Abstract：
OBJECTIVE: This work explores the enhancement of ionization clustering and its radial dependence around a gold nanoparticle (NP), indicative of the induction of DNA lesions, a potential trigger for cell-death.
Approach: Monte Carlo track structure simulations were performed to determine (a) the spectral fluence of incident photons and electrons in water around a gold NP under charged particle equilibrium conditions and (b) the density of ionization clusters produced on average as well as conditional on the occurrence of at east one interaction in the nanoparticle using Associated Volume Clustering. Absorbed dose was determined for comparison with a recent benchmark intercomparison. Reported quantities are normalized to primary fluence, allowing to establish a connection to macroscopic dosimetric quantities.
Main results: The modification of the electron spectral fluence by the gold NP is minor and mainly occurs at low energies. The net fluence of electrons emitted from the NP is dominated by electrons resulting from photon interactions. Similar to the known dose enhancement, increased ionization clustering is
limited to a distance from the NP surface of up to 200 nm. The number of clusters per energy imparted is increased at distances of up to 150
nm, and accordingly the enhancement in clustering notably surpasses that of dose enhancement. Smaller NPs cause noticeable peaks in the conditional frequency of clusters between 50 nm to 100 nm from the NP surface.
Significance: This work shows that low energy electrons emitted by nanoparticles lead to an increase of ionization clustering in their vicinity exceeding that of energy imparted.
While the electron component of the radiation field plays an important role in determining the background contribution to ionization clustering and energy imparted, the dosimetric effects of nanoparticles are governed by the interplay of secondary electron production by photon interaction and their ability to leave the nanoparticle.
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摘要：
目的：这项工作探索了围绕金纳米颗粒（NP）的电离聚类及其径向依赖性的增强，指示DNA损伤的诱导，细胞死亡的潜在触发因素.＆＃xD;＆＃xD;方法：进行了蒙特卡洛轨道结构模拟，以确定（a）在带电粒子平衡条件下金NP周围水中的入射光子和电子的光谱注量，以及（b）平均产生的电离簇的密度以及使用关联体积聚类在纳米粒子中发生至少一个相互作用的条件。确定吸收剂量以与最近的基准相互比较进行比较。报告的数量被标准化为主要注量，允许建立与宏观剂量测定量的联系。＆＃xD;＆＃xD;主要结果：金NP对电子光谱注量的修改很小，主要发生在低能量下。从NP发射的电子的净通量由光子相互作用产生的电子主导。类似于已知的剂量增强，增加的电离成簇是
限于从NP表面的距离高达200nm。每个能量赋予的簇的数量在高达150
nm的距离处增加，因此，聚类的增强明显超过剂量增强。较小的NP会在距NP表面50nm至100nm之间的簇的条件频率中引起明显的峰值。＆＃xD;＆＃xD;意义：这项工作表明，纳米粒子发射的低能电子导致其附近的电离聚类增加，超过所赋予的能量。＆＃xD;虽然辐射场的电子成分在确定背景对电离成簇和赋予能量的贡献方面起着重要作用，纳米粒子的剂量效应受光子相互作用产生的二次电子的相互作用和它们离开纳米粒子的能力支配。
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