Figure 263e-3 shows a model for hospital arrangement for triage. Persons contaminated either externally or internally should be identified, externally decontaminated, and, if need be, treated immediately and specifically for internal contamination as detailed below. In all other cases, the need for treatment of radiation injuries does not constitute a medical emergency. Early actions—e.g., blood sampling both to assess the severity of the exposure and to perform blood typing and cross-matching for possible transfusion—need to be taken promptly if ARS is evident or if whole-body exposure is suspected.
In the hospital entrance, a distinct decontamination area should be set up promptly. Separation between clean and contaminated areas is essential. Medical personnel in contaminated areas should wear protective gear, as noted above, and should be rotated in their assignments every 1–2 h to ensure minimal exposure to radiation. If patients are critically wounded and require either surgery or resuscitation, they need to be transported directly to “contaminated” operating rooms or resuscitation sites for lifesaving procedures. Once the condition of such patients is stable, they should be decontaminated. It is important to obtain details concerning the exposure, to look for prodromal signs of radiation sickness, and to conduct a physical examination. One of the simplest ways to estimate exposure clinically is to measure the time of prodromal appearance. The earlier the prodromal signs and symptoms appear, the higher is the dose of radiation exposure. A few laboratory tests need to be done routinely, such as complete blood count and urinalysis. If internal contamination is suspected, specific treatment should be given as outlined below.
TREATMENT Radionuclide Contamination
Table 263e-2 summarizes the common treatment regimens for internal radionuclide contamination. Treatment for internal radionuclide contamination, also referred to as decorporation, should be started as soon as possible after suspected or known exposure. The approximate upper limit of radionuclide contamination that can reasonably be ignored from a radiation safety point of view is not well defined. These are judgments that will depend on the circumstances of the event and the resources available. The Clinical Decision Guide within the National Council on Radiation Protection and Measurements (NCRP) Report 161 is a decision tool for determining the need for treatment of a contaminated person. Purchase of these volumes by major triage centers (available at http://www.ncrppublications.org/Reports/161_I) may be a prudent investment that would help health care workers in a critical situation to determine which patients should undergo decorporation.
The goal is to leave the smallest amount of radionuclide possible in the body. Treatment is given to reduce absorption and enhance elimination and excretion. Some decorporation agents are not approved by the U.S. Food and Drug Administration (FDA) for these indications, and few clinical data support the efficacy of their use.
The gastrointestinal tract may be cleared by stomach lavage, with emetics (such as apomorphine, 5–10 mg; or ipecac, 1- to 2-g capsules or 15 mL in syrup), or by use of purgatives, laxatives, ion exchangers, and aluminum antacids. Prussian blue (1 g tid for a minimum of 3 weeks) is an ion exchanger used to treat cesium-137 internal contamination. Aluminum antacids (such as aluminum phosphate gel) may reduce strontium uptake in the gut if given immediately after exposure. Aluminum hydroxide is less effective.
Radionuclide interaction with tissues can be prevented or reversed through use of agents that block absorption; dilute, mobilize, or release radionucleotides from tissues; or chelate radionucleotides.
Blocking agents prevent the entrance of radioactive materials. The best-recognized effective blocking agent is potassium iodide (KI), which blocks the uptake of radioactive iodine (131I) by the thyroid. KI is most effective if taken within the first hour after exposure and is still effective 6 h after exposure. Its effectiveness subsequently declines until 24 h after exposure; however, it is recommended that KI be taken up to 48 h after exposure. The KI dose is based on age, predicted thyroid exposure, and pregnancy and lactation status. Adults between the ages of 18 and 40 should receive 130 mg/d for 7–14 days if exposed to ≥10 cGy of radioactive iodine. Other thyroid-blocking agents include propylthiouracil (100 mg tid for 8 days) and methimazole (10 mg tid for 2 days followed by 5 mg tid for 6 days). These agents are somewhat less effective than KI.
Diluting agents decrease the absorption of the radionuclide; for example, water may be used as a diluting agent in the treatment for tritium (3H) contamination. The recommended amount is 3–4 L/d for at least 3 weeks.
Mobilizing agents are most effective when given immediately; however, they may be effective for up to 2 weeks after exposure. These agents include antithyroid drugs, parathyroid extract, glucocorticoids, ammonium chloride, diuretics, expectorants, and inhalants. All of the latter agents should induce the release of radionuclides from tissues.
Chelating agents can bind many radioactive materials, after which the complexes are excreted from the body. In this regard, diethylenetriaminepentaacetic acid (DTPA)—as either Ca-DTPA or Zn-DTPA—is superior to ethylenediaminetetraacetic acid (EDTA); DTPA has been approved by the FDA to treat internal contamination with plutonium, americium, and curium, but it also chelates berkelium, californium, and any other material with an atomic number >92. Ca-DTPA is more effective than Zn-DTPA during the first 24 h after internal contamination, and the two drugs are equally effective after the initial 24 h. If both drugs are available, Ca-DTPA should be given as the first dose. If additional treatment is needed, treatment should be switched to Zn-DTPA. The dose is 1 g of Ca-DTPA or Zn-DTPA, dissolved in 250 mL of normal saline or 5% glucose and given intravenously over 1 h daily. The duration of chelation treatment depends on the amount of internal contamination and the individual response to treatment. DTPA also can be administrated by nebulized inhalation; 1 g is given in a 1:1 dilution with water or saline over 15–20 min. Nebulized Zn-DTPA is recommended if inhalation was the only route of internal contamination. The IV route is recommended and should be used if the route of internal contamination is not known or if multiple routes of internal contamination are likely. DTPA penta-ethyl ester is a prodrug that has a favorable oral-absorption profile and whose therapeutic effects have been demonstrated in initial efficacy studies. Because it can be given orally, this prodrug may ultimately prove more useful in the setting of mass casualties than IV or nebulized forms of the drug. Treating uranium contamination with DTPA is contraindicated due to synergistic damage to the kidneys.
Lung lavage can reduce radiation-induced pneumonitis and is indicated only when a large amount of radionuclide enters the lungs and has the potential to cause acute radiation injury. The procedure requires anesthesia.