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Conformal radiation therapy

Conformal radiation therapy is a type of external beam radiation therapy. For this procedure, the same type of machine used for regular radiotherapy treatment is combined with a specialized device called a multi-leaf collimator.

  • The multi-leaf collimator is made up of metal bars fixed to the radiotherapy machine.
  • The bars block the radiation beams to change the shape of the area being treated.
  • Each bar can be adjusted so that the radiation beams conform to the shape and size of the tumour.

Conformal radiation may also aim the radiation beams from several directions to better target the tumour and spare more of the nearby structures than conventional radiation therapy.


Conformal radiation therapy allows higher doses of radiation to be given to the tumour. The surrounding normal tissue receives less radiation, which lessens the chances of side effects. Conformal radiation is used to treat many cancers. It is especially useful if the tumour is close to important organs or body structures because high doses of radiation can be given with little risk to healthy tissue.


Computed tomography (CT) scans or magnetic resonance imaging (MRI) are used to create a precise 3-dimensional (3-D) image of the tumour. The exact shape of the tumour is programmed into a computer and used to plan radiation treatment. The computer model of the tumour is used to set the multi-leaf collimators so the radiation beams match the shape of the tumour.


There are 2 main types of conformal radiation therapy:

  • 3-dimensional conformal radiation therapy (3-D CRT)
    • 3-D CRT delivers shaped radiation beams aimed from several different directions at the tumour.
    • The radiation beams are all the same strength.
  • intensity-modulated radiation therapy (IMRT)
    • IMRT is a way of giving conformal radiation therapy in a targeted way.
    • The beam strength varies across the treatment area. The tumour receives radiation from a series of small beams of different strengths.
    • A multi-leaf collimator is used to shape and deliver these small beams. The bars of the multi-leaf collimator are moved while the radiation is given. A crossfire technique (beams come from 2 or more directions at the same time) creates a constant dose and spares the surrounding tissues.
    • IMRT shapes the treatment beams very precisely and allows the dose of radiation to be adjusted for different parts of the treatment area.
    • IMRT uses specialized equipment, so it might not be available at all cancer treatment centres in Canada.

computed tomography (CT) scan

An imaging technique that uses a computer to put a series of x-ray images together to create a 3-dimensional picture of organs, tissues, bones and blood vessels inside the body. A contrast medium may be injected to make organs and structures show up clearly on the x-ray images.

The image produced is called a CT scan.

Also called computerized axial tomography (CAT) scan.

magnetic resonance imaging (MRI)

An imaging technique that uses a magnetic field to produce pictures of areas inside the body. A contrast medium may be injected into the body to make structures and organs show up clearly on the image.

Doctors use MRI to make detailed images of organs and tissues in the body.

Also called nuclear magnetic resonance imaging (NMRI).


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