Casualties and radiation dosimetry of the atomic bombings on Hiroshima and Nagasaki

The 60th anniversary of the Hiroshima-Nagasaki atomic bombings was commemorated in August 2005. By the end of 1945, according to the reports from both city governments, 140,000 and 70,000 deaths had occurred among inhabitants in Hiroshima and Nagasaki, respectively. In order to investigate late effects of atomic bomb radiation on humans, 94,000 survivors were selected and registered as cohort members of an epidemiological study, LSS (Life Span Study). On the other hand, comprehensive efforts have been continued to estimate radiation dose to individual survivors. The latest version of the dosimetry system, DS02 (Dosimetry System 2002) was adopted in 2003. Radiation dose at 1 m above the ground in open field at 1 km from the hypocenter was estimated to be 4.5 and 8.7 Gy in Hiroshima and Nagasaki, respectively, while at 2 km it was 0.08 and 0.14 Gy. According to the recent LSS report for the period of 1950-2000, among 86,611 survivors to whom individual dose was estimated, there have been 47,685 deaths (55%), including 10,127 from solid cancer and 296 from leukemia. The statistical analysis of the recent LSS data supports a linear-quadratic dose-response model for solid cancer, while the previous analyses indicated a linear dose-response. A linear-quadratic model is suggested for leukemia.