Pathological observation of the effects of exposure to radioactive microparticles on experimental animals

Internal radiation exposure from neutron-induced radioisotopes that were environmentally activated following an atomic bombing or nuclear accident should be considered for a complete picture of the pathologic effects on survivors. Inhaled hot particles expose neighboring tissues to very high doses of particle beams, which can cause local tissue damage. Experimentally, a few μm of ⁵⁵MnO₂ powder was irradiated with neutrons at a nuclear reactor in order to generate ⁵⁶MnO₂ that emits β-rays. Rats were irradiated via inhalation. Pathological changes in various rat tissues were examined. In addition, the ⁵⁶Mn β energy spectrum around the particles was calculated to determine the local dose rate and the cumulative dose. This review focuses on our latest pathological findings in lungs with internal radiation injury and discusses the pathological changes of early event damage caused by localized, very high-dose internal radiation exposure, including apoptosis, elastin stigma, emphysema, hemorrhage and severe inflammation. The pathological findings of lung tissue due to internal radiation exposure of 0.1 Gy were severe, with no pathological changes observed due to external exposure to γ radiation at a dose of 2.0 Gy. Therefore, it is suggested that new pathological analysis methods for internal exposure due to radioactive microparticles are required.