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death The patient is susceptible to infection due to lack of granulocytes and because pathogens can readily enter the body across the damaged GI tract lining At dose levels of more than 50 Gy, the cardiovascular/neurovascular syndrome predominates There is almost immediate nausea, vomiting, prostration, hypotension, ataxia, and convulsions The permeability of blood vessels increases and there is brain edema and hypotension caused by the difficulty of maintaining a normal intravascular space Death usually occurs within to days TABLE 90.14 ACUTE RADIATION SYNDROME—SYMPTOMS Prodromal (0–2 a ) Latent (2–20 a ) Fatigue Nausea and vomiting Generally asymptomatic Sepsis Bleeding Diarrhea Diarrhea Headache Dizziness a Days after exposure Manifest illness (21–60 a) FIGURE 90.12 Effect of whole-body radiation on lymphocytes in the first days after exposure Estimating the whole-body radiation dose may be difficult, especially when complicated by injuries that are not due to radiation The signs and symptoms during the prodromal period are quite nonspecific except for a rapidly decreasing lymphocyte count Nausea and vomiting are sensitive but nonspecific symptoms Patients who not have nausea and vomiting are unlikely to have been exposed to a radiation dose that is large enough to cause acute radiation syndrome However, individuals may have nausea and vomiting for reasons other than exposure to radiation The whole-body radiation dose from radiation accidents is rarely uniform The nonuniform nature of the radiation dose makes it more difficult to predict the biologic effects from the exposure Chromosome analysis (cytogenetic dosimetry) may be helpful in estimating the radiation dose, but the results may not be available for about week The second type of radiation exposure that can occur is local exposure, which involves a radiation dose to a small part of the body Large doses can be tolerated if only a small part of the body is exposed Local radiation injuries may cause bone marrow depression if accompanied by a significant whole-body radiation dose Local injuries are rarely life threatening, but they are difficult to manage because they often cause a slowly progressive injury that takes months and sometimes years to fully evolve The injury develops slowly because the radiation causes progressive fibrosis of the blood vessels, which, in turn, causes tissue necrosis The ultimate extent of the injury may not be appreciated initially Healing following amputation or reconstructive surgery is poor because of deficient blood supply TABLE 90.15 APPROXIMATE ABSORBED DOSE TO PRODUCE SKIN CHANGES FROM LOCAL RADIATION INJURY Absorbed dose (Gy) Findings 3-6 Threshold for erythema 15 20 Moist desquamation Skin ulceration with slow healing >30 Gangrenous changes The hand is the most common site for localized radiation injuries The next most common sites are the thighs and buttocks because individuals are likely to put things that they find into their pockets A patient who has undergone a fluoroscopic procedure could have local radiation injury to the skin overlying the region imaged For example, the radiation source is typically positioned posterior to a patient undergoing a cardiac catheterization and therefore a radiation burn would be on the back Most industrial radiography sources deliver an extremely high radiation dose In contrast, analytical x-ray crystallography machines, which emit x-rays of much lower energy than the photons of 192Iridium, are not likely to cause deep blood vessel injury Local radiation injuries can typically be differentiated from thermal burns The effects of a thermal burn appear immediately If a patient presenting with a burnlike injury does not know the cause or time of the injury, a local radiation injury should be suspected Table 90.15 lists the dose-related findings expected after an acute local radiation exposure If erythema is seen within the first 48 hours, ulceration may occur later The erythema may come in waves that appear, disappear, and then reappear With transepidermal injury, blister formation may occur at to weeks with doses in the range of 100 Gy and at weeks after dose levels of 30 to 50 Gy Treatment is required to prevent infection and to relieve pain Skin grafting, especially musculocutaneous flaps, may be appropriate if the radiation exposure was localized and superficial Progressive gangrene, due to the obliterative changes in the small vessels, will occur if the radiation exposure is large and involves deep structures Under these circumstances, amputation may be necessary FIGURE 90.13 Effect of whole-body radiation on blood cell counts in the days after exposure Contamination Contamination represents the other major type of radiation injury Contamination occurs when radioactive dirt or liquid remains on the patient (external contamination) or, when inhaled or ingested, inside the patient (internal contamination) Contamination is the only type of radiation injury that requires the medical staff to take radiation-related precautions Although there is usually little danger to the medical staff when caring for a contaminated person once they are in the hospital, medical personnel who respond to the accident site may be exposed to large, potentially life-threatening doses of radiation For these rescue workers, 0.5 Gy is the voluntary limit suggested by the National Council on Radiation Protection and Measurements (NCRP) for lifesaving activities External contamination External contamination rarely is a significant medical problem To prevent additional radiation exposure to the patient, medical staff, and the public, external contamination should be removed, and dispersal of radioactive materials should be prevented The goal of treatment of any contaminated patient is to keep radiation exposures “as low as reasonably achievable.” This is called the ALARA principle and requires advance planning, specific supplies, and appropriate protective clothing Preventing the dispersal of