In order to clarify biological effects on whole body due to damage of cells by ionizing radiation, authors used the following assumption; absorbed dose was allocated only to ionization of water molecule in a place of DNA damage. The number of DNA damage calculated from ionized water was about 2.6 times of previously reported ones. The value calculated is considered to correspond to the maximum number of DNA damage.
When all deaths due to spontaneous cancer of natural occurring were assumed due to only DNA double-strand breaks (DSB) by ionizing radiation, the number of DSB was over-estimated to be about 1,500-2,000 times of the number of DSB necessary for death due to cancer produced by acute exposure of ionizing radiation. It would be necessray to consider at least the dose rate effect for biological effects on human body when estimating the simply accumulated dose of low-level ionizing radiation.