Werner B L, Cho P S, Pfund J
Oncology Systems, Picker International, Inc., Wayne, PA 19087, USA.
Phys Med Biol. 1998 Feb;43(2):291-311. doi: 10.1088/0031-9155/43/2/006.
The FE-lspd model is a two-component electron beam model that distinguishes between electrons that can be described by small-angle transport theory and electrons that are too widely scattered for small-angle transport theory to be applicable. The two components are called the primary beam and the laterally scattered primary distribution (lspd). The primary beam component incorporates a simple version of the Fermi-Eyges model and dominates dose calculations at therapeutic depths. The lspd component corrects erros in the lateral spreading of the primary beam component, thereby improving the accuracy by which the FE-lspd model calculates dose distribution in blocked fields. Comparisons were made between dose profiles and central-axis depth dose distributions in small fields calculated by the FE-lspd, Fermi-Eyges and EGS4 Monte Carlo models for a 10 MeV beam in a homogeneous water phantom. The maximum difference between the dose calculated using the FE-lspd model and EGS4 Monte Carlo is about 6% at a field diameter of about 1 cm, and less than 2% for field sizes greater than 3 cm diameter. The maximum difference between the Fermi-Eyges and Monte Carlo calculations is about 18% at a field diameter of about 2.5 cm. A comparison was made with the central-axis depth dose distribution measured in water for a 3 cm diameter field in a 10 MeV clinical electron beam. The errors in the dose distribution were found to be less than 2% using the FE-lspd model but almost 18% using the Fermi-Eyges model. A comparison was also made with pencil beam profiles calculated using the second-order Fermi-Eyges transport model.
FE-lspd模型是一种双组分电子束模型，它区分了可由小角度输运理论描述的电子和散射角度过大以至于小角度输运理论不适用的电子。这两个组分分别称为原射线束和侧向散射原分布（lspd）。原射线束组分采用了费米 - 艾格斯模型的简化版本，并且在治疗深度的剂量计算中占主导地位。lspd组分校正了原射线束组分侧向展宽中的误差，从而提高了FE-lspd模型计算遮挡野中剂量分布的准确性。对均匀水模体中10 MeV电子束在小射野下由FE-lspd模型、费米 - 艾格斯模型和EGS4蒙特卡罗模型计算得到的剂量剖面和中心轴深度剂量分布进行了比较。在射野直径约为1 cm时，使用FE-lspd模型和EGS4蒙特卡罗模型计算的剂量之间的最大差异约为6%，对于直径大于3 cm的射野，差异小于2%。在射野直径约为2.5 cm时，费米 - 艾格斯模型和蒙特卡罗计算之间的最大差异约为18%。对10 MeV临床电子束直径3 cm射野在水中测量的中心轴深度剂量分布进行了比较。发现使用FE-lspd模型时剂量分布的误差小于2%，而使用费米 - 艾格斯模型时误差几乎为18%。还与使用二阶费米 - 艾格斯输运模型计算的笔形束剖面进行了比较。
