射波刀系统射野输出因子测量及对比

Measurement and comparison of output factors of the radiation field for CyberKnife system

目的:通过实际测量和计算机模拟等方法得到射波刀(CyberKnife)各准直器的输出因子,对比分析各方法的结果,从而得到准确的输出因子。方法:采用蒙特卡罗模拟、半导体探测器测量(PTW 60017、PTW 60016)、电离室探测器测量(PTW 31010)和热释光探测器测量(?1.5mm、离散度1%)等方法,在相同的参考条件下,源轴距800 mm以及深度15 mm(SAD=800 mm,Depth=15 mm),得到相应的输出因子。结果:在射野较大(≥25 mm)时,各种方法的输出因子差异不大,但是在射野较小(≤20 mm)时,各方法之间的差异较大,尤其是在最小射野(5 mm)的情况下,热释光探测器测量以及蒙特卡罗模拟结果略低于半导体探测器测量,最大误差分别为13%和7%,而电离室探测器测量误差高达37%。结论:输出因子可以通过多种方式获得,而半导体探测器相对于其他探测器,具有更好的灵敏度和稳定性,便于在临床应用中展开,因此可采用半导体探测器测量和热释光探测器测量的方式测量射波刀系统的射野输出因子。

Objective:To study the output factors of various collimators of CyberKnife system through actual measurement and computer simulation,and to compare and analyze the results of various method so as to obtain the accurate output factors.Methods:In this study,series of tools and methods including Monte Carlo simulation(BEAMnrc),semiconductors(PTW60017,PTW60016),ionization chamber(PTW31010)and thermoluminescence(?1.5mm,1%of dispersion)were adopted.Under the same reference conditions,the corresponding output factors of radiation field were obtained when the source axis distance was800mm and the depth was15mm(SAD=800mm,Depth=15mm).Results:When the range of radiation field was relatively larger(≥25mm),the difference of output factors among various methods were not obviously,but there were obvious differences among these methods when the range of radiation field was relatively smaller(≤20mm).Especially under the minimum range of radiation field(5mm),the results of adopting thermoluminescence and Monte Carlo simulation(BEAMnrc)were slightly lower than that of using semiconductors,and in this time,the maximum errors of them were13%and7%,respectively.And the error of using ionization chamber has achieved37%.Conclusion:The output factors could be obtained from various methods,while the semiconductor detector has better sensitivity and stability than other detectors,and it is convenient to be applied in clinical practice.Therefore,the measurement of semiconductor detector and the measurement of thermoluminescent detector should be adopted to measure output factors of radiation field of Cyberknife system.