Most radiation accidents are due to local radiation injury from partial-body exposure. Partial-body irradiation rarely causes systemic manifestations; rather, it leads to a dose-dependent cutaneous involvement. Typically, the injury in the first week tends to be asymptomatic, although there may be transient erythema (6 Gy/600 rad), hyperesthesia, and itching. The second week is characterized by the development of erythema that progresses to hair loss (3 Gy/300 rad). The development of skin tenderness, swelling, and pruritus heralds the third week after exposure. Within the fourth week, the wound will develop dry (10 to 15 Gy/1000 to 1500 rad) or wet (15 to 20 Gy/1500 to 2000 rad) desquamation and/or ulceration (>25 Gy/2500 rad).12
Skin findings may be indistinguishable from thermal burns. Radiation injuries are hallmarked by episodes of transient erythema and delayed onset of prolonged and severe pain. As long as the exposure is less than 50 Gy (5000 rad), these injuries develop over a much longer time period than thermal burns. When doses exceed 50 Gy, these injuries will progress similarly to thermal burns, and the onset of pain will occur immediately. Surgical intervention such as resection and grafting may be required.
Acute Radiation Syndrome occurs after a significant exposure to penetrating ionizing radiation within a 24-hour time period (Table 10-5). It should be expected in cases in which a whole-body gamma dose exceeds of 2 Gy (200 rad). External sources of alpha and beta radiation are unable to penetrate the body, although internal contamination may lead to this syndrome. Neutron sources, although rarely encountered, can also lead to acute radiation syndrome.
TABLE 10-5Acute Radiation Syndrome ||Download (.pdf) TABLE 10-5 Acute Radiation Syndrome
|Approximate Dose ||Onset of Prodrome ||Duration of Latent Phase ||Manifest Illness |
|>2 Gy (200 rad) ||Within 2 d ||1–3 wk ||Hematopoietic syndrome with pancytopenia, infection, and hemorrhage; survival possible |
|>6 Gy (600 rad) ||Within hours ||<1 wk ||GI syndrome with dehydration, electrolyte abnormalities, GI bleeding, and fulminant enterocolitis; death likely |
|>20–30 Gy (2000–3000 rad) ||Within minutes ||None ||Cardiovascular/CNS syndrome with refractory hypotension and circulatory collapse; fatal within 24–72 h |
Acute radiation syndrome develops in four distinct phases: prodrome, latent phase, manifest-illness, and recovery. The initial prodrome involves the transient autonomic nervous system response to the exposure. It is directly related to the dose received. High doses cause acute and severe symptom onset, whereas lower doses may lead to prolonged onset and milder symptoms. Nausea, vomiting, anorexia, and diarrhea may be accompanied by hypotension, pyrexia, diaphoresis, cephalgia, and fatigue.
The prodrome is followed by the latent phase, a symptom-free interval whose duration depends on the received dose. Larger doses result in a shorter duration of this phase. Doses less than 4 Gy are associated with a period that may last 1 to 3 weeks, whereas in doses greater than 15 Gy, this phase may only last a few hours.
The manifest-illness phase is subdivided into three dose-dependent syndromes that are hallmarked by the affected organ system. The syndromes are not independent of one another, and there is synergy and overlap leading to the clinical manifestations. The final stage is recovery.
Hematopoietic Syndrome The hematopoietic system is the first organ system that demonstrates injury when doses exceed 1.5 Gy. The prodromal phase of this subsyndrome occurs within hours to a few days from the exposure, resolves within 48 hours, and is followed by a latent phase that on average lasts 1 to 3 weeks.
Radiation damages the bone marrow stem cells and destroys circulating hematopoietic cells, particularly lymphocytes (Figure 10-1). Because of the preferential destruction of lymphocytes, the peripheral lymphocyte count is currently the best marker to grade the extent of the injury. Granulocytes and platelets are also affected. However, being markers of inflammation, their counts rise in the immediate time period following the exposure, and later decline and reach a nadir within 30 days of the injury. Red blood cells are also affected but not to the same extent of the other lines due to the lack of nuclear material. Morbidity and mortality depend on associated pancytopenia, immunosuppression, and hemorrhage. Aggressive medical management with blood products and growth factors may increase survival.
Typical hematologic course and clinical stages after sublethal (~3 Gy/300 rad) exposure to total-body irradiation.
GI Syndrome Doses greater than 6 Gy (>600 rad) cause the GI syndrome. Nausea, vomiting, and diarrhea develop within hours of exposure. This is followed by a short latent phase lasting up to 1 week. The manifest-illness phase is characterized by the recrudescence of severe nausea, vomiting, diarrhea, and abdominal pain. The initial insult leads to the apoptotic death of the GI mucosa, with associated insult to the underlying stem cells responsible for their replenishment. Impaired mucosal integrity causes massive fluid and electrolyte losses and allows the translocation of enteric flora into the bloodstream. Fulminating enterocolitis results.
Cardiovascular and CNS Syndrome The last subsyndromes of the manifest-illness phase are the cardiovascular and CNS syndromes, resulting from doses greater than 20 to 30 Gy (>2000 to 3000 rad). There is immediate hypotension, prostration, nausea, vomiting, and explosive bloody diarrhea. Hypotension is persistent and unresponsive to treatment. CNS symptoms manifest within hours and include seizures, lethargy, disorientation, ataxia, and tremors. The lymphocyte count, the quickest marker available to determine the extent of injury, very quickly falls to near-zero levels. Death from circulatory collapse ensues within 72 hours.