Improved dosimetry and risk assessment for plutonium-induced lung disease using a microdosimetric approach

The risk of developing radiation-induced lung cancer is currently estimated using models based on epidemiological data from populations exposed either to relatively uniform, low-LET radiation, or from uranium miners exposed to radon and its progeny. Because inhaled alpha-emitting radionuclides (e.g., Pu, Am) produce nonuniform, chronic irradiation of the parenchymal region of the lung, a better scientific basis is needed for assessing the risk of developing radiation-induced disease from these radionuclides. Scientists at FIB-1 and LRRI are using a unique resource at the FIB-1, i.e., a set of about 600 lung specimens fixed in 10% formalin, and obtained from a population of workers at the Mayak Production Association, many of whom inhaled significant quantities of Pu and other alpha-emitting radionuclides during their careers. The objectives of this research are to measure the microscopic distribution of Pu by quantitative autoradiography, to determine the spatial distribution of Pu in human lung tissue with respect to specific lung structures and to determine the effect of chronic tobacco-smoke exposure on the distribution of local Pu radiation dose. The approach to analyzing these lung samples is to utilize contemporary stereological sampling and analysis techniques together with quantitative alpha-particle autoradiography. Our initial results have validated the usefulness of these lung specimens for determining Pu particle distribution with respect to anatomic location, as well as identifying normal and diseased compartments in the lung. In brief, particles were most often found associated with parenchymal and nonparenchymal scars, with other particles in organized lymphoid tissue or the interstitium of the pulmonary parenchyma (respiratory bronchioles and alveolar region). Based on comparison of one lung from a smoker and one from a nonsmoker, there was an increased fraction of Pu particles associated with tissue scars in the smoker vs the nonsmoker, and this corresponded to the larger volume fraction of scars in the smoker. In both cases, the fraction of particles associated with conducting airways and lumens was small. These preliminary results support a hypothesis, which is based on data from experimental animal studies, that Pu particles are nonuniformly distributed in the lung, and mostly in the parenchymal regions. (author)