ConarD Effects of Ionizing Radiations 488 Table I. Thyroid lesions in Marshallese exposed to fallout Island group (radiation dose-gamma) Age at exposure Rongelap <10 >10 all 160? - Rongelap 69 rads Utirik 175 rads 14 rads Rongelap unexposed Estimates Thyroid dose rads, Thyroid lesions percent* 500-1400 89.5 (17/19) 5.3 (1/19) <10 >10 all 275-550 55 - 0.0 (0/6) 12.5 (1/8) 7.1 (1/14) - <10 55-100 0.0 (0/40) - radioiodines* >10 14 8.8 (3/34) 39.6 (21/53) 5.1 (3/59) | Malignant lesions percent* 5.9 (2/34) 5.7 (3/53) 1,7 (1/59) all - 3.0 (3/99) 1.0 (1/99) <10 >10 all - 0.0 (0/61) 2.3 (3/133) 1.5 (3/194 - 1 Dose from 194) 22, 133, 1357, 2 Based on number nowliving. 3 Children 10-20 years of age at exposure received doses between 160 and 500 rads. 40-year-old woman (in 1965) and 2 recent cases (in 1969), 1 in a 36-year-old womanand the other in a 21-year-old female?. The ages at exposure were 29, 21 and 7 years. The latter caseis the first noted in the group of 19 children exposedat less than 10 years of age. Table I summarizes findings in the various populations. At surgery the thyroid showed multiple discrete nodules a few millime- ters to several centimeters in diameter, soft to firm in consistency, and some showed hemorrhagic and cystic changes. Microscopic examination revealed that the benign nodules had marked variation in size of follicles and evidence of radiation damage could be detected in many cells. The malignant lesions were present as One or more firm tumors(see fig. 1) and microscopically var- ied in structure from papillary to mixed papillary andfollicular. All showed capsular invasion. In 2 cases there was localized lymph node metastasis and in 2, localized blood vessel metastasis was seen. 2 One additional thyroid cancer was found in a woman from Utirik Island and in view of the low thyroid dose received by these Islanders (about 30 rads) it is less likely that this case was radiation-induced. 30612530