Contributors: Vetstream Ltd, Sam Jakovljevic

 Species: Canine   |   Classification: Miscellaneous

Introduction

  • Radiation is a form of energy:
    • Ionizing radiation (eg X-rays) has sufficient energy to ionize atoms and cause damage to biological tissues. The source of ionizing radiation includes for example X-Ray generators and radio-active material.
    • Non-ionizing radiation (eg UV, microwaves, radio waves) is less energetic and unable to cause ionization.
  • It is essential to follow rigid safety guidelines when dealing with ionizing radiation that is a serious safety hazard because:
    • It is invisible.
    • It is painless.
    • It penetrates and interacts with biological tissues to produce:
      • Cumulative effects.
      • Latent effects, which may manifest at a later time.

Interaction of ionizing radiation with matter

  • General interactions of X-Rays with tissues:
    • A 100 kVp incident beam on a tissue will result in:
      • 98% being absorbed.
      • 1% being scattered.
      • 1% being transmitted.
  • Absorbed dose: total amount of radiation absorbed by an object (International System of unit or SI unit: Gray (Gy)).
  • Equivalent dose: absorbed dose x radiation weighing factor, to account for how harmful a type of radiation is to biological tissues (SI unit: Sievert (Sv)).
  • Effective dose: equivalent dose x tissue weighing factor, to account for the radiosensitivity of different organs and the increased risk of the patient developing stochastic (see below) effects (SI unit: Sievert (Sv)).

Biological effects of ionizing radiation

​Types of damage

  • Direct damage: results in break of molecular bonds within cells (eg DNA).
  • Indirect damage: results in interaction with water leading to creation of free radicals, which in turn can break molecular bonds within cells.

Types of effects

  • Deterministic effects: they occur at a specific dose threshold and represent tissue reactions; the severity of these effects is dose-dependent. Rapidly dividing cells are most sensitive and radiation sickness reflects body systems affected (eg dermatitis, burns, cataract, gastrointestinal disturbance or changes in blood). The latter are known as somatic effects.
  • Stochastic effects: represent effects that have no threshold and occur randomly. The severity of the effects is not dose-dependent, but the probability for the effects to occur is dose-dependent.
    • Carcinogenic effect: tumors may be induced decades after the radiation exposure
    • Genetic effects: mutations may occur in the chromosomes of germ cells in the ovaries or testes, with potential effects in the offspring.

Radioprotection in radiography

  • The main goal is to keep the radiation dose As Low As Reasonably Practicable (Achievable) at all times: the ALARP (ALARA) concept:
    • Doses are kept lower than the threshold for deterministic effects.
    • As there is no threshold for stochastic effects, doses should always be kept as low as possible.
  • In radiography, the ALARP concept can be applied to:
    • X-Ray equipment.
    • Radiographic technique.
    • Protection of staff.
    • The radiography room.

X-ray equipment

  • Well-maintained equipment (eg generator, X-Ray tube and support, table, processor(s)) and leakage radiation through tube head should be checked annually.
  • Long exposure cable should be installed (2 meters).
  • Light beam diaphragm:
    • The X-ray beam and light beam alignment should be regularly checked. Position a cassette on the radiography table and set the focus to cassette distance at 1 m, outline the corners of the light beam with metallic paperclips and expose the cassette. After processing, misalignment between the X-ray beam and the light beam can be assessed and should be less than 1 cm.

Radiographic technique

  • Use correct exposure factors:
    • All the exposures should be recorded in a logbook.
    • Preferably based on a well-established technique chart individualized for a specific radiographic system. Keep in mind that:
      • Too high kVp will lead to increased scatter production by the patient, increased scatter in the radiography room and reduced image contrast.
      • Too low kVp may lead to increased exposure time, with a likelihood of motion artifacts and a need for repeat examination.
  • Use maximum adequate collimation (in any case never allow the primary beam to expose an area beyond the confines of the imaging recording device) in order to minimize scatter emitted by the patient and loss of image contrast.
  • Use a grid for subjects >10 cm thick.
  • For table top techniques, it is recommended that radiography be performed with the cassette positioned on top of a lead sheet in order to:
  • Reduce penetration of the primary beam through the table.
  • Absorb scattered radiation from the patient and from the table (backscatter) towards the cassette.

Protection of staff

  • Protection of staff means in effect protecting staff against secondary radiation (lower energy radiation) - no part of a staff body should ever be located in the primary beam (higher energy radiation).
  • Scatter (secondary radiation) is produced in any direction when the primary beam is incident on an object. Therefore:
  • Methods of protection against scatter radiation (time, distance, shielding):
    • Time:
      • Always minimize your time close to a source of radiation.
      • Reduce number of radiographic examinations to the necessary minimum.
    • Distance:
      • Maximize your distance to any source of radiation. The radiographer should stand as far away (at least 2 m) from the patient and tube head as possible (a long exposure cable permits this).
        • If standing less than 2 m away from the source of radiation is absolutely necessary, wear personnel protective equipment (PPE) or stand behind an adequate lead screen.
        • Cracks in the lead lining of the X-Ray tube may allow radiation to escape in any direction (the integrity of the lead shield should be regularly checked).
    • Shielding:
      • Personnel protective equipment (eg lead aprons and thyroid shields (at least 0.25 mm lead equivalent protection), lead gloves  (at least 0.5 mm lead equivalent)) should be worn by anyone within the controlled area and not behind a lead screen during an exposure:
        • PPE do not protect against primary radiation, only against scatter (secondary) radiation.
        • Lead aprons should cover trunk, gonads and extend to mid-thigh .
        • Lead aprons should be stored on hangers or racks and never folded to avoid creating cracks which compromise protection .
        • Hands should be contained within a shield, ie not a lead sheet draped over hands as this does not protect against scattered radiation arising from the patient being radiographed.
      • If using horizontal beam radiography, the tube should be orientated towards a lead screen to suppress radiation beyond the screen.
      • Provide a lead sheet to lay on the radiography table underneath the imaging recording device when using table top techniques.
    • Patient restraint:
      • Manual restraint of patients should be strictly avoided whenever possible; positioning should be facilitated by:
        • Sedation or anesthesia of the patient as necessary.
        • Providing a range of positioning aids (eg foam pads of different shapes, ropes, sandbags, tape Radiography: positioning aids).
      • If manual restraint during radiography is absolutely essential, PPE should be used, standing as far from the primary beam and animal as possible by extending the arms, closing the eyes and turning the head away from the patient during the exposure.
    • Radiation protection training: provisions should be in place for training new radiation staff and providing regular refreshers to existing staff.
  • Dosimetry:
    • Monitoring radiation exposure:
      • Film badges or thermoluminescent dosimeters, which are usually sent away for processing. Ideally radiation exposure for staff should be below the minimum reporting level (zero reading).
      • All those regularly involved in radiography should wear monitoring devices. They should be worn on the trunk beneath protective clothing.
      • Additional dosimeters may be worn on collar to measure dose to unprotected parts of body, on forehead to measure eye dose or on a finger to measure dose to arms and hands.
      • Dosimeters may also be placed in the radiography room, adjacent rooms or nearby areas to monitor environmental risk.
      • Radiation doses are documented and retained for each member of staff.
      • Exposure is measured in Gray (absorbed dose).
    • Film badges:
      • They contain small pieces of photographic film.
      • Various aluminium filters are enclosed within the badge.
      • After being worn for a period of time the film is developed.
      • The exposure can be calculated by the degree of film blackening under different filters.
    • Thermoluminescent dosimeters (TLD):
      • They contain radiation-sensitive crystals.
      • Radiation exposure causes electrons to be trapped within the crystals.
      • When the material is heated to hundreds of °C, the electrons escape from the traps and their energy released as visible light.
      • TLDs are small and chemically inert.
      • They are capable of storing dose readings for long periods of time.
    • Dose limits:
      • Average annual dose of the UK population:
        • About 80% is from natural background radiation (cosmic rays, food and drink, radon gas, ground and buildings). The remainder 20% represents man-made radiation exposure (mostly medical, but also air travel, fallouts from nuclear weapons, nuclear industry, occupational).
        • The average effective dose of natural background radiation to someone living in the UK is about 2.7 mSv/year (1 to 8 mSv depending on living location, the variation being mainly due to radon gas).
        • The annual effective dose, based on 700 hours of flight for subsonic aircraft and 300 hours for the Concorde, can be estimated at between 2 mSv for the least exposed routes and 5 mSv for the more exposed routes.
        • < 0.1 mSv is the effective dose typically recorded on a whole body badge from a vet in 2 months.
      • Maximum Permissible Doses (MPD):
        • MPD are doses not thought to constitute a greater risk to health than encountered in everyday life.
        • Levels are set for acceptable exposure to different body parts, eg lens of the eye.
        • Classified workers are those likely to receive more than three tenths of any relevant MPD (eg staff working in the nuclear industry). Veterinary workers are rarely designated as classified personnel.
        • MPD (per year) under IRR17:
        • Employees and trainees (18 y and over):
          • Whole body: 20 mSv.
          • Skin and extremities: 500 mSv.
          • Eye: 20 mSv.
        • Trainees (16-17 y):
          • Whole body: 6 mSv.
          • Skin and extremities: 150 mSv.
          • Eye: 15 mSv.
        • Any other person:
          • Whole body: 1 mSv.
          • Skin and extremities: 50 mSv.
          • Eye: 15 mSv.
  • Radiography room:
    • A self-contained room with brick walls should be designated as the x-ray room.
    • A controlled area around the primary beam where the average dose rate of exposure exceeds a limit set by regulations should be established (never larger than the X-Ray room):
      • Usually within a 2 m radius from the primary beam.
      • The controlled area is defined by the Radiation Protection Advisor (RPA).
      • The controlled area must be demarcated and defined by adequate signage, so it is practically easy to define the X-Ray room as a controlled area.
      • A “Mains On” light and exposure warning light must be visible outside the access to the controlled area.
      • When the x-ray machine is disconnected from its power source the room reverts to a normal room.
    • Local Rules should be posted in the X-ray room. All the staff involved with radiography should acknowledge that they have read and understood the Local Rules and this should be recorded.
    • Ideally personnel in the room should be able to stand more than 2 m from the tube head and the primary beam during exposure. If this is not possible, a lead screen (fixed or mobile) should be made available within the room.
    • Special considerations should be made (the Radiation Protection Adviser should be involved) if there is a room beneath or above the designated room!

The Law (in a nutshell)

  • The new Ionizing Radiation Rules 2017 (IRR17) came into force on 1st January 2018.
  • Broadly speaking, there is little change from the Ionizing Radiation Regulations 1999 (IRR99).
  • The regulations are accompanied by ACOP, the Approved Code of Practice and guidance; it is a non-statutory guidance and practical advice on how to comply with the legislation.
  • The current UK Health and Safety Legislation for Ionizing radiation work is enforced by the HSE (Health and Safety Executive).
  • Most of the practical application of the regulations are the legal responsibility of the employer.
  • Legislation and what to do:
    • 1. Valid radiation risk assessment in place: it is the employer’s responsibility to protect employees against the danger of any type of radiation at the place of work (including radon)
    • 2. New graded system of authorization for work with ionizing radiations: the higher the radiation protection risk, the greater the requirements. A system of notification (lowest risk), registration (medium risk, includes most veterinary practices) and consent (highest risk) is now in place:
      • Ensure that you can comply with consent/registration questions when applying to HSE.
    • 3. The dose limit for exposure to the lens of the eye reduced form 150 mSv to 20 mSv:
      • Risk estimates must include an eye dose estimate.
    • 4. The definition of an outside worker has been extended and applies now to both non-classified (staff in most veterinary practices) and classified workers (eg staff in nuclear industry):
      • Establish which employees work as outside workers and which are employed by other employers performing radiation work.
      • Put in place procedures to ensure that outside workers entering your controlled areas receive the same degree of radioprotection as your employees.
      • Establish cooperation with other employers if necessary.
    • 5. Estimated doses to public from your work with ionizing radiations must be established.
    • 6. Pregnancy must be declared in writing to the employer. It is then the employer’s duty to ensure that fetal exposure is ALARP and in any case <1 mSv for the remainder of the pregnancy.
    • 7. Contingency plans need to be in place and stated in the Local Rules only for those situations that require immediate action.
      • Non-termination of an exposure is likely the only such a situation in general practice.
    • 8. Radiation Protection Adviser (RPA):
      • An RPA is appointed from outside the practice in writing. There is no need to re-appoint an RPA under the new regulations (IRR17).
      • Usually a veterinarian with a Diploma in Veterinary Radiology/Veterinary Diagnostic Imaging and associated knowledge of radiation physics. An RPA can be a medical physicist with an interest in veterinary radiography.
      • Advises on all aspects of radiation protection:
        • Local Rules.
        • Requirements for controlled and supervised areas.
        • Prior examination of plans for new or modified facilities (eg engineering controls (including shielding), design features etc).
        • Calibration of radiation monitoring equipment and its correct use.
        • Periodic examination and testing of engineering controls, design features, safety features and warning devices and systems of work.
    • 9. Radiation Protection Supervisor (RPS):
      • An RPS (or several in large practices) is (are) appointed from within the practice.
      • Usually a senior person within the practice.
      • Responsible for ensuring radiography is carried out safely according to the Local Rules.
      • Need not be present at each examination.
      • The employer must ensure that the RPS has all the necessary means to perform their role.
    • 10. Local Rules:
      • Set of instructions written by the RPA to govern the use of equipment and system of work.
      • Should be displayed in the radiography room.
      • Copy given to and read by anyone involved in radiography:
        • Includes a written system of work describing a guide to performing radiography:
          • i. Where possible direct the x-ray beam vertically downwards.
          • ii. Only indispensable staff should be present in the controlled area during an exposure.
          • iii. Everyone present in a controlled area should be wearing PPE or stand behind an adequate lead screen during an exposure.
          • iv. Primary beam should be adequately collimated.
          • v. Patient restrained adequately with positioning aids, sedation or general anesthesia (manual restraint only under exceptional circumstances).
        • Includes details of who may perform radiographic exposures: nobody under 16 should be present in the controlled area during an exposure.
        • Staff members 16-18 years old have lower maximum permissible doses and therefore should have a limited involvement.
        • Pregnant women should avoid radiography.
    • 11. It is a legal requirement that the employer provides regular radioprotection refresher training sessions to staff involved with radiation work, and that a record of attendance to these sessions is maintained.
    • 12. Any newly purchased PPE must be compliant with new standards for lead equivalence (CE mark).