**4. Volumetric modulated arc therapy (VMAT)**

Intensity-Modulated Arc Therapy (IMAT) has been improved with the addition of variable gantry rotation speeds and dose rates and was introduced as Volumetric-Modulated Arc Therapy (VMAT) in 2007 to describe rotational Intensity Modulated Radiotherapy (IMRT) delivered in a "single arc" [13]. VMAT can provide highly conformal dose distributions and can significantly improve the Intensity Modulated Radiotherapy (IMRT) delivery efficiency. The faster treatments reduce the effects of intra-fractional motion on both tumors and organs, and of course, the shorter

treatment times also increase patient comfort. The high plan quality and fast treatment delivery of Volumetric-Modulated Arc Therapy (VMAT) are attractive, and it has been widely applied to many disease sites.
