Dose-Response Relationship of Neutrons and γ Rays to Leukemia Incidence among Atomic Bomb Survivors in Hiroshima and Nagasaki by Type of Leukemia, 1950-1971

Abstract

The incidence of leukemia during 1950-1971 in a fixed mortality sample of atomic bomb survirors in Hiroshima and Nagasaki [Japan] was analyzed as a function of neutron and .gamma.-kerma and marrow doses. Two dose-response models were tested for acute leukemia, chronic granulocytic leukemia and all types of leukemia, respectively. Each model postulates that the leukemia incidence depends on the sum of separate risks imposed by .gamma. and neutron doses. On model I the risk from both types of radiation is assumed directly proportional to the respective doses, while model II assumes that if the risk from neutrons is directly proportional to the dose, the risk from .gamma.-rays is proportional to dose-squared. The dose-response of the 2-types of leukemia differed by type of radiation. The response of acute leukemia was best explained by model II, while the response of chronic granulocytic leukemia depended almost linearly upon neutron dose alone, because the regression coefficients associated with .gamma.-radiation for models I and II were not significant. The relative biological effectiveness of neutrons in relation to .gamma. rays for incidence of acute leukemia was estimated to be approximately 30/(Dn)1/2 [95% confidence limits; 17/(Dn)1/2 .apprx. 54/(Dn)1/2] for kerma and 32/(Dn)1/2 [95% confidence limits; 18/(Dn)1/2 .apprx. 58/(Dn)1/2] for marrow dose (Dn = neutron dose). If acute and chronic granulocytic leukemias are considered together as all types of leukemia, model II apparently fits the data slightly better than model I, but neither model is statistically rejected by the data.