Medical Radiation

Radiation exposure facts

Understanding radiation

As a patient, you should understand what kinds of tests you’re having and why. Learn the facts about radiation exposure so you can talk to your doctor about your tests and any increase in your cancer risk from radiation exposure.

What is medical radiation?

Radiation is energy that travels as a wave or particle. Some types of radiation, called ionizing radiation, can be harmful. Radioactivity is ionizing radiation given off by substances, such as uranium, as they decay.

About half of the ionizing radiation we’re exposed to comes from nature. It’s in rock, soil and the atmosphere. The other half comes from man-made sources such as medical tests and treatments, sometimes referred to as medical radiation, and nuclear power plants.

How much medical radiation is dangerous?

There’s always a risk of damage to cells or tissue from being exposed to any amount of ionizing radiation. Over time, exposure to medical radiation may cause cancer and other health problems; but in most cases, the risk of getting cancer from being exposed to low amounts of radiation is small.

The chance of getting cancer varies from person to person. It depends on the source and amount of medical radiation exposure, the number of exposures over time and your age at exposure. In general, the younger you are when you’re exposed to radiation, the greater the risk of cancer.

For example:

  • Someone who has had many CT scans starting at a young age is more likely to get cancer later in life than someone who hasn’t had any or as many of these tests. CT scans generally use more radiation than other X-ray tests. The risk of an adult getting cancer from a CT scan is less than one in 1,000. The risk of a child getting cancer from the same CT scan can be much higher.
  • A child who was treated with radiation for cancer is more likely to get another cancer later in life.
  • A person who’s been exposed to large amounts of radiation from a nuclear accident is more likely to get cancer than someone who hasn’t been exposed.

Exposure to small amounts of radiation doesn't cause any symptoms. But exposure to large amounts all at once may cause radiation sickness and death

How do different sources of radiation compare?

Some sources of radiation give off larger amounts than others. For example, when you go through a full-body airport scanner, you’re exposed to very small amounts of radiation. But if you live near the site of a nuclear accident, you’re exposed to large amounts of radiation.

You may be exposed to more radiation than other people if you:

  • Live at high altitude.
  • Have certain medical tests (such as X-rays or CT scans) or treatments (such as radiation therapy or treatment for cancer).
  • Are exposed to radon gas in your home.

To understand more about radiation exposure, you may find it helpful to compare some common sources of radiation to a standard dose from a chest X-ray. A chest X-ray gives off very small amounts of radiation.

For example:

  • You would need to go through a full-body airport scanner about 1,000 times to get the same amount of radiation you would get from one chest X-ray.
  • A 10-hour plane flight is about the same exposure as one chest X-ray. • One mammogram test is about the same as five chest X-rays.
  • Living at high altitude (such as in Denver) for a year is about the same as having five chest X-rays.
  • One CT scan is about the same as 200 chest X-rays.

What can you do to protect yourself?

You cannot avoid radiation that occurs naturally, but there are some things you can do to reduce your exposure to man-made sources such as medical radiation.

If you’re concerned about the risk of getting cancer from having a CT scan, talk to your doctor about the amount of radiation this test may give you.

  1. Confirm the test is needed.
  2. Ask whether another test, such as an ultrasound or an MRI, can be done instead.

In some cases, the benefits of having a CT scan outweigh the small risk of getting cancer. If you have concerns about radiation exposure from a full-body airport scanner, ask if you can get a pat-down instead. (But the amount of radiation exposure from one of these scanners is very low.)