TREATMENT 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 need for treatment for a contaminated person. Purchase of these volumes by major triage centers may be a prudent investment that would assist workers in determining 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 of the decorporation agents are not U.S. Food and Drug Administration (FDA)-approved for these indications, and there are little clinical data to support the efficacy of their use.
Clearance of the GI tract may be achieved 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 using 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.
Prevention or reversal of radionuclide interaction with tissues can be done through use of agents that block absorption, dilute, mobilize or release radionucleotides from tissues, and chelate radionucleotides.
Blocking agents prevent the entrance of radioactive materials. The most well-recognized example of an 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. The 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 them should induce the release of radionuclides from tissues.
Chelating agents can bind many radioactive materials, after which the complexes are excreted from the human body. In this regard, diethylenetriaminepentaacetic acid (DTPA) as either Ca-DTPA or Zn-DTPA is superior to ethylenediamine tetraacetic acid (EDTA); DTPA was approved by the FDA to treat internal contamination with plutonium, americium, and curium, but it also chelates berkelium, californium, and any material with an atomic number >92. Ca-DTPA is more effective than Zn-DTPA during the first 24 h after internal contamination, and both 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 Ca-DTPA or Zn-DTPA, dissolved in 250 mL of normal saline or 5% glucose, 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 1:1 dilution with water or saline over 15–20 min. Nebulized Zn-DTPA is recommended if the internal contamination is only by inhalation. 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 is favorable for oral absorption, and therapeutic effects have been demonstrated in initial efficacy studies. Because it can be given orally, it may ultimately prove more useful in the effect of mass casualty than IV or nebulized forms of the drug (Sueda K). Treating uranium contamination with DTPA is contraindicated due to its 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 for acute radiation injury. The procedure requires anesthesia. Table S4-2 summarizes the common treatment regimens for internal radionuclide contamination.