Scientific approach to radiation-induced cancer risk.

When evaluating cancer risk of low-dose radiation, it is difficult to distinguish the actual effect from that of chance, bias, and confounding as they become relatively large. This is why the relation between radiation doses of less than 100 mSv and cancer risk is considered unknown. Based on data of atomic bomb survivors in Hiroshima and Nagasaki, the cancer risk at 100 mSv is calculated at 1.05 times. On the other hand, the risk ratio for the relation between passive smoking and lung cancer is estimated at approximately 1.3 and judging the actual effects faced difficulties. It is almost impossible for epidemiology research alone to show that the risk ratio of 1.05 is the actual effects of radiation. The ICRP estimation, " exposure to 100 mSv increases cancer risk by 0.5%" , has been frequently cited, however, it is not a simple excess lifetime risk of death. It will be more appropriate to indicate a value with clear definition to people in general, such as excess lifetime risk of death or excess lifetime risk of morbidity rather than the value obtained from such complicated process. Radiation epidemiology equally uses ratio and difference to indicate degrees of risk increase. Difference largely changes depending on effects of background factors whereas ratio is often relatively stable. Therefore the use of ratio would be more appropriate when comparing other cancer risk factors.