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基于 3D 随机细胞模型，使用千伏级和兆伏级光子对金纳米颗粒导致的辐射沉积增加进行蒙特卡罗研究。

Monte Carlo investigation of the increased radiation deposition due to gold nanoparticles using kilovoltage and megavoltage photons in a 3D randomized cell model.

机构信息

School of Chemistry and Physics, University of Adelaide, North Terrace, Adelaide, South Australia 5000, Australia.

出版信息

Med Phys. 2013 Jul;40(7):071710. doi: 10.1118/1.4808150.

DOI:10.1118/1.4808150

PMID:23822414

Abstract

PURPOSE

Investigation of increased radiation dose deposition due to gold nanoparticles (GNPs) using a 3D computational cell model during x-ray radiotherapy.

METHODS

Two GNP simulation scenarios were set up in Geant4; a single 400 nm diameter gold cluster randomly positioned in the cytoplasm and a 300 nm gold layer around the nucleus of the cell. Using an 80 kVp photon beam, the effect of GNP on the dose deposition in five modeled regions of the cell including cytoplasm, membrane, and nucleus was simulated. Two Geant4 physics lists were tested: the default Livermore and custom built Livermore/DNA hybrid physics list. 10(6) particles were simulated at 840 cells in the simulation. Each cell was randomly placed with random orientation and a diameter varying between 9 and 13 μm. A mathematical algorithm was used to ensure that none of the 840 cells overlapped. The energy dependence of the GNP physical dose enhancement effect was calculated by simulating the dose deposition in the cells with two energy spectra of 80 kVp and 6 MV. The contribution from Auger electrons was investigated by comparing the two GNP simulation scenarios while activating and deactivating atomic de-excitation processes in Geant4.

RESULTS

The physical dose enhancement ratio (DER) of GNP was calculated using the Monte Carlo model. The model has demonstrated that the DER depends on the amount of gold and the position of the gold cluster within the cell. Individual cell regions experienced statistically significant (p < 0.05) change in absorbed dose (DER between 1 and 10) depending on the type of gold geometry used. The DER resulting from gold clusters attached to the cell nucleus had the more significant effect of the two cases (DER ≈ 55). The DER value calculated at 6 MV was shown to be at least an order of magnitude smaller than the DER values calculated for the 80 kVp spectrum. Based on simulations, when 80 kVp photons are used, Auger electrons have a statistically insignificant (p < 0.05) effect on the overall dose increase in the cell. The low energy of the Auger electrons produced prevents them from propagating more than 250-500 nm from the gold cluster and, therefore, has a negligible effect on the overall dose increase due to GNP.

CONCLUSIONS

The results presented in the current work show that the primary dose enhancement is due to the production of additional photoelectrons.

摘要

目的

使用 Geant4 中的三维计算细胞模型研究金纳米粒子（GNPs）在 X 射线放射治疗过程中导致的辐射剂量沉积增加。

方法

在 Geant4 中设置了两个 GNPs 模拟场景；一个直径为 400nm 的金纳米簇随机置于细胞质中，另一个 300nm 厚的金层围绕细胞的核。使用 80kVp 光子束，模拟了 GNPs 对包括细胞质、细胞膜和细胞核在内的细胞五个模型区域的剂量沉积的影响。测试了两种 Geant4 物理列表：默认的 Livermore 和自定义的 Livermore/DNA 混合物理列表。在模拟中，有 10（6）个粒子在 840 个细胞中进行模拟。每个细胞以随机取向和直径在 9 到 13μm 之间随机放置。使用数学算法确保 840 个细胞中没有重叠。通过模拟细胞中的两种能量谱（80kVp 和 6MV），计算了 GNPs 物理剂量增强效应的能量依赖性。通过比较两种 GNPs 模拟场景，同时激活和去激活 Geant4 中的原子退激发过程，研究了俄歇电子的贡献。

结果

使用蒙特卡罗模型计算了 GNPs 的物理剂量增强比（DER）。该模型表明，DER 取决于金的数量和金簇在细胞内的位置。取决于所使用的金几何形状，各个细胞区域的吸收剂量（DER 介于 1 到 10 之间）发生了具有统计学意义的（p<0.05）变化。附着在细胞核上的金簇产生的 DER 影响更为显著（DER≈55）。与 80kVp 光谱计算的 DER 值相比，在 6MV 下计算的 DER 值至少小一个数量级。基于模拟，当使用 80kVp 光子时，俄歇电子对细胞中总剂量增加的影响具有统计学意义（p<0.05）。产生的俄歇电子能量低，阻止它们从金簇传播超过 250-500nm，因此，由于 GNPs，对总剂量增加的影响可以忽略不计。