二维半导体矩阵在日常监测直线加速器射野离轴剂量分布特性中的作用

Use of 2D Diode Array for Daily Monitoring of Linear Accelerator Beam Profile Characters

目的:分析二维半导体矩阵检测直线加速器射野离轴剂量分布特性的准确性。方法:在标准摆位条件下,分别用二维半导体矩阵测量和三维水箱电离室扫描射野的平坦度和对称性。分析对应曲线的偏离度,计算平坦度和对称性等参数,并进行分析比较。结果:在80%射野范围内曲线对应各点最大偏离度为1·97%,平均偏离度为-0·54%。射野边缘的偏离度T侧最大为-40·80%,G侧最大为43·30%。除了2个射野平坦度差别较大(分别为-21·72%、41·48%,绝对偏差-0·63%、1·12%)之外,其他射野的平坦度偏差均小于5%,对称性偏差均小于3%。结论:二维半导体矩阵测量的射野离轴剂量分布曲线与电离室扫描结果具有较好的一致性,可以用于加速器的射野离轴剂量分布的日常监测。

Objective：To analyze the accuracy of linear accelerator beam profile characters measured by 2D diode array.Methods：In standard setup conditions,a set of beam profile parameters were mearsured using 2D diode array and ion chamber scan mounted on 3D tank respectively.The deviation of two corresponding profiles were analyzed and the numbers of flatness and symmetry calculated were compared.Results：The maximum deviation of 4 pairs of profiles in 80% field region was 1.97% and the mean deviation was -0.54%.The maximum deviation on the edge of beams was -40% on T side and 43.30% on G side.Except 2 fields with large deviation about flatness （respectively -21.72% and 41.48%,absolute deviation was -0.63% and 1.12%）,the flatness of other fields were all smaller than 5% and all symmetry were smaller than 3%.Conclusion：The profiles measured by 2D diode array and ion chamber scan are agreeable relatively,so the 2D diode array can be used to daily monitor the beam profile parameters.