Department of Medical Physics, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, Iran.
Solid Tumor Research Center, Cellular and Molecular Medicine Institue, Urmia University of Medical Sciences, Urmia, Iran.
Sci Rep. 2022 Feb 2;12(1):1779. doi: 10.1038/s41598-022-05748-0.
Gold nanoparticles (GNPs) are materials that make the tumor cells more radiosensitive when irradiated with ionizing radiation. The present study aimed to evaluate the impact of different physical interaction models on the dose calculations and radiochemical results around the GNP. By applying the Geant4 Monte Carlo (MC) toolkit, a single 50-nm GNP was simulated, which was immersed in a water phantom and irradiated with 5, 50, and 150 MeV proton beams. The present work assessed various parameters including the secondary electron spectra, secondary photon spectra, radial dose distribution (RDD), dose enhancement factor (DEF), and radiochemical yields around the GNP. The results with an acceptable statistical uncertainty of less than 1% indicated that low-energy electrons deriving from the ionization process formed a significant part of the total number of secondary particles generated in the presence of GNP; the Penelope model produced a larger number of these electrons by a factor of about 30%. Discrepancies of the secondary electron spectrum between Livermore and Penelope were more obvious at energies of less than 1 keV and reached the factor of about 30% at energies between 250 eV and 1 keV. The RDDs for Livermore and Penelope models were very similar with small variations within the first 6 nm from NP surface by a factor of 10%. In addition, neither the G-value nor the REF was affected by the choice of physical interaction models with the same energy cut-off. This work illustrated the similarity of the Livermore and Penelope models (within 15%) available in Geant4 for future simulation studies of GNP enhanced proton therapy with physical, physicochemical, and chemical mechanisms.
金纳米颗粒（GNPs）是一种材料，当用电离辐射照射时，可使肿瘤细胞对辐射更敏感。本研究旨在评估不同物理相互作用模型对 GNP 周围剂量计算和放射化学结果的影响。通过应用 Geant4 蒙特卡罗（MC）工具包，模拟了一个 50nm 的单个 GNP，将其浸入水模型中，并分别用 5、50 和 150MeV 的质子束照射。本工作评估了各种参数，包括二次电子能谱、二次光子能谱、径向剂量分布（RDD）、剂量增强因子（DEF）和 GNP 周围的放射化学产额。结果表明，在 GNP 存在的情况下，电离过程产生的低能电子形成了产生的次生粒子总数的重要组成部分，且具有可接受的小于 1%的统计不确定性；Penelope 模型产生的这些电子数量是 Livermore 模型的约 30 倍。在能量低于 1keV 时，Livermore 和 Penelope 之间的二次电子谱的差异更为明显，在 250eV 至 1keV 之间的能量范围内，差异达到约 30%。Livermore 和 Penelope 模型的 RDD 非常相似，在 NP 表面前 6nm 范围内，变化很小，差异约为 10%。此外，选择不同的物理相互作用模型不会影响 G 值和 REF，只要它们具有相同的能量截止值。本工作说明了 Geant4 中可用的 Livermore 和 Penelope 模型（在 15%以内）的相似性，可用于 GNP 增强质子治疗的物理、物理化学和化学机制的未来模拟研究。
