A study on patient specific quality assurance in volumetric modulated arc therapy

Abstract

In Radiation therapy, quality assurance programs must be structured to meet the clinical requirements to achieve optimum treatment outcome in terms of maximizing tumour control probability and minimizing normal tissue complications. This thesis work is an overview of patient specific quality assurance in volumetric modulated arc therapy. Characterization of responses of 2D array Seven29 detector and its combined use with Octavius phantom for the patient specific quality assurance in RapidArc treatment delivery was studied. The study shows that 2D array seven29 is a reliable and accurate dosimeter and a useful tool for quality assurance. Pinpoint chamber underestimates the calculated isocentre dose by maximum 4.8%. Absolute dose measurements using semiflex ionization chamber with intermediate volume (0.125cm3) show good agreement with the TPS calculated dose among the detectors used in this study. Also it is suggested to average the dose over the sensitive volume for larger volume chambers. Two different volumetric modulated arc therapy delivery techniques were evaluated (Varian RapidArc and Elekta VMAT). Treatment plans were generated for a total dose of 50 Gy for all the plans with a dose per fraction of 2 Gy. All plans were done for RapidArc using Eclipse and for Elekta VMAT with Monaco treatment planning system. Plans were evaluated based on dose volume histogram, dose homogeneity index, and conformity index, treatment planning time, estimated radiation delivery time, integral dose, and monitoring units needed to deliver the prescribed dose. RapidArc plans had less estimated beam on time, higher conformity index, and better homogeneity index. The mean dose to healthy tissue and integral dose reduced significantly with Elekta VMAT. Trivial differences were noted in all the plans for organ at risk and the two techniques provided satisfactory dose conformity and homogeneity. newline newline newline