Ethical Issues Related to the Promotion of a "100 mSv Threshold Assumption" in Japan after the Fukushima Nuclear Accident in 2011: Background and Consequences. 
This article describes the debates in Japan regarding the 100 mSv threshold assumption and ethical issues related to it, and explores the background to distorted risk information and absence of risk communication in Japan.  Then we seek proper risk communication based on scientific evidence.  On March 11, 2011 an accident occurred at the Fukushima Daiichi Nuclear Power Plant due to the Great East Japan Earthquake.  Since then a number of misunderstandings have become common in Japan as a result of public statements by the Japanese and local governments that have no basis in medical science or are contradictory to medical science.  Consequently, not only the population of Fukushima Prefecture, but also others, have been subjected to unnecessary exposure to radiation, against the As Low As Reasonably Achievable (ALARA) principle.  The number of cases of thyroid cancer has increased by one or two orders of magnitude since the accident in Fukushima.  However, the population has hardly been given any correct information from the central and local governments, medical societies, and media.  The center of this problem is a statement on radiation-induced cancer (including thyroid cancer) made by the Japanese Government and Japanese medical academic societies indicating that "exposure of less than 100 mSv gives rise to no excess risk of cancer, and even if there is some resulting cancer it will be impossible to detect it" (this will be referred to as "the 100 mSv threshold assumption" from now onward).  They have been saying this since April 2011 and have made no effort to correct it.  Many Japanese began to notice this but correct information on radiation protection has reached only one part of the population.  Risk communication should be based on scientific evidence, and providing it as information for the public is a key element.  In Japan, governments and academic societies tried to communicate with the public without doing it.  Ethical problems after the accident in Fukushima can be understood from the consequences of the mistakes in both risk information and risk communication in Japan after 2011.