Impact of accelerator operating errors on γ passing rate during dose verification of volumetric modulated arc therapy for pelvic tumors
10.3760/cma.j.cn113030-20181015-00522
- VernacularTitle:加速器运行误差对盆腔肿瘤容积旋转调强放疗计划剂量验证的影响
- Author:
Qingqing YUAN
1
;
Yanlong LI
;
Dajiang WANG
;
Hong QUAN
;
Guangjun LI
;
Sen BAI
Author Information
1. 四川大学华西医院肿瘤中心放疗科，成都 610041；武汉大学物理科学与技术学院 430072
- From:
Chinese Journal of Radiation Oncology
2020;29(9):779-783
- CountryChina
- Language:Chinese
-
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%/3 mm, 3%/2 mm and 2%/2 mm, 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%/3 mm, 3%/2 mm and 2%/2 mm 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.
