Center of Molecular Imaging, Radiotherapy and Oncology, Institut de recherche expérimentale et clinique, Université catholique de Louvain, Avenue Hippocrate 54, 1200 Brussels, Belgium.
Med Phys. 2013 Nov;40(11):111705. doi: 10.1118/1.4823469.
Describing the implementation of nuclear reactions in the extension of the Monte Carlo code (MC) PENELOPE to protons (PENH) and benchmarking with Geant4.
PENH is based on mixed-simulation mechanics for both elastic and inelastic electromagnetic collisions (EM). The adopted differential cross sections for EM elastic collisions are calculated using the eikonal approximation with the Dirac-Hartree-Fock-Slater atomic potential. Cross sections for EM inelastic collisions are computed within the relativistic Born approximation, using the Sternheimer-Liljequist model of the generalized oscillator strength. Nuclear elastic and inelastic collisions were simulated using explicitly the scattering analysis interactive dialin database for (1)H and ICRU 63 data for (12)C, (14)N, (16)O, (31)P, and (40)Ca. Secondary protons, alphas, and deuterons were all simulated as protons, with the energy adapted to ensure consistent range. Prompt gamma emission can also be simulated upon user request. Simulations were performed in a water phantom with nuclear interactions switched off or on and integral depth-dose distributions were compared. Binary-cascade and precompound models were used for Geant4. Initial energies of 100 and 250 MeV were considered. For cases with no nuclear interactions simulated, additional simulations in a water phantom with tight resolution (1 mm in all directions) were performed with FLUKA. Finally, integral depth-dose distributions for a 250 MeV energy were computed with Geant4 and PENH in a homogeneous phantom with, first, ICRU striated muscle and, second, ICRU compact bone.
For simulations with EM collisions only, integral depth-dose distributions were within 1%/1 mm for doses higher than 10% of the Bragg-peak dose. For central-axis depth-dose and lateral profiles in a phantom with tight resolution, there are significant deviations between Geant4 and PENH (up to 60%/1 cm for depth-dose distributions). The agreement is much better with FLUKA, with deviations within 3%/3 mm. When nuclear interactions were turned on, agreement (within 6% before the Bragg-peak) between PENH and Geant4 was consistent with uncertainties on nuclear models and cross sections, whatever the material simulated (water, muscle, or bone).
A detailed and flexible description of nuclear reactions has been implemented in the PENH extension of PENELOPE to protons, which utilizes a mixed-simulation scheme for both elastic and inelastic EM collisions, analogous to the well-established algorithm for electrons/positrons. PENH is compatible with all current main programs that use PENELOPE as the MC engine. The nuclear model of PENH is realistic enough to give dose distributions in fair agreement with those computed by Geant4.
描述在蒙特卡罗代码（MC）PENELOPE 的扩展中实现核反应（PENH），并与 Geant4 进行基准测试。
PENH 基于对弹性和非弹性电磁碰撞（EM）的混合模拟力学。采用 Dirac-Hartree-Fock-Slater 原子势的 eikonal 近似计算 EM 弹性碰撞的微分截面。EM 非弹性碰撞的截面是在相对论 Born 近似下，使用 Sternheimer-Liljequist 广义振子强度模型计算的。核弹性和非弹性碰撞是通过明确的散射分析交互拨号数据库模拟的，用于（1）H 和 ICRU 63 数据用于（12）C、（14）N、（16）O、（31）P 和（40）Ca。二次质子、α 粒子和氘核都被模拟为质子，其能量适应于确保一致的射程。根据用户请求也可以模拟瞬发伽马发射。在关闭或开启核相互作用的水模体中进行模拟，并比较积分深度剂量分布。二进制级联和预复合模型用于 Geant4。考虑了 100 MeV 和 250 MeV 的初始能量。对于没有模拟核相互作用的情况，在所有方向的分辨率为 1mm 的水模体中进行了额外的模拟，使用了 FLUKA。最后，在具有 ICRU 条纹肌肉和 ICRU 致密骨的均质模体中，使用 Geant4 和 PENH 计算了 250 MeV 能量的积分深度剂量分布。
对于仅带有 EM 碰撞的模拟，在剂量高于布拉格峰剂量的 10%以上时，积分深度剂量分布的误差在 1%/1mm 以内。对于具有紧密分辨率的模体中的中心轴深度剂量和横向分布，Geant4 和 PENH 之间存在显著差异（深度剂量分布的差异高达 60%/1cm）。与 FLUKA 的一致性要好得多，偏差在 3%/3mm 以内。当开启核相互作用时，PENH 和 Geant4 之间的一致性（在布拉格峰之前为 6%）与核模型和截面的不确定性一致，无论模拟的材料如何（水、肌肉或骨骼）。
已经在 PENELOPE 对质子的扩展 PENH 中实现了对核反应的详细和灵活的描述，该扩展利用了用于弹性和非弹性 EM 碰撞的混合模拟方案，类似于已建立的电子/正电子算法。PENH 与所有当前使用 PENELOPE 作为 MC 引擎的主要程序兼容。PENH 的核模型足够真实，可以与由 Geant4 计算的剂量分布很好地吻合。
