Radiation exposure is an important topic in medicine, especially for those working in environments where diagnostic imaging is frequently used. While it is important to understand the principles of managing radiation exposure accidents, they are thankfully extremely rare, and most of us will never encounter one. The consideration of radiation exposure in the workplace is perhaps of more practical importance.
Emergency medicine doctors and staff frequently encounter situations involving diagnostic imaging and therapeutic procedures that expose them to radiation. Even at low levels, prolonged or repeated exposure to ionising radiation can pose significant health risks. It is, therefore, imperative for emergency healthcare professionals to understand these risks and adhere to safety protocols to minimise exposure.
Types of radiation
Radiation can be subdivided into two categories: ionising and non-ionising. The primary difference between these two types of radiation lies in their ability to ionise atoms and molecules.
Ionising Radiation:
- Ionisation capability: High-energy radiation with enough energy to remove tightly bound electrons from atoms, creating ions.
- Types: Include X-rays, gamma rays, alpha particles, beta particles, and neutron radiation.
- Sources: Include medical imaging equipment (e.g., X-rays, CT scans), nuclear reactors, and radioactive materials.
- Biological effects: Can cause DNA damage, leading to mutations, cancer, and cell death. Short-term exposure can lead to acute radiation syndrome, while long-term exposure increases the risk of chronic health conditions like cancer.
- Uses in medicine: Primarily used in diagnostic imaging and cancer treatment.
Non-Ionising Radiation:
- Ionisation capability: Low-energy radiation that does not have enough energy to ionise atoms.
- Types: Includes ultraviolet (UV) light, visible light, infrared (IR) radiation, microwaves, and radiofrequency (RF) radiation.
- Sources: Sunlight (UV light), household appliances (microwaves), wireless devices (RF radiation), and infrared heaters.
- Biological effects: Generally considered less harmful than ionising radiation. Can cause thermal effects (heating of tissues), and prolonged exposure to high levels of non-ionising radiation, such as UV light, can lead to skin damage and increase the risk of skin cancer.
- Uses in medicine: Used in various therapeutic and diagnostic procedures, such as MRI (which uses radio waves) and laser therapies.
Pathophysiology of radiation exposure
Radiation exposure can lead to a range of biological effects, from cellular damage to systemic health issues, depending on the type of radiation, dose, distance and duration of exposure.
Radiation damage occurs in two ways:
- Direct damage: This occurs when ionising radiation directly ionises atoms within the DNA molecule, causing breaks in the DNA strands and disruption of DNA function. Direct ionisation can also inactivate proteins and enzymes, disrupting cellular processes.
- Indirect damage: This occurs when radiation interacts with non-critical target atoms or molecules, most commonly water. Radiation can ionise water molecules, producing free radicals, which can cause extensive damage to cellular components, including lipids, proteins, and nucleic acids.
The biological effects of radiation are classified into two categories:
- Stochastic effects: These occur by chance and typically without a threshold level of dose. The probability increases with dose. Examples include cancer and genetic mutations.
- Deterministic effects: These have a threshold dose and increase in severity with the dose. Examples include skin burns and radiation sickness.
Measurement of radiation
Radioactivity is quantified by determining the rate at which radioactive atoms decay, releasing alpha particles, beta particles, and/or gamma rays. The standard unit for measuring radioactivity is the becquerel (Bq), which represents one decay per second.
Radiation is measured using a variety of different units of measurement. The sievert (Sv) is the most well-known quantity and is used to quantify equivalent and effective doses, aiming to minimise stochastic effects like cancer risk. For practical purposes in medical imaging, millisievert (mSv) is often used. In contrast, the gray (Gy) is the reference unit for measuring tissue reactions, which are critical under high-exposure scenarios such as radiation emergencies.
Radiation safety in the medical workplace
Radiation safety is an important consideration for emergency medicine doctors who frequently work with diagnostic imaging involving ionising radiation. Adhering to safety protocols is essential to minimise exposure and protect healthcare professionals from potential health risks.
The ALARA (As Low As Reasonably Possible) principle is a safety principle designed to minimise radiation exposure by implementing practical measures. To maintain ALARA doses, medical staff should follow the three key principles of radiation protection:
- Time: Minimise the time spent near the radiation source.
- Distance: Increase the distance from the radiation source. Radiation dose falls with distance, as demonstrated by the inverse square law; doubling the distance between your body and the radiation source reduces radiation exposure by a factor of four.
- Shielding: Use appropriate shielding (lead aprons, thyroid shields, gloves) to protect against radiation.
The safety of individuals exposed to radiation at work is governed by the Ionising Radiation Regulations 2017 (IRR17), enforced by the Health and Safety Executive (HSE). Key limits and guidelines include:
- Effective Dose Limit: The limit for employees or trainees aged 18 and above is 20 mSv per calendar year.
- Equivalent Dose Limits:
- Lens of the Eye: 20 mSv per calendar year, or 100 mSv over five consecutive years, with a maximum of 50 mSv in any single year.
- Skin: 500 mSv per calendar year, averaged over any 1 cm² area of skin, regardless of the total exposed area.
- Extremities: 500 mSv per calendar year.
Radiation safety for pregnant and breastfeeding staff
- Upon declaration of pregnancy, the employer must conduct a risk assessment to ensure that radiation dose limits are adhered to. The dose limit for the fetus is 1 mSv over the duration of the pregnancy, which typically translates to a 2 mSv dose limit to the abdomen of the pregnant employee. No additional precautions are generally required for breastfeeding staff unless they are working in the nuclear medicine department.
Radiation Protection Advisors (RPAs): RPAs are external experts regulated by the Health & Safety Executive (HSE). Hospitals must consult them to ensure compliance with IRR17 regulations.
Radiation Protection Supervisors (RPSs): Appointed by hospitals, typically based in the radiology department, RPSs ensure adherence to local radiation safety rules and are the first point of contact for radiation-related concerns.
Reporting of Injuries, Diseases and Dangerous Occurrences (RIDDOR): Employers are required to report any workplace-related illnesses, including those related to ionising radiation exposure, such as occupational cancers, to the HSE.
Acute radiation syndrome (ARS):
Acute Radiation Syndrome (ARS), also known as radiation sickness, is a severe illness that occurs when the body is exposed to high levels of radiation, typically over a short period. ARS usually manifests after whole-body or significant partial-body irradiation, generally at doses greater than 1 Gy. The syndrome can affect various organ systems, including the hematopoietic, cutaneous, gastrointestinal, cardiovascular and neurological systems, either individually or in combination.
The severity of ARS symptoms correlates directly with the radiation dose received. Higher doses result in more severe clinical signs and symptoms, underscoring the importance of understanding and managing radiation exposure to mitigate health risks.
ARS has three phases:
- Prodromal phase: Occurs 0-2 days from exposure. Presents with varying degrees of nausea, vomiting, and diarrhoea occurring within hours of exposure. Severity depends upon exposure dose.
- Latent phase: After the prodromal phase, there is a symptom-free period, during which the exposed person shows no signs or symptoms of ARS. The extent of the latent period is also dose-dependent and typically lasts between 2-20 days.
- Manifest illness phase: This typically occurs between 21-60 days after exposure. Symptoms depend on the dose, and the classic syndromes are hematopoietic syndrome, gastrointestinal syndrome, neurovascular syndrome and cutaneous syndrome.
Hematopoietic syndrome:
- Pathophysiology: Hematopoietic syndrome primarily affects the bone marrow, which is highly sensitive to radiation. Doses greater than 2-3 Gy damage the hematopoietic system significantly. Radiation damages stem cells in the bone marrow, leading to decreased blood cell production. This results in immunosuppression, anaemia, and thrombocytopenia.
- Latency Period: Symptoms may not appear immediately but typically manifest within a few days to weeks.
- Symptoms: Include fatigue, weakness, increased susceptibility to infections, fever, and bleeding due to pancytopenia.
- Management: Treatment involves supportive care, infection control, blood transfusions, and, in severe cases, bone marrow or stem cell transplants.
Gastrointestinal syndrome:
- Pathophysiology: Gastrointestinal syndrome affects the cells lining the gastrointestinal tract, occurring at higher doses of 5-12 Gy. High doses of radiation cause damage to the rapidly dividing cells in the gastrointestinal mucosa, leading to the breakdown of the gut barrier, fluid loss, and infection risk.
- Latency Period: Shorter than hematopoietic syndrome, with symptoms typically appearing within a few days.
- Symptoms: Nausea, vomiting, diarrhoea, loss of appetite, and severe abdominal pain. Dehydration and electrolyte imbalances are common.
- Management: Supportive care, including fluid and electrolyte replacement, antiemetics, pain management, and antibiotics. Severe cases may require intensive care.
Neurovascular syndrome:
- Pathophysiology: Neurovascular syndrome occurs at doses exceeding 10-12 Gy and affects the central nervous and cardiovascular systems. It is the most severe form of ARS. Radiation-induced damage to the blood-brain barrier, cerebral oedema, and vascular injury. This results in acute inflammation increased intracranial pressure, and severe neurological impairment.
- Latency Period: Very short, with symptoms appearing within hours to a few days.
- Symptoms: Severe nausea and vomiting, disorientation, loss of coordination, seizures, and coma. Rapid onset of hypotension, shock, and cardiovascular collapse.
- Management: Primarily supportive, focusing on managing symptoms and preventing complications. The prognosis is poor, and survival is unlikely due to extensive damage to critical systems.
Cutaneous syndrome:
- Pathophysiology Radiation damages the rapidly dividing basal cells in the skin, causing inflammation, vascular injury, and impaired tissue regeneration. The severity depends on the radiation dose and the depth of penetration into the skin. It is especially common and important in patients with ARS consequent to a non-uniform exposure. It can occur either alone or in conjunction with other forms of ARS.
- Latency Period: Symptoms can develop early, within 1-2 days post-exposure, but the syndrome may take years to manifest fully.
- Symptoms:
- Acute phase: Erythema, oedema, blistering, pain, and itching.
- Latent phase: Temporary improvement with symptom reduction.
- Manifest illness phase: Recurrent inflammation, ulceration, necrosis and secondary infections.
- Chronic phase: Skin fibrosis, pigmentation changes, and increased risk of skin cancer.
- Management:
- Acute Management: Symptomatic relief with analgesics and anti-inflammatory drugs, meticulous wound care to prevent infections, and use of topical antibiotics if needed.
- Chronic Management: Advanced wound care with specialised dressings, growth factors, and possible skin grafts; scar management using silicone gel sheets, pressure garments, and laser therapy; regular surveillance for early detection of malignancies.
Long-term effects of radiation exposure:
- Carcinogenesis: Radiation exposure increases the risk of developing various cancers due to DNA mutations.
- Fibrosis: Chronic radiation exposure can lead to fibrosis in organs such as the lungs, liver, and kidneys.
- Cardiovascular Disease: There is an increased risk of cardiovascular disease due to damage to blood vessels and the heart.
Management of radiation exposure incidents
The management of radiation exposure incidents requires meticulous preparation, a swift acute response, and diligent long-term care. Proper training, equipment, and protocols are essential to ensure the safety and effective treatment of both patients and healthcare providers.
Preparation:
Preparation is critical and involves several key steps:
- Command and control: Establish clear lines of authority and responsibility.
- Training: Ensure all relevant personnel, including senior medical and nursing staff, receive comprehensive training in chemical, biological, radiological, and nuclear (CBRN) response.
- Equipment: Obtain appropriate protective clothing and radiation detection equipment.
- Notification: Develop clear criteria for when and how to notify appropriate authorities and departments.
- Resources: Utilise resources such as the Health Protection Agency (HPA) for guidelines and support.
Acute crisis management:
During the acute phase of a radiation incident, the following steps are crucial:
- Triage: Quickly assess and categorise patients based on the severity of their injuries.
- Exposure limitation: Implement measures to limit further radiation exposure to both the population and response personnel.
- Decontamination and Evacuation: Organise systematic decontamination procedures and ensure the safe evacuation of affected individuals.
Personal safety recommendations:
- At radiation levels of 0.1 mGy/h, personnel can safely administer life-saving or time-critical treatments.
- At levels above 0.1 mGy/h, the exposure is life-threatening, and personnel should not proceed.
- All staff should wear protective clothing and carry personal radiation meters.
Initial assessment and triage:
- Use the airway, breathing and circulation (ABC) system to assess patients.
- Prioritise treatment for those with life-threatening injuries and categorise others for further assessment.
- Evacuate non-injured and less severely injured individuals upwind for contamination assessment.
Decontamination:
- On-scene decontamination may not be feasible for large groups; however, removing clothing can eliminate up to 90% of contamination.
- Further decontamination involves hosing down with warm water and detergent using a rinse-wipe-rinse system, taking care not to abrade the skin.
Emergency Department procedures:
- Segregation: Divide the ED into areas for radiation-contaminated patients and non-contaminated patients.
- Safe transfer: Wrap patients in sheets to limit cross-contamination during transfer.
- Further segregation: Upon arrival, segregate patients into those with external contamination only, internal contamination only, and those with combination injuries (e.g., blast, flash, and thermal injuries).
Management of external radiation injuries
- Wound care: Rinse wounds with saline and leave them open until debrided and decontaminated. Surgical excision may be necessary for long half-life materials.
- Infection prevention: Close or cover wounds post-decontamination to prevent infection.
- Additional care: Provide adequate analgesia and antibiotic prophylaxis, consider vasodilator therapy, and refer to plastic surgery for grafting or amputation as needed.
Management of internal contamination:
- Dose reduction: Strategies include reducing absorption, dilution, blocking, displacement by non-radioactive nucleotides, increased elimination, chelation and decorporation.
- Specific treatments: The choice of treatment depends on the radioactive substance involved. For example, Prussian blue is used for caesium exposure, and bicarbonate is used for uranium exposure.
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