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Radiation Therapy—External
What is it? Overview Usage Side Effects and Warnings

Radiation Therapy—External Overview

Written by FoundHealth.


Radiation therapy is a treatment of cancer and other diseases. It uses high-energy particles to damage the genetic code (DNA) in the cancer cells. This makes the cells unable to grow or divide.

There are two main types of radiation therapy:

  • External—radiation is delivered by a machine that shoots particles at the cells from outside the body
  • Internal —radioactive materials are placed in the body near the cancer cells (also called implant radiation or brachytherapy)

In certain cases, your doctor may recommend a combination of these. Radiation is often used with other types of treatment, such as surgery, chemotherapy , and immunotherapy (stimulates the immune system to fight infection).

This fact sheet will focus on external radiation therapy.

What to Expect

Prior to Procedure

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

  • You will lie on an exam table. A radiation therapist uses a CT scan to define the exact place(s) where radiation will be directed. They may mark the exact area on your skin with colored ink. You may also have a small tattoo (or several) placed on your skin. This is as a permanent mark to help aim the radiation beam.
  • Depending on the type of treatment required, you may also be measured for devices like braces that will help you stay still during treatment.

Description of the Procedure

You will be positioned on the treatment table or chair. The radiation therapist will leave the room and enter a control room. The machine will deliver radiation to certain areas of your body. The most common sources of radiation are x-rays, electron beams, and cobalt-60 gamma rays.

You must be very still during treatment. The therapist can see you on a screen. You can talk with them if you feel uncomfortable or sick.

External Radiation of a Tumor
Radiation of Tumor
© 2009 Nucleus Medical Media, Inc.

How Long Will It Take?

The treatment takes 1-5 minutes. You should allow at least 30 minutes for each session. Most treatments last 2-8 weeks. They are given once a day, five days per week. In some cases, you may be treated twice daily or only three times a week. Treatment schedules will depend on different factors. Talk to your radiation oncologist 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

Be sure to follow your doctor’s instructions .

You will leave and resume your normal activities. You are not radioactive. You are not a threat to anyone else around you, in terms of radiation exposure.

During treatment, your doctor will want to see you at least once a week. You may have routine blood tests to check for the effects of radiation on your blood cells.

After treatment is completed, you will have regular visits to monitor healing and to make sure the treatment affected the disease as planned. Follow-up care will vary for each person. Care may include further testing, medicine, or rehabilitative treatment.

Tell your doctor if you experience side effects. Many side effects can be controlled with medicine or diet. Your doctor may change or delay the course of your treatment if the side effects are too much. Most side effects will gradually go away after treatment.



National Cancer Institute

Oncolink, Abramson Cancer Center, University of Pennsylvania


Canadian Cancer Society

Cancer Care Ontario


Cancer treatment information. Oncolink, University of Pennsylvania Cancer Center website. Available at: . Accessed June 17, 2008.

Definition of radiation therapy. National Cancer Institute website. Available at: . Accessed June 17, 2008.

Radiation therapy fact sheets. CancerNet, National Cancer Institute website. Available at: . Accessed June 17, 2008.

Radiation therapy for cancer: questions and answers. National Cancer Institute website. Available at . Accessed September 29, 2009.



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