Physical and Dosimetric Characteristic of Volumetric Modulated Arc Therapy VMAT

Abstract

Radiotherapy is one of the primary modalities for the treatment of cancer. The science and technology of radiotherapy had significantly evolved over the last more than a century when it was first tried for the treatment of some superficial conditions in the last decade of 19th century. Starting with the low energy x-rays and gamma rays emitted from radium, the first revolutionary step was the advent of linear accelerators (LINACs) in the 1950s. Soon after the beginning, it became evident that to improve the results of radiotherapy sparing of normal tissues surrounding the tumour from high radiation dose was critical. With the LINACs, it became possible to use megavoltage x-rays as well as electron beams for treating both superficial and deep-seated tumours with considerable improvement in sparing of the normal tissues. 3-dimensional conformal radiotherapy (3-DCRT) in the last two decades of 20th century and intensity modulated radiotherapy (IMRT) since the mid-1990s using LINACs made it possible to conform the radiation dose envelope to the delineated tumour/target volume. newlineVolumetric modulated arc therapy (VMAT) is yet another step in the technological advancement of the conventional fixed-beam IMRT. In the former, the radiation is delivered while the LINAC gantry rotates around the patient. The radiation dose is shaped using three variables: MLC shape, gantry rotation speed, and dose rate. The primary advantage of VMAT over fixed-beam IMRT is that VMAT treatments can be delivered significantly faster. This treatment technique is time efficient and produces absorbed dose distributions of high conformity. An introduction to a novel technique into clinical practice requires a substantial dosimetric verification to assure correct treatment delivery. This includes both quality assurance (QA) on the patient-specific level and general machine performance. Since VMAT delivery system is an exceptionally complex modality for radiotherapy treatments; a versatile QA system is an indispensable requirement for its proper imp