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Medical management of heavily exposed victims: an experience at the Tokaimura criticality accident

A criticality accident occurred at the uranium conversion plant in Tokaimura, Ibaraki Prefecture, Japan on 30 September 1999. When uranyl nitrate was overloaded to a critical mass level, uncontrolled fission reaction occurred. A procedure was carried out according to the JCO manual, although not an officially approved manual. Three workers were heavily exposed to neutrons and γ-rays produced by nuclear fission, and they subsequently developed acute radiation syndrome (ARS). The average doses to the whole body of the three workers were approximately 25, 9, and 3 GyEq (biologically equivalent dose of γ-exposure), respectively; dose distribution analysis later revealed extreme heterogeneity of these doses in two workers. They were triaged according to the predicted clinical needs. Two of these workers developed severe bone marrow failure and received haematopoietic stem cell transplantation: one with peripheral stem cell transplantation from his Human Leukocyte Antigen compatible sister and the other with umbilical cord blood transplantation. The graft was initially successful in both workers; autologous haematopoietic recovery was observed after donor/recipient mixed chimerism in one of them. Despite of all medical efforts available including haematopoietic stem cell transplantation, investigational drugs, skin graft, two workers died of multiple organ involvement and failure 83 and 211 days after the accident, respectively. Clinically as well as pathologically, the direct cause of death was deemed to be intractable gastrointestinal (GI) bleeding in one, and thoraco-abdominal compartment syndrome due to dermal fibrosis/sclerosis in the other. The third worker also developed bone marrow suppression but was treated with granulocyte colony-stimulating factor. He recovered without major complications and is now under periodical medical follow-up. These experiences suggest that treatment of bone marrow is not a limiting factor for saving the life of ARS victims severely exposed. Successful treatment of other organs such as lungs, skin, and GI tract is also essential. Furthermore, the whole-body dose may not always reflect the prognosis of ARS victims because of the nature of accidental exposure, heterogenous exposure.