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Sensitivity of passing rates of intensity-modulated radiotherapy plans in dose verification against gantry angle errors
Wang Ning,Wang Bin,Chen Along,Huang Xiaoyan
Department of Medical Imaging,Zhongshan Traditional Chinese Medicine Hospital,Zhongshan 528400,China (Wang N); State Key Laboratory of Oncology in South China,Department of Radiation Oncology,Cancer Center,Sun Yat-sen University,Guangzhou 510060,China (Wang B,Chen AL,Huang XY)
Abstract Objective To analyze the sensitivity of passing rates of intensity modulated radiation therapy (IMRT) plans in dose verification against gantry angle errors. Methods Gantry angle errors (±2.0°, ±1.0°, and ±0.5°) were introduced into the clinical IMRT plans of 9 patients. There were 7 IMRT plans for each patient, containing 1 original IMRT plan and 6 IMRT plans with gantry angle errors. The dose distribution of the original and modified plans for each patient was measured by ArcCHECK array. Based on the dose distribution of the original plan, the passing rate of each plan was calculated using absolute distance to agreement (DTA) analysis and Gamma analysis with the criteria of 3%/3 mm and 2%/2 mm. The obtained passing rates were analyzed by non-parametric Wilcoxon rank test. Results Under the criteria of 3%/3 mm, the mean passing rate in 9 original IMRT plans was 95.2% using DTA analysis and 96.5% using Gamma analysis. According to Gamma analysis, the plans with gantry angle errors of-2.0°,2.0°,1.0°,-0.5°, and 0.5°had the mean passing rates decreased by 12.2%, 23.5%, 6.3%, 0.9%, and 2.9%, respectively (P=0.008,0.008,0.008,0.036,0.012). According to DTA analysis, the above plans had the mean passing rates decreased by 16.2%, 23.8%, 1.7%, 6.8%, and 3%, respectively (all P=0.008). The passing rates calculated by DTA method were more sensitive to the gantry angle errors than those by Gamma method, while the passing rates under the criterion of 2%/2 mm were more sensitive than those under the criterion of 3%/3 mm. Conclusions The greater the gantry angle errors, the larger the decrease in the mean passing rate. IMRT dose verification is even sensitive enough to detect the gantry angle errors within 0.5°. Enhanced quality control and assurance of gantry angle is needed to guarantee the accuracy of IMRT delivery.
Wang Ning,Wang Bin,Chen Along et al. Sensitivity of passing rates of intensity-modulated radiotherapy plans in dose verification against gantry angle errors[J]. Chinese Journal of Radiation Oncology, 2016, 25(12): 1327-1330.
Wang Ning,Wang Bin,Chen Along et al. Sensitivity of passing rates of intensity-modulated radiotherapy plans in dose verification against gantry angle errors[J]. Chinese Journal of Radiation Oncology, 2016, 25(12): 1327-1330.
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2016, Vol. 25 
