Comments
Thyroid cancer was strongly associated with exposure to ionizing radiation in Japanese A-bomb survivors, patients treated with radiation to the head and neck (tinea capitis, thymus, and hemangiomas); and children exposed to Chernobyl fallout. Negative associations have been found in studies of nuclear workers, uranium processors, Chernobyl cleanup workers, and populations exposed to background radiation. A negative association means that "no significant association found, although study was reasonably powerful." [Boice, p. 261] According to the "Thyroid Cancer" chapter in Cancer Epidemiology and Prevention, 3rd Edition, "Although the studies employed different methodologies and included populations from many countries exposed to a broad range of doses, all have demonstrated significantly increased risks of thyroid carcinomas following radiation exposure during childhood. In contrast, exposure during adulthood, to either external radiation or internal 131I, has not been linked convincingly to thyroid cancer." [Schottenfeld, p. 983] Thyroid cancer was not included in the list of SHE(O)s published by NIOSH in 1992. [Mullan RJ, Murthy LI. Occupational Sentinel Health Events: An Up-Dated List for Physician Recognition and Public Health Surveillance. Am J Ind Med 1991;19:775-799.] "The most studied (19 of 30 studies) and the most consistent associations were observed for radiation-exposed workers and health care occupations. . . . However, in the largest study, a registry-based retrospective occupational cohort of 15 million people in five Nordic Countries, Pukkala et al. did not observe an increase in thyroid cancer risk for any health care occupations." [See Hyperlink]