Jabari Masoud, Rajabi Hossein, Dadashzadeh Simin
Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University.
Department of Pharmaceutics, School of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Nucl Med Commun. 2020 Feb;41(2):110-119. doi: 10.1097/MNM.0000000000001112.
As the main pathway for the clearance of radiopharmaceutical from the body, kidney is a dose-limiting organ in medical application of radionuclides. Because of its unique physiology, radioactivity is seen to concentrate on kidney nonuniformly. This nonuniformity can be considered in nephron microstructures. A microdosimetry model of kidney is necessary to include the nonuniform distribution in internal radiation dosimetry.
Implementing the microdosimetry model requires, first, a geometry phantom of nephrons. Stylized phantoms cannot distribute activities inside nephron compartments nonuniformly. A phantom of nephron was generated by a preliminary three-dimensional graphic model and was converted to a proper format of digital phantom. The phantom was fed to GATE Monte Carlo toolkits. Simulations were performed and S-values for five radionuclides (Tc-99m, In-111, Lu-177, Ac-225 and Bi-212) were calculated and compared with corresponding results published in the literature derived with a stylized phantom of nephron. Activity was distributed nonuniformly according to the kinetics of two mainly used diagnostic tracers (diethylenetriaminepetaacetate and ethylenedicysteine) and absorbed dose of nephron cells were calculated.
A good correlation was shown between the generated phantom microdosimetry model and stylized model and revealed the phantom can be used for future microdosimetry studies of kidney to evaluate radiobiological effects of internal radiation from various diagnostic and therapeutic radiopharmaceuticals. Absorbed dose of cells for nonuniform distribution showed that some cells in a nephron compartment receive higher dose than (more than two-fold) that of compartment average dose.
Average dose of nephron is not a reliable parameter for nephrotoxicity evaluation.
肾脏作为放射性药物从体内清除的主要途径，是放射性核素医学应用中的剂量限制器官。由于其独特的生理学特性，放射性在肾脏中呈非均匀分布。这种非均匀性可在肾单位微观结构中加以考虑。在内部辐射剂量学中纳入这种非均匀分布，需要一个肾脏的微剂量学模型。
要实现微剂量学模型，首先需要一个肾单位的几何模型。理想化模型无法在肾单位各部分内非均匀地分布放射性。通过初步的三维图形模型生成了一个肾单位模型，并将其转换为合适格式的数字模型。将该模型输入到GATE蒙特卡罗工具包中。进行了模拟，并计算了五种放射性核素（锝-99m、铟-111、镥-177、锕-225和铋-212）的S值，并与文献中使用理想化肾单位模型得出的相应结果进行了比较。根据两种主要使用的诊断示踪剂（二乙烯三胺五乙酸和乙二巯基半胱氨酸）的动力学非均匀地分布放射性，并计算了肾单位细胞的吸收剂量。
生成的模型微剂量学模型与理想化模型之间显示出良好的相关性，表明该模型可用于未来肾脏的微剂量学研究，以评估各种诊断和治疗放射性药物内部辐射的放射生物学效应。非均匀分布的细胞吸收剂量表明，肾单位某一部分中的一些细胞接受的剂量高于（超过两倍）该部分的平均剂量。
肾单位的平均剂量不是评估肾毒性的可靠参数。
