Thyroid carcinoma after exposure to the atomic radiation of Hiroshima, 1958-1979

Clinical thyroid carcinoma occurred in 125 (15 males and 110 females) of 75,493 subjects on the list of the life span study extended sample of the Radiation Effects Research Foundation. The crude annual incidence rate in a population of 100,000 was 2.7 for the males and 12.4 for the females, and the risk increased with increasing dosage for both sexes. This tendency was remarkable among young women. In view of the ratio of expected to observed numbers (O/E), the incidence increased with increasing dosage for the two sexes both separately and collectively. Test of linearity revealed dose effects among the females and in the sum of both groups. The younger a subject, the more definite was the dose effect. The relative risk of the group exposed to more than 50 rad against the control group was 4.2. According to the age group, the risk of the group aged below 20 yrs. was as high as 7.9 with statistical significance. Occult carcinoma was found in 155 of the 4,425 autopsied cases in the same period. The relative risk of the group exposed to more than 50 rad was significantly high, 1.9, and the O/E ratio was significant only for the females. (Chiba, N.)