Objective To explore the stability of Octavius 4D system in the three-dimensional dose verification of volumetric modulated arc therapy (VMAT). Methods The responses of semiflex ionization chamber and Octavius 729 detector array to field size, dose linearity, dose rate linearity and output factors were assessed for 6 MV and 10 MV beams. When Octavius 4D system was running, the angular deviations between inclinometer and gantry were measured. With gantry in rotating state or fixed at 0°, the two-dimensional dose distributions of (10×10) cm2arc plans and VMAT plans were analyzed with 3%/3 mm criteria. VMAT plans were assessed by 3%/3 mm gamma analysis standard. Results A warm-up dose larger than 6 Gy was essential for detector stability. Dose response of detector array was linear, and dose-rate measurements were stable at different nominal dose rates. During rotating irradiation, the angular deviation of accelerator gantry angle and rotation angle of Octavius 4D phantom was found to be within 0.4°. When 3%/3 mm criteria was applied, the average gamma passing rate of three-dimensional dose distribution were 96.03% and 95.56% for VMAT plan with 6 MV or 10 MV beams. Conclusion Octavius 4D phantom combined with Octavius 729 detector array is a stable device and is reliable for pretreatment verification of VMAT.%目的:探讨Octavius 4D系统用于容积旋转调强放射治疗(VMAT)三维剂量验证的稳定性.方法:比较分析semiflex电离室和Octavius 729探测器阵列在6 MV、10 MV射束下对射野大小、剂量线性、剂量率线性和射野输出因子的响应.测量观察Octavius 4D系统旋转过程中角度仪示值与机架角的角度偏差.用3 %/3 mm标准分析(10×10)cm2旋转照射计划和VMAT计划机架归零与旋转照射的二维剂量分布;用3%/3 mm gamma分析标准评估VMAT计划.结果:预热剂量大于6 Gy是探测器稳定的必要条件.探测器阵列剂量响应是线性的,不同标称剂量率下剂量测量是稳定的.旋转照射过程中加速器机架角和Octavius 4D模体旋转角度误差在0.4°以内.6 MV和10 MV射束VMAT计划在分析标准为3%/3 mm时,三维剂量分布的平均通过率分别为96.03%和95.56%,满足临床计划剂量验证的标准.结论:Octavius 4D模体联合Octavius 729探测器阵列是一套稳定性装置,用于治疗前验证VMAT计划是可靠的.
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