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Planning your external radiotherapy

Your radiotherapy team carefully work out how much radiation you need to treat the cancer and exactly where you need it. 

As cancer cells may sometimes spread into the tissues close to the tumour, your radiotherapy specialist will decide on the exact area to be treated around the cancer. They will also make allowances for possible movement of the tumour during treatment due to breathing or normal movement of body organs. 

About external radiotherapy planning

The radiotherapy planning makes sure that the cancer gets the prescribed dose of radiation while normal body tissues get as little as possible.

The area of your body exposed to radiation is called the radiotherapy field.

Some normal tissue immediately around the tumour will be exposed to the same dose but your doctors aim to keep this as low as possible to reduce the risk of side effects.

To plan the treatment your doctor will take into account:

  • your type of cancer
  • the position of the cancer in the body
  • the size of the cancer
  • whether it is close to structures that are sensitive to radiation
  • how far the radiation needs to travel into the body
  • your general health and medical history

More than one planning session may be needed. It depends on the size and position of the tumour.

Before your planning, your nurse or radiographer will ask you to sign a consent form.

If you have any questions about the treatment, make sure that you ask them before you sign your form. You can take a copy of the form home with you if you want to.

It's important to feel that you are involved in your treatment, so ask as many questions as you like. The more you understand your treatment, the easier it is to cope.

Your planning appointment

Your planning appointment may take from 15 minutes up to a couple of hours.

You will have a planning CT scan. The scan shows the cancer and the structures around it.

Photo of a CT scanner

You lie on the scanner couch with the treatment area exposed. The radiographers cover you up as much as possible.

They put some markers on your skin. The markers show up on the scan as bright white dots. Your radiographers use them to position you for your radiotherapy. 

You have to lie very still so that the measurements are accurate and the radiographers can record your exact position. This record means the radiographer can make sure you are lying in the correct position every time you have treatment.

They may need to use some equipment to support you in the right position, such as a chest board, neck rest or arm pole.

The scan

Once you are in position the radiographers move the couch up and through the scanner. The scanner is a doughnut shape.

The radiographers leave the room and the scan starts. It takes about 5 minutes. You won't feel anything. The radiographers watch from the next door room and you can talk to them on an intercom if you need to.

Before the planning appointment

You may also have an MRI scan, PET scan or x-rays. This is so that your radiotherapy doctor (clinical oncologist) has as much information as possible about your treatment needs. 

They can feed the other scans into the planning scanner as part of the planning process.

How you have radiotherapy planning

The radiographer measures your body size and shape in the treatment area. Sometimes they need to do extra things to get a clear picture of your body structures. For example:

  • you may have an injection of dye to show up your kidneys
  • you may have wires put on scars or around lumps
  • before the scan you may need to drink a jug of liquid containing a dye that shows up your bladder
  • if you are having treatment to your chest area, you may have a barium liquid drink to show up your food pipe (oesophagus) and stomach

Ink marks

While planning your radiotherapy, the radiographers may make pin point sized tattoo marks on your skin.

These marks make sure they treat exactly the same area every day. They may also highlight the tattoo with pen marks that make it look like a cross.

Moulds or masks

If you are having treatment to your head or neck, you may need to have a mould (shell) made to keep you perfectly still while you have treatment.

You may also have a mould if you have to keep an arm or leg perfectly still. The moulds are made in the mould room or in the CT scanning room.

The video below shows you what happens at radiotherapy planning:

After your planning session

You might have to wait a few days or up to 2 weeks before you start treatment. During this time the physicists and your radiotherapy doctor decide the final details of your plan.

Then the physicists and staff called dosimetrists plan the treatment very precisely using advanced computers.

Last reviewed: 
15 Feb 2016
  • De Vita, Hellman, and Rosenberg's Cancer: Principles and Practice of Oncology (9th edition)
    De Vita, V.T., Lawrence, T.S. and Rosenberg S.A.
    Lippincott, Williams and Wilkins, 2011

  • External Beam Therapy
    Peter Hoskin
    OUP Oxford, 30 Aug 2012

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