External Breast Radiation



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:

  • External—radiation is delivered by a machine that aims particles at the cells from outside the body
  • Internal —radioactive materials are placed in the body near the cells

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.

Possible Complications

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:

  • Fatigue
  • Skin changes (redness, irritation)
  • Reduced white blood cell count
  • Hair loss
  • Nausea, vomiting, or diarrhea
  • Lack of hunger

Talk to your doctor about the side effects you may have.

Factors that may raise the risk of problems include:

  • Previous RT
  • If you have had systemic lupus erythematosus , scleroderma , or dermatomyositis

A woman who is pregnant or could be pregnant should avoid being around radiation. It could harm the growing fetus.



This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Edits to original content made by Denver Health.

a (Ionizing Radiation; Radiotherapy)


American Cancer Society https://www.cancer.org 

Radiology Info—Radiological Society of North America https://www.radiologyinfo.org 


Canadian Association of Radiologists https://car.ca 

Canadian Cancer Society https://www.cancer.ca 


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.