Impact of accelerator operating errors on γ passing rate during dose verification of volumetric modulated arc therapy for pelvic tumors
Yuan Qingqing1,4, Li Yanlong2, Wang Dajiang3, Quan Hong4, Li Guangjun1, Bai Sen1
1Radiotherapy Department of Cancer Center of West China Hospital, Sichuan University, Chengdu 610041, China; 2Department of Oncology, The Second Xiangya Hospital of Central South University, Changsha 410011, China; 3Department of Radiation Oncology, Zhongnan Hospital of Wuhan University, Wuhan 430071, China; 4School of Physics and Technology, Wuhan University, Wuhan 430072, China
Abstract：Objective To investigate the impacts of gantry rotation angle errors, monitor unit (MU) errors, collimator and multi-leaf collimator (MLC) position errors upon the γ passing rate of dose verification in volumetric modulated arc therapy (VMAT). Methods Ten patients with rectal cancer and 10 patients with uterine tumors were selected. The operating errors of accelerator parameters were introduced during the VMAT execution. By comparing the γ passing rates during dose verification between the simulating and original plans, the impact and sensitivity of the operating errors of each accelerator parameter on γ passing rate were analyzed. Results When the γ criteria were set as 3%/3mm, 3%/2mm and 2%/2mm, the γ passing rate decreasing gradient was less than 7.0% after the introduction of gantry rotation angle, MU and collimator position errors, respectively. However, after the reverse, opposite, and co-directional motion errors of the MLC blades on both sides were introduced,the γ passing rate decreasing was less than 19.13 %, 18.53%, 0.19 %; 19.87%, 20.01%, 0.42 % and 23.11%, 23.45%,0.65 % for absolute dose verification, respectively. Conclusion During VMAT, the reverse and opposite motion errors of MLC blades exert more significant effect on the γ passing rate compared with the gantry rotation angle errors, MU errors, collimator position errors and co-directional motion errors of the MLC blades. When the γ criteria of 3%/3mm, 3%/2mm and 2%/2mm are adopted, the impact of accelerator operating errors upon the γ passing rate is strengthened in sequence. Therefore, when performing dose verification for a specific patient, appropriate γ criteria should be chosen and absolute dose verification should be taken as the reference index to evaluate the consistency between the calculated and measured dose distribution.
Yuan Qingqing,Li Yanlong,Wang Dajiang et al. Impact of accelerator operating errors on γ passing rate during dose verification of volumetric modulated arc therapy for pelvic tumors[J]. Chinese Journal of Radiation Oncology, 2020, 29(9): 779-783.
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