Dr. Tsubokura's Radiation Lecture Vol.146

Author: Masaharu Tsubokura M.D., PhD.

Editors: Akihiko Ozaki M.D.,PhD., Yuki Senoo MUDr.

291. The health risks of low-dose radiation is very small

　Although it is difficult to completely prove/disprove the health effects of low-dose radiation, an effective radiation control measure cannot be constructed based on vague standards. For this reason, radiation control measures are determined based on the hypothesis that the known health effects of high-dose radiation will occur in proportion to the level of radiation when receiving low doses of 100 millisieverts or less radiation exposure.

　Numerous researches have been conducted to assess potential association between radiation and health effects in different countries. There is a range of research with different study subjects: residents of high background natural radiation areas, those exposed to radioactive materials from nuclear tests, workers at nuclear facilities, and healthcare workers occupationally exposed to radiation for treatment and diagnosis.

　Of these researches, the reports on the atomic bombing survivors of Hiroshima and Nagasaki are internationally recognized as the most accurate. This is because the Hiroshima and Nagasaki studies have been continuously conducted to date after World War II, providing details on the level of radiation exposure and exposure time of a large number of participants. In contrast, most other surveys have limitations, such as a lack of details on each individual’s radiation exposure dose or having too short of a follow-up period.

　Our current knowledge of low-dose radiation exposure is based on the sacrifices and cooperation of many people that radiation exposure has affected. It is still unknown whether low-dose radiation exposure has any health effects, but this also means that the effect is minimal, if there is any.

292. The longer the exposure time, the smaller the health effect

　　　　Recently, radiation control measures have been determined based on the hypothesis that the known health effects of high-dose radiation will occur in proportion to the level of radiation when receiving low doses of 100 millisieverts or less radiation exposure.

　However, the impacts of radiation exposure on our bodies are different between receiving a large exposure dose at once and incrementally over time.

　For the same level of radiation exposure, the health impact is smaller when a person is exposed little by little over time. This is because cells in our body can heal or remove cells that incurred damages from radiation exposure and replace them with new cells. The previous studies confirmed that the health impact of gamma rays and X-rays, which are closely related in our lives compared to neutrons, become less pronounced when exposed over a long period of time.

　The circumstances in the atomic bombing of Hiroshima and Nagasaki, where people were exposed to high-dose radiation all at once in a short time, is different from that of the 2011 Fukushima Daiichi nuclear power plant accident, where the contamination effects have persisted for a long time. Based on the various study results, the current prevailing view is to control radiation by assuming that, for the same exposure dose, the health effects of radiation exposure over a long time becomes half of that in a short time.

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The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, 16th and 23rd, August, 2020 was reproduced for MRIC Global under the author's permission.