Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland.
Phys Med Biol. 2013 May 7;58(9):2841-59. doi: 10.1088/0031-9155/58/9/2841. Epub 2013 Apr 8.
The electron Monte Carlo (eMC) dose calculation algorithm available in the Eclipse treatment planning system (Varian Medical Systems) is based on the macro MC method and uses a beam model applicable to Varian linear accelerators. This leads to limitations in accuracy if eMC is applied to non-Varian machines. In this work eMC is generalized to also allow accurate dose calculations for electron beams from Elekta and Siemens accelerators. First, changes made in the previous study to use eMC for low electron beam energies of Varian accelerators are applied. Then, a generalized beam model is developed using a main electron source and a main photon source representing electrons and photons from the scattering foil, respectively, an edge source of electrons, a transmission source of photons and a line source of electrons and photons representing the particles from the scrapers or inserts and head scatter radiation. Regarding the macro MC dose calculation algorithm, the transport code of the secondary particles is improved. The macro MC dose calculations are validated with corresponding dose calculations using EGSnrc in homogeneous and inhomogeneous phantoms. The validation of the generalized eMC is carried out by comparing calculated and measured dose distributions in water for Varian, Elekta and Siemens machines for a variety of beam energies, applicator sizes and SSDs. The comparisons are performed in units of cGy per MU. Overall, a general agreement between calculated and measured dose distributions for all machine types and all combinations of parameters investigated is found to be within 2% or 2 mm. The results of the dose comparisons suggest that the generalized eMC is now suitable to calculate dose distributions for Varian, Elekta and Siemens linear accelerators with sufficient accuracy in the range of the investigated combinations of beam energies, applicator sizes and SSDs.
电子蒙特卡罗（eMC）剂量计算算法可用于 Eclipse 治疗计划系统（Varian Medical Systems），它基于宏观 MC 方法，并使用适用于瓦里安线性加速器的束流模型。如果将 eMC 应用于非瓦里安机器，这将导致准确性受限。在这项工作中，eMC 被推广到 Elekta 和西门子加速器的电子束，也能进行精确的剂量计算。首先，应用先前研究中为瓦里安加速器的低电子束能量而进行的修改。然后，使用主电子源和主光子源开发了一个通用束流模型，分别代表散射箔中的电子和光子，电子边缘源、光子传输源和电子及光子线源分别代表刮刀或插件中的粒子和头部散射辐射。关于宏观 MC 剂量计算算法，改进了次级粒子的输运代码。使用 EGSnrc 在均匀和非均匀体模中进行相应的剂量计算，对宏观 MC 剂量计算进行了验证。通过在水模中对瓦里安、Elekta 和西门子机器的各种束能、照射器尺寸和 SSD 进行计算和测量剂量分布的比较，对推广的 eMC 进行了验证。比较结果以每 MU 的 cGy 为单位。总体而言，发现所有机器类型和所有研究参数组合的计算和测量剂量分布之间存在 2%或 2mm 的一般一致性。剂量比较的结果表明，推广的 eMC 现在适用于在研究的束能、照射器尺寸和 SSD 组合范围内，对瓦里安、Elekta 和西门子线性加速器进行剂量分布计算，具有足够的准确性。
