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External beam radiation therapy

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.

You will lie on a treatment table or “couch” under the machine. 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.


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.

EBRT needs to be carefully planned to ensure that enough radiation reaches the cancer, while as little as possible reaches healthy tissues and organs. The planning steps below may occur over a few appointments.

Consultation session

  • May take up to two hours.
  • Your radiation oncologist will assess whether radiation therapy is the right treatment for you by talking to you, doing a physical examination, and looking at all your tests and scans.
  • The radiation oncologist will explain the benefits and side effects of radiation therapy and what to expect during planning and treatment.
  • You will also meet the radiation oncology nurse and a radiation therapist. They can provide support and information.
  • The radiation oncologist may arrange further x-rays, scans or other tests to find out more about the cancer.
  • You may want to take someone with you to keep you company, ask questions and make notes.

CT planning session

  • You will need a planning CT scan even if you had a CT scan to diagnose the cancer. This step, known as CT planning or simulation, is usually a few days after the consultation session.
  • You will have this scan in the same position you will be placed in for treatment.
  • The images will build up a three-dimensional picture of your body. This will show the exact location that needs to receive the radiation.
  • The radiation therapists will send the images to a computer. This allows the radiation oncologist to outline exactly the area they need to treat. The oncologist will prescribe the appropriate dose of radiation, which will help the medical physicist and therapists plan the treatment.
  • You may have a special CT scan to track your breathing or short breath holds. This may improve treatment accuracy and reduce side effects.

Helping you to keep still

  • You will usually need some type of device to ensure you are in the exact same position for each session and to help keep you still during treatment.
  • This is known as an immobilisation device. It will be made during the CT planning session. Depending on the area being treated, the device could be a breast board, a knee or foot cushion, or a bag that moulds to the shape of your body.
  • For radiation therapy to the head or neck, you may need to wear a plastic immobilisation mask. This will be custom-made to fit you. A mask can feel strange and confining, but you will still be able to hear, speak and breathe.
  • Depending on the area being treated, a device known as a spacer may be inserted to move normal tissue away from the area receiving radiation. Examples of spacers include gels and balloons.

Skin markings

  • To make sure you are in the same position each session, a few very small permanent ink spots (tattoos) may be marked on your skin. These tattoos are the size of a small 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 during the course of treatment, but it will gradually fade.
  • If you have to wear a mask or cast, the markings may be made on this rather than on your skin.
  • For image-guided radiation therapy, you may have a small surgical procedure to insert markers (usually gold grains) into or near the cancer. These internal markers can then be seen on scans during the treatment.

You will usually have your first treatment session a few days or weeks after the planning session. There will be at least two radiation therapists at each treatment session. They may ask you to change into a hospital gown and remove any jewellery from the treatment area before taking you into the treatment room. You will be able to leave your belongings in a secure locker. The treatment room will be in semi-darkness so the therapists can see the light beams from the treatment machine and line them up with the tattoos or marks on your body or mask.

If you are having image-guided radiation therapy, the radiation therapists will take x-rays or a CT scan to make sure you are in the same position you were in during the planning session. They may move the table or physically move your body. They will check the scans straightaway and make any adjustments needed.

Receiving the treatment

Once you are in the correct position on the treatment table, the radiation therapists will leave and you will be alone in the treatment room. You’ll be able to talk to the therapists over an intercom and they will watch you on a television screen. The therapists will operate the machine from a nearby room. The machine will not touch you. You won’t 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 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. You will usually be able to breathe normally during the treatment. For treatment to some areas, such as the chest, you may be asked to take a deep breath and hold it while the radiation is delivered.

The treatment itself takes only a few minutes, but each session may last around 15–25 minutes because of the time it takes the radiation therapists to set up the equipment and put you into the correct position. The first session may take longer while checks are performed. You will be able to go home once the session is over.

You will see the radiation oncologist, a registrar (a hospital doctor in training to be a radiation oncologist) or a radiation oncology nurse regularly to check your progress and discuss any side effects.

Managing anxiety

The treatment machines are large and kept in an isolated room. This may be confronting, especially at your first treatment session. You may feel more at ease as you get to know the staff, procedures and other patients. Tell the radiation therapists if you feel anxious or claustrophobic before or during treatment. They can suggest breathing or relaxation exercises, or arrange for you to have a mild sedative.

Discomfort during treatment

EBRT itself is painless – you won’t feel it happening. You may feel some discomfort when you’re lying on the treatment table, either because of the position you’re in or because of pain from the cancer. In this case, talk to the radiation oncology nurse about whether to take pain medicine before each session.

Some people who have treatment to the head say they see flashing lights or smell unusual odours. These effects are not harmful, but tell the radiation therapists if you have them.

Safety precautions

EBRT does not make you radioactive because the radiation does not stay in your body after each treatment session. You will not need to take any special precautions with bodily fluids (as you would with chemotherapy). It is safe for you to be with family, friends, children and pregnant women, and for them to come to the radiation therapy centre with you. However, they cannot be in the room during the treatment.

During planning and treatment, you may need to have some of the following tests to show the exact position and shape of the cancer. Your  treatment team will explain what to expect from each test, or you can call Cancer Council 13 11 20 for more information.

X-ray – Intense but low-energy radiation passes through the body and creates an image on x-ray film, with black areas representing soft tissues and lighter areas showing denser tissues, such as bones.

CT scan – A CT (computerised tomography) scan uses x-ray beams to create detailed pictures of the inside of the body. Before the scan, you may have an injection of dye into one of your veins to make the pictures clearer. You will lie on a table that moves slowly through the CT scanner.

MRI scan – An MRI (magnetic resonance imaging) scan uses a powerful magnet and radio waves to create detailed cross-sectional pictures of the inside of the body. A dye may be injected into a vein before the scan to make the pictures clearer. You will lie on a table that slides into a large metal tube. The machine can be quite noisy.

PET scan – Before a PET (positron emission tomography) scan, you will be injected with a solution containing a small amount of radioactive material. Cancer cells absorb more of the solution and show up brighter on the scan.

PET–CT scan – This combines a PET scan and a CT scan in one machine. The machine looks similar to a CT scanner.

Ultrasound – An ultrasound uses soundwaves to create pictures of your internal organs. A small device called a transducer is passed over an area of the body. The transducer sends out soundwaves that echo when they meet something dense, like an organ or tumour.

Before having scans, tell the doctor if you have any allergies or have had a reaction to dyes during previous scans. You should also let them know if you have diabetes or kidney disease or are pregnant. 

EBRT can be given using different techniques and different types of radiation. Your treatment centre may not offer all methods, but your radiation oncologist will recommend the most appropriate combination for you.

Three-dimensional conformal radiation therapy (3DCRT) 

  • Common type of EBRT.
  • The radiation therapy team use CT scans to map out the precise location of the cancer and the normal organs that need to be protected.
  • The radiation beam is then shaped (conformed) so that the cancer receives most of the radiation, and surrounding tissues receive much less.
  • Used to treat many different types of cancer.

Intensity-modulated radiation therapy (IMRT)

  • Highly accurate type of conformal radiation therapy.
  • Shapes and divides multiple beams of radiation into tiny beams (beamlets) that vary in dose.
  • Used for most cancer types, especially for curative treatment.
  • Volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) are specialised forms of IMRT that deliver radiation continuously as the treatment machine rotates around the body.

Image-guided radiation therapy (IGRT)

  • Uses a treatment machine that takes x-rays or CT scans at the start of each session to check that you are in the correct position for treatment.
  • Markers (usually grains of gold) may have been inserted into or near the cancer so they can be seen in the x-rays or scans and used to guide positioning.
  • Positioning can be very finely adjusted to deliver treatments with millimetres accuracy.
  • Commonly used with many types of radiation therapy to any area of the body.
  • May also be recommended for areas likely to be affected by movement, such as the lungs from breathing.

Stereotactic radiosurgery (SRS) and stereotactic radiation therapy (SRT)

  • Specialised type of radiation therapy.
  • Combines many small radiation fields to give precisely targeted radiation.
  • SRS is delivered as one high dose and SRT is delivered as a small number of high doses.
  • Used to treat small cancers in the brain while minimising the radiation reaching healthy brain tissue.
  • A custom-made mask is worn to keep the head still.
  • Despite the name, SRS is not surgery and does not involve any surgical cuts.

Stereotactic body radiation therapy (SBRT)

  • Similar to SRS, this method delivers tightly focused beams of high-dose radiation precisely onto the tumour from many different angles.
  • May be used to treat small cancers in the body, including small lung or liver cancers or small metastases (cancer that has spread away from the primary cancer).
  • Sometimes called stereotactic ablative body radiation therapy (SABR).

Proton therapy

  • Uses radiation from protons rather than x-rays.
  • Protons are tiny parts of atoms with a positive charge that release most of their radiation within the cancer.
  • Proton therapy is useful when the cancer is near sensitive areas, such as the brainstem or spinal cord, especially in children.
  • Special machines called cyclotrons and synchrotrons are used to generate and deliver the protons.
  • Proton therapy is not yet available in Australia (as at November 2019), but there is funding in special cases to allow Australians to travel overseas for treatment.

Featured resource

Understanding Radiation Therapy

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