15.2: Volumetric Modulated Arc Therapy

Volumetric Modulated Arc Therapy (VMAT) is a newer method of delivering conformal dose that is potentially faster and with less dosage to the patient than conventional step and shoot IMRT.


VMAT allows for dynamic modulation of:

  • The speed of gantry rotation
  • The rate of dose delivery
  • The position and movement speed of MLCs.

It is often capable of delivering a treatment that would require 7-9 IMRT fields in a single or two arcs, shortening treatment time to 2-4 minutes as opposed to 10-15 minutes.


VMAT requires more extensive QA of machines and plans than conventional IMRT. This includes testing field flatness and dose distribution for different dose rates and testing of MLC positioning and movement.