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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 discuss the matters needing attention in measuring the edge of radiation field with two-dimensional ionization chamber matrix. MATERIALS AND METHODS: VARIAN’s 23EX accelerator field was measured using the MATRIXX two-dimensional ionization chamber matrix from IBA. The ionization chamber matrix is placed horizontally on the accelerator bed with the center of the ionization chamber at the isocenter, SAD = 100 cm. Field size from 4.0cm × 4.0cm to 16cm × 16cm. Each shot field beam 50MU, record the measurement results. Analyze the measurement data using the OmniPro I’mRT (1.5) software. Results: The penumbral size of the four sides of X1, X2, Y1 and Y2 showed periodic changes with the size of the field, and the distance between adjacent wave troughs was (3.79 ± 0.25) mm. The bottom of the trough is flat with a flat width of (2.3 ± 0.3) mm and a flat peak at the crest with a width of (2.2 ± 0.2) mm. The height of bee wave trough is (4.0 ± 0.1) mm. Conclusion: When using the two-dimensional ionization chamber matrix to measure the penumbra, the influence of the position of the ionization chamber matrix on the measurement results should be fully considered. For the same field, the difference of 4mm can be caused due to the different positions of the matrix. Changing the matrix position and repeating the measurement from different positions can reduce the impact of the matrix position.