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Producing your radiotherapy plan

Nurse and patients talking about cancer

This page tells you about how your radiotherapy team produces your treatment plan. There is information about

 

Scans for treatment planning

Your treatment team uses a specialised CT scanner to plan your radiotherapy treatment. You lie on the scanner couch in the same position that you will have the treatment. You can see a picture of the planning CT scanner on our page about planning treatment.

While you are lying on the scanning couch, the radiographer takes some measurements of your body. They may also measure the distance from the treatment couch to the skin markings on your body. This is because the distance between the radiotherapy machine and the cancer is very important in working out the radiotherapy dose.

Putting all this information together allows the planning computers to work out the best positioning of the radiotherapy beams. The scanning computers use very powerful and complex software to plan how to give a high dose of radiation to treat the cancer. They also plan how to avoid healthy body organs in the area.

 

Reading CT or MRI scans

This picture shows a typical CT scan cross section (slice). The slice shown is of the bottom of the rib cage. Note that the left on this scan is actually the right side of the body.

Reading a CT scan

This is what you can see

  • On the left is a large crescent – this is the liver
  • On the right, at the bottom, is a round shape – this is the kidney
  • In the centre, at the bottom, is a lighter round shape – this is the spinal cord inside the backbone
  • In the middle is an irregular shape, which is the pancreas with a cancer inside it
 

Looking at the tumour in 3D

A radiotherapy planning computer can create a 3D picture of the cancer from CT scans and sometimes other types of scan. This picture shows a 3D computer image.

Tumour in 3D

This is what you can see

  • The cancer is shown in red
  • The liver is shown in brown
  • The spleen is shown in blue/green
  • The left kidney is shown in pink
  • The spine is shown in yellow

Looking at a 3D picture can be very useful, as it can be rotated and looked at from different angles. This is very helpful when planning treatment. It helps the radiotherapy doctor (clinical oncologist) to work out the best way to arrange the radiotherapy beams to cover the whole cancer and miss the major organs.

 

Building the radiotherapy plan

To treat cancers deep within the body, 2 to 4, or sometimes more, beams are pointed at the cancer from different angles. The area where all the beams meet is where the tumour is. This is where the highest dose of radiotherapy is given. This picture shows how 3 beams can be directed at the tumour. The white lines show the middle of the beams. The beams are actually like torch beams so they get wider as they travel away from the radiotherapy machine. By the time they reach the cancer each beam may be up to 8 to 10 cm in width. 

This picture is of the bottom of the rib cage.

The 2D plan

  • On the left is a large crescent – this is the liver
  • On the right, at the bottom, is a round shape – this is the kidney
  • In the centre, at the bottom, is a smaller round shape – this is the spinal cord inside the backbone
  • In the middle is an irregular shape – this is the pancreas with a cancer inside it

One beam is aimed from in front of the patient. This is the beam at the top of the picture. The other two beams are aimed from the sides at an angle so that they avoid the spinal cord and kidney.

 

Marking your skin

Once the treatment area is lined up, marks are made on the skin. These skin marks are used by the radiographers to set up the radiotherapy machine in the same way every day.

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Updated: 23 April 2014