percent overall statistical risk of death from cancer over a person's lifetime; 200 to 250 of every 1,000 children will eventually die of cancer if they were never exposed to medical radiation.  The estimated increased risk of cancer over a person's lifetime from a single CT scan is just a fraction of this risk (0.03 to 0.05 perecent).

To learn more, Image Gently is an awareness and educational campaign launched in 2007 by the Alliance for Radiation Safety in Pediatric Imaging. Its website has a wealth of information regarding the different medical imaging modalities for children. The following are its recommendations to minimize radiation risks to children:

  • Image when there is a clear medical benefit.
  • Use the lowest amount of radiation for adequate imaging based on the child's size.
  • Image only the indicated area.
  • Avoid multiple scans.
  • Use alternative diagnostic studies (such as ultrasound or MRI) when possible.

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