气温和气压对医用直线加速器输出剂量刻度的影响

Influences of temperature and pressure on output dose scale of medical linear accelerator

目的 :研究治疗室的气温和气压对医用直线加速器输出剂量刻度的影响。方法 :采用医科达Precise电子直线加速器产生的6 MV高能X线,以水模体为介质,通过IAEA 277报告及剂量学原理进行吸收剂量的测量与计算。分别以治疗室的实测气温、气压值和假定气温、气压值作为测量时的修正参数,进行实验性测量,并对采集的数据进行对比分析。结果:气温一定时,气压每波动0.01 atm(1 atm=101 325 Pa),输出剂量波动约1%;气压一定时,气温每波动3℃,输出剂量波动约1%。随着气压的升高,输出剂量呈线性递减;随着气温的升高,输出剂量呈线性递增。结论:气温和气压对医用直线加速器输出剂量刻度影响较大。标定医用直线加速器输出剂量时,除其他校准参数正确外,必须按治疗室实测的气温和气压值进行修正。

Objective To study the effects of temperature and pressure on the output dose scale of medical linear accelerator. Methods The absorbed dose was measured and calculated with 6 MV high-energy X ray by Elekta Precise electron linear accelerator, water phantom, IAEA 277 report and dosimetry principles. Experimental measurement was carried out with the correction parameters of measured and assumed values of temperature and pressure, and the comparison analysis was performed on the obtained data. Results In case the temperature kept constant, the output dose changed by 1%as the pressure was altered by 0.01 atm（1 atm=101 325 Pa）; In case the pressure kept constant, the output dose changed by 1% as the temperature was altered by 3%. The output dose showed negative linear correlation with the pressure while positive one with the temperature. Conclusion Temperature and pressure pose great influences on the scale of medical linear accelerator output dose. The calibration of medical linear accelerator output dose has to be implemented in case of the measured temperature and pressure besides other calibration parameters.