Volumetric modulated arc therapy [VMAT]

VMAT is a novel radiation therapy technique that delivers the radiation dose continuously as the treatment machine rotates

Overview

Volumetric modulated arc therapy (VMAT) is a novel radiation therapy technique that delivers the radiation dose continuously as the treatment machine rotates. This technique accurately shapes the radiation dose to the tumour, while minimising the dose to the organs surrounding the tumour. Both the angle, as well as the dose rate of the radiation treatment, are constantly adjusted to enable the radiation dose to be shaped.

The linear accelerator has a device called a multi-leaf collimator which is made up of thin leaves. These leaves move independently and form shapes that fit precisely around the treatment area. This technique allows the dose to be shaped to the tumour by modulating — or controlling — the intensity of the radiation beam.

VMAT allows more difficult tumours, such as ones wrapped around other important structures, to be targeted precisely.

Radiation therapy delivery

Volumetric modulated arc therapy (VMAT) involves the use of external radiation therapy beams being directed in a series of arcs or angles by a rotating machine to allow for greater access to a cancerous tumour. During each rotation, the cone beam is continuously shaped (or modulated) by the multi-leaf collimator. In addition, the dose rate (how much radiation delivered for each second) and gantry speed (how fast the beam rotates) are also optimised to generate highly conformal dose distributions (highly accurate radiation doses targeted directly to the cancerous tumour) and ensure the radiation is delivered to the intended area only.

This therapy reduces the likelihood of impacting healthy surrounding tissues, and allows more difficult tumours, such as ones wrapped around other important structures, to be targeted precisely.

The added advantage of VMAT treatment is that the treatment time is significantly shorter and thus the patient does not need to spend a long time on the treatment couch.

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