Garnica-Garza H M
Department of Ionizing Radiation Metrology, Secondary Standards Dosimetry Laboratory, National Institute for Nuclear Research, Salazar, Mexico.
Med Biol Eng Comput. 2008 Oct;46(10):1029-37. doi: 10.1007/s11517-008-0389-9. Epub 2008 Sep 9.
A method to determine the X-ray spectrum delivered by a medical linear accelerator is presented. This method consists of an analytical calculation of the primary spectrum using the Schiff bremsstrahlung cross-section formula. A correction factor that accounts for the scatter component of the spectrum is estimated by comparing the signal in two screen-film systems to a theoretical prediction using a model of energy deposition in such detectors. The model makes use of the quantum absorption efficiency and the average energy deposited per interacting photon concepts. These two quantities are calculated by means of Monte Carlo simulations of the screen-film systems used. This method is capable of determining the spectrum as a function of the spatial position across a plane perpendicular to the beam central axis. It does not, however, render information about the direction cosines of the X-ray fluence crossing such a plane, a requirement in order to produce a full phase-space file that can be used in conjunction with a Monte Carlo dose calculation engine.
本文提出了一种确定医用直线加速器所输出X射线能谱的方法。该方法包括使用希夫轫致辐射截面公式对初始能谱进行解析计算。通过将两个屏-片系统中的信号与使用此类探测器中能量沉积模型的理论预测结果进行比较，估算出一个考虑能谱散射分量的校正因子。该模型利用了量子吸收效率和每个相互作用光子沉积的平均能量概念。这两个量是通过对所使用的屏-片系统进行蒙特卡罗模拟计算得出的。该方法能够确定垂直于束流中心轴的平面上能谱随空间位置的变化情况。然而，它无法提供关于穿过该平面的X射线注量的方向余弦的信息，而这是生成可与蒙特卡罗剂量计算引擎结合使用的完整相空间文件所必需的。
