Radiation Sickness

Radiation sickness, or acute radiation syndrome (ARS), is the systemic illness that follows whole body or large partial body exposure to ionising radiation, typically over 1 gray (Gy), delivered within a short time. Sources include nuclear accidents, orphan radiation sources (lost medical or industrial caesium-137, cobalt-60, iridium-192 sources), nuclear detonation and radiological dispersal devices, and radiotherapy equipment errors.

Radiation kills rapidly dividing cells. Syndromes are determined by dose: the haematopoietic syndrome (1 to 6 Gy) from bone marrow failure, the gastrointestinal syndrome (6 to 10 Gy) from loss of crypt cells, and the neurovascular syndrome (over 10 to 20 Gy) with cerebral oedema and cardiovascular collapse and death in days. Skin injury accompanies large doses.

LD50 without treatment is about 3.5 to 4.5 Gy and rises to about 6 Gy with supportive care. Course proceeds through four phases: prodromal (hours), latent (days to weeks), manifest illness, and recovery or death. The earlier the onset of vomiting and the faster the fall in lymphocytes, the higher the dose.

• Prodrome: nausea, vomiting, anorexia, fatigue, diarrhoea, headache and fever; onset within 1 hour indicates over 6 Gy, 1 to 2 hours 4 to 6 Gy, and later than 4 hours less than 2 Gy.
• Latent phase: apparent recovery; shorter at higher doses (days for the gastrointestinal syndrome, 2 to 5 weeks for haematopoietic).
• Haematopoietic: infection from neutropenia (days 14 to 30), bleeding from thrombocytopenia, anaemia.
• Gastrointestinal: severe watery or bloody diarrhoea, abdominal pain, dehydration, sepsis, ileus.
• Cutaneous: erythema, desquamation, blistering, epilation, ulceration.
• Neurovascular: confusion, ataxia, seizures, hypotension, coma; usually fatal.
• Red flags: vomiting within 1 hour, watery diarrhoea within 24 hours, absolute lymphocyte count below 0.5 x 10^9/L at 48 hours, fever with neutropenia.

• Obtain a history of radiation source, time, distance, shielding, and duration; dosimeter readings; time of first vomiting and onset of diarrhoea.
• Serial lymphocyte count every 6 hours for 48 hours, then daily (Andrews nomogram): 48-hour lymphocytes over 1.5 x 10^9/L suggests under 1 Gy, 0.5 to 1.5 mild to moderate, 0.1 to 0.5 severe, under 0.1 very severe (over 6 Gy).
• Full blood count with differential daily for 3 weeks; neutrophil and platelet nadir at 3 to 5 weeks.
• Dicentric chromosome assay on peripheral blood lymphocytes (gold standard for dose estimation, 24 hours after exposure, available at specialist laboratories); electron paramagnetic resonance of teeth or nails; blood based biomarkers where available.
• Count rates from swabs and a whole body monitor, urine and faecal sample for internal contamination (radionuclide analysis for 24-hour samples).
• Blood group and HLA typing for possible transplant; liver and kidney function, electrolytes, amylase (raised after parotid exposure).
• Exclude gastroenteritis, food poisoning, other chemical poisoning, infection and psychogenic vomiting.

• Priority: treat life threatening trauma and burns first; decontaminate (remove clothing which removes 90 percent of contamination, wash with soap and water). Staff wear gown, gloves, mask, shoe covers; patient is not a radiation hazard unless contaminated.
• Triage by time to vomiting and lymphocyte count; exposure under 1 Gy needs only observation and outpatient blood counts.
• Antiemetic: ondansetron 8 mg orally or intravenously every 8 hours (children 0.15 mg/kg), for as long as needed, usually for the first 3 days; fluids and electrolyte replacement.
• Haematopoietic syndrome with exposure estimated at 2 Gy or more: filgrastim 5 micrograms/kg subcutaneously once daily (or pegfilgrastim 6 mg once, repeated after 7 days), started within 24 hours and continued until the neutrophil count is over 1.0 x 10^9/L on 3 consecutive days (or over 10 x 10^9/L on 1 day); alternatively sargramostim 7 micrograms/kg subcutaneously daily.
• Infection prophylaxis when neutrophils are below 0.5 x 10^9/L: ciprofloxacin 500 mg orally twice daily, fluconazole 400 mg orally once daily, and aciclovir 400 mg orally 3 times daily if herpes seropositive; for fever 38.3 degrees C or more treat as febrile neutropenia with piperacillin tazobactam 4.5 g intravenously every 6 hours, adding vancomycin 15 mg/kg intravenously every 12 hours for line infection or skin infection, until neutrophils recover and cultures are negative.
• Transfusions: irradiated, leucodepleted blood products; platelets when below 10 x 10^9/L (20 x 10^9/L with fever), and red cells for haemoglobin below 8 g/dL.
• Gastrointestinal syndrome: intravenous fluids, parenteral nutrition, loperamide 4 mg orally then 2 mg after every loose stool (maximum 16 mg per day) in the absence of infection, and early broad spectrum antibiotics; palliative for doses over 10 Gy.
• Haematopoietic stem cell transplant in rare cases with a donor and when doses of 7 to 10 Gy are accompanied by prolonged marrow aplasia; not for those with significant gastrointestinal injury.
• Internal contamination, give in the first hours: potassium iodide 130 mg orally once daily for adults (children 3 to 12 years 65 mg, 1 month to 3 years 32 mg, neonates 16 mg) for iodine-131 for 7 to 14 days; Prussian blue (ferric hexacyanoferrate) 3 g orally 3 times daily for 3 weeks (children 1 g 3 times daily) for caesium-137 and thallium; calcium or zinc diethylenetriaminepentaacetic acid (DTPA) 1 g intravenously once daily (nebulised for inhalation) for plutonium, americium and curium; use zinc DTPA in pregnancy.
• Skin lesions: non-adherent dressings, with paracetamol 1 g orally every 6 hours and opioids as needed.
• Psychological care and reassurance are essential for the worried well.
• Follow up: blood counts weekly for 6 weeks, then monthly for 1 year; cataract, cancer, and fertility screening; counselling about long term cancer risk, with leukaemia peaking at 5 to 7 years and solid tumours later.
• Prevention: source security and labelling, dosimeters, and emergency plans.