External beam radiation therapy (EBRT)

External beam radiation therapy (EBRT) uses a radiation machine (usually a linear accelerator) to direct high-energy radiation beams at the cancer. The radiation is precisely targeted at the parts of the body with cancer. Treatment is carefully planned to do as little harm as possible to healthy tissues.

Learn more about:

• The radiation therapy machine
• The treatment course
• Planning the EBRT treatment
• What to expect at treatment sessions
• Imaging scans you may have
• Techniques and types of EBRT

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The radiation therapy machine

You will lie on a treatment table or “couch” under the machine (see illustration below). The machine does not touch you, but it may rotate around you to deliver radiation beams to the area containing 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

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. There may also be imaging devices on or near the linear accelerator, which help position you accurately on the couch.

The treatment course

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 15–25 minutes, 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. How long you need to have radiation therapy will vary, depending on the type of cancer, the total dose required, the location of the cancer and the aim of treatment.

In general, higher total doses of radiation are used for curative treatment. A fraction of the dose will be given each day, Monday to Friday, for 3–8 weeks. Dividing the total dose into separate treatment 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 between one and 10 treatment sessions.

Each fraction of radiation causes a little more damage to cancer cells, so it’s important to try to attend all of your scheduled sessions. This helps ensure you receive the amount of radiation needed to eventually kill the cancer cells or relieve symptoms. When you miss sessions, cancer cells have more time to repair the damage, so your radiation therapy may not work as well. Occasionally, treatment breaks are hard to avoid, and you may have extra sessions to make up for the missed sessions.