Technical Report No. 11-92
Radiation cataracts among Hiroshima atomic-bomb survivors, 1949-64
Schull WJ, Otake M, Funamoto SSummary
This report reexamines the quantitative relationship of exposure to ionizing radiation to the occurrence of cataracts (posterior lenticular opacities) seen in the years 1949-64 among 2249 Hiroshima atomic-bomb survivors with known Dosimetry System 1986 (DS86) doses. Among several dose-response relationships with or without two thresholds, the best fit based on binomial odds-regression models is achieved with a linear-linear dose-response relationship that assumes different thresholds for the two types of radiation. The neutron and gamma-ray regression coefficients, 199 Gy (90% CI: 28-473 Gy) and 5.14 Gy (95% CI: 1.38-14.77 Gy), based on this model, are suggestively higher for the neutron dose, and significantly higher for the gamma-ray dose than previously reported. The estimates of the two thresholds also differ significantly from zero: 0.06 Gy with 95% lower and upper bounds of 0.03 and 0.10 Gy for the neutron dose and 1.08 Gy with 95% bounds of 0.51 and 1.45 Gy for the gamma-ray dose. The safety zone for radiation-induced cataracts is estimated to be a 1.75-Sv threshold with 95% lower and upper bounds of 1.31 and 2.21 Sv using DS86 eye-organ-dose equivalents, assuming a neutron relative biological effectiveness of 18, derived from the ratio of the two thresholds, that is, 1.08 Gy for gamma rays and 0.06 Gy for the neutrons.
This report reexamines the quantitative relationship of exposure to ionizing radiation to the occurrence of cataracts (posterior lenticular opacities) seen in the years 1949-64 among 2249 Hiroshima atomic-bomb survivors with known Dosimetry System 1986 (DS86) doses. Among several dose-response relationships with or without two thresholds, the best fit based on binomial odds-regression models is achieved with a linear-linear dose-response relationship that assumes different thresholds for the two types of radiation. The neutron and gamma-ray regression coefficients, 199 Gy (90% CI: 28-473 Gy) and 5.14 Gy (95% CI: 1.38-14.77 Gy), based on this model, are suggestively higher for the neutron dose, and significantly higher for the gamma-ray dose than previously reported. The estimates of the two thresholds also differ significantly from zero: 0.06 Gy with 95% lower and upper bounds of 0.03 and 0.10 Gy for the neutron dose and 1.08 Gy with 95% bounds of 0.51 and 1.45 Gy for the gamma-ray dose. The safety zone for radiation-induced cataracts is estimated to be a 1.75-Sv threshold with 95% lower and upper bounds of 1.31 and 2.21 Sv using DS86 eye-organ-dose equivalents, assuming a neutron relative biological effectiveness of 18, derived from the ratio of the two thresholds, that is, 1.08 Gy for gamma rays and 0.06 Gy for the neutrons.