External radiotherapy

During external radiotherapy, high-energy x-rays are directed at the cancer site from a machine outside the body. You will lie on a treatment table (sometimes called a treatment couch) under a machine which directs radiation beams towards the body.

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

Often external radiotherapy is given using a machine called a linear accelerator. Several specialised types of external radiotherapy may be used to treat certain cancers. This may include:

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

Many of these techniques allow the radiation beams to be delivered from several different directions. This more accurately targets the cancer and limits higher radiation doses to surrounding normal tissues, which reduces side effects.

Stopping smoking during and after treatment can make the treatment more effective. Call Quitline 13 78 48 for support.

Linear accelerator radiotherapy

How long is a course of treatment?

A course of treatment refers to the number of radiotherapy treatments you receive. A course varies between people, depending on the total dose required to treat the cancer, its location and the reason for treatment.

In general, higher doses are given for curative treatment, and they are usually given over a longer period of time.

The total dose is usually divided into smaller doses called fractions. Most people have radiotherapy from Monday to Friday for 6–8 weeks. Weekend rest breaks allow the normal cells to recover. Some people have only one or a few treatments. Occasionally, two treatments per day may be recommended.

Each dose of radiation causes a little more damage to cancer cells, so it’s important to go to all your scheduled sessions to get the full effect of treatment (i.e. enough radiation to eventually kill the cancer cells or relieve symptoms).

Planning treatment

Before you start treatment, it needs to be planned to ensure that enough radiation reaches the cancer, but does as little damage as possible to the surrounding healthy tissues and organs. The medical team will check if any equipment is required to keep you in a stable, comfortable position every time you receive treatment. Planning consists of several steps, which may occur over a few appointments:


Your radiation oncologist will examine you and may request further x-rays or scans to find out more about the cancer. They will then decide which part of your body to treat, how much radiation to use (the dose) and the number of treatments you will have.

Planning appointment

This may take up to two hours, but the actual treatment sessions will be much shorter (sometimes only a few minutes). You may want to take someone else to this appointment to keep you company, ask questions and take notes.


You will be asked to lie still on a table while the radiation therapist takes measurements of your body. This is done using a CT (computerised tomography) scanner, or less commonly, an x-ray machine called a simulator. The machine takes pictures from different angles to build up a three-dimensional picture of the body. You may also have other types of scans.

The scans help your radiation oncologist see how much cancer is in your body and prescribe the dose. Measurements and scan information are fed into a computer that helps the radiation therapist plan your treatment precisely, according to instructions from the radiation oncologist.

During the simulation, you will lie in exactly the same position as when you have your treatment.

Moulds and casts

You may need a stabilisation device to help keep a part of your body still during treatment sessions. This helps ensure that radiation is directed at the same place each time, and protects normal, healthy organs and tissues. For example, if you need radiotherapy to your head or neck, you will wear a plastic mask called a shell or cast, and markings can be made on the shell rather than your skin (see opposite). You will be able to hear, speak and breathe while wearing the shell, but it may feel strange and claustrophobic at first. Tell the staff if you feel worried or anxious, as they may be able to help you cope.

Skin markings

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

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

Having treatment

You may be asked to change into a hospital gown before you are taken into the treatment room. The treatment itself takes only a few minutes, but each session may last 10–20 minutes because of the time it takes to set up the equipment and put you into position.

The room will be in semi-darkness while this is done, so the radiation therapists can easily see the lasers and align them to the tattoos/marks. If a stabilisation device was made for you (such as a mask), it will be used during treatment.

You will be given instructions about what to wear or what to avoid using during radiotherapy. Your medical team may also give you specific direction (e.g. to have a full or empty bladder) for your planning and treatment appointments.

The shielding inside the radiotherapy machine, called a multileaf collimator, allows the machine to change the shape of the radiation beams. This protects healthy tissue by limiting treatment exposure to these parts of the body. An extra piece of rubber-like material or a wax block may also be placed on the skin. This makes sure that the skin gets the correct dose of radiation.

Before treatment begins, the therapists may need to take x-rays to ensure you are in the correct position. They may move the treatment couch you are lying on or physically move your body.

Once you are in the correct position, the radiation therapist will go into a nearby room to operate the machine. You will be alone in the treatment room, but you can talk to the radiation therapist over an intercom, and they will watch you on a television screen. If you can’t speak – for example, because you’re wearing a mask – you can raise your arm to signal to the staff. You can often listen to music while you are having radiotherapy to help you relax.

You can breathe normally during treatment, but you need to stay very still while the machine is working. This ensures that the treatment is accurate.

If treatment is needed from different angles, the radiation therapist will move the machine several times. This is often done from outside the treatment room.

It is important that you remain still while the machine is being rotated around the treatment table. The radiation therapist will tell you when it is okay to move. If you feel uncomfortable, tell the therapist – they can switch off the machine and start treatment again when you’re ready.

You may hear the term EPID. This means electronic portal imaging device. The EPID receives pictures of the radiation beam as it passes through your body. It helps to ensure your treatment is being given accurately – it is not used to see if the tumour is changing. Sometimes after the image is taken, you will feel the treatment table move a little to ensure your alignment is correct.

Fear of radiotherapy

The machines used for radiotherapy are large and kept in an isolated room. This may be confronting or frightening, especially when you have treatment for the first time. Some people feel more at ease as they get to know the staff and procedures at the treatment centre. If you are afraid of confined spaces (claustrophobic), let the technician or nurses know so they can help you.

It might help to have reading material or activities to pass the time and keep your mind occupied while you are waiting for treatment.

Will radiotherapy be painful?

Radiotherapy is painless. During treatment you will usually not see or feel anything, but you may hear the machine buzzing.

You may find that while lying on the treatment table you have pain due to the cancer. Or, you may feel uncomfortable because of the position you are in. Some people who have treatment to the head report seeing flashing lights or smelling unusual scents. This is common, but it’s generally not harmful.

If you feel ill or uncomfortable at any time, tell the radiation therapist. Treatment can be paused if necessary.

Will I be radioactive?

No. External radiotherapy does not make you radioactive because the radiation doesn’t stay in your body during or after treatment.

It is safe for you to be with children, family and friends, and women who are pregnant or might be pregnant.

This information was last reviewed in February 2014
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