Conformal radiotherapy, 3D conformal radiotherapy (3DCRT)
Conformal radiotherapy is also called 3D conformal radiotherapy. It uses a special way of planning and giving radiotherapy. Planning radiotherapy in the standard way was done using X-rays. X-rays give images of tumours in two dimensions (2D), width and height. This type of radiotherapy is not commonly used any more.
With computer technology we can see the tumour in three dimensions (3D), width, height and depth, using CT scans or MRI scans.
The information from these scans feeds directly into the radiotherapy planning computer. So doctors can see the treatment area in 3 dimensions. The computer programme then designs radiation beams that follow the shape of the tumour more closely. So the radiation beam avoids healthy tissue as far as possible. This is called 3D conformal radiotherapy (3DCRT).
Of course, doctors have always tried to avoid affecting as much healthy tissue as possible with radiotherapy. But the main benefit with conformal radiotherapy is that it is more precise, because it allows doctors to plan in 3D. Conformal radiotherapy can give a better chance of killing the cancer by delivering a higher dose of radiation straight to it. Less healthy tissue is included in the radiotherapy field and so you are likely to have fewer long term side effects.
If doctors took too much of the surrounding area out of the radiotherapy treatment field, there could be a risk of cancer cells being missed. But radiotherapy doctors (clinical oncologists) are extremely careful to strike the right balance between keeping all the cancer inside the radiotherapy field, while as much healthy tissue as possible is kept out.
Planning conformal radiotherapy treatment is very similar to planning other types of external radiotherapy. But planning may take longer. It involves several steps, which usually begin with a virtual simulation session. This session involves
- Planning the radiotherapy to make sure that all the tumour is inside the radiotherapy field
- Making marks on the skin to make sure the same area is treated each session (see skin markings)
- Making moulds to keep certain parts of your body still during treatment
Doctors use an X-ray machine called a simulator to plan radiotherapy treatment. It is called a simulator because it is built to be like (or simulate) a radiotherapy machine, but without giving treatment. The specialist uses the pictures it produces, along with any scans, to plan the treatment area very precisely. Your specialist may use CT scans to do all the planning of your conformal radiotherapy. Or they may also use information from MRI scans or PET scans to refine the treatment plan even further.
If you are having conformal radiotherapy to your head or neck, you may need to wear a perspex mould during your treatment. You may hear this called a shell or mask. Some types of mask are see through, others aren't. You can have a mould for other parts of the body, such as the breast, limbs and sometimes the whole body. The mould keeps the area completely still. So your treatment will be as accurate as possible. This also means that you can have any markings you need made on the mask, instead of on your skin.
After this session you usually have to wait between 3 to 7 days for the physicist and your radiotherapy doctor to create your treatment plan. You then get an appointment for your first dose of radiotherapy.
Having conformal radiotherapy is very much like having other types of external radiotherapy. The treatment doesn’t hurt and it only takes a few minutes to have your dose of radiotherapy. But it may take a bit longer for the radiographers to get you into the right position and put on any moulds that you may need. There is a lot more information about having your treatment in the external radiotherapy section.
Conformal radiotherapy is most useful for tumours that are close to important organs and structures in your body. This is because it helps to avoid radiation damage to healthy body tissues and organs. It can be used to treat
One type of conformal radiotherapy is called intensity modulated radiotherapy (IMRT). Like conformal radiotherapy, IMRT shapes the radiation beams to closely fit the area where the cancer is. But it also changes the radiotherapy dose depending on the shape of the tumour. This means that the central part of the cancer receives the highest dose of radiotherapy and a surrounding area of tissue gets lower doses.
IMRT can also create an indented (concave) area within the radiotherapy field to avoid structures that would be damaged by the radiotherapy. This is very helpful in areas such as the head and neck, for example to avoid the spinal cord or salivary glands.
You can have IMRT on a standard radiotherapy machine, called a linear accelerator (LINAC). The LINAC has a device called a multileaf collimator, which moves around the patient and shapes the beams of radiotherapy to fit the tumour.
Clinical trials have tested IMRT in a number of cancer types, including breast cancer and head and neck cancer. It is now a standard form of treatment for some cancer types. But research is always going on, looking into using new treatments for more types of cancer. Or looking into improving the way you have treatment. You can search for IMRT trials that are currently recruiting patients on our clinical trials database. Type 'IMRT' into the search box.
There are different types of IMRT, including Tomotherapy and VMAT.
Tomotherapy combines image guided radiotherapy and IMRT. The machine looks more like a CT scanner. Below is a 360° photograph of a room with a Tomotherapy machine. If you can't see the photograph, you can download the Adobe Flash Player from the Adobe website. Use the arrows to move the picture and look around the room.
VMAT is a new type of IMRT technique. It can be given from a machine called RapidArc. The radiotherapy machine rotates around the patient during treatment. The machine continuously reshapes and changes the intensity of the radiation beam as it moves around the body. Giving the radiotherapy in this way makes it very accurate, shortens the treatment time, and uses a lower overall dose of radiation.
With conformal radiotherapy there is less normal tissue in the field of the radiotherapy. So the risk of side effects is lower. But unfortunately you can still have side effects. As with any external beam radiotherapy, the side effects only affect the part of the body that the radiotherapy treatment is aimed at. There is more information about side effects of radiotherapy in the radiotherapy section.
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