Radiation injury

Introduction

• Ionising radiation
  • High-energy, short-wavelength, high-frequency with enough energy to remove an electron from an atom and generate charged particles
  • Alpha particles, beta particles, neutrons and sole energy waves that include x-rays and gamma rays
• Alpha particles
  • Charge +2. 2 protons and 2 neutrons. 
  • Penetrate a few centimetres in air. Shielded by paper and keratin layer of skin. 
  • Must be ingested, inhaled or absorbed for injury
  • Source – Plutonium, uranium, radon
• Beta particles
  • Charge -1. Penetrate 8mm into skin. Shielded by clothing.
  • Hazardous if internally deposited
  • Most radio-isotopes decay by beta followed by gamma emission
• Positron
  • Charge +1. 8mm into skin. Shielded with lead, steel or concrete. 
  • Interact with electrons to release photons of energy
  • Source: Medical tracers
• Neutron
  • Charge 0
  • Variable penetration. Shieled by material with high hydrogen content e.g. heavy water
  • Source: Nuclear power plants, particle accelerators, weapons plants
• Gamma and X-rays
  • Charge 0
  • Several cm into tissue
  • Shielded by concrete and lead
  • Most radio-isotopes decay by beta followed by gamma emission

ALLOWED DOSE

• Background radiation is 6.2 mSv
• Allowed 1mSv over this as per International Commission on Radiological Protection
• Lethal dose
  • LD 50/60 is the lethal dose at which 50% of the population die within 60 days of exposure = 3.5-4.5 Gy (350-450 rad)
  • With supportive medical therapy can rise to 4.8-5.4 Gy
  • With stem cell therapy and haematopoietic growth factor administration, theoretically risen to 11 Gy

Clinical Effects of Radiation

• Local radiation injury
  • Usually partial-body exposure causing dose-dependent cutaneous involvement
  • Week 1 – Transient erythema, hyperaesthesia and itching
  • Week 2 – Erythema with hair loss
  • Week 3 – Skin tenderness, swelling and pruritis
  • Week 4 – Dry (10-15 Gy) or wet (15-20 Gy) desquamation (and/or ulceration (>25Gy)
  • If >50Gy, will present similarly to thermal burns and onset of pain will be immediate

Acute radiation syndrome

• Should be expected in which whole body gamma dose exceeds 2 Gy
• Internal contamination of alpha or beta particles could also cause this
• Neutron sources are rare but could lead to this

• Four phases:
  • Prodrome – Transient autonomic response directly related to dose
    • High doses cause acute severe symptoms
    • Low dose cause prolonged onset and milder symptoms
    • Nausea, vomiting, anorexia, diarrhoea, hypotension, pyrexia, diaphoresis, cephalgia and fatigue
  • Latent phase – Symptom-free interval. Larger doses have shorter latent
    • 4Gy 1-3 weeks vs. >15Gy only hours
  • Manifest-illness phase
    • Three dose-dependent syndromes hallmarked by affected organ system
    • Haematopoietic, GI and Cardiovascular/CNS
  • Recovery

• Haematopoietic syndrome
  • Seen if doses >1.5 Gy 
  • Latent phase 1-3 weeks
  • Destroys bone marrow stem cells and circulating cells (esp. lymphocytes)
  • Peripheral lymphocyte count is best marker
  • Morbidity and mortality depend on associated pancytopaenia, immunosuppression and haemorrhage
  • Blood products and GF may increase survival

• GI syndrome
  • >6Gy 
  • Nausea, vomiting and diarrhoea within hours then latent phase for up to 1 week, then manifest recurrent nausea, vomiting, diarrhoea and abdo pain
  • Mucosal destruction and death of stem cells prevents regeneration and allows translocation of enteric flora into bloodstream

• Cardiovascular/CNS
  • >20-30Gy
  • Immediate hypotension, prostration, nausea, vomiting and explosive bloody diarrhoea
  • Hypotension resistant to therapy
  • CNS within hours with seizures, lethargy, disorientation, ataxia and tremors
  • Lymphocyte count falls to zero within hours and death from circulatory collapse within 72 hours

Emergency Response Planning

• Pre-hospital
  • Incident command, PPE, transportation of seriously ill individuals (even if contaminated) and radiation monitoring + decontamination of medically stable patients at scene
• ED notification and preparation
  • Initiate hospital disaster plan
  • Prepare the ED: Ad hoc triage area, contaminated and clean areas, cover flooors with plastic, remove pregnant women and non-essential equipment/personnel, request extra gloves/PPE
  • Standard precautions for all staff – Double glove with inner gloves taped in place, frequent radiometer scanning of staff and dosimeters worn at collar

Triage principles

• Radioactive contamination is never immediately life-threatening so do not delay treatment of life-threatening injuries for radiologic surveying
• Morbidity and mortality rise significantly from ionising radiation in the setting of major trauma, thermal burns or significant medial illness

Treatment

• Stabilise life-threatening issues
• External exposure
  • Evalute for ARS and local radiation injury
  • Identify radionuclide
  • If persistent vomiting, consider whole body external exposure dose assessment
  • Serial FBC, amylase, CRP QID for 3 days
  • Dose assess local external exposure examining for erythema/blistering/desquamation

• External contamination
  • Admit to controlled area
  • Remove clothing and any shrapnel and contain in lead
  • Determine radiation type (alpha, beta, gamma)
  • ID Contaminant
  • Radiation survey of body areas with docuemntation
  • Collect samples from nose/mouth
  • Decontaminate wounds, body orifices and intact skin
  • Re-survey
  • Cut and roll clothing away from face
  • Wash wounds with water
  • Cleanse intact skin and avoid scrubbing
  • Repeat washing until radiation is <2x background
  • Cover wounds with waterproof dressings

• Internal decontamination
  • Consider if persistently high radiation survey readings and all nose/mouth contamination cases
  • Collect nasal/mouth swabs
  • ID contaminant
  • Assess intake
  • Minimise uptake and facilitate excretion
    • May warrant cathartics, whole bowel irrigation, activated charcoal or gastric lavage or radionuclide-specific decorporation agents
  • Bioassay samples (24 hr urine/faeces collection)
  • Dose assess

• Acute radiation syndrome
  • Analgesia
    • Avoid NSAID’s as risk of GI haemorrhage if dose >5-6 Gy
  • Antiemetics + loperamide as needed
  • Biologic dosimetry uses lab analysis (rate and nadir of lymphocyte depletion) + clinical symptoms/signs to estimate absorbed dose
  • Cytogenetic analysis for chromosomal aberrations (dicentrics) is gold standard
  • Not time of onset of all symptoms, especially vomiting and diarrhoea, as crucial for biologic dosimetry
  • If vomiting and diarrhoea occur within first 2-3 hours (dose >2Gy) consider need for HLA-typing in anticipation of pancytopaenia
  • Monitor vitals, ALOC, ataxia, motor or sensory deficits, reflex abnormaliities, papilloedema, GI tenderness and GI bleeding
  • Monitor for severe infectious and metabolic complications

• Local radiation injury
  • Analgesia
  • Traditional burn care
  • Typical steroids are helpful
  • Vitamin A, C, E and pentoxifylline (reduced blood viscosity and increases blood flow) supplementation help
  • Systemic steroids not recommended

Prenatal exposures

• Foetus is protected by uterus and surrounding tissues
• Alpha and beta particles unlikely to reach fetus
• Internal contamination can expose fetus to high amounts of radiation as may accumulate in bladder of mother
• <2 weeks = all or none
  • >0.1Gy considered lethal
• 2-8 weeks = organogenesis
  • Neurological and motor system derangement
• >8 weeks
  • Ongoing CNS organoegneesis with risk of mental retardation and miscarriage
  • <0.05Gy would not be expected to produce an increased risk of non-cancer health effects

Last Updated on November 23, 2021 by Andrew Crofton