TomoTherapy HT系统长期剂量及能量稳定性监测

摘要

目的 对Tomothepapy HT系统剂量及能量稳定性进行监测与评价,研究更换系统重要部件对剂量及能量稳定性的影响.方法 用A1SL电离室,TomoElectronmeter矩形固体水模体,参照美国医学物理学会TG-148号报告,对Tomotherapy HT系统质控规程中剂量输出、能量稳定性进行长期监测,并收集整理数据及分析结果.数据囊括了2011年3月到2017年3月所有日检剂量输出结果和月检静态模式下束流能量稳定性测量结果.结果 6年日检剂量输出平均绝对偏差是1.2%,更换固定靶前后绝对偏差值分别是1.30%、1.30%(P=0.986).系统安装剂量伺服系统(Dose Servo System,DCS)前后偏差均值分别为1.30%、0.96%(P＜0.001).6年能量稳定性监测(ratio_P20/P10)平均绝对偏差是0.82%.更换固定靶前后平均偏差分别是0.82%、1.11%(P=0.248).安装DCS前后绝对偏差是1.11%、0.64%(P=0.088).结论 TomoTherapy HT系统长期剂量和能量稳定性较好.固定靶与旋转靶对输出剂量和能量稳定性影响均无差异.剂量伺服系统的安装提高了输出剂量的稳定性而对能量稳定性无影响.%Objective To monitor and evaluate the dose and energy stability of Tomothepapy HT system and investigate the influence of the replacing important components of system on the dose and energy stability. Methods A long-term detection for output and energy stability of the Tomotherapy HT system was conducted according to the AAPM TG-148 report by using A1SL ionization chamber and TomoElectronmeter and rectangular solid water phantom. The data were collected and the results were analyzed. The data included the results of all the daily output and the monthly energy stability of the beam under the static model from March 2011 to March 2017. Results The average absolute deviation of the daily output was 1.2% in six years. The mean of absolute deviation before and after the fixed target was 1.30%, 1.30% respectively (P=0.986). The mean deviations before and after the installation of dose servo system (DCS) was 1.30%, 0.96% respectively (P＜0.001). The mean absolute deviation of the energy stability monitoring (Ratio_P20/P10) was 0.82% in six years. The average deviation before and after the fixed target was 0.82%, 1.11% respectively (P=0.248). Before and after the installation of DCS, the absolute deviation was 1.11%, 0.64% respectively (P=0.088). Conclusion The long-term dose and energy stability of TomoTherapy HT system is good. The effects of fixed target and rotating target on the output dose and energy stability are not different. The installation of the DCS increases the stability of the output dose without affecting the energy stability.