Radiation and clinical medicine of thyroid cancer

Described are the comparison of Accidents of Chernobyl and Fukushima (CA in 1986 and FA in 2011, respectively), effect of radiation on thyroid (Th), clinical feature and therapy of Th cancer, based on author's experience of lasting (from 1999) Chernobyl and daily clinical practices. Radioiodine, once incorporated in Th, is converted to organic Th hormones, stored in the cell, and gives the radiation damage to DNA leading to cancer formation. In Belarus near Chernobyl, well known are 3- and 72.5-fold increases of incidence of Th cancer in adults and children, respectively, after CA. Th cancer is observed in as many as 770 cases (52.5%) of the age 0-6 y in total 1,467 patients of 0-19 y at CA. The prevalence of pediatric Th cancer begins to increase 4 years after CA, reaches a peak in 1995 and then declines while adult prevalence is elevating still at 2004. In general, most of the pediatric cancer including radiation-induced one are more advanced than that in adult at the first diagnosis, but surgical treatment similar to the method for sporadic papillary carcinoma results in good prognosis. Authors' low invasive video-assisted neck surgery (VANS) of endoscopic thyroidectomy can be applicable to the <1 cm small cancer, after which recurrence has been scarcely seen. FA differs from CA in the scale of the accident (1/6-10 of CA), in the nature (critical explosion in CA vs radioactive contamination), and in iodine environment (CA/ FA, in poor/rich iodine region, respectively). The effect of radioiodine on Th may be smaller in FA than CA possibly due to the third factor. Means are taken as the Prefectural Health Management Survey for all prefectural residents, and as the periodical ultrasonic test of Th for 360 thousands residents of age <18 y at FA to be continued for their whole lifetime. (T.T.)