Report on the recently-updated study of cancer mortality in the A-bomb survivors: insights for radiation protection

The Radiation Effects Research Foundation (RERF) in Hiroshima has recently released an updated study of cancer mortality in the Life Span Study (LSS) cohort of survivors of the atomic bombings at Hiroshima and Nagasaki. (The LSS is believed to contain about one-half of the total number of survivors who were within 2.5 km of the hypocentre.) The update has considerably more statistical power than previous studies because of five more years of follow-up(1986-1990 inclusive) and because of adding 10.536 survivors for whom DS86 dose estimates recently became available. Together these add about 550.000 person-years of follow-up compared to the previous report, which covered mortality to the end of 1985. Moreover, about 25% of the excess solid cancer deaths have occurred in these last five years of follow-up. Since the LSS is the most important source of information about the risk of induced cancer in humans following acute radiation exposures, this paper first summarizes this important new information. This is a keystone of radiation risk assessment and therefore of our radiation protection history; one cannot make sense of the current controversy concerning linearity without understanding what this data says and doesn't say. This communication then moves into a discussion of what implications there may be from this updated information, in the context of current debates about whether the linear-no threshold model is an appropriate one for radiation protection use. (DM)