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External beam radiation therapy

External beam radiation therapy (EBRT) is the most common type of radiation therapy. It directs high-energy radiation beams at the cancer.

How EBRT works

EBRT is delivered using a radiation machine. The most common type is a linear accelerator. 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 to the area with cancer from different directions. This allows the radiation to be more precisely targeted at the cancer and limits the radiation given to surrounding normal tissues.

Linear accelerator

Below is a general illustration of a linear accelerator (LINAC). It’s large and often kept in a separate room. A CT scan machine is usually attached to the linear accelerator. 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.

Click on image to enlarge

After the planning session, your radiation oncologist will work out the total dose of radiation needed to treat the cancer and the total number of treatments.

Fractions – In most cases, the total dose will be divided into a number of smaller doses called fractions, which are given on different days. The length of each session will depend on the type of EBRT.

Course – A course of treatment refers to the total number of sessions of radiation therapy. How often and how long you need to have  radiation therapy depends 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 once a day, Monday to Friday, for 3–8 weeks. Dividing the total dose into separate treatment sessions with weekend rest breaks allows the healthy cells time to recover. Occasionally, the radiation oncologist may recommend two treatments a day, with usually six hours between the sessions.

A course of radiation therapy used to relieve symptoms (palliative treatment) is usually shorter. You may have 1–15 sessions. Palliative radiation therapy may not be given every day.

Each fraction of radiation causes a little more damage to cancer cells, so it’s important to go to all of your scheduled sessions if your treatment is curative. When you miss sessions, cancer cells have more time to repair the damage, so your radiation therapy may not work as well. If a treatment break is necessary, 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 radiation as possible reaches healthy tissues and organs. The planning steps below may take place over a few appointments.

Consultation session

  • This may take up to two hours.
  • To assess whether radiation therapy is the right treatment for you, the radiation oncologist will talk to you, do a physical examination, and look at all your test results and scans.
  • The radiation oncologist will explain how radiation therapy will help you, what will happen during planning and treatment, and what side effects to expect.
  • You will also meet the radiation oncology nurse and a radiation therapist. They can provide support and further information. They will usually explain what side effects to expect and how to manage them.
  • The radiation oncologist may arrange further x-rays, scans or other tests to find out more about the cancer.
  • Consider taking someone with you to keep you company, ask questions and make notes.

CT planning session

  • You’ll have a planning CT scan even if you had a CT scan to diagnose the cancer. It shows where you need to receive radiation. The CT planning or simulation scan is usually done soon after the consultation session.
  • You will have the CT planning scan in the same position you will be placed in for treatment.
  • You might have an injection of dye to help show up certain parts of your body.
  • You may need to hold your breath during the scan. You may also have a special CT scan, called a 4DCT, to track your breathing or be taught how to take deep breath holds. This may improve treatment accuracy and helps protect the heart.
  • The images are sent to a computer. This allows the radiation oncologist to work out where to direct the radiation. The oncologist will prescribe the dose of radiation to help the radiation therapists and medical physicist plan treatment.

Helping you to keep still

  • You will usually need some type of device to help you stay in exactly the same position for each session and to 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 area, you may need to wear a plastic immobilisation mask. This will be 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 marks off or if need to keep them until the end of the treatment. The ink may 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 device rather than on your skin.
  • To help with image guidance, you may have a small surgical procedure to insert markers (usually made of gold) into or near the cancer. These internal markers can then be seen on scans during the treatment.

You will usually start radiation therapy a few days or weeks after the planning session. There will be at least two radiation therapists at each treatment session. You may be asked to change into a hospital gown and remove any jewellery before you are taken into the treatment room. 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.

Positioning you for treatment – 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 as you were during the planning session. This may mean moving the table or your body. They will check the scans straightaway and make any adjustments needed.

Receiving the treatment – Once you are in the correct position, the radiation therapists will leave the treatment room. They can see you on a television screen and you can talk to them over an intercom. The radiation therapists will control the machine from a nearby room. The machine may move around you into different positions but it will not touch you. You won’t see or feel the radiation but you may hear a buzzing noise from the machine while it is working and when it moves. The radiation therapist may turn off the machine and come into the room to change your position or adjust the machine.

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. 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 of EBRT may last around 10–40 minutes because of the time it takes the radiation therapists to set up the equipment, place you into the correct position and then do the CT scan. The first session may take longer while checks are performed. You will be able to go home once the session is over.

Managing discomfort during treatment – EBRT itself is painless and you won’t feel it happening. If you feel some discomfort when you’re lying on the treatment table, tell the therapists – they can switch off the machine and start it again when you’re ready. If you’re in pain because of the position you’re in or because of pain from the cancer, talk to the radiation oncology nurse. They may suggest you 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.

Taking 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 other people including 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.

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

Managing anxiety before and during EBRT

The radiation therapy machines are large and kept in an isolated room. This may be confronting, especially at your first treatment session. You may feel more comfortable as you get to know the staff, procedures and other patients.

If you are having radiation therapy for a head and neck or brain cancer, you may have to wear a mask during each session. Wearing the mask may make you feel anxious or claustrophobic. Tell the radiation therapists if you feel anxious or claustrophobic before or during treatment.

With the support of the radiation therapy team, many people find that they get used to wearing the mask. The team may suggest you try breathing or relaxation exercises, or listening to music to help you relax. A mild sedative may also help.

Listen to our ‘Finding Calm During Cancer’ podcast

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 darker 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.

If you are having radiation therapy for prostate, uterine or cervical cancer, the volume of your bladder will be checked during the scan. This is because the size and shape of the bladder affects the position of the prostate, uterus and cervix. You’ll be asked to drink a set amount of water before treatment to make sure the bladder is full and the prostate, uterus or cervix is in the same position each time.

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 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 or breastfeeding.

EBRT can be given using different techniques and types of radiation. The radiation oncologist will recommend the most suitable method for you. If you need a type of radiation therapy that is not available at your local hospital, they may arrange for you to have it at another centre.

Three-dimensional conformal radiation therapy (3DCRT)

  • What it is – most common type of EBRT
  • When used – used to treat many different types of cancer
  • How it works – the radiation beam is shaped (conformed) to fit the treatment area; this means that the tumour receives most of the radiation, and healthy tissues receive much less
  • Machine type – LINAC
  • How often – usually once a day, Monday to Friday

Intensity-modulated radiation therapy (IMRT)

  • What it is – highly accurate type of conformal radiation therapy
  • When used – used for most types of cancer, especially for curative treatment
  • How it works – shapes and divides multiple beams of radiation into tiny beams (beamlets) to closely fit the tumour while healthy tissue nearby  receives lower doses of radiation therapy
  • Machine type – LINAC
  • How often – once a day, Monday to Friday

Volumetric modulated arc radiation therapy (VMAT) or Rapid Arc

  • What it is – type of IMRT
  • When used – used for most types of cancer, especially if near sensitive body organs
  • How it works – machine moves around you and reshapes and changes the intensity of the radiation beam to the tumour
  • Machine type – LINAC
  • How often – once a day, Monday to Friday

Image-guided radiation therapy (IGRT)

  • What it is – uses x-rays or CT scans at the start of each session to check that you are in the correct position for treatment
  • When used – may be recommended for cancer in areas that are likely to move a lot, such as the lungs from breathing
  • How it works – repeated imaging allows for your position or radiation dose to be adjusted during treatment; this helps protect normal tissue
  • Machine type – LINAC or MR-LINAC (combines MRI with LINAC)
  • How often – once a day, Monday to Friday

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

  • What it is – specialised type of radiation therapy; SRS is not surgery and does not involve any surgical cuts
  • When used – used for brain tumours
  • How it works – many small beams of radiation are aimed at the tumour from different directions to target the exact shape of the tumour
  • Machine type – LINAC but may use a CyberKnife or Gamma Knife machine
  • How often – can vary, usually given in one dose

Stereotactic body radiation therapy (SBRT) or stereotactic ablative body radiation therapy (SABR)

  • What it is – delivers tightly focused beams of high-dose radiation precisely onto the tumour from many different angles
  • When used – 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)
  • How it works – combines many small beams of radiation from different angles to target the exact shape of the tumour
  • Machine type – LINAC or Gamma Knife machine
  • How often – up to five doses, given once a day

Total body irradiation (TBI)

This is a form of radiation therapy that’s given to the whole body for blood cancers. Sometimes TBI is given with chemotherapy to prepare people  for a stem cell or bone marrow transplant.

You will be admitted to hospital before you have TBI. A course of TBI is usually given in very low doses, twice a day over 2–4 days, with the treatments being at least six hours apart. Side effects may include nausea, diarrhoea, fatigue and skin redness.

Proton therapy

This type of EBRT, 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. This is different to standard radiation therapy beams, which pass through the area and some nearby healthy tissue.

Special machines called cyclotrons and synchrotrons are used to generate and deliver the protons. Proton therapy is useful when the cancer is near sensitive areas, such as the brain stem or spinal cord, especially in children. Using proton therapy may help to reduce side effects.

Proton therapy is not yet available in Australia (as at December 2021), but there is funding in special cases to allow Australians to travel overseas for treatment.

Featured resource

Understanding Radiation Therapy

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This information is reviewed by

This information was last reviewed December 2021 by the following expert content reviewers: Prof June Corry, Radiation Oncologist, GenesisCare, St Vincent’s Hospital, VIC; Prof Bryan Burmeister, Senior Radiation Oncologist, GenesisCare Fraser Coast, Hervey Bay Hospital, and The University of Queensland, QLD; Sandra Donaldson, 13 11 20 Consultant, Cancer Council WA; Jane Freeman, Accredited Practising Dietitian (Cancer specialist), Canutrition, NSW; Sinead Hanley, Consumer; David Jolly, Senior Medical Physicist, Icon Cancer Centre Richmond, VIC; Christine Kitto, Consumer; A/Prof Grace Kong, Nuclear Medicine Physician, Peter MacCallum Cancer Centre, VIC; A/Prof Sasha Senthi, Radiation Oncologist, The Alfred Hospital and Monash University, VIC; John Spurr, Consumer; Chris Twyford, Clinical Nurse Consultant, Radiation Oncology, Cancer Rapid Assessment Unit and Outpatients, Canberra Hospital, ACT; Gabrielle Vigar, Nurse Unit Manager, Radiation Oncology/Cancer Outpatients, Cancer Program, Royal Adelaide Hospital, SA.