by EBSCO Medical Review Board
(Ionizing Radiation; Radiotherapy)


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.

Reasons for Procedure

RT may be done to:

  • Control the growth or spread of cancer
  • Try to cure your cancer
  • Reduce pain or other cancer symptoms

RT is used to treat:

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:

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

What to Expect

Prior to Procedure

You will go through a process called simulation. This takes between 30 minutes and 2 hours.

  • You will lie on an exam table. A CT scan will be used to define the exact place(s) where the radiation will go. The site on your skin may be marked with colored ink. You may also have a small tattoo (or several) placed on your skin. This is helps aim the radiation beam.
  • You may also be measured for devices like braces that will help you stay still during RT.

Description of the Procedure

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
Radiation of Tumor
Copyright © 2002 Nucleus Communications, Inc. All rights reserved.

How Long Will It Take?

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.

Will It Hurt?


Average Hospital Stay

There is no hospital stay. External radiation is typically done at an office visit.

Post-procedure Care

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

Call your doctor if you have:

  • Signs of infection, such as fever and chills
  • Diarrhea or loss of hunger
  • Weight loss without a known cause
  • Pain or burning with urination
  • Frequent urination
  • New or unusual swelling or lumps
  • Nausea and vomiting
  • Pain that doesn't go away with the medicines you were given
  • Changes in skin, such as bruises, rashes, discharge, or bleeding
  • Cough, problems breathing, or chest pain
  • New or unexpected symptoms

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: Accessed January 28, 2021.

Radiation. Oncolink, University of Pennsylvania Cancer Center website. Available at: Accessed January 28, 2021.

Radiation therapy. American Cancer Society website. Available at: Accessed January 28, 2021.

Radiation therapy for cancer. National Cancer Institute website. Available at: Accessed January 28, 2021.

Revision Information