Some aspects of the Fukushima Daiichi nuclear accident

Average whole-body doses after the Fukushima accident remained within the limits of natural radiation background. Thyroid doses were much lower than after the Chernobyl accident. Associations between detection rate of thyroid cancer (TC) and radiation doses after the Fukushima accident were reported, although there have been contradicting data. There are various factors and bias that can contribute to the associations: screening effect, recall bias, dose-dependent quality of diagnostics, selection, and self-selection. There have been methodological differences of the screening in different areas. In the screened young-age group, TCs were found predominantly in adolescents, but not in vulnerable children ≤5 years at exposure, suggesting that tumors are not radiogenic. A possibility of overdiagnosis was pointed out, i.e., detection of thyroid tumors that would not, if left untreated, result in symptoms. Furthermore, exaggeration of perinatal complications may cause anxiety and lead to interruption of wanted pregnancies, as it happened after the Chernobyl accident. In conclusion, no discernible increase of radiation-related health effects is expected after the Fukushima accident. There are no reasons to disagree with the judgment by the UNSCEAR that an increased risk of thyroid tumors among most exposed children could be theoretically inferred, although occurrence of large numbers of radiation-induced cases can be discounted. The monitoring of populations exposed to low-dose radiation is important, but will hardly add much reliable information. It can be expected that the screening and increased attention of exposed people to their health would result in more reports on elevated risks that would prove no causality.