Department of Nuclear Engineering, School of Mechanical Engineering, Shiraz University, Shiraz, Iran.
Phys Med Biol. 2020 Apr 17;65(8):085002. doi: 10.1088/1361-6560/ab7a70.
High-Z nanoparticles (NP) as radio-sensitization agents provide the feasibility of dose localization within the tumor in radiotherapy. Dose enhancement of NPs in the presence of a magnetic field (MF) could be challenged when magnetic resonance imaging (MRI) systems are used as an image-guided system. The MF can influence dose enhancement of NPs at their interfaces and surrounding medium and affect their dose deposition behavior. In the TOPAS Monte Carlo code, gold nanoparticle (GNP) and superparamagnetic iron oxide nanoparticle (SPION) were irradiated using 70 and 150 MeV proton beams, in presence of transverse MF strengths with 0, 1, 3, and 7 T. The changes in the liberated secondary electrons from NPs and their dose enhancement ratio (DER), magnetic dose enhancement ratio (MDER), and angular dose distribution in 10 nm shell thicknesses up to 500 nanometers from their centers were measured. The central plane of NPs was considered as a scorer. Its thickness was 2 nm and divided into 6-degree sectors with 10 nm radial length. The dose deposition in this voxelated scorer was calculated. The values of the deposited doses around NPs decrease rapidly while the DERs resulted from the secondary electrons are increased. MDERs are changed within [Formula: see text] and [Formula: see text] for 20 and 50 nm radius NPs, respectively. The variation in the angular dose distribution around a singular NP was not considerable when different MF strengths were applied. The dose values in the voxelated central plane show very similar results for the same NPs types in the different MF strengths. The typically used MF in the MRI systems would not considerably affect the energy deposition behavior of the secondary electrons produced in the interaction of proton beam with NPs, at least in the near vicinity of NPs. The DERs of NPs in a water medium resulted from emerged secondary electrons, experience a low degree of perturbation in the presence of an MF. The results of this study show that the NPs as dose enhancement agents can also be used in an MF without pronounced modification in their efficacy.
高 Z 纳米颗粒 (NP) 作为放射增敏剂，为放射治疗中肿瘤内的剂量定位提供了可行性。当磁共振成像 (MRI) 系统用作图像引导系统时，磁场 (MF) 的存在可能会挑战 NP 的剂量增强。MF 可以影响 NP 在其界面和周围介质中的剂量增强，并影响它们的剂量沉积行为。在 TOPAS 蒙特卡罗代码中，使用 70 和 150 MeV 质子束辐照金纳米颗粒 (GNP) 和超顺磁性氧化铁纳米颗粒 (SPION)，同时存在 0、1、3 和 7 T 的横向 MF 强度。测量了从 NPs 释放的二次电子的变化及其剂量增强比 (DER)、磁剂量增强比 (MDER)，以及在距 NPs 中心 10nm 壳层厚度至 500nm 的角度剂量分布。将 NPs 的中心平面视为评分器。其厚度为 2nm，分为 6 度扇区，每个扇区的径向长度为 10nm。在这个分块评分器中计算了剂量沉积。在二次电子产生的 DER 增加的同时，NP 周围沉积剂量的值迅速下降。对于 20nm 和 50nm 半径的 NPs，MDER 在[公式：见正文]和[公式：见正文]范围内变化。当应用不同的 MF 强度时，单个 NP 周围的角度剂量分布变化不大。在不同的 MF 强度下，相同 NP 类型的分块中心平面中的剂量值显示出非常相似的结果。在 MRI 系统中通常使用的 MF 不会对质子束与 NPs 相互作用产生的二次电子的能量沉积行为产生显著影响，至少在 NP 的近邻区域是这样。在 MF 存在的情况下，水中 NP 产生的二次电子的 DER 经历了低程度的干扰。本研究结果表明，NP 作为剂量增强剂，在不显著改变其疗效的情况下，也可以在 MF 中使用。
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