ANSWERS

1. What 2 factors ensure the safety of the metal casing surrounding the entire x-ray tube?
   • It is earthed.
   • It is lead lined
2. What must be permanently fixed across the tube window, and why is its removal illegal?
   An aluminium filter; the purpose of which is to remove low energy photons that are not powerful enough to pass through the patient, but may be absorbed or scattered. These represent a serious hazard.
3. What is the collimation device of choice, and how is this superior to the old style cone?
   The light beam diaphragm. This allows much greater accuracy in collimation and centering of the primary beam. Collimation to the smallest area possible poses less risk of scattered radiation.
4. What is meant by a ratings chart?
   The details of maximum safe combinations of kV, mA and mAs according to the x-ray machine manufacturer's recommendations. These safety guidelines are important in order to prevent overload by excess heat production.
5. What is scattered radiation?
   Secondary radiation produced by incident photons which interact with the tissues of the patient and bounce off in random directions as lower energy x-ray photons. Scatter represents a serious hazard.
6. Is scattered radiation more of a risk in large or small patients (state your reason)?
   Large patients, since higher kVs are required in order to penetrate thick or dense tissues. The higher the kV, the greater the risk from scatter. In small patients, most scatter is reabsorbed by the animal's body tissues.
7. In addition to representing a serious health hazard, how else is scatter a problem?
   • May cause fogging of the radiographic image.
   • May cause flat films of low contrast.
   • May cause blurring of the image margins.
8. List precautions that may be taken to reduce radiation risks to personnel.
   • Collimation of the primary beam to as smaller area as possible.
   • Use the lowest kV possible.
   • Use a grid for tissues of a depth greater than 10cm.
   • Use a compression band for radiography of thick areas such as the abdomen.
   • Ensure that lead is sandwiched between the cassette and tabletop to avoid back-scatter.
   • Always use safety clothing such as lead aprons, sleeves and gloves.
   • Avoid manual restraint.
   • Ensure that staff rotation is employed for radiographic procedures.
   • A lead lined wall or lead screen should be positioned between the radiographer and the patient.
9. List categories of person who should not be involved in radiography.
   • The general public (owners may want to be present, but MUST be dissuaded).
   • Pregnant women and personnel actively trying to conceive.
   • Personnel under the age of 18 years.
   • Any member of staff who has not been fully trained in all aspects of radiography and ionising safety regulations.
10. What health hazards are posed by ionising radiations?
    • Somatic effects - causing changes in the tissues of the body.
    • Carcinogenic effects - causing tumours.
    • Genetic effects - causing mutations in the chromosomes of germ cells.
11. X-rays are described as latent and cumulative. Explain these terms in respect of radiation hazards.
    Most danger from radiation arises from repeated exposure to small quantities. Since x-rays are both invisible and painless, it is not possible to see their effects until irreversible damage has been done.
12. What law governs the use of radiation and radioactive materials?
    The Ionising Radiation Regulations 1999.
13. All veterinary personnel involved in radiography must have read and understood the Ionising Radiation Regulations. In addition, guidance notes should be available that explain the law with respect to radiography in veterinary practice. What is the name of this booklet?
    The Guidance Notes for the Protection of Persons against Ionising Radiations Arising from Veterinary Use (July 1988). This is currently being re-written (as at 30/04/2001).
14. What is the role of the radiation protection supervisor?
    A senior member of staff who holds the responsibility for radiation safety in accordance with the regulations and local rules relevant to ionising radiations and radiographic procedures.
15. What is the role of the radiation protection adviser?
    An external adviser holding the Diploma in Veterinary Radiography. It is the responsibility of the RPA to demarcate the controlled area and draw up local rules and written systems of work. Things may change in 2003 in light of IRR99.
16. List 10 specifications that must be applied in relation to the controlled area.
    • The area must be physically demarcated and clearly labelled.
    • The radiation warning symbol must be displayed on the door.
    • A red light or sign must be displayed on the door and illuminated when radiography is in progress.
    • The area should ideally be within a specific room designed for radiography.
    • The room should possess thick walls; ideally lead-ply or barium plaster reinforced.
    • 2 members of staff should have room to stand at least 2m away from the x-ray tube head.
    • The local rules and written systems of work must be displayed
    • A lead-lined radiography table, or lead sheeting of a thickness of at least 1mm should be used.
    • Service records and exposure charts should be easily accessible.
    • Safety clothing and dosemeters should always be worn.
17. How should lead safety garments be stored and serviced?
    Aprons, gloves and sleeves should always be stored flat. Aprons must be hung on strong wooden coat hangers or purpose built rails. All lead garments should be periodically radiographed in order to detect any small cracks or holes that may not be immediately obvious.
18. Describe the 2 types of dosemeter commonly used in veterinary radiography.
    • Film badges - these contain a small piece of x-ray film.
    • Thermoluminescent badges - these contain radiation sensitive crystals.