三维分析仪与两维矩阵射野测量的比较

Comparison of Radiation Field Measured by Using Three-dimensional Analysis Device and Two-dimensional Matrix

目的:应用不同仪器与方法测量加速器6 MV X线射野的特性,比较各方法的优劣和局限性,探讨快速简便检测射野特性的方法。材料与方法:分别采用电离室和半导体探头配合三维射野分析仪测量加速器6 MV X线不同射野大小的百分深度剂量曲线PDD和离轴比曲线OCR,并以二维电离室矩阵测量相同条件的OCR。(1)比较采用电离室和半导体探头测量PDD的差别。(2)比较两维矩阵与电离室半导体探头测量射野的对称性、平坦度、射野大小和半影等的差别。结果:对小于15 cm×15 cm照射野,半导体探头和电离室测量PDD的结果一致性较好,两者偏差小于1.3%。对于20 cm×20 cm照射野,半导体探头的测量结果大于电离室,最大差别3.5%,偏差为2.6%。用半导体探头与电离室测量射野的大小,两者的最大差别为0.6 mm,两者有较好的一致性,二维电离室矩阵测量与前两者比较,最大差别为2.9 mm,最小差别0.5 mm。三种方法测量的射野平坦度差别在1.2%~2.6%,矩阵的测量数值在半导体和电离室测量范围之内。结论:在检测加速器射野性能时,二维矩阵可以快速检测射野平坦度、对称性,但测量射野大小时可能有较大误差,不宜用作验收加速器和收集...

Objective: To study the characteristics of 6 MV X-ray radiation field through comparison of radiation field measured by using different methods and devices.Materials and Methods: We adopt ionization chamber and diode detector with three dimensional analysis devices to measure 6 MV X-ray PDD curve and OCR profile of different radiation fields.(1) Compare the differences of PDD curve respectively measured by using ionization chamber and diode detector.(2) Compare the differences of symmetry,flatness and penumbra of radiation field measured by using two dimensional matrix and ionization chamber with three dimensional device.Results: During less than 15 cm×15 cm radiation field,PDD data measured by using semiconductor is consistent with ionization chamber.The deviation is less than 1.3%.About 20 cm×20 cm radiation field,the deviation is 2.6%.The maximum deviation of radiation fields measured by using semiconductor and ionization chamber is 0.6mm.By comparing of those two methods,the maximum deviation of radiation fields measured by two dimensional matrix is 2.9mm,and the minimum deviation is 0.5mm.The difference of the flatness and symmetry measured by the three methods is very little.Conclusions: When we exam the accelerator,we can use the two dimensional matrix to rapidly measure symmetry and flatness of radiation fields.But it isn't suitable to measure the size of radiation fields using two dimensional mattrix.