1 Tetsuya Ono Dept Cell Biol, Tohoku Univ Grad Sch Med Sendai, JapanAn Overview of the Session; A Challenge to Scientific Risk Estimation on Health Effects of Low Dose Radiation Tetsuya Ono Dept Cell Biol, Tohoku Univ Grad Sch Med Sendai, Japan

2 We are facing many environmental toxic agents. The risk estimation of these agents should be based on dose response curve. Response Dose The response in a low dose range could be extrapolated from high doses if it is a physical system. However, it is not true in biological systems.

3 Biological response to low dose radiation is complicated.Bystander effect Biological Response ICRP (International Commission on Radiological Protection) Adaptive response Dose

4 Bystander effect X X Adaptive response

5 In the biological systems,the dose response at low dose level cannot be extrapolated from high dose response. Instead, experimental as well as epidemiological studies are needed to clarify the dose response.

6 Biological responses at low dose rate radiation is different from those at high dose rate radiation Total dose Dose rate

7 Institute for Environmental Sciences 8Gy/400d 0.4Gy/400d 20mGy/400d2mGy/yr (BG)

8 Schematic illustration of gpt-delta mouseChr. 17 80 gpt-delta mouse red gam 48kbp T. Nohmi et al., Env Mol Mutag 28 (1996)

9 920 mGy/min

10 920 mGy/min 1 mGy/min

11 920 mGy/min 1 mGy/min 12.5μGy/min

12 Speakers of the sessionWei Zhang: Chromosomal abnormality in people living in high background area. Takehiko Nohmi: DNA changes induced when chemical carcinogen and low dose radiation are exposed at the same time. Mitsuru Nenoi: Changes in gene expression after a long period of exposure to low dose rate radiation. Noriyuki Ouchi: Computer modeling of radiation effects including DNA damage and repair.