Han K, Ballon D, Chui C, Mohan R
Med Phys. 1987 May-Jun;14(3):414-9. doi: 10.1118/1.596120.
We have used the Stanford Electron Gamma Shower (EGS) Monte Carlo code to compute photon spectra from an AECL Theratron 780 cobalt-60 unit. Particular attention has been paid to the careful modeling of the geometry and material construction of the cobalt-60 source capsule, source housing, and collimator assembly. From our simulation, we conclude that the observed increase in output of the machine with increasing field size is caused by scattered photons from the primary definer and the adjustable collimator. We have also used the generated photon spectra as input to a pencil beam model to calculate the tissue-air ratios in water and compared it to a model which uses a monochromatic photon energy of 1.25 MeV.
我们使用了斯坦福电子伽马射线簇射（EGS）蒙特卡罗代码来计算AECL Theratron 780钴-60治疗机产生的光子能谱。我们特别关注了对钴-60源胶囊、源外壳和准直器组件的几何结构和材料构造进行精确建模。通过模拟，我们得出结论，该机器输出随射野尺寸增大而增加的现象是由初级限束器和可调准直器散射的光子导致的。我们还将生成的光子能谱作为输入，用于笔形束模型以计算水中的组织空气比，并将其与使用1.25 MeV单色光子能量的模型进行比较。
