DELAYED RADIATION EFFECTS IN ATOMIC-BOMB SURVIVORS

Since 1948 the ABCC has been evaluating the health of survivors of the atomic bombs in Hiroshima and Nagasaki. In a study of about 70,000 children conceived after the explosion, six indicators of genetic damage failed to reveal an unequivocal effect of radiation. Furthermore, this group displayed no evidence of cytogenetic abnormality, in contrast to the increased frequency of complex chromosomal aberrations found among those exposed in utero or at any time during the entire life span. The effect was most pronounced among persons whose exposures occurred when they were 30 years of age or older. Although a wide variety of congenital malformations have been produced in experimental animals by irradiation of the pregnant mother, the only anomaly observed among the Japanese survivors to date has been small head circumference associated with mental retardation, the effect being proportionate to the radiation dose. The ABCC study leaves no doubt that whole-body irradiation in sufficient dose is leukemogenic in man. A similar effect following partial-body irradiation has been observed among British men given radiotherapy for ankylosing spondylitis. In both studies the effect was proportionate to the dose, the peak occurred about 6 years after first exposures, and the increase was in acute leukemias and chronic granulocytic leukemia, not in the chronic lymphocytic form of the disease. In the past few years, a high risk of leukemia has been associated with several human attributes and with radiation exposure. These circumstances have in common an unusual genetic feature, though not of a single type. In several studies conducted in the United States or Great Britain, very small doses of x-ray were reported to be equally oncogenic whether exposure occurred before conception or during intrauterine life; whether the neoplasm studied was leukemia or any other major cancer of childhood; and whether the study was based on interviews, which are subjective, or on hospital records, which are not. Among the features that argue against a causal relationship are the similarity of results despite the dissimilarity of subject matter and, with regard to radiation before the child's conception, the failure, in a prospective study by ABCC, to find an excess of leukemia in 22,400 children conceived after their parents had been heavily exposed to radiation from the atomic bomb. Increases in cancers other than leukemia have recently been reported among the Japanese survivors. Twice the normal frequency of lung cancer was found among persons exposed to doses of 90 rad or more, in a study handicapped by failure to demonstrate specificity with regard to histologie type, as in U.S. uranium miners. A report of an excess of breast cancer was based on 6 cases observed as compared with 1.53 expected among women who were exposed to doses of 90 rad or more. Certain biases, difficult or impossible to avoid, could produce this small excess. Thyroid cancer, on the other hand, does appear to have been induced by radiation, since a dose-response relationship was apparent and the results are consistent with those observed following therapeutic irradiation. Other effects attributable to radiation but relatively small in magnitude were an increase in general mortality, exclusive of death from leukemia, during the first 10 years after exposure; a statistically significant but biologically small retardation in growth and development; infrequent radiation cataracts, none of which greatly diminished visual acuity; and a polychromatic sheen on the posterior subcapsule of the lens of the eye, which caused no disability but was related to radiation dose.