Malignant neoplasms among atomic bomb survivors following radiation therapy.

A second follow-up survey for radiation therapy exposure among a fixed cohort of A-bomb survivors originally numbering 20 000 persons identified 55 more who had received radiation therapy, and 7 more therapy-associated malignancies. In the previous and present investigations, 12 postirradiation malignancies were identified among 190 cohort members (6%) who received radiation therapy. This investigation underscored the necessity for documenting exposures to ionizing radiation for medical reasons, especially exposures incurring relatively high doses, among persons at relatively high risk of developing neoplasms, such as A-bomb survivors, and in malignancy epidemiology to exclude bias in estimates of risk.