Radiation therapy (RT) treats cancer and other diseases. It uses high-energy particles to break the DNA in the cancer cells. The cells can’t grow or divide when the DNA is damaged
There are 2 main types of RT:
In certain cases, your doctor may advise using both. It is also used with surgery, chemotherapy, and therapy to spark the immune system to fight infection.
This fact sheet will focus on external RT.
RT may be done to:
RT is used to treat:
External RT does not cause your body to become radioactive. It can cause side effects. The radiation harms healthy cells and cancer cells. Here are some common side effects:
Talk to your doctor about the side effects you may have.
Factors that may raise the risk of problems include:
A woman who is pregnant or could be pregnant should avoid being around radiation. It could harm the growing fetus.
You will go through a process called simulation. This takes between 30 minutes and 2 hours.
You will be positioned on a table or chair. The therapist will leave the room and enter a control room. The machine will send radiation to the sites on your body. The most common sources of RT are x-rays, electron beams, and cobalt-60 gamma rays.
You must remain still. The therapist can see you on a screen. You can talk with the therapist if you feel sick.
External Radiation of a Tumor
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It takes 1 to 5 minutes. You should allow at least 30 minutes for each session. Most RT lasts 2 to 8 weeks. They are given once a day, 5 days per week. In some cases, you may be treated twice a day or only 3 times a week. The number of sessions depends on many factors. Talk to your doctor about the schedule planned for you.
There is no hospital stay. External radiation is typically done at an office visit.
During RT, your doctor will want to see you at least once a week. You may have routine blood tests to check your blood cells.
After RT is done, you will have fixed visits. The doctor will check your healing and make sure the RT worked as planned. Care may also mean further testing, medications, or rehabilitation.
Call your doctor if you have:
If you think you have an emergency, call for emergency medical services right away.
American Cancer Society
Radiology Info—Radiological Society of North America
Canadian Association of Radiologists
Canadian Cancer Society
External beam therapy (EBT). Radiological Society of North America Radiology Info website. Available at: https://www.radiologyinfo.org/en/info.cfm?pg=ebt. Accessed January 28, 2021.
Radiation. Oncolink, University of Pennsylvania Cancer Center website. Available at: https://www.oncolink.org/cancer-treatment/radiation. Accessed January 28, 2021.
Radiation therapy. American Cancer Society website. Available at: https://www.cancer.org/treatment/treatments-and-side-effects/treatment-types/radiation.html. Accessed January 28, 2021.
Radiation therapy for cancer. National Cancer Institute website. Available at: https://www.cancer.gov/about-cancer/treatment/types/radiation-therapy/radiation-fact-sheet. Accessed January 28, 2021.
Last reviewed January 2021 by
EBSCO Medical Review Board
Mohei Abouzied, MD, FACP
Last Updated: 1/28/2021