Fix M K, Frei D, Volken W, Born E J, Aebersold D, Manser P
Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland.
Med Phys. 2012 Jun;39(6Part21):3873. doi: 10.1118/1.4735815.
Although the Monte Carlo (MC) method allows accurate dose calculation its usage is limited due to long computing time. In order to gain efficiency, a new macro MC (MMC) technique for proton dose calculations in homogeneous materials has been developed.
The macro MC is based on a local to global MC approach. The local simulations using Geant4 consist of mono-energetic proton pencil beams (10 to 250 MeV) impinging perpendicularly on slabs of different thicknesses (1-10 mm) and different materials (water, lung, muscle, adipose, bone). During the local simulation multiple scattering, ionization, elastic and inelastic interactions have been taken into account and the physical characteristics such as lateral displacement and energy loss have been scored for primary and secondary particles. The scored data from appropriate slabs is then used for the stepwise transport of the protons in the MMC simulation while calculating the energy loss along the path between entrance and exit position. Additionally, ions and neutrons are taken into account for the dose calculation. In order to validate the MMC, calculated dose distributions using the MMC transport and Geant4 have been compared for different mono-energetic proton pencil beams impinging on phantoms with different homogeneous materials.
The agreement of calculated integral depth dose curves is better than 1% or 1 mm for all pencil beams and materials considered. For the dose profiles the agreement is within 1% or 1 mm for all energies, depths and materials. The efficiency of MMC is about 200 times higher than for Geant4.
The dose comparisons demonstrate that the new MMC results in very accurate and efficient dose calculations for proton beams in homogeneous materials. In future, the MMC method will be extended to inhomogeneous situations in order to allow patient dose calculations for proton beams. This work was supported by Varian Medical Systems.
尽管蒙特卡罗（MC）方法能够进行精确的剂量计算，但由于计算时间长，其应用受到限制。为提高效率，已开发出一种用于均匀材料中质子剂量计算的新型宏蒙特卡罗（MMC）技术。
宏蒙特卡罗基于从局部到全局的蒙特卡罗方法。使用Geant4进行的局部模拟包括单能质子笔形束（10至250 MeV）垂直入射到不同厚度（1 - 10 mm）和不同材料（水、肺、肌肉、脂肪、骨骼）的平板上。在局部模拟过程中，考虑了多次散射、电离、弹性和非弹性相互作用，并对初级和次级粒子的横向位移和能量损失等物理特性进行了记录。然后，将来自适当平板的记录数据用于MMC模拟中质子的逐步传输，同时计算沿入射和出射位置之间路径的能量损失。此外，剂量计算中还考虑了离子和中子。为验证MMC，比较了使用MMC传输和Geant4计算的不同单能质子笔形束入射到具有不同均匀材料的体模上的剂量分布。
对于所有考虑的笔形束和材料，计算得到的积分深度剂量曲线的一致性优于1%或1 mm。对于剂量分布，在所有能量、深度和材料下，一致性在1%或1 mm以内。MMC的效率比Geant4高约200倍。
剂量比较表明，新的MMC能够对均匀材料中的质子束进行非常准确和高效的剂量计算。未来，MMC方法将扩展到非均匀情况，以便能够进行质子束的患者剂量计算。本研究得到瓦里安医疗系统公司的支持。
