External beam radiation therapy

External beam radiation therapy (EBRT) uses a radiation machine to precisely direct radiation beams at the cancer. The radiation is targeted only at the part of the body where the cancer is; for example, if you have breast cancer, the radiation will treat only the breast.

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The radiation therapy machine

You will lie on a treatment table or “couch” under the machine, which will usually be a linear accelerator (see illustration below). The machine does not touch you, but it may rotate around you to deliver radiation beams to the area of the cancer from different directions. This allows the radiation to be more precisely targeted at the cancer and limits the radiation to surrounding normal tissues. You won’t be able to see or feel the radiation. Once the machine is switched off, it no longer gives off radiation.

Linear accelerator

Linear accelerator

This is a general illustration of a linear accelerator (linac), the most common type of radiation therapy machine. The machine used for your treatment may look different.

How long is a course of treatment?

Your radiation oncologist will work out the total dose needed to treat the cancer. In most cases, this will then be divided into several smaller doses called fractions that are given on different days. Each session lasts about half an hour, with the treatment itself taking only a few minutes.

A course of treatment refers to the total number of sessions of radiation therapy you receive. The length of the course varies between people depending on the type of cancer, the total dose required, the location of the cancer and the reason for having the treatment.

In general, higher total doses are used for curative treatment, and a fraction will be given each day, Monday to Friday, for 3–8 weeks. Dividing the dose into separate sessions with weekend rest breaks allows the healthy cells to recover. Occasionally, the radiation oncologist may recommend two treatments per day, with several hours between the sessions.

If you are having radiation therapy as palliative treatment to relieve symptoms, you may have only one or a few treatments.

Each fraction of radiation causes a little more damage to cancer cells, so it’s important to attend all of your scheduled sessions. This ensures you receive the required amount of treatment to eventually kill the cells or relieve symptoms. When you miss sessions, cancer cells have more time to repair the damage, so your treatment may become less effective.

This information was last reviewed in December 2017
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