Electron emission spectra from gold-nanoparticles for dose estimation in radiation therapy

用于放射治疗剂量估计的金纳米颗粒电子发射光谱

基本信息

项目摘要

Radiotherapy is one of the most common modalities for cancer treatment. As the radiation passes through cells and tissues, it deposits energy and forms ions which can result in cancer cell death. Such cytotoxic effects are initiated by the primary particle and even more by secondary electrons. Because ionizing processes are not cell specific and damage tumor and healthy cells alike, a deposition of radiation absorbing elements into the tumor can sensitize it to radiation, which effectively reduces the dose to healthy tissue. Studies have shown that the use of gold nanoparticles can produce a dose enhancement for irradiation with X-rays [1] and proton beams [2]. Due to the steep dose gradient in the vicinity of nanoparticles, conventional macroscopic dosimetry is insufficient for the characterization of dose distribution. Monte Carlo track structure simulations are therefore required to account for localized nanoscopic interactions of secondary electrons [3]. These simulations are currently based in simplified theoretical scattering models, which are no longer valid for energies below a few keV resulting in extrapolations with large uncertainties. In the case of water (often used as a substitute for biological matter), these models could be adjusted to experimental data so that the simulation is valid for microscopic applications [4]. For gold, however, the required atomic scattering cross sections cannot be obtained experimentally, but experimental electron spectra from gold nanoparticles can be used to benchmark the simulated data, and thus, reduce the uncertainty of subsequent dose calculations.Measured electron spectra from gold nanoparticles were recently reported for low keV energies, where the agreement with Geant4 MC simulation was poor [5]. To account for the localized dose-enhancement at therapeutic X-ray energies, it is crucial to investigate electron emission at photon energies sufficient to trigger a large Auger cascade with many low-energy secondary electrons. The energy loss and self-absorption of electrons within the gold nanoparticle should also be determined, in terms of the particle size.The resent proposal aims to measure energy spectra of electrons emitted from gold nanoparticles of different size for X-rays and proton beam irradiation. The proposed X-ray energies are above the gold L-edge (12 keV) and produced by a synchrotron and clinical X-ray sources. The proposed proton energy is 100 keV, which is within the Bragg-peak. The project will obtain important fundamental data to estimate the dose distribution and dose enhancement by gold nanoparticle and thereby promote the translation of such radiosensitizers into clinical applications.[1] J.F. Hainfeld et al., J. Pharm., 60, 977-85 (2008).[2] J.C. Polf et al., Appl. Phys. Lett., 98, 3-5 (2011).[3] H.N. McQuaid et al., Sci. Rep., 6, 19442 (2016).[4] S. Incerti et al., Med. Phys., 37, 4692-4708 (2010).[5] R. Casta et al., Phys. Med. Biol., 60, 9095-9105 (2015).
放射治疗是最常见的癌症治疗方式之一。当辐射穿过细胞和组织时,它会沉积能量并形成离子,从而导致癌细胞死亡。这种细胞毒性作用是由初级粒子引起的,甚至更多是由次级电子引起的。由于电离过程不是细胞特异性的,对肿瘤和健康细胞的损伤是一样的,因此在肿瘤中沉积辐射吸收元素可以使肿瘤对辐射敏感,从而有效地减少对健康组织的剂量。研究表明,使用金纳米粒子可以在x射线[1]和质子束[2]照射下产生剂量增强。由于纳米颗粒附近的剂量梯度较大,常规的宏观剂量法不足以表征剂量分布。因此,需要蒙特卡罗轨道结构模拟来解释次级电子[3]的局部纳米级相互作用。这些模拟目前基于简化的理论散射模型,这些模型不再适用于低于几个keV的能量,导致外推具有很大的不确定性。在水(通常用作生物物质的替代品)的情况下,这些模型可以根据实验数据进行调整,从而使模拟适用于微观应用[10]。然而,对于金,所需的原子散射截面不能通过实验获得,但金纳米粒子的实验电子能谱可以用来作为模拟数据的基准,从而减少后续剂量计算的不确定性。最近报道了低keV能量的金纳米粒子的电子能谱测量结果,与Geant4 MC模拟结果的一致性很差。为了解释治疗x射线能量下的局部剂量增强,研究足以触发具有许多低能次级电子的大俄歇级联的光子能量下的电子发射是至关重要的。根据颗粒大小,还应确定金纳米颗粒内的能量损失和电子的自吸收。该提案旨在测量不同尺寸的金纳米粒子在x射线和质子束照射下发射的电子能谱。所提出的x射线能量高于金l边(12 keV),由同步加速器和临床x射线源产生。所得质子能量为100 keV,在布拉格峰内。该项目将获得重要的基础数据,以估计金纳米颗粒的剂量分布和剂量增强,从而促进这些放射增敏剂向临床应用的转化J. f . Hainfeld等人,J. Pharm。[j] .生物医学工程学报,2008,33 (5):577 - 585J.C.波尔夫等人,苹果公司。理论物理。列托人。[j] .中国农业科学,1998,3 -5 (2011).H.N. McQuaid等,Sci。Rep. 6, 199442 (2016).[4]S. Incerti et al.,医学,物理学。[j] .中国农业科学,2011,31 (4):481 - 481R. Casta等人,物理学。地中海,杂志。中文信息学报,60,9095-9105(2015)。

项目成果

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Dr. Hans Rabus, since 4/2020其他文献

Dr. Hans Rabus, since 4/2020的其他文献

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