The study of angular dependence of gamma index for Delta4 phantom / 中华放射肿瘤学杂志

ABSTRACT

Objective To study the effect of the uncertain deflection of the Delta4 phantom (ScandiDos AB,Sweden) in setting up on the Gamma index passing rate during the VMAT plan verification.Methods Two patients with head and neck cancer,two with lung cancers and one with pelvic cancer receiving VMAT radiotherapy were randomly chosen.By means of Eclipse8.6 TPS the treatment plans elaborated for the five patients were picked up to make the verification plans and Delta4 was used to perform dose verification On VARIAN Clinac Ⅸ.The Delta4 phantom was precisely set up first,and then it was deflected in a given angle towards the horizontal direction in relation to the center of the linear accelerator isocenter to perform the dose verification for 11 times successively.To figure out the relationship between the deflection angle of the Delta4 phantom and the Gamma index passing rate.Results As the Delta4 phantom was deflected by 0.0°,0.2°,0.4°,0.6°,0.8°,1.0°,1.2°,1.4°,1.6°,1.8° and 2.0° in sequence,the measured Gamma index passing rates presented a slight decline,but all greater than 90％ (DD 3％,DTA 3 mm).Conclusions In the VMAT plan verification,the Gamma index passing rate of Delta4 has no dependence on the uncertain deflection of the Delta4 phantom provided that the uncertain deflection of the Delta4 phantom is no greater than 2°,but the passing rates of DD and DTA vary significantly with the uncertain deflection of the Delta4 phantom.