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FIGURE 90.11 The effect of distance on radiation exposure from a point source of radiation Recognition Radiation exposures can be recognized by understanding three questions: (i) Who is likely to be affected by a radiation exposure or accident? (ii) What are the likely sources of radiation? and (iii) What are the likely injuries? The people most likely to be involved in a radiation exposure event are individuals whose work involves radiation Other individuals who may be exposed to radiation include members of the general public who inadvertently come into contact with a radiation hazard, for example, the population surrounding a nuclear powerplant, those who are intentionally poisoned, and patients who have undergone medical procedures (e.g., fluoroscopy or radiation therapy) To cause a significant radiation injury, an intense radiation source is needed The four major types of possible intense radiation sources are listed in Table 90.12 Because of their various physical properties, different sources are likely to cause different types of radiation injuries Radiation induces injury either through exposure or contamination Because patients exposed to radiation not have radioactive elements on or in them, they not emit radiation and can be treated without any additional precautions on the part of healthcare workers Two types of injury from radiation exposure are possible—whole body and local injury A high dose of penetrating radiation over a short period of time to a large portion of the body (i.e., whole-body radiation) causes the acute radiation syndrome Large doses of radiation over a short period of time to a small portion of the body cause a local radiation injury Analogous medical situations would be whole-body radiation as conditioning for bone marrow transplantation and localized radiation therapy for breast cancer The signs and symptoms of the acute radiation syndrome ( Table 90.13 ) begin to appear after whole-body radiation doses of approximately Gy Organs with rapidly dividing cells such as bone marrow and GI tract lining are the most susceptible to radiation damage The amount of damage that occurs is dependent both on the dose and on the dose rate, for example, a dose of Gy/min would probably cause symptoms but Gy at a dose rate of 10 mGy/day for 100 days would likely be asymptomatic Acute doses of about Gy may be lethal in approximately 50% of people if they not receive medical treatment With maximum medical treatment, the dose of radiation that will kill 50% of people may be as low as Gy TABLE 90.12 INTENSE RADIATION SOURCES Type of source Examples Likely injuries Sealed Industrial radiography Contamination unlikely Brachytherapy Local radiation injury with small source Some radiation therapy machines Industrial sterilizers Whole-body exposure with large source Unsealed Medical radionuclides (e.g., External and internal 131 I, 32 P) contamination likely Accidental release by a reactor Radium dial painters Radiation devices Cyclotron Linear accelerator Uncontrolled fission Fluoroscopy unit Nuclear reactor Uranium enrichment Local radiation injury likely Large whole-body doses likely On- and off-site contamination possible for nuclear reactors Weapons production The acute radiation syndrome consists of three distinct phases ( Table 90.14 ): prodromal, latent, and manifest illness The prodromal phase begins minutes to hours after the radiation exposure, lasts for to days, and common symptoms are nausea, vomiting, diarrhea, fatigue, and/or headache The prodromal phase is followed by the latent phase, in which the patient is relatively asymptomatic and generally lasts days or weeks after the exposure The manifest illness phase poses the greatest risk for infection and bleeding due to bone marrow suppression and GI epithelial damage As the radiation dose increases, the duration of the prodromal phase increases and the length of the latent phase decreases TABLE 90.13 DOSE–EFFECT RELATIONSHIP AFTER ACUTE WHOLE-BODY RADIATION EXPOSURE Whole-body absorbed dose (Gy) Comments 0.1 Asymptomatic (minimal detectable dose using cytogenetics) Asymptomatic (minor depression of white blood cell and platelets) Nausea and vomiting in approximately 15% of patients within days of exposure 0.5 Nausea and vomiting in most patients Nausea, vomiting, and diarrhea within 48 hrs; severe hematologic depression; 50% mortality without medical treatment 100% mortality within 30 days without medical treatment; 50% mortality with medical treatment Gastrointestinal syndrome; survival unlikely; death in 2–3 wks 50 Cardiovascular/Neurovascular syndrome; death in 24–72 hrs With doses of to Gy, the primary effect of whole-body radiation is to depress the bone marrow Although the absolute lymphocyte count ( Fig 90.12 ) decreases rapidly within the first 24 hours, there is no need for specific medical treatment The patient will be at greatest risk to weeks after the radiation exposure when the total white blood cell, neutrophil, and platelet counts reach a nadir ( Fig 90.13 ) At this time, the patient is vulnerable to death from infection and bleeding If the patient can be supported during this period of vulnerability and if the bone marrow is not irreversibly damaged, a recovery phase ensues The gastrointestinal syndrome occurs from absorbed doses of more than approximately Gy During the prodromal phase there is prompt onset of severe nausea, vomiting, and diarrhea There is a latent period of approximately week and then recurrence of GI symptoms, sepsis, electrolyte imbalance, and likely