Acute and late effects of A-bomb radiation studied in a group of young girls with a defined condition at the time of bombing.

Ninety girl students have been identified, who were 14-15 years old when exposed to the atomic bomb while at the Central Telephone Office in Hiroshima located at a distance of 550 meters from the hypocenter. The mortality rate of the students exposed on the second floor of the building was estimated to be 50.9% and those exposed on the first floor (ground level) 33.3%. Doses to the students exposed on the second floor were estimated from cytogenetic evidence to be around 6 Gy in the T65 Dose system or appear to be 4 Gy in the DS86 system. These data indicate that LD50 is around 4 Gy in these young females. Among 28 students who were confirmed to be alive in 1965 and followed to the end of 1988, six students had breast cancer, mostly of invasive ductal type carcinoma. The incidence of breast cancer in the adolescent group was very high, the relative risk being 23.1 with 95% confidence limits of 12.9 to 42.2.