Abstract
The health effects of radiation is well established. However, as Upton pointed out (Upton, Cancer Invest 1989), biological effects of low-dose and dose-rate radiation exposure have a lot of uncertainties in their quality and quantity. They appear to be different from those of high-dose radiaton exposure not only in their magnitude but also in their nature. In this paper, discussions will be made as to solid cancer risk of low-level external exposure, mainly on the basis of results obtained from epidemiological studies. The epidemiological studies that are important for evaluating the health effects of low-level radaition are the studies of atomic bomb survivors, nuclear workers, and the residents of high-background radiation areas (HBRA) in India and China. Although much attention had not been paid to HBRA studies until recently, the studies in India are particularly important. In the HBRA in Kerala, India, collaborative studies with IAEA, IARC, France, USA are already initiated in addition to the studies led by Dr Sugahara, the former chariman of the Health Reasearch Foundation (Chairman: Dr Torizuka).
