Acute Radiation Sickness all about and treatment

Acute Radiation Syndrome (ARS) (sometimes known as radiation toxicity or radiation sickness) is an acute illness caused by irradiation of the entire body (or most of the body) by a high dose of penetrating radiation in a very short period of time (usually a matter of minutes). The major cause of this syndrome is depletion of immature parenchymal stem cells in specific tissues. Examples of people who suffered from ARS are the survivors of the Hiroshima and Nagasaki atomic bombs, the firefighters that first responded after the Chernobyl Nuclear Power Plant event in 1986, and some unintentional exposures to sterilization irradiators. The required conditions for Acute Radiation Syndrome (ARS) are: The radiation dose must be large (i.e., greater than 0.7 Gray (Gy)1, 2 or 70 rads). Mild symptoms may be observed with doses as low as 0.3 Gy or 30 rads. The dose usually must be external ( i.e., the source of radiation is outside of the patient’s body). Radioactive materials deposited inside the body have produced some ARS effects only in extremely rare cases. The radiation must be penetrating (i.e., able to reach the internal organs). High energy X-rays, gamma rays, and neutrons are penetrating radiations. The entire body (or a significant portion of it) must have received the dose3. Most radiation injuries are local, frequently involving the hands, and these local injuries seldom cause classical signs of ARS. The dose must have been delivered in a short time (usually a matter of minutes). Fractionated doses are often used in radiation therapy. These are large total doses delivered in small daily amounts over a period of time. Fractionated doses are less effective at inducing ARS than a single dose of the same magnitude. The three classic ARS Syndromes are: Bone marrow syndrome (sometimes referred to as hematopoietic syndrome) the full syndrome will usually occur with a dose between 0.7 and 10 Gy (70 – 1000 rads) though mild symptoms may occur as low as 0.3 Gy or 30 rads4. The survival rate of patients with this syndrome decreases with increasing dose. The primary cause of death is the destruction of the bone marrow, resulting in infection and hemorrhage. Gastrointestinal (GI) syndrome: the full syndrome will usually occur with a dose greater than approximately 10 Gy (1000 rads) although some symptoms may occur as low as 6 Gy or 600 rads. Survival is extremely unlikely with this syndrome. Destructive and irreparable changes in the GI tract and bone marrow usually cause infection, dehydration, and electrolyte imbalance. Death usually occurs within 2 weeks. Cardiovascular (CV)/ Central Nervous System (CNS) syndrome:the full syndrome will usually occur with a dose greater than approximately 50 Gy (5000 rads) although some symptoms may occur as low as 20 Gy or 2000 rads. Death occurs within 3 days. Death likely is due to collapse of the circulatory system as well as increased pressure in the confining cranial vault as the result of increased fluid content caused by edema, vasculitis, and meningitis. The four stages of ARS are: Prodromal stage (N-V-D stage): The classic symptoms for this stage are nausea, vomiting, as well as anorexia and possibly diarrhea (depending on dose), which occur from minutes to days following exposure. The symptoms may last (episodically) for minutes up to several days. Latent stage: In this stage, the patient looks and feels generally healthy for a few hours or even up to a few weeks. Manifest illness stage: In this stage the symptoms depend on the specific syndrome (see Table 1) and last from hours up to several months. Recovery or death: Most patients who do not recover will die within several months of exposure. The recovery process lasts from several weeks up to two years. Cutaneous Radiation Syndrome (CRS) The concept of cutaneous radiation syndrome (CRS) was introduced in recent years to describe the complex pathological syndrome that results from acute radiation exposure to the skin. ARS usually will be accompanied by some skin damage. It is also possible to receive a damaging dose to the skin without symptoms of ARS, especially with acute exposures to beta radiation or X-rays. Sometimes this occurs when radioactive materials contaminate a patient’s skin or clothes. When the basal cell layer of the skin is damaged by radiation, inflammation, erythema, and dry or moist desquamation can occur. Also, hair follicles may be damaged, causing epilation. Within a few hours after irradiation, a transient and inconsistent erythema (associated with itching) can occur. Then, a latent phase may occur and last from a few days up to several weeks, when intense reddening, blistering, and ulceration of the irradiated site are visible. In most cases, healing occurs by regenerative means; however, very large skin doses can cause permanent hair loss, damaged sebaceous and sweat glands, atrophy, fibrosis, decreased or increased skin pigmentation, and ulceration or necrosis of the exposed tissue. Patient Management Triage: If radiation exposure is suspected: Secure ABCs (airway, breathing, circulation) and physiologic monitoring (blood pressure, blood gases, electrolyte and urine output) as appropriate. Treat major trauma, burns and respiratory injury if evident. In addition to the blood samples required to address the trauma, obtain blood samples for CBC (complete blood count), with attention to lymphocyte count, and HLA (human leukocyte antigen) typing prior to any initial transfusion and at periodic intervals following transfusion. Treat contamination as needed. If exposure occurred within 8 to 12 hours, repeat CBC, with attention to lymphocyte count, 2 or 3 more times (approximately every 2 to 3 hours) to assess lymphocyte depletion. Diagnosis The diagnosis of ARS can be difficult to make because ARS causes no unique disease. Also, depending on the dose, the prodromal stage may not occur for hours or days after exposure, or the patient may already be in the latent stage by the time they receive treatment, in which case the patient may appear and feel well when first assessed. If a patient received more than 0.05 Gy (5 rads) and three or four CBCs are taken within 8 to 12 hours of the exposure, a quick estimate of the dose can be made (see Ricks, et. al. for details). If these initial blood counts are not taken, the dose can still be estimated by using CBC results over the first few days. It would be best to have radiation dosimetrists conduct the dose assessment, if possible. If a patient is known to have been or suspected of having been exposed to a large radiation dose, draw blood for CBC analysis with special attention to the lymphocyte count, every 2 to 3 hours during the first 8 hours after exposure (and every 4 to 6 hours for the next 2 days). Observe the patient during this time for symptoms and consult with radiation experts before ruling out ARS. If no radiation exposure is initially suspected, you may consider ARS in the differential diagnosis if a history exists of nausea and vomiting that is unexplained by other causes. Other indications are bleeding, epilation, or white blood count (WBC) and platelet counts abnormally low a few days or weeks after unexplained nausea and vomiting. Again, consider CBC and chromosome analysis and consultation with radiation experts to confirm diagnosis. Initial Treatment and Diagnostic Evaluation Treat vomiting5, and repeat CBC analysis, with special attention to the lymphocyte count, every 2 to 3 hours for the first 8 to 12 hours following exposure (and every 4 to 6 hours for the following 2 or 3 days). Sequential changes in absolute lymphocyte counts over time are demonstrated below in the Andrews Lymphocyte Nomogram (see Figure 1). Precisely record all clinical symptoms, particularly nausea, vomiting, diarrhea, and itching, reddening or blistering of the skin. Be sure to include time of onset. Diagnosis When a person has experienced known or probable exposure to a high dose of radiation from an accident or attack, medical personnel take a number of steps to determine the absorbed radiation dose. This information is essential for determining how severe the illness is likely to be, which treatments to use and whether a person is likely to survive. Information important for determining an absorbed dose includes: Known exposure. Details about distance from the source of radiation and duration of exposure can help provide a rough estimate of the severity of radiation sickness. Vomiting and other symptoms. The time between radiation exposure and the onset of vomiting is a fairly accurate screening tool to estimate absorbed radiation dose. The shorter the time before the onset of this sign, the higher the dose. The severity and timing of other signs and symptoms also may help medical personnel determine the absorbed dose. Blood tests. Frequent blood tests over several days enable medical personnel to look for drops in disease-fighting white blood cells and abnormal changes in the DNA of blood cells. These factors indicate the degree of bone marrow damage, which is determined by the level of an absorbed dose. Dosimeter. A device called a dosimeter can measure the absorbed dose of radiation but only if it was exposed to the same radiation event as the affected person. Survey meter. A device such as a Geiger counter can be used to survey people to determine the body location of radioactive particles. Type of radiation. A part of the larger emergency response to a radioactive accident or attack would include identifying the type of radiation exposure. This information would guide some decisions for treating people with radiation sickness. Treatment The treatment goals for radiation sickness are to prevent further radioactive contamination; treat life-threatening injuries, such as from burns and trauma; reduce symptoms; and manage pain. Decontamination Decontamination involves removing external radioactive particles. Removing clothing and shoes eliminates about 90 percent of external contamination. Gently washing with water and soap removes additional radiation particles from the skin. Decontamination prevents radioactive materials from spreading more. It also lowers the risk of internal contamination from inhalation, ingestion or open wounds. Treatment for damaged bone marrow A protein called granulocyte colony-stimulating factor, which promotes the growth of white blood cells, may counter the effect of radiation sickness on bone marrow. Treatment with this protein-based medication, which includes filgrastim (Neupogen), sargramostim (Leukine) and pegfilgrastim (Neulasta), may increase white blood cell production and help prevent subsequent infections. If you have severe damage to bone marrow, you may also receive transfusions of red blood cells or blood platelets. Treatment for internal contamination Some treatments may reduce damage to internal organs caused by radioactive particles. Medical personnel would use these treatments only if you've been exposed to a specific type of radiation. These treatments include the following: Potassium iodide (ThyroShield, Iosat). This is a nonradioactive form of iodine. Iodine is essential for proper thyroid function. If you're exposed to significant radiation, your thyroid will absorb radioactive iodine (radioiodine) just as it would other forms of iodine. The radioiodine is eventually cleared from the body in urine. If you take potassium iodide, it may fill "vacancies" in the thyroid and prevent the absorption of radioiodine. Potassium iodide isn't a cure-all and is most effective if taken within a day of exposure. Prussian blue (Radiogardase). This type of dye binds to particles of radioactive elements known as cesium and thallium. The radioactive particles are then excreted in feces. This treatment speeds up the elimination of the radioactive particles and reduces the amount of radiation cells may absorb. Diethylenetriamine pentaacetic acid (DTPA). This substance binds to metals. DTPA binds to particles of the radioactive elements plutonium, americium and curium. The radioactive particles pass out of the body in urine, thereby reducing the amount of radiation absorbed. Supportive treatment If you have radiation sickness, you may receive additional medications or interventions to treat: Bacterial infections Headache Fever Diarrhea Nausea and vomiting Dehydration Burns Sores or ulcers End-of-life care A person who has absorbed very large doses of radiation has little chance of recovery. Depending on the severity of illness, death can occur within two days or two weeks. People with a lethal radiation dose will receive medications to control pain, nausea, vomiting and diarrhea. They may also benefit from psychological or pastoral care.