6. How do you limit the dose to patients and yourself?

Question 1

LOs

Answer 1

• Explain the dose limitation principles of justification, optimisation, and limitation
• Give details of the radiation limits for patients and dentists and their staff
• Describe the practical radiation protection measures used for patients, including those women who may be pregnant
• Describe the practical radiation protection measures required for dentists and their staff within the dental surgery

Question 2

Classification of ionising radiation effects

Answer 2

Question 3

Aims of radiation protection

Answer 3

• Prevent DETERMINISTIC (certainty) effects
  + guaranteed to occur
  + have threshold dosage
  + have rules & have guidelines based on scientific evidence to prevent magnitude exceeding threshold dosage
• Limit probability of stochastic effects to acceptable levels
  + determine level of risk
  + physical methods of dose reduction

Question 4

what is an acceptable level of risk

Answer 4

• CANNOT be quantified
• different for everyone
• for x-rays patients do not choose to be exposed to ionising radiation
• dentist and Dr has to decide what is acceptable hence needs to know benefits and magnitude of risk

Question 5

how are radiation dose limits decided?

Answer 5

• X-rays = dangerous hence governed by law to ensure that the risk to various individuals is as small as possible
• based on recommendations by the International Commission on Radiological Protection (ICRP)
  (gather research)

Question 6

ICRP 3 principles on dose limitation

Answer 6

1. JUSTIFICATION
   - No practice shall be adopted unless there is a net positive benefit
2. OPTIMISATION
   - All exposures shall be kept as low as reasonably practicable
3. LIMITATION
   - The equivalent dose to individuals does not exceed the limit set by the commission

Question 7

Importance of X-ray examinations directly associated with illness

/

Number + type of radiographs taken is responsibility of clinician
Based on:

Answer 7

No set dose limits

Number + type of radiographs taken is responsibility of clinician
Based on:

• correct assessment of indications
• expected yields ( How much info is obtained )
• how the results will influence diagnosis and treatment
• clinician should have adequate knowledge of physical properties + biology effects of ionising radiation

Question 8

How is the dose to patients limited ?

Answer 8

Equipment = X-ray generating and image receptors

Clinical judgement

Radiographic technique

Question 9

What is the X-ray equipment requirements for dose limitation to patients ?

Answer 9

70 kV
Aluminium filtration
Adjustable kV , mA and time
- short exposure times

DC-constant potential

Long fsd - 200mm

Rectangular collimation

Critically examined and acceptance test

Question 10

What are the image receptor requirements for dose limitation to patients ?

Answer 10

Fast film ( E/F speed )

Rare earth intensifying screens

Digital - solid state or phosphor plate

Question 11

Benefit of having a higher kV

Answer 11

• Penetrating power of beam is increased
• Less photons stop in patient
• Lowers dose
• Produces more photons in continuous spectrum but increases the energy of the photons

Question 12

Benefit of using aluminium filtration

Answer 12

Removes lowest energy photons from the beam
Harmful protons cannot pass through aluminium filter

Question 13

Benefit of adjustable kV, mA and time

Answer 13

Able to optimise dose

Increase diagnostic yield

Ability to vary contrast and degree of film blackening

Question 14

Benefit of having DC-constant potential

Answer 14

Ensures X-ray production is kept at a peak

Overall energy of photon bean is higher and shorter exposure times

Question 15

Benefit of rectangular collimation

Answer 15

Reduces size of beam

Same size as film packet

Reduces area of face/body being irradiated

Question 16

Benefit of a long fsd

Answer 16

Emerging beam is narrower

Less divergence

Reduces area of patient that is being irradiated

Question 17

Current dental X-ray generating equipment recommendations

Answer 17

Operating range = 60-70 kV

1.5mm aluminium filter

Adjustable kV , mA and exposure time

DC - constant potential

Rectangular collimation = 40 x 50 mm

200 mm fsd

Exposure timer switch has to continuously be depressed

Question 18

Benefit of using faster intra oral film

Answer 18

Speed E or F

Shorter exposure times

Question 19

Benefit of using indirect action film + rare earth intensifying screens

Answer 19

Fewer photons required to produce green light which affects green sensitive emulsion to create visual image

Faster than traditional calcium tungstate screens

Question 20

Benefit of using digital sensors

Answer 20

Solid state

DC-constant potential

Question 21

Selection criteria for clinical judgement whether to use X-ray

Answer 21

Descriptions of clinical conditions

Derived from patient signs + symptoms

Identify patients who are likely to benefit from a particular radiographic technique

Evidence based recommendations

Question 22

Radiographic techniques used for dose limitation

Answer 22

Use image receptor holders with beam aiming devices to produce geometrically accurate images

Take minimum number of images

Avoid retakes

Chemically process films under optimum conditions
- manual or automatic

Optimise digital images to maximise diagnostic yield

Adhere to strict quality assurance procedures

Use appropriate protective lead aprons
- thyroid shield
- thyroid has own weighting factor
- radiosensitive structure

Question 23

Dose limitation requirements for pregnant patients

Answer 23

• Only take radiographs if clinically necessary
• Check justification
• Avoid periodic health checks
• Reassure and utilise all routine radiation safety measures
• Could offer protective lead apron
  + not essential
  + psychological benefit

Question 24

Physical methods of dose limitation form members of dental team

Answer 24

All staff must know risks to own health created by exposure to X-rays

All female staff should know risk of pregnancy + X-ray

All staff to know safety precautions

Golden rules

Question 25

Golden rules

Answer 25

2 metres away from X-ray machine + patient / behind a protective lead screen

Never stand in line of main beam

Always stand out of controlled area

Never hold X-ray film packet or image receptor in patients mouth