Radiation can different body parts in different ways and depends upon the dosage and exposure.In the head area it can cause hair loss, headache, weakness and in the mouth it could lead to inflammation of mouth and gum disease. By targeting the heart area it can cause rapid heartbeat and inflammation of heart.
It can deplete the count of white blood cells up to 58% and that too within 48 hours. It can also cause ulcers in stomach, permanent skin darkening in the skin and low platelet count in blood. The risk is measured in Sieverts (Sv). The normal exposure to radiation per year is 0.0022 Sv.
In a chest scan the one can absorb 0.01 Sv which is well above the normal. Think of 100 X-rays, what effect that will have on the body. The maximum radiation effect detected at Fukushima in Japan is 1.5 Sv. If the radiation level touches 20 Sv then it can lead to death.