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Preparing your radiotherapy plan

Nurse and patients talking about cancer

This page tells you about planning for external radiotherapy. There is information about


What radiotherapy planning is

Before you begin your treatment, the radiotherapy team carefully plan your external beam radiotherapy. This means working 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. 

The area of your body exposed to radiation is called the radiotherapy field. For standard conformal radiotherapy there may be between 1 and 4, or sometimes more, beams aimed at the cancer from different angles. The point where the beams overlap is the area that receives the highest dose of radiotherapy. Doctors call this the target volume. 

The radiotherapy planning makes sure that the cancer gets the prescribed dose of radiation while normal body tissues get as little as possible. 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. Modern radiotherapy techniques, such as conformal radiotherapy or intensity modulated radiotherapy, closely match the radiation to the shape of the tumour. 

Some radiotherapy techniques such as stereotactic radiotherapy use many radiotherapy beams from different angles to target the treatment area very precisely. This gives a very high dose to the tumour and a very low dose to surrounding healthy tissues. Some newer radiotherapy techniques adjust for slight movement of the tumour during the treatment, for example, due to breathing.

The steps involved in radiotherapy planning vary with the type of cancer and its position in the body.


Your planning appointment

You may have a planning CT scan, MRI scan, PET scan or X-rays before or during your proper radiotherapy planning appointment. This is so that your radiotherapy doctor (clinical oncologist) has as much information as possible about your treatment needs. It allows them to plan the right dose for the cancer and to make sure that healthy cells around the tumour receive as low a dose as possible. 

Your planning appointment may take up to a couple of hours but the treatment appointments will be much shorter.

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

Sometimes you'll need more than one planning session. It depends on the size and position of the tumour. It's important to feel you are involved in your treatment. Ask as many questions as you like. Often patients feel that staff are too busy to answer their questions. It's true that they are busy but they are always happy to help. The more you understand your treatment, the easier it is for you to cope.


How you have planning

Your radiotherapy team will plan your treatment using your scans and X-rays. You may have planning using a specialised CT scanning machine. The machine shines lights at your body in straight lines so that the radiographer can find the correct position for the radiotherapy machine.

Planning takes from 15 minutes up to a couple of hours. You lie on a fairly hard couch, which some people find uncomfortable. You have to lie very still so that the measurements are accurate and your exact position can be recorded. 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 radiographer will measure 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

  • To plan radiotherapy to the area between your hip bones (your pelvis), you may have a liquid put into your back passage or bladder which shows up on X-ray
  • A woman may need to have an internal examination and a tampon put in to her vagina to show its exact position
  • You may have an injection of dye to show up your kidneys
  • You may have wires put on scars or around lumps
  • If you are having treatment to your chest area, you may have barium liquid to drink to show up your food pipe (oesophagus) and stomach

Sometimes you need to have radiotherapy treatment from different directions – for example, from the front and side – and each position needs to be planned.

Ink marks

Once the treatment team has planned your radiotherapy, they may put pin point sized ink marks on your skin to make sure they treat exactly the same area every day. We have information about radiotherapy skin markings.

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. We have information about making radiotherapy moulds.

The video below shows you what happens at radiotherapy planning:

View a transcript of the video showing what happens at radiotherapy planning (opens in new window).


After your planning session

You may have to wait a few days before you start treatment while the physicists and your radiotherapy doctor decide the final details of your plan. Your doctor will plan the areas that need treatment and outline areas to limit the dose to or avoid completely. They call this contouring. Then the physicists and staff called dosimetrists plan the treatment very precisely using computers.

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Updated: 4 January 2013