To scan or not to scan: are CT scans safe for kids?

With imaging on the rise in medical clinics, emergency rooms, and in airports, many parents are concerned about radiation exposure to their children.  Computed tomography (CT or “CAT” scanning) alone comprises 70% of the medical radiation dose to Americans.  A quick search on the web shows a plethora of websites, articles, and news items all expressing opinions on the safety of medical imaging. This post offers a summary of medical imaging and radiation safety for kids, as well as a brief note on airport scanners.

What is radiation and what types do I need to worry about?
Radiation is defined as energy released as a source travels through space or material.  Radiation is classified into two groups based on how it interacts with matter.  Non-ionizing radiation including light, heat, and radiowaves  are considered harmless at routine doses, but excessive exposures will cause tissue damage.  All forms of ionizing radiation have sufficient energy to ionize atoms which in turn can destabilize molecules within cells and lead to tissue damage. Therefore, ionizing radiation is the more harmful type.

What medical imaging procedures expose patients to ionizing radiation?

  • Computed Tomography (aka “CT scan”)
  • Fluoroscopic procedures such as contrast enemas, upper GIs,  fluoroscopy, voiding cystourethrograms
  • Interventional radiologic procedures including angiography
  • Nuclear medicine procedures including bone scans or PET scans
  • X-ray imaging
  • Dental radiography

*Please Note: ultrasounds and MRIs do not release ionizing radiation.  They release non-ionizing radiation.

How much radiation is being released from these devices?
For comparison, here is a table that compares the amount of radiation being released.
Radiation Source    Equivalent days of background radiation
Background    1 day
A single chest x-ray    1 day
Cross-country airline passenger    4 days
Head CT    Up to 8 months
Abdominal CT    Up to 20 months

If my child undergoes one of the medical imaging procedure, will she have a higher risk of cancer?
Major epidemiologic studies have shown that people exposed to high levels of ionizing radiation are at increased risk for developing cancer. However, these studies are based primarily on health effects to the victims of the atom bombings in Hiroshima and Nagasaki which involved very high exposures to ionizing radiation.

The popular theory for evaluating radiation risk is based on the assumption that there is no dose that is without risk. In other words, there is no safe amount of radiation. We also believe that the higher the dose the higher the risk, so with lower doses there is low risk of cancer.

Without any radiation exposure at all, 200-250 children out of every 1000 will eventually die of cancer. If the entire population receives one CT scan each, the risk for developing cancer increases by a small fraction (roughly 0.03%-0.05%). One way to think of this risk is to relate it to vehicle accident risk.  The risk of developing cancer from one abdominal CT scan is comparable to getting in an accident after driving 7,500 miles or motorcycling for 1,000 miles. This shows that the risk from a single CT scan is very small, but multiple CT scans can cause a cumulative effect.

In summary, parents need to weigh the benefits vs. risks of medical imaging in their children. For serious medical conditions, imaging can help determine the problem or the extent of disease.  But there should be clear reasons for obtaining the test. If your child needs medical imaging ask the following:

1.    Does the benefit from the test outweigh the risk?
2.    Are there alternative diagnostic tests (like ultrasound or MRI) available?
3.    Will my child receive a child-sized radiation dose?
4.    Is it possible to shield or block the areas not being imaged?
5.    Will the CT examination be performed at a reputable facility and by a radiologist and radiology team familiar with pediatric CT scanning?

Finally, the Image Gently campaign recommends keeping a “medical imaging record.” Two sizes are downloadable here:
2 x 3.5 Wallet: www.pedrad.org/associations/5364/files/Dose_Record_2x3.5_fold.pdf
8.5 x11: www.pedrad.org/associations/5364/files/Dose_Record_8.5x11_fold.pdf

Is there a risk with airport scanners?
Recent concerns have been raised about the radiation risk of airport scanners. There are two types of full-body scanners, millimeter-wave scanners and backscatter x-ray scanners. Millimeter-wave scanners use radio waves and produce no ionizing radiation. Backscatter x-ray scanners use ionizing radiation in the form of very low-dose x-rays. With over 500 full-body scanners in use at American airports, 50% of them backscatter x-ray scanners, frequent fliers may have reason for concern about the amount of exposure to radiation.

A full-body scan from a backscatter x-ray scanner exposes a person to between 0.03 microsievert and 0.1 microsievert of radiation. Natural background radiation exposes us to about 2.4 millisieverts of radiation annually which is 24,000 time the radiation from a backscatter airport scanner.  So, the risk of radiation from a backscatter x-ray scanner is extremely small compared to natural background radiation exposure.

by Marissa Alcantar, Medical Student, University of Illinois at Chicago College of Medicine

[edited by Susan Buchanan, MD, MPH]

Resources:
http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/ucm298899.htm
http://www.imagegently.org
http://www.cancer.gov/cancertopics/causes/radiation/radiation-risks-pediatric-CT
http://pediatrics.aappublications.org/content/101/4/717.full
http://www2.aap.org/sections/radiology/RadiologyPediatricianPage.pdf
http://www.health.harvard.edu/family-health-guide/updates/are-full-body-airport-scanners-safe

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