Papiez L, McLellan J, Sandison G A, Sawchuk S, Lu X, Battista J J
Department of Radiation Oncology, Indiana University Medical Centre, Indianapolis 46202-5289.
Med Phys. 1994 Oct;21(10):1591-8. doi: 10.1118/1.597211.
Energy straggling along electron trajectories has been incorporated into a numerical algorithm for electron beam dose calculations. Landau's theory is used to predict, at any point in the absorber, the broadening of the primary electron energy spectrum due to energy loss straggling. Numerical calculations have been performed for electron beams with energies of 10-30 MeV incident upon water in order to determine the variation of dose with depth and variation of energy spectra with pathlength. These calculations are compared with the results of Monte Carlo simulations performed with the EGS4 code. The inclusion of energy loss straggling in the numerical calculations leads to predictions of energy spectra and dose deposition that are in good agreement with modified Monte Carlo simulations in which bremsstrahlung is ignored and the energy given to knock-on electrons is deposited at the site of their creation. Less satisfactory agreement was achieved when these calculations were compared to full Monte Carlo simulations that included the bremsstrahlung events and transported the knock-on electrons. It is concluded that bremsstrahlung energy loss must also be included into this algorithm, if an acceptable dose computation accuracy is to be achieved for clinical applications.
沿电子轨迹的能量离散已被纳入用于电子束剂量计算的数值算法中。朗道理论用于预测在吸收体中的任何一点，由于能量损失离散导致的初级电子能谱展宽。对能量为10 - 30 MeV的电子束入射到水中的情况进行了数值计算，以确定剂量随深度的变化以及能谱随路径长度的变化。将这些计算结果与使用EGS4代码进行的蒙特卡罗模拟结果进行了比较。在数值计算中纳入能量损失离散后，所得到的能谱和剂量沉积预测结果与修正的蒙特卡罗模拟结果吻合良好，在修正的蒙特卡罗模拟中忽略了轫致辐射，并且将给予反冲电子的能量沉积在其产生的位置。当将这些计算结果与包括轫致辐射事件并传输反冲电子的完整蒙特卡罗模拟结果进行比较时，吻合度不太令人满意。得出的结论是，如果要在临床应用中实现可接受的剂量计算精度，该算法还必须纳入轫致辐射能量损失。
