possible—whole body and local injury A high dose of penetrating radiation over a short period of time to a large portion of the body (i.e., whole-body radiation) causes the acute radiation syndrome Large doses of radiation over a short period of time to a small portion of the body cause a local radiation injury Analogous medical situations would be whole-body radiation as conditioning for bone marrow transplantation and localized radiation therapy for breast cancer The signs and symptoms of the acute radiation syndrome ( Table 90.13 ) begin to appear after whole-body radiation doses of approximately Gy Organs with rapidly dividing cells such as bone marrow and GI tract lining are the most susceptible to radiation damage The amount of damage that occurs is dependent both on the dose and on the dose rate, for example, a dose of Gy/min would probably cause symptoms but Gy at a dose rate of 10 mGy/day for 100 days would likely be asymptomatic Acute doses of about Gy may be lethal in approximately 50% of people if they not receive medical treatment With maximum medical treatment, the dose of radiation that will kill 50% of people may be as low as Gy