Planning and Acting Network for Low Dose Radiation Research (PLANET)

The mission of the Institute for Radiological Science (NIRS), a division of the National Institutes for Quantum Science and Technology (QST), includes radiation effects research, radiation protection research, and radiation emergency medicine in response to nuclear disasters and other situations. In radiation effects research, an important issue is to reduce the uncertainty in risk estimation, especially for low-dose and low-dose-rate radiation exposure.

To steadily and continuously conduct research for this issue, it is necessary to establish an all-Japan network of academia and research institutions that facilitates collaboration among relevant parties, including regulatory authorities. NIRS established a Preparatory Committee on such a network in 2016, and the Preparatory Committee compiled a report (here) on the network. The network is named the Planning and Acting Network for Low Dose Radiation Research (PLANET). PLANET prioritizes research needs taking into account the potential of Japan and proposes strategies to improve the estimation of low-dose and low-dose-rate radiation risks. PLANET also proposes a support system for cooperation and collaboration with relevant researchers and research institutions in Japan and aims to promote collaboration with international organizations.

The PLANET Steering Committee was established in 2017 and is considering specific research tasks with the aim of advancing the five priority issues identified by the Preparatory Committee. The tasks include epidemiological studies of the health effects of low-dose and low-dose-rate radiation, elucidation of biological mechanisms, bridging animal experiments and epidemiology, modifying effects of age, sex, genetic predisposition, and lifestyle, and archiving of data. The Steering Committee established the Working Group on Dose-Rate Effects of Animal Experiments (WG1) to extract and summarize specific findings on dose-rate effects from animal experiments.

To obtain estimates of the dose rate effectiveness factor (DREF), WG1 analyzed cancer mortality data of B6C3F1 female mice chronically and acutely exposed to Cs-137 γ-rays, as reported by NIRS and the Institute for Environmental Sciences, Japan. This study applied a model that accounts for differences in risk depending on age at exposure, suggesting a significantly reduced risk in mice exposed to 21 mGy per day compared to mice exposed to acute irradiation. Consequently, under the conditions of the present analysis, the DREF was greater than 1 and approximately 3 when adjusted for age dependence of susceptibility (Doi et al., Radiat. Res., 2020).

WG1 also reviews papers on low dose rate effect studies in animal models. Epidemiological data have contributed significantly to the estimation of dose and dose rate effectiveness factor (DDREF) for human populations. Studies using animal models, on the other hand, have contributed significantly to providing qualitative and quantitative data on the magnitude and mechanisms of risk. This review examines animal model studies related to cancer development and organizes the findings with a focus on how the underlying biological mechanisms of carcinogenesis are involved in the dose-rate effects of radiation-induced carcinogenesis (Suzuki et al., J. Radiat. Res., 2023).

Steering Committee (2022)

Kai, Michiaki (Head) Nippon Bunri University
Imaoka, Tatsuhiko QST
Iwasaki, Toshiyasu Central Research Institute of Electric Power Industry
Kobayashi, Junya International University of Health and Welfare
Misumi, Munechika Radiation Effects Research Foundation
Sakai, Kazuo Tokyo University of Health Sciences, Radiation Effects Association
Sugihara, Takashi Institute for Environmental Sciences
Suzuki, Keiji Nagasaki University
Tauchi, Hiroshi Ibaraki University
Yasuda, Hiroshi Hiroshima University
Yoshinaga, Shinji Hiroshima University

WG1 (Dose Rate Effects in Animal Experiments) 2022

Suzuki, Keiji (Head) Nagasaki University
Doi, Kazutaka QST
Imaoka, Tatsuhiko QST
Sasatani, Megumi Hiroshima University
Tanaka, Satoshi Institute for Environmental Sciences
Tomita, Masanori Central Research Institute of Electric Power Industry