- This data was created based on the "Readings of Accumulated Dose by The Federation of Electric Power Companies of Japan (Member Companies)" released to the public in the Monitoring Information of Environmental Radioactivity Level portal site by the Secretariat of the Nuclear Regulation Authority.
- The accumulated dose measurements were conducted every week from March 2011 at the fixed observation points outside the 20 km zone of Fukushima Dai-ichi NPP. From April 2016, measurements were conducted every three months.