External radiotherapy

During external radiotherapy or external beam radiotherapy (EBRT), high-energy x-rays are directed at the cancer site from a machine called a linear accelerator. The radiation is aimed only at the part of the body where the cancer is; for example, if you have breast cancer, the radiation will be aimed only at your breast.

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The radiotherapy machine

You will lie on a treatment table or treatment couch under the linear accelerator. The machine does not touch you, but it may rotate to send radiation to your body from different directions. This more accurately targets the cancer and limits the radiation to surrounding normal tissues. Once the linear accelerator is switched off, it no longer gives off radiation.

Different types of linear accelerators may be used – they each vary slightly in how they look and work. The type used will depend on the part of your body being treated and the reason for the radiotherapy. Some types are better at treating cancer near the skin; others are better for cancers deeper in the body.

The linear accelerator is large and kept in an isolated room. This may be confronting or frightening, especially at your first treatment session. Some people feel more at ease with each session as they get to know the staff and procedures at the treatment centre. If you are afraid of confined spaces (claustrophobic), let the radiation therapists know so they can help you.

Linear accelerator

Read more about the radiotherapy machine

Types of external radiotherapy

Several specialised types of external radiotherapy may be used to treat certain cancers. These include:

  • three-dimensional conformal radiation therapy (3D-CRT)
  • intensity modulated radiation therapy (IMRT)
  • volumetric modulated arc therapy (VMAT)
  • image-guided radiation therapy (IGRT).

Visit targetingcancer.com.au/radiation-therapy/ebrt for more information about the different types of external radiotherapy and to watch a video explaining the radiotherapy process.

How long is a course of treatment?

A course of treatment refers to the number of sessions of radiotherapy you receive, that is, the time between your first and last radiotherapy sessions.

Courses vary between people depending on the type of cancer, the total dose required, the location of the cancer and the reason for treatment (e.g. curative treatment or symptom control). The total dose is usually divided into smaller doses called fractions.

In general, higher doses are given for curative treatment, usually over a longer period of time. If you are having radiotherapy as palliative treatment to relieve symptoms, you may have only one or a few treatments in smaller doses.

Most people have radiotherapy from Monday to Friday for 4–8 weeks. Weekend rest breaks allow the healthy cells to recover. Occasionally, the radiation oncologist may recommend two treatments per day.

Each dose of radiation causes a little more damage to cancer cells, so it’s important to attend all of your scheduled sessions to ensure you receive the required amount of treatment to eventually kill the cells or relieve symptoms.

Planning treatment

Treatment needs to be planned to ensure that enough radiation reaches the cancer while doing as little damage as possible to the surrounding healthy tissues and organs. To keep you in a stable position, your treatment team will decide whether any equipment is required, such as a cast or mould.

Planning consists of several steps, which may occur over a few appointments. Procedures may vary slightly depending on the treatment centre. While the information on this page will apply in most cases, you may find things are done differently where you have treatment.

Initial appointment and examination

This may take up to two hours. Your radiation oncologist will discuss the benefits and side effects of radiotherapy and what to expect at each session and after treatment finishes.

You will have a physical examination and may be referred for x-rays or scans to find out more about the cancer.

You may want to take someone with you to keep you company, ask questions and take notes.


You will be asked to lie still on a table while the radiation therapists prepare you for a CT scan. Less commonly, they will use an x-ray machine called a simulator instead. For the scan, you will be placed in the same position on the table that you will be in for treatment.

The images from the CT scanner or simulator will build up a three-dimensional picture of your body. This will show the exact location and size of the cancer. You may also have other types of scans, such as an MRI scan, a PET scan or an ultrasound.

The radiation therapists will send the images from the scans to a computer for examination by the radiation oncologist. The oncologist will prescribe the appropriate dose of radiotherapy, which will help the therapists to further plan your treatment.

Skin markings

To ensure you are positioned in the same way for each treatment session, 2–3 very small permanent ink spots (tattoos) will be marked on your skin. These tattoos are less than the size of a freckle and can’t be easily seen.

Sometimes temporary ink marks are made on the skin. Ask the radiation therapist if you can wash these off or if you need to keep them until the full course of treatment is finished. The ink can be redrawn periodically during the course of treatment, but it will gradually fade.

If you have to wear a cast or shell, the markings will be made on this rather than on your skin.

Casts and moulds

If you need radiotherapy to your head or neck, you may wear a plastic mask called a cast or shell to help keep you still and to make sure the radiation is targeted at the right area. The cast will be specially made to fit you.

You will be able to hear, speak and breathe while wearing the cast, but it may feel strange and confining at first. Tell the radiation therapists if you feel worried or anxious, as they can suggest breathing or relaxation exercises, or give you a mild sedative.

You may need a stabilisation device (mould) to help keep a part of your body still during treatment sessions. This helps ensure that radiation is directed at the same part of your body each time. It also helps to protect healthy organs and tissues.

Read more about planning treatment

Treatment sessions

There will be two radiation therapists at each treatment session. They may ask you to change into a hospital gown before taking you into the treatment room. You will be able to leave your belongings in a secure locker.

The room will be in semi-darkness so the therapists can see the light beams from the linear accelerator and line them up with the tattoos or marks on your body or cast (if you are wearing one).

Waiting to go into the treatment room can make people feel anxious. Take something to read or listen to while you wait, or ask a friend or family member to keep you company. To help you relax during the session, try meditation or breathing exercises, or ask the radiation therapists if you can listen to music.

If you smoke, try to quit before treatment starts to help make the treatment more effective. Quitting can be difficult, so talk to your doctor or call the Quitline on 137 848.

X-rays and scans

Before treatment begins, the therapists may need to take x-rays or a CT scan to ensure you are in the correct position on the treatment table. They may move the table or physically move your body. They will check the scans straightaway and make any adjustments so treatment can start.

Having treatment

Once you are in the correct position, the radiation therapists will go into a nearby room to operate the machine. You will be alone in the treatment room, but you can talk to the therapists over an intercom, and they will watch you on a television screen throughout the session.

If you can’t speak – for example, because you are wearing a cast – you can raise your arm to signal to the therapists, or you may be given a bell to ring to get their attention.

The therapists will move the machine automatically from outside the treatment room if you need treatment from different angles. The machine will not touch you.

You will not usually see or feel anything unusual, but you may hear a buzzing noise from the machine while it is working and when it moves.

It’s okay to breathe normally, but it is important to stay very still to ensure the treatment targets the correct area. The radiation therapists will tell you when you can move. If you feel uncomfortable, tell the therapists – they can switch off the machine and start it again when you’re ready.

The treatment itself takes only a few minutes, but each session may last 10–20 minutes because of the time it takes the radiation therapists to set up the equipment and put you into the correct position. You will be able to go home once the session is over.

Read more about treatment sessions

Is radiotherapy painful?

Radiotherapy itself is painless. While lying on the treatment table, you may have pain due to the cancer, or you may feel uncomfortable because of the position you are in. The radiation therapists may suggest that you take pain medicine before each session to prevent any pain or discomfort.

Some people who have treatment to the head report seeing flashing lights or smelling unusual odours. This is common, but it is not harmful. Tell the radiation therapists if you experience these effects so they can monitor you.

Will I be radioactive?

External radiotherapy does not make you radioactive because the radiation does not stay in your body during or after treatment. You will not need to take any special precautions with bodily fluids, and it is safe for you to be with family, friends, children and pregnant women.

This information was last reviewed in June 2016
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