Abstract

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Author(s):: NIU Zhenyang1; 2; FEI Zhenle2; CHEN Zhi1; 1. University of Science and Technology of China, Hefei 230027, China; 2. the 105 Hospital of the Chinese People’s Liberation Army, Hefei 230031, China

Keywords:: ; Octavius 4D system; volumetric modulated arc therapy; detector array; gamma passing rate; stability

Abstract:: 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) cm2 arc 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.