L5 Methods of Dose Reduction and Regulations Relating to Ionising Radiation Flashcards
What are the 3 principles of dose limitations by the international commission for radiological protection (ICRP)?
- No practice shall be adopted unless its introduction produces a net positive benefit
- All exposures shall be kept as low as reasonably practical
- The equivalent dose to individuals shall not excees the limits recommended by the commission
What are the 3 groups that the ICRP has concluded for the purposes of recommending and setting specific radiation dose limits?
- Occupationally exposed (workers)
- General public
- Patients (no dose limit)
What are the annual radiation dose limits for each group?
- Employees aged 18 or above: 20mSv
- Trainees aged under 18 and non-classified workers (e.g. dentists): 6mSv
- General public: 1mSv
How can X-ray equipment be optimised to reduce patient dose?
- Use rectangular collimation
- Aluminium filter in beam to filter out low energy photons
- High kV (60-70) less likely to be absorbed by patient so overall lower dose
- Use DC unit to ensure X-ray beam is constantly high energy and pateint recieves lower dose
How can image receptors be modified to reduce patient dose?
- Recommended to use digital systems
- Holders and beam aiming devices should be used
- If film is used, a cassette with intensifying screen should be used, and speed of film-screen system at least 400
How can radiographic technique be modified to reduce patient dose?
- Use paralleling technique instead of bisecting technqiue
- Have a long focus to skin distance, reduces area of patient being irradiated, less likely to irradiate salivary glands
When is PPE recommended in dental X-rays?
- Lead aprons are never recommended, the primary beam should never be directed towards the abdomen
- Thyroid shield recommended for dental CBCT, panoramic, cephalometric or occlusal view X-rays
- Certain patient groups requiring unusual position techniques which may place the thyroid in the primary beam will also be recommended to wear a thyroid shield
What distance should staff be from the x-ray set?
1.5 metres
How can doses to operators be monitored?
- Film badge: cheap, provide permanent record, however film must be processed and it is a retrospective form of monitoring
- Thermoluminescent dosimeter: sensitive, re-usable, no processing, retrospective, expensive
- Electronic personal dosimeter: instant readout, accurate, no permanent record of exposure, not sensitive to low energy radiation
What considerations should be made for members of the general public in terms of dose reduction?
- Position of equipment
- Thickness and material of partition walls
- Surgery design, consult with RPA (radiation protection advisers)
