目的 使用国产二维水箱在螺旋断层加速器(TOMO)上测量百分深度剂量(PDD)和射野离轴剂量分布,探索其应用于TOMO束流质控的可行性.方法 使用国产二维水箱在 TOMO 上采集数据.选择 40.0 cm × 1.0 cm、40.0 cm × 2.5 cm、40.0 cm × 5.0 cm 3 个射野测量水下1.5、5.0、10.0、15.0、20.0 cm深度的横向离轴剂量分布,选择25.0 cm × 1.0 cm、25.0 cm × 2.5 cm、25.0 cm × 5.0 cm 3个射野测量百分深度剂量曲线以及水下1.5、5.0、10.0、15.0、20.0 cm深度的纵向离轴剂量分布,将所有数据导入TEMS软件进行γ分析.结果 以厂家金标准数据为基准,国产水箱PDD曲线在3个射野条件下基本吻合,建成区差异偏大,PDD20/PDD10相对偏差＞1％.横向离轴剂量分布在3个不同射野条件下除20.0 cm外其他4个深度处所测四分之一高宽(FWQM)均＜1％;在3个不同射野、不同深度条件下所测数据在2％/1 mm标准下γ值均＞1.纵向离轴剂量分布除射野25.0 cm × 1.0 cm外,其他两个射野不同深度条件下所测半高宽(FWHM)均＜1％;除射野25.0cm × 5.0cm、深度为15.0和20.0 cm外,其他不同射野不同深度条件下所测数据在2％/1％射野宽度的分析标准下γ值均＞1.结论 国产二维水箱部分满足TOMO日常质控需求但仍需进一步优化改进以完全满足TOMO的临床验收需求.
Feasibility of a domestically developed two-dimensional water tank for quality control of beam of a helical TomoTherapy system
Objective To measure percentage depth dose(PDD)and the off-axis dose profiles of radiation fields using a domestically developed two-dimensional(2D)water tank on a helical TomoTherapy(TOMO)system and to explore the feasibility of the 2D water tank in the application to the beam quality control of the TOMO system.Methods The beam data of the TOMO system were collected using the domestically developed 2D water tank.Three radiation fields,40.0 cm × 1.0 cm,40.0 cm × 2.5 cm,and 40.0 cm×5.0 cm,were selected to measure the transverse off-axis dose profiles at depths of 1.5,5.0,10.0,15.0 and 20.0 cm.Other three radiation fields,25.0 cm × 1.0 cm,25.0 cm ×2.5 cm,and 25.0 cm × 5.0 cm,were employed to determine the PDD curves and longitudinal off-axis dose profiles at depths of 1.5,5.0,10.0,15.0 and 20.0 cm.The gamma analysis of all data was performed using the TomoTherapy ElectroMeter Measurement System(TEMS).Results Compared to the manufacturer's gold standard data,the PDD curves of the domestically developed 2D water tank agreed well under three radiation fields but differed greatly in the build-up regions,with the relative deviation of the PDD20/PDD10 ratio greater than 1％.Under three different radiation fields,the transverse off-axis dose profiles displayed full width at quarter maximum(FWQM)less than 1％measured at four depths except for 20.0 cm.The data measured under three different radiation fields and depths had gamma values greater than 1 based on a gamma criterion of 2％/1 mm.Under different depths and the three radiation fields except for 25.0 cm × 1.0 cm,the longitudinal off-axis dose profiles displayed FWHM less than 1％.Except for radiation field 25.0 cm × 5.0 cm and depths 15.0 and 20.0 cm,the data measured under other different radiation fields and depths had gamma values larger than 1 based on a gamma criterion of 2％/(1％of radiation field width).Conclusions The domestic 2D water tank partially meets the demand for the daily quality control of a TOMO system.Nevertheless,further optimization and improvement are still required to fully meet the requirements of the clinical acceptance of a TOMO system.
Domestic 2D water tankHelix TomotherapyGamma analysis
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