Acute Radiation Syndrome is a combination of clinical signs and symptoms occurring in stages over a period of hours to weeks due to a significant partial-body (70%) or whole-body exposure of > 1 Gy (100cGy of ionizing radiation), as injury to various tissues and organs is expressed. ARS is caused by >1 Gy / 100 rad whole-body doses of ionizing radiation. ARS follows a predictable clinical course through four phases: 1) prodromal, 2) latent, 3) manifest illness, 4) recovery or death. The transition time between phases depends on the dose of radiation absorbed. The higher the whole-body dose, the shorter each of the phases. Table 8 below depicts time to onset of prodromal symptoms based on dose.16