Global Dosimetry Ltd., 1 Macdonald Close, Didcot, Oxon OX11 7BH, United Kingdom.
Posthumous.
Health Phys. 2019 Aug;117(2):133-142. doi: 10.1097/HP.0000000000000827.
Epidemiological studies have shown that the main risk arising from exposure to plutonium aerosols is lung cancer, with other detrimental effects in the bone and liver. A realistic assessment of these risks, in turn, depends on the accuracy of the dosimetric models used to calculate doses in such studies. A state-of-the-art biokinetic model for plutonium, based on the current International Commission on Radiological Protection biokinetic model, has been developed for this purpose in an epidemiological study involving the plutonium exposure of Mayak workers in Ozersk, Russia. One important consequence of this model is that the lung dose is extremely sensitive to the fraction (fb) of plutonium, which becomes bound to lung tissue after it dissolves. It has been shown that if just 1% of the material becomes bound in the bronchial region, this will double the lung dose. Furthermore, fb is very difficult to quantify from experimental measurements. This paper summarizes the work carried out thus far to quantify fb. Bayesian techniques have been used to analyze data from different sources, including both humans and dogs, and the results suggest a small, but nonzero, fraction of < 1%. A Bayesian analysis of 20 Mayak workers exposed to plutonium nitrate suggests an fb between 0 and 0.3%. Based on this work, the International Commission on Radiological Protection is currently considering the adoption of a value of 0.2% for the default bound fraction for all actinides in its forthcoming recommendations on internal dosimetry. In an attempt to corroborate these findings, further experimental work has been carried out by the US Transuranium and Uranium Registries. This work has involved direct measurements of plutonium in the respiratory tract tissues of workers who have been exposed to soluble plutonium nitrate. Without binding, one would not expect to see any activity remaining in the lungs at long times after exposure since it would have been cleared by the natural process of mucociliary clearance. Further supportive study of workers exposed to plutonium oxide is planned. This paper ascertains the extent to which these results corroborate previous inferences concerning the bound fraction.
流行病学研究表明，接触钚气溶胶的主要风险是肺癌，此外还会对骨骼和肝脏造成其他有害影响。而要准确评估这些风险，又取决于在这些研究中用于计算剂量的剂量学模型的准确性。为此，在一项涉及俄罗斯奥泽尔斯克（Ozersk）马雅克（Mayak）工作人员钚暴露情况的流行病学研究中，基于现行国际辐射防护委员会（ICRP）生物动力学模型，开发了一种钚的最先进生物动力学模型。该模型的一个重要结论是，肺部剂量对钚溶解后与肺部组织结合的分数（fb）极其敏感。如果只有 1%的物质结合在支气管区域，肺部剂量就会翻倍。此外，fb 很难通过实验测量来定量。本文总结了迄今为止为定量 fb 所开展的工作。贝叶斯技术已被用于分析来自不同来源的数据，包括人类和狗的数据，结果表明 fb 很小，但不为零，<1%。对 20 名接触过钚硝酸盐的马雅克工作人员进行的贝叶斯分析表明，fb 在 0 到 0.3%之间。基于这项工作，国际辐射防护委员会目前正在考虑在即将发布的内部剂量学建议中，为所有锕系元素的默认结合分数采用 0.2%的值。为了验证这些发现，美国超铀元素和铀登记处开展了进一步的实验工作。这项工作涉及对已接触可溶性钚硝酸盐的工作人员呼吸道组织中的钚进行直接测量。如果没有结合，人们不会期望在暴露后很长时间内肺部仍残留任何活性物质，因为它会通过黏液纤毛清除的自然过程被清除。计划进一步研究接触钚氧化物的工作人员。本文证实了这些结果在多大程度上证实了先前关于结合分数的推断。
