X-rays, Gamma Rays, and Cancer Risk

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Medical radiation

X-rays, gamma rays, and other forms of ionizing radiation are used to diagnose and treat some medical conditions. This can be in the form of radiation that penetrates from outside the body, or radioactive particles that are swallowed or inserted into the body.

Imaging tests

Certain types of imaging tests, such as x-rays, CT scans, and nuclear medicine tests (such as PET scans and bone scans) expose people to low levels of radiation in order to create internal pictures of the body. (Some imaging tests, such as MRI and ultrasound do not expose patients to ionizing radiation.)

In adults: The amount of radiation varies depending on the test. For example, the exposure from a 2-view chest x-ray is about 0.1 mSv, while exposure from a regular chest CT is about 7 or 8 mSv. The exposure from a PET/CT scan (which combines a PET scan of the body with a CT scan) can be as high as 30 mSv. Fluoroscopy, which uses x-rays to make real-time moving images, is like getting many x-rays in a row. It exposes people to different amounts of radiation depending on how long it is used. The amount of radiation used in many imaging tests has gone down over time as technology has improved.

In children: Radiation exposure also varies based on the test. Unless the settings on the scanner are adjusted for body size, exposure levels can be higher than they would be for an adult. For example, one study found that an abdominal CT may expose an adult’s stomach to about 10 mSv, while a newborn baby’s stomach would be exposed to 20mSv by getting the same test.

For children, exposure to radiation from imaging tests is of particular concern, because:

  • Children are much more sensitive to radiation than adults
  • Children are expected to live longer than adults, so they have a longer time to develop problems from radiation exposure
  • With tests like CT scans, children might receive a higher radiation dose than necessary if the CT settings are not adjusted for their smaller body size

These factors mean that for a young child, the risk of developing a radiation-related cancer could be several times higher than for an adult exposed to the same imaging test. The risks from these tests are not known for sure, but to be safe, most doctors recommend that children only get these tests when they are absolutely needed. When such tests are done, it is important to use the minimum amount of radiation needed to get the image.

Radiation therapy

X-rays, gamma rays, and other forms of ionizing radiation offer an effective way to treat certain kinds of cancer. During radiation therapy, high doses of ionizing radiation (much higher than those used for imaging tests) are directed at the cancer, resulting in the death of the cancer cells. However, this can lead to DNA mutations in other cells that survive the radiation, which may eventually lead to the development of a second cancer. Radiation therapy is also sometimes used to treat serious medical conditions besides cancer.

Our document Second Cancers Caused by Cancer Treatment talks in detail about cancer risks from radiation therapy for cancer.


Last Medical Review: 05/02/2013
Last Revised: 04/18/2014