The deterministic effects are health effects that displayed symptoms due to the killing of tissue stem cells in those exposed to ionizing radiation at more than threshold doses for tissue reactions. The threshold dose for tissue reactions is defined as a dose to induce tissue injury at the level of 1% incidence [7]. Typical early effects resulting in symptoms appearing over several weeks after exposure to ionizing radiation, are acomia and permanent infertility, as well as skin lesions and hematopoietic disorders. Cataracts are a typical late effect with symptoms arising after a long latent period extending to decades after exposure to ionizing radiation. The threshold doses for acomia, permanent infertility and cataracts are 3, 2.5–6, and 0.5 Gy delivered to the whole body, respectively. When pregnant women are exposed to ionizing radiation, embryonic death and malformation are the deterministic effects, which are provoked in fetuses. The threshold doses for both are 0.1 Gy as whole body exposure dose (0.1 Sv, here, the sievert [Sv] is a unit of radiation dose used for radiation protection to assess the health risk on humans), which is the minimal threshold dose among the various deterministic effects. On the other hand, the stochastic effects are health effects displayed stochastically by accumulating DNA mutations in cells of the tissues exposed to ionizing radiation. Typical stochastic effects are solid cancer and leukemia. Therefore, health effects provoked by ionizing radiation at below 0.1 Gy as a whole body exposure dose (0.1 Sv) are only the stochastic effects. There is still no evidence, however, for the stochastic effects provoked by whole body exposure to ionizing radiation of less than 0.1 Gy (0.1 Sv).