Field Radiography and Radiation Safety Regulations

Field Radiography

• Learning Objectives:
  • Apply safe radiation use in field settings.
  • Understand the balance between safe ionising radiation use and equine handling safety.
  • Optimise image quality for equine radiographs.

Ionising Radiations Regulations 2017

• Approved code of practice and guidance.
• Dose limits set.
• Estimate doses to members of the public.
• Outline duties of employees and employers for regulatory compliance.

Health and Safety Executive (HSE) 2021 Update

• All generators must be placed on a stand.
• Holding generators is unacceptable due to increased exposure risk and potential electric shock.

Radiation Safety - 3 Major Principles

• Clear clinical indications are required for any procedure involving ionising radiation.
• Avoid unnecessary X-ray safaris.
• Justify radiographic use with detailed clinical examination and diagnostic analgesia where applicable.
• Exposure of personnel must be kept as low as reasonably achievable (ALARA principle).
• Dose limits for individuals must not be exceeded.

Field Radiography Challenges

• Expensive equipment around large animals.
• Lack of permanent control zones; need to apply local regulations for ionising radiation.
• Variable facilities availability.
• Working with owners and untrained staff.
• Time constraints and pressures.
• Frightened horses make poor decisions.

Personnel

• Number of people required for equine limb radiographs.

Controlled Area

• Ideal locations for radiographs, avoiding stables where possible.
• Adequate space, level, dry ground.
• Power supply.
• Dark areas for clear visualisation of centering and collimation lights.
• Minimise traffic within the area.

Temporary Radiation Control Zone

• Biggest risk: 2m around the horse.
• Minimize personnel in the controlled zone.
• Maintain distance from the beam.
• Double the distance reduces exposure risk by 4x.
• The controlled radiation area for mobile X-ray is dependant on beam direction, distance attenuation and shielding.

Radiation Protection

• Personnel within the controlled area must wear appropriate protective clothing including lead-lined gowns, gloves, and thyroid protectors.
• Staff must also wear radiation dosimeters beneath protective clothing.
• Generator stands should be used.
• Cassette holders or plate blocks should be utilised.
• Personnel assisting should be over 18 years old and not pregnant.
• Obtain signed consent from clients assisting.

Personal Protective Equipment (PPE) considerations

• Avoid placing body parts behind the X-ray plate to avoid primary beam exposure.
• Be aware of scatter to protect all personnel.
• Gloves and gowns do not prevent primary beam exposure.

Personal Monitoring

• Specific dose limits for different classes of person.
  • 20mSv/year for 18+ employees
  • 6mSv for 16-18 year olds
  • 1mSv for members of the public and others
• Electronic personal radiation dosimeters and film badge dosimeters.

Patient Preparation

• Horses must be adequately restrained with person controlling the head.

• Potential uses of stocks.

• Sedation options with considerations for appropriate level and potential adverse effects in field conditions for quality images:

• Light to moderate sedation using alpha-2 agonist (Xylazine, Detomidine, Romifidine). The effect on sedation differs between each drug.

• +/- Butorphanol for an additional moderate effect.

• Safety and better quality images.

• Sedation/movement considerations for proximal anatomy, duration of exposure.

• Ensure the horse is standing on a flat and even surface.

• Thoroughly clean the area with removal of mud and organic matter to avoid artefacts.

• Hoof preparation, potentially removing shoes where applicable and cleaning and preparing the hoof.

• Use Playdoh to remove air interface considerations.

Packing the Feet

• Method and considerations.

Exposure Factors

• Use exposure charts to reduce retake rate, specific to relevant equipment.
• Understand FFD (focus-to-film distance) for the generator.
• Increased tissue thickness requires more mAs
• Decreased tissue depth reducesmAs required accordingly.
• Considerations of kV (contrast) and mAs (opacity).

Positioning

• Considerations for the horse and area of interest.
• Limb and joint positioning.
• Location of X-ray generator and plate.
• Horse needs a firm, level standing with limbs squarely below.
• Foot blocks for foot series, positioning.
• Ensuring cable reaches both sides of horse.

Processing

• Selecting the correct body part in the DR (direct radiography) system.
• Algorithms; ensuring best quality is possible, cannot be changed after the fact.
• Marker placement dorsal or lateral to region being imaged, important for symmetrical areas such as foot and fetlock.

Spot the Difference

• Recognising areas/issues from images provided.

When to Refer

• Situations requiring higher exposures, (neck, back, chest).
• Limitations of portable generators (kV exposure range).
• Maintaining alignment between generator and plate in the field environment without a bucky. Need for grid in required conditions.

Anatomical Positioning Terminology

• Oblique views explanation.

Foot

• Standard radiographic series.
  • Lateromedial
  • Dorsopalmar/Dorsoplantar
  • Dorsoproximal/Palmarodistal oblique.
• Additional views depending on pathology.

Fetlock

• Standard radiographic series.
• Additional views depending on pathology.

Metacarpus/Metatarsus

• Standard radiographic series.

Carpus

• Standard radiographic series.
• Additional views depending on pathology.

Hock

• Standard radiographic series.

Stifle

• Standard radiographic series.
• Consider additional views that may depend on pathology.

Others

• Radiographic areas that are best performed within a clinic.
  • Heads /dental
  • Neck
  • Back
  • Chest
  • Abdomen

Take Home Messages

• Protecting the health and safety of all.
• Appropriate working practices.
• Appropriate restraint.
• Appropriate patient preparation.
• Good positioning
• Appropriate exposures.
• Collimation.
• Understanding of projections for each area.
• Understand limitations of field work.