3.11(Fukushima) and Hiroshima

Gray area: Effects of exposure to low-level radiation, Part 5 [4]

Search by scientists: New direction for risk assessment

by Jumpei Fujimura, Staff Writer

In early June, researchers from the Japan Health Physics Society (JHPS) gathered in a meeting room in Otemachi, Tokyo. It was the first meeting of a special team charged with studying low-dose exposure to radiation and methods to evaluate the risk of that exposure. The team of researchers is aiming to develop, within the next two years, a new method for assessing risk that can replace the linear non-threshold (LNT) model, currently used for radiation protection guidelines.

The LNT model assumes that even very small amounts of radiation exposure are harmful in proportion to their dose. Kazuo Sakai, a professor of radiation biology at Tokyo Healthcare University and the leader of the team, views the LNT model in favorable terms, saying it serves as a convenient tool for protection. But with regard to the actual effects of low-dose radiation, he feels differently, contending that very small doses do not increase the risk to human health because living creatures contain their own defense mechanisms.

Combination of two fields

In the course of their research, the team will first analyze study trends and theses in epidemiology and biology which are considered specialized fields that hold the key to the solution they seek. Next, they will investigate problems that must be tackled for further development in the future. After that, they will start preparing a process sheet for establishing a methodology to estimate radiation risk based on the study and knowledge of the fields of epidemiology and biology.

Although the need to combine the fields of epidemiology and biology has been discussed for the past 20 years, there have been no concrete results thus far. Offering a metaphor to explain why, Mr. Sakai said, “As the fog gradually cleared, researchers found that the mountain appearing in front of them was unexpectedly high.” This is because epidemiology puts priority on subject groups and teases out trends from the dispersion of values, while biology investigates individual differences to understand phenomena.

How, then, will the researchers overcome the hurdles in front of them? Mr. Sakai recognizes the potential of access to greater data in the act of combining these two fields. He now sees a way of determining appropriate radiation dose limits for individuals by entering such data as age, gender, lifestyle habits, and diet. “Although we can’t ensure safety based on radiation dose limits, they can serve as the basis for judgments in situations where the health effects of radiation must be taken seriously,” he said.

Cooperation among radiation-affected areas

As a result of the earthquake and tsunami that hit Fukushima in 2o11, a new trend of cooperation has developed involving research organizations in the A-bombed cities and the areas affected by radiation exposure from the nuclear accident. As part of this trend, the Research Institute for Radiation Biology and Medicine (RiRBM) of Hiroshima University, Nagasaki University’s Atomic Bomb Disease Institute, and Fukushima Medical University’s Fukushima Global Medical Science Center began working together in fiscal year 2016 as a joint research center designated by the Ministry of Education, Culture, Sports, Science and Technology (MEXT). Their research so far includes 10 subjects, including an investigation into the effects of low-dose radiation.

This research will continue for six years, until fiscal year 2021. RiRBM was already designated an independent research center studying the effects of low-dose radiation by the education ministry in fiscal 2010, so as a result of the new designation, it will be working on this research effort for nearly 12 years. Shinya Matsuura, the president of RiRBM, said that the organization has mainly been engaged in basic research involving mechanisms and that their research results have generally remained in the laboratory, but the collaboration with the other groups will change such practices in the future.

By July 2016, RiRBM had selected about 230 research projects from among those collected from the public at home and abroad, and is now set to start their full-scale investigations. Nagasaki University is experienced at field work, while Fukushima Medical University has supported the reconstruction work in the radiation-affected areas of the Tohoku region. Cooperation among these institutes is expected to generate strong synergy. Mr. Matsuura said with enthusiasm, “The effects of low-dose radiation are a topic that scientists are deeply interested in. I hope we can get to the heart of this issue, to the degree possible.”

(Originally published on July 29, 2016)