Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland.
Phys Med Biol. 2013 Apr 7;58(7):2027-44. doi: 10.1088/0031-9155/58/7/2027. Epub 2013 Mar 4.
Although the Monte Carlo (MC) method allows accurate dose calculation for proton radiotherapy, its usage is limited due to long computing time. In order to gain efficiency, a new macro MC (MMC) technique for proton dose calculations has been developed. The basic principle of the MMC transport is a local to global MC approach. The local simulations using GEANT4 consist of mono-energetic proton pencil beams impinging perpendicularly on slabs of different thicknesses and different materials (water, air, lung, adipose, muscle, spongiosa, cortical bone). During the local simulation multiple scattering, ionization as well as elastic and inelastic interactions have been taken into account and the physical characteristics such as lateral displacement, direction distributions 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, based on local simulations the radiation transport of neutrons and the generated ions are included into the MMC simulations for the dose calculations. In order to validate the MMC transport, calculated dose distributions using the MMC transport and GEANT4 have been compared for different mono-energetic proton pencil beams impinging on different phantoms including homogeneous and inhomogeneous situations as well as on a patient CT scan. The agreement of calculated integral depth dose curves is better than 1% or 1 mm for all pencil beams and phantoms considered. For the dose profiles the agreement is within 1% or 1 mm in all phantoms for all energies and depths. The comparison of the dose distribution calculated using either GEANT4 or MMC in the patient also shows an agreement of within 1% or 1 mm. The efficiency of MMC is up to 200 times higher than for GEANT4. The very good level of agreement in the dose comparisons demonstrate that the newly developed MMC transport results in very accurate and efficient dose calculations for proton beams.
尽管蒙特卡罗（MC）方法允许对质子放射治疗进行精确的剂量计算，但由于计算时间长，其使用受到限制。为了提高效率，开发了一种新的质子剂量计算宏观 MC（MMC）技术。MMC 传输的基本原理是局部到全局的 MC 方法。局部模拟使用 GEANT4 包括垂直入射在不同厚度和不同材料（水、空气、肺、脂肪、肌肉、松质骨、皮质骨）平板上的单能质子铅笔束。在局部模拟中，考虑了多次散射、电离以及弹性和非弹性相互作用，并对初级和次级粒子的横向位移、方向分布和能量损失等物理特性进行了评分。然后，将来自适当平板的评分数据用于 MMC 模拟中质子的逐步传输，同时计算入口和出口位置之间路径上的能量损失。此外，基于局部模拟，将中子和生成离子的辐射传输纳入 MMC 模拟中，以进行剂量计算。为了验证 MMC 传输，使用 MMC 传输和 GEANT4 计算了不同单能质子铅笔束撞击包括均匀和不均匀情况以及患者 CT 扫描的不同体模的剂量分布，并进行了比较。对于所有考虑的铅笔束和体模，计算积分深度剂量曲线的一致性优于 1%或 1mm。对于剂量分布，在所有体模中，对于所有能量和深度，一致性都在 1%或 1mm 以内。在患者中使用 GEANT4 或 MMC 计算的剂量分布的比较也表明，一致性在 1%或 1mm 以内。MMC 的效率比 GEANT4 高 200 倍。剂量比较的非常好的一致性水平表明，新开发的 MMC 传输可实现质子束非常准确和高效的剂量计算。
