Contents
Introduction
Acute radiation syndrome (ARS) primarily refers to damage to the hematopoietic system, myeloid system, and gastrointestinal (GI) system that occur after a whole-body or significant partial-body (60%) exposure of >1 Gy total dose, delivered acutely at a relatively high-dose-rate.
Pathophysiology
Dose response in respect to radiation injury:
- ARS is the host response against exogenous radiation injury, which may be fatal for the exposed person
Organ dysfunction in ARS
- Even at low irradiation doses bone marrow stem cells will be affected, and thus neutrophils, monocytes, and erythrocytes
- The function of organ fixed macrophages will also be harmed, which in turn will reduce outermost host defence barrier
- Lung is the most vulnerable vital organ when exposed to acute irradiation because of the “double hit” radiation exposure, ie, a combined exposure of inhaled particles (P) and from gamma radiation (γ) similar to the rest of the body
| > 20Gy dose | Neurovascular syndrome onset | (>10 Gy) Multiple organ failure probable death |
| (8–10 Gy) Consider stem cell transplant | ||
| 6 Gy dose | GI syndrome onset | (6–7 Gy) LD50/60 with supportive care |
| (3–5 Gy) LD50/60 without treatment | ||
| 1 Gy dose | Hematopoietic syndrome onset | (0–2 Gy) ∼100% survival without treatment |
- LD50/60 is defined as the dose necessary to cause death in 50% of an irradiated population in 60 days
Effect on skin:
- Thermal burns from infrared heat radiation (seen in nuclear explosions)
- Beta burns from shallow ionizing beta radiation (this would be from fallout particles; the largest particles in local fallout would be likely to have very high activities because they would be deposited so soon after detonation and it is likely that one such particle upon the skin would be able to cause a localised burn); however, these particles are very weakly penetrating and have a short-range.
- Gamma burns from highly penetrating gamma radiation. This would likely cause deep gamma penetration within the body, which would result in uniform whole-body irradiation rather than only a surface burn. In cases of whole-body gamma irradiation (circa 10 Sv) caused by accidents involving medical product irradiators, some of the human subjects have developed injuries to their skin between the time of irradiation and death. In the picture to the left, the normal clothing that the woman was wearing would have been unable to attenuate the gamma radiation and it is likely that any such effect was evenly applied to her entire body. Beta burns would be likely all over the body caused by contact with fallout, but thermal burns are often on one side of the body as heat radiation does not penetrate the human body. In addition, the pattern on her clothing has been burnt into the skin. This is because white fabric reflects more infrared light than dark fabric. As a result, the skin close to dark fabric is burned more than the skin covered by white clothing.
- There is also the risk of internal radiation poisoning by ingestion of fallout particles.
Clinical features
Clinical stages:
- Prodromal stage (first 48 hours)
- Latent stage (up to a month)
- Manifest illness stage
- Recovery/death
| Syndrome | Signs and symptoms
|
|||
|---|---|---|---|---|
| Prodromal phase first 48 hours | Latent phase lasts up to a month | Manifest illness phase | Final outcome: survival or death | |
| Gastrointestinal Occurs at doses between 5 Gy and 12 Gy |
Nausea, vomiting, diarrhoea, anorexia, haemorrhage, weakness through denuded areas Loss of absorptive capacity Increased intensity 4–8 hours |
Tiredness and anorexia | Vomiting and fever; progression of bloody diarrhoea to shock and death or treatment | Radiation 8–30 Gy dose range cause death from gastrointestinal syndrome |
| Hematologic High dose between 2–3 Gy and 8 Gy. Low dose (<2 Gy) radiation |
Often asymptomatic Some fatigue, fever, and bacteremia |
Lymphopenia Granulocytopenia Thrombocytopenia |
Neutropenia (ANC < 0.5) Fever, sepsis, haemorrhage, purpura, electrolyte disturbances, and epilation |
Agranulocytosis irresponsive to GM-CSF after first cell cycle |
| Central nervous system | No specific signs and symptoms Unspecific fatigue, malaise, anorexia, and drowsiness Not consistently correlated to exposed dose |
Latency up to a month Asymptomatic phase except for tiredness and weakness |
Headache Impaired cognition, disorientation, seizure, tremor, ataxia Grand mal seizures |
Irreversible brain damage secondary to continuous cramps |
| Pulmonary dysfunction | Acute radiation pneumonitis Cough, shortness of breath ALI with inflammatory coagulation activation |
Pulmonary edema Pneumonitis | ARDS Intubation and mechanical ventilation Severe pneumonia Lung fibrosis after 14–30 days from first exposure |
Absolute respiratory insufficiency Severely reduced oxygen transport capacity |
Diagnosis
Biodosimetry:
| Dosimetry | Methods | Utility |
|---|---|---|
| Biological | Whole-body counting | Not practical, generally not available |
| Chromosomal aberrations (dicentrics and ring forms) | The “gold standard,” however it takes 4–5 days processing time | |
| Clinical | Signs and symptoms | In spite of high practicability, clinical dosimetry has low sensitivity particularly at low doses |
Management
Initial steps
- Removing any contaminated clothing (↓ exposure by 80%)
- Within the first hours of contamination: Nonradioactive potassium iodide (KI) (stable iodine): Saturates iodine binding sites within the thyroid and inhibits incorporation of radioiodines into the gland.
- Special priority to mothers & children
Supportive management:
- Fluid management and early treatment of any signs of infection
- Prevention of thyroid cancer must be a priority
- Stop breastfeeding (if possible)
- Anti-emetics will be helpful to control nausea.
- Pain control for burns and other injuries should be a priority.
Neutropenia:
- Antibiotics, antiviral and antifungal agents for prevention or treatment of infections.
- Moderate exposure: Granulocyte-colony stimulating factor (G-CSF) (5 μg/kg body weight/day subcutaneously)
- Hematopoietic cell transplantation