Acute Radiation Syndrome results from exposure to high doses of ionizing radiation which damages cellular DNA. It progresses through three stages - prodromal (GI symptoms within hours), latent (asymptomatic bone marrow suppression within days to weeks) and manifest (multi-system organ involvement within weeks). The severity of illness depends on radiation dose with doses over 1 Sievert likely causing acute radiation syndrome and over 3 Sieverts being potentially lethal without treatment. Management involves supportive care, antibiotics, blood products, and growth factors with prognosis guided by initial lymphocyte counts.

1. Acute Radiation Syndrome

3. Pathophysiology Strips electrons from atomic nuclei, damaging cellular DNA; rapidly dividing tissues (GI, hematopoietic, epidermal) are most susceptible to ionizing radiation.

4. Cytogenetic abnormalities noted after irradiation in peripheral blood lymphocytes of a patient exposed to high-dose radiation. Dicentric chromosomes and ring abnormalities are relatively radiationspecific and are characteristic of changes observed. dicentric chromosome ring aberration fragments normal chromosome

5. Units of Radiation Exposure Units of activity describe the amount of radioactivity present Conventional unit: Roentgen Absorbed dose Units of exposure measure the amount of X-ray or gamma radiation that produces a given number of ionizations in air Conventional unit: rad International system of unit: Gray 1 Gy = 100 rad Dose equivalent Units of absorbed dose can be applied to any type of radiation and reflect the energy imparted to matter Conventional unit: Roentgen equivalents man (rem) International system of unit: Sievert 1 Sv = 100 rem

6. *1 rem (dose equivalent) = 1 rad (absorbed dose or exposure)

7. Acute Radiation Syndrome

8. Phases of Radiation Injury Ann Intern Med. 2004;140:1037–1051.

9. Acute Radiation Syndrome Stage I: Prodromal stage (chieflygastrointestinal) Onset: minutes to hours ARS is fatal if GI symptoms develop within 2-4 hrs Duration: 48-72 hrs Presentation: nausea, vomiting; also diarrhea, cramps

10. Acute Radiation Syndrome Stage II: Latent stage (chieflyhematopoietic) Onset: hours to days Duration: 1.5-2 wks Presentation: asymptomatic  bone marrow supression

11. Acute Radiation Syndrome Stage III: Manifest stage (multisystem involvement) Onset: 3-5 wks Duration: variable Presentation: CNS/CVS (>15 Sv) Cardiorespiratory/GI system (>5 Sv) Reticuloendothelial system (>1 Sv)

12. Acute Radiation Syndrome Stage IV: Recovery or Death Onset: weeks Duration: weeks to months Presentation: leading cause of death before recovery is sepsis

13. Typical hematologic course and clinical stages after sublethal (~3 Gy) exposure to total-body irradiation

14. Prognosis According to the Lymphocyte Count within the First 48 Hours after Acute Exposure to Penetrating Whole-Body Radiation Ann Emerg Med. 2005;45:643-652.

15. Commonly Treated Forms of Internal Contamination

16. Top 10 Key Points For Medical Management of Radiation Casualties Medical Treatment of Radiological Casualties: Current Concepts Ann Emerg Med. 2005;45:643-652

17. All patients should be medically stabilized from their traumatic injuries, without delay, before radiation injuries are considered. Patients are then evaluated for either external radiation exposure or radioactive contamination.

18. An external radiation source with enough intensity and energy can cause tissue damage (eg, skin burns or marrow depression). This exposure from a source outside the person does not make the person radioactive. Even such lethally exposed patients are no hazard to medical staff.

19. Nausea, vomiting, diarrhea, and skin erythema within 4 hours may indicate very high (but treatable) external radiation exposures. Such patients will show obvious lymphopenia in 8 to 24 hours. Evaluate with serial CBCs. Primary systems involved will be skin, intestinal tract, and bone marrow. Treatment may involve fluids, antimicrobial agents, transfusions, and marrow-stimulating factors. In cases involving explosions, during the ED phase of treatment, early hypotension and CNS changes from radiation effects may be indistinguishable from trauma-related causes. If there are early CNS findings or unexplained hypotension, survival is unlikely.

20. Radioactive material may have been deposited on or in the person (contamination). More than 90% of surface radioactive contamination may be removed by removal of the clothing. Most remaining contamination on exposed skin is effectively removed with soap, warm water, and a washcloth. Do not damage skin by overvigorous scrubbing.

21. Protect yourself from radioactive contamination by observing standard precautions, including protective clothing, gloves, and a mask.

22. Radioactive contamination in wound or burns should be handled as if it were simple dirt. If an unknown metallic object is encountered, it should be handled only with instruments such as forceps and saved in a protected or shielded area for forensic analysis.

23. In a terrorist incident, there may be continuing exposure of the public that is essential to evaluate. Initially suggest sheltering and a change of clothing or showering. Evacuation may be necessary. Administration of potassium iodide is indicated only when there has been a confirmed release of radioiodine.

24. When there is any type of radiation incident, many persons will want to know whether they have been exposed or are contaminated. Provision needs to be made to potentially screen thousands of such persons.

25. Clinically significant acute radiation syndrome seldom if ever occurs in people receiving less than 1 Gyof whole-body radiation. The risk of developing cancer after exposure to radiation is a function of the dose received and begins to accrue even with very low doses (ie, there is no minimum threshold dose). For contaminated patients, the amount of radioactivity present is measured in bequerels (Bq) (1 disintegration per second). Sometimes, it may be also expressed in counts per minute. Decontamination is usually stopped if the item is reduced to 2 or 3 times the background count rate or if repeated decontamination efforts are ineffective at further reducing the count rate.

26. The principles of time/distance/shielding are key. Even in the treatment of Chernobyl workers, doses to the medical staff were only about 10 mGy or 10 mSv. Doses to first responders at the scene, however, can be much higher, and appropriate dose-rate meters must be available for evaluation. Radiation dose is diminished by reducing time spent in the radiation area (moderately effective), increasing distance from a radiation source (very effective), or using metal or concrete shielding (less practical).

27. Reference Radiation Injuries. Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 2011, pp 56-61 Disaster Management and Emergency Preparedness. Advanced Trauma Life Support, 2008, pp 333-334 Medical Treatment of Radiological Casualties: Current Concepts. Ann Emerg Med. 2005;45:643-652