Department of Physics, Ryerson University, 350 Victoria St., Toronto, Ontario, M5B 2K3, Canada.
Physiol Meas. 2020 Aug 11;41(7):075014. doi: 10.1088/1361-6579/ab921f.
Lanthanum (La) retention in bone has been shown to occur in individuals who are orally administered lanthanum carbonate (LaC), a drug to treat hyperphosphatemia. The breakdown of LaC in the gastrointestinal tract into La and carbonate ions results in residual quantities of La being deposited in bone. We previously reported on a non-invasive x-ray fluorescence (XRF) system that was developed to quantify bone La concentrations and applied it to a series of excised cadaver tibiae. However, given interpatient variability in bone shape and size, differential signal attenuation that occurs in bone and tissue, patient movement and overlying tissue thickness at the measurement site, quantifying bone La concentrations during in vivo measurements in live subjects needs to be investigated further along with the radiation dose associated with the measurement.
Coherent normalization was investigated as a function of overlying tissue thickness, source-subject distance and bone radius through Monte Carlo simulation and experimental work. This was accomplished by observing the ratio of the net La K x-ray peak area to the coherently scattered peak area at 59.5 keV. In addition, the dose delivered during a 2000 s measurement was determined using radiochromic film.
The coherent normalization of the La x-ray signal was shown to be independent of overlying tissue thickness, source-subject movement and bone radius, which indicates that this normalization procedure can correct for these factors. The equivalent skin dose and effective dose were 18.0 mSv and 3.2 μSv, respectively for a five-year-old.
While coherent normalization for the bone lead (Pb) and bone gadolinium (Gd) systems has been shown to be successful, we also report that this normalization procedure can correct for these interpatient variabilities in the in vivo Am-La K XRF system.
已证明口服碳酸镧（LaC）治疗高磷血症的个体中会发生镧（La）在骨骼中的蓄积。LaC 在胃肠道中分解为 La 和碳酸根离子，导致残留的 La 沉积在骨骼中。我们之前报道了一种非侵入性的 X 射线荧光（XRF）系统，该系统旨在定量骨骼中的 La 浓度，并将其应用于一系列切除的尸体胫骨。然而，鉴于患者之间骨骼形状和大小的差异、骨骼和组织中发生的差异信号衰减、患者在测量部位的运动和覆盖组织的厚度，需要进一步研究活体患者体内测量时定量骨骼 La 浓度的方法，以及与测量相关的辐射剂量。
通过蒙特卡罗模拟和实验工作研究了相干归一化与覆盖组织厚度、源-受试者距离和骨骼半径的关系。这是通过观察 59.5keV 处净 La K X 射线峰面积与相干散射峰面积的比值来实现的。此外，使用光致变色胶片确定了在 2000 秒测量期间传递的剂量。
证明 La X 射线信号的相干归一化与覆盖组织厚度、源-受试者运动和骨骼半径无关，这表明该归一化程序可以纠正这些因素。对于一个五岁的孩子，等效皮肤剂量和有效剂量分别为 18.0mSv 和 3.2μSv。
虽然已经证明骨骼铅（Pb）和骨骼钆（Gd）系统的相干归一化是成功的，但我们还报告说，这种归一化程序也可以纠正活体 Am-La K XRF 系统中这些患者间的变异性。
