Yu C X, Mackie T R, Wong J W
Washington University School of Medicine, St. Louis, Missouri, USA.
Med Phys. 1995 Jul;22(7):1157-65. doi: 10.1118/1.597611.
Significant advances have been made in recent years to improve photon dose calculation. However, accurate prediction of dose perturbation effects near the interfaces of different media, where charged particle equilibrium is not established, remain unsolved. Furthermore, changes in atomic number, which affect the multiple Coulomb scattering of the secondary electrons, are not accounted for by current photon dose calculation algorithms. As local interface effects are mainly due to the perturbation of secondary electrons, a photon-electron cascade model is proposed which incorporates explicit electron transport in the calculation of the primary photon dose component in heterogeneous media. The primary photon beam is treated as the source of many electron pencil beams. The latter are transported using the Fermi-Eyges theory. The scattered photon dose contribution is calculated with the dose spread array [T.R. Mackie, J.W. Scrimger, and J.J. Battista, Med. Phys. 12, 188-196 (1985)] approach. Comparisons of the calculation with Monte Carlo simulation and TLD measurements show good agreement for positions near the polystyrene-aluminum interfaces.
近年来，在改善光子剂量计算方面取得了重大进展。然而，对于不同介质界面附近未建立带电粒子平衡的剂量扰动效应的准确预测仍未解决。此外，当前的光子剂量计算算法未考虑影响二次电子多次库仑散射的原子序数变化。由于局部界面效应主要是由二次电子的扰动引起的，因此提出了一种光子 - 电子级联模型，该模型在计算非均匀介质中的初级光子剂量分量时纳入了显式电子输运。初级光子束被视为许多电子笔形束的源。后者使用费米 - 艾格斯理论进行输运。散射光子剂量贡献采用剂量扩展阵列方法计算。[T.R. 麦基、J.W. 斯克里姆格和 J.J. 巴蒂斯塔，《医学物理》12，188 - 196 (1985)] 计算结果与蒙特卡罗模拟和热释光剂量计测量结果的比较表明，在聚苯乙烯 - 铝界面附近的位置具有良好的一致性。
