Preparing your radiotherapy plan

Before you begin your treatment, your external beam radiotherapy is carefully planned. This means working out how much radiation you need to treat the cancer and 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 radiotherapy there may be between 1 and 4 beams aimed at the cancer from different angles. The point where the beams overlap is where the highest dose of radiotherapy is given. Doctors call this the target volume. 

The radiotherapy planning makes sure that the cancer gets the prescribed dose of radiation while normal body tissues have as little as possible. Some normal tissue will be exposed to the same dose as the tumour but your doctors will try to keep this as low as possible. Some radiotherapy techniques, such as conformal radiotherapy or intensity modulated radiotherapy, closely match the radiation to the shape of the tumour. For some types of cancer this may reduce the amount of damage to normal tissues. Some radiotherapy techniques such as stereotactic radiotherapy use radiotherapy beams given from many different angles to give a 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.

You may have a planning CT scan before or during your proper radiotherapy planning appointment. This is so that the radiotherapist has as much information as possible about your treatment needs. Your planning appointment may take 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. You may have to wait a few days before you start treatment while the physicist and your radiotherapist decide the final details of your plan. 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 the more you understand your treatment, the easier it is for you to cope.

Your radiotherapy team plan the treatment using a machine called a simulator. Sometimes the simulator shines lights at your body in straight lines so that the radiographer can see where to position the radiotherapy machine.

The simulator moves in exactly the same way as the treatment machines. But it takes X-ray pictures and feeds them into a computer so the radiographer can find the correct position for your treatment. Some simulators use CT scans instead of X-rays to plan your treatment.

Planning takes about 15 to 45 minutes. 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 check you are lying in the correct position every time you have treatment. Your specialist may want to use some equipment to support you in the right position, such as a chest board, neck rest or arm pole.

Sometimes radiotherapy treatment has to be given from different directions - for example, from the front and side - and each position needs to be planned.

The radiographer will measure your body size and shape in the treatment area. Sometimes the radiographer needs to do extra things to get a clear picture of your body structures. For example

• To plan radiotherapy to your pelvis (the area below your tummy button), you may have a liquid which shows up on X-ray put into your rectum (back passage) or bladder
• A woman may need to have an internal examination of her vagina and a tampon put in to show the exact position of the vagina
• You may have an injection of dye to show up the kidneys
• You may have wires put on scars or around lumps
• You may have a barium swallow to show up your food pipe (oesophagus) and stomach if you have a cancer in the chest area

Once your radiotherapy has been planned, marks are made on the skin to make sure the same area is treated every day. Sometimes, a mould (shell) needs to be made to keep an area perfectly still while you have treatment. This may be needed if you have treatment to your head or neck. Or to keep an arm or leg perfectly still.