Intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT)

Intensity modulated radiotherapy

Intensity-modulated radiation therapy (IMRT) is a type of conformal radiotherapy that uses a linear accelerator to deliver an advanced type of high-precision radiotherapy that shapes the radiation beam to closely fit the area of the tumour.

The linear accelerator has a device called a multileaf collimator which is made up of thin leaves which move independently and form shapes that fit precisely around the treatment area. This means that the tumour receives a high dose and normal healthy cells nearby receive a much lower dose.

IMRT allows the dose to be shaped to the tumour by modulating (controlling) the intensity of the radiation beam. This allows different doses of radiation to be given across the tumour.

IMRT can also create a U shaped (concave) treatment area. This avoids high radiation doses to structures that would otherwise be damaged by the radiotherapy and reduce the risk of long term side effects.

It is a routine treatment at The Christie for many cancer types.

Volumetric Modulated Arc Therapy

Volumetric Modulated Arc Therapy (VMAT) is a new type of IMRT. The linear accelerator 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.

It is a routine treatment at The Christie for many cancer types.

Last updated: March 2023