Delta4模体通过率与其角度依赖性研究

The study of angular dependence of gamma index for Delta4 phantom

目的 研究瑞典ScandiDos公司的Deha4模体在VMAT计划验证时摆位不确定性偏转对γ通过率的影响.方法 从接受VMAT患者中随机抽取2个头颈部、2个肺部和1个盆腔部位共5个病例.在Eclipse8.6 TPS中分别对5个病例的放疗计划制作验证计划,采用Delta4在瓦里安Clinac Ⅸ直线加速器下做剂量验证测量.在Delta4模体精确摆位后,分别将模体以直线加速器等中心为中心在水平方向偏转一定角度,完成11次剂量验证测量.分析Delta4模体发生偏转后对γ通过率的影响.结果 Delta4模体依次偏转0.0°、0.2°、0.4°、0.6°、0.8°、1.0°、1.2°、1.4°、1.6°、1.8°、2.0°时测量所得γ通过率略有下降,但均＞90％（剂量偏差为3％,吻合距离为3 mm）.结论 Delta4在VMAT计划验证中,在模体摆位不确定性偏转≤2°范围内,其γ通过率对模体摆位的不确定性偏转无依赖性,而在模体不确定性偏转后剂量偏差、吻合距离的通过率均发生明显变化.

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.