二维电离室矩阵测量射野边缘

Measuring of Field Edge Using a Two-dimension Ion Chamber Arrary

目的:探讨用二维电离室矩阵测量放射野边缘应注意的事项。材料与方法:使用IBA公司的MATRIXX二维电离室矩阵对VARIAN公司的23EX加速器的射野进行测量。把电离室矩阵水平放置在加速器床面上,电离室中心处于等中心位置,SAD=100cm。射野大小从4.0cm×4.0cm变到16cm×16cm。每射野出束50MU,记录测量结果。用OmniPro I'mRT(1.5)软件分析测量数据。结果:在X1、X2、Y1、Y2四个边半影大小随射野大小变化而呈现波浪式周期性变化,相邻波峰波谷间距为(3.79±0.25)mm。波谷底部平坦,平区宽度为(2.3±0.3)mm,波峰顶部也平坦,平区宽度为(2.2±0.2)mm。波蜂波谷高度相差为(4.0±0.1)mm。结论:用二维电离室矩阵测量射野半影时应充分考虑电离室矩阵的位置对测量结果的影响,对于同一个射野,由于摆放矩阵位置不同,可引起4mm的差别。改变矩阵位置,从不同位置重复测量,可减小矩阵位置的影响。

objective： To study the dosimetric characteristics of 2D ion chamber array matrix for measuring of radiation field edge. Material and Methods： We have used a 2D ion chamber array detector （IBA MATRIXX） to measure the fields of VARIAN 23EX accelerator. The matrix was lied horizontally on the accelerator couch. The centre of matrix coincided with the accelerator isocentre, SAD=100cm.The field size was changed from 4cm×4cm to 16cm×16cm. Irradiating 50 MU per field, the measure data was recorded ,and was analysed with the software, OmniPRO I＇mRT（1.5）. Results： The penumbra size in four edge （X1, X2, Y1, Y2） displays wave mode cyclicity change.The average distance between the border penumbra wave crest and trough equals （3.79±0.25） mm. The bottom of the wave trough bottom is even, the average width of the bottom equals （2.3±0.3） mm. The top of the wave crest is even too, the average width of the top equals （2.2±0.2）mm.The distance from the trough to the crest is （4.0±0.1） mm. Conclusions： Measuring the penumbra, the impact of ion chamber arrary location over measurement result should be considered sufficiently. To the same field, since location of the ion array is different, the measurent results may have 4 mm difference. Change matrix location, repeat measurement, may diminish matrix location effect.