How do you limit the dose to the patients and yourselves?

Question 1

What is the difference between everyday risks and diagnostic radiology?

Answer 1

The difference is that patients do not choose to be put at risk - it is the clinician’s decision and they have to decide what is an acceptable level of risk for the patient, therefore, they need to be aware of the magnitude of the risks involved as well as the potential benefits

Question 2

What way can the risks associated with ionising radiation be eliminated?

Answer 2

The only way they can be eliminated is by not using x-rays at all

(this is unacceptable as it is necessary to take x-rays within dental practice)

Question 3

What is the legislation that is principally concerned with the safety of workers and the general public i.e. designed to protect workers?

Answer 3

Ionising Radiation Regulations 1999 (IRR)

Came into force 1st Jan 2000
Replaced IRR 1985
Full details can be found on 2001 Guidance Notes Dental Practitioners

Question 4

Which regulations are concerned with the safety of patients?

Answer 4

Ionising Radiation Medical Exposure Regulations (IRMER) 2000

Came into force 13th May 2000
Replaced the Ionising Radiation (Protection of persons undergoing medical examination or treatment) Regulations 1988

All details can be found in 2001 Guidance notes Dental Practitioners

Question 5

What is set out by the IRMER 2000 regulations?

Answer 5

• Defines new positions of responsibility - employers, referrers, practitioners and operators. Employers responsible for overall radiation safety and must provide written procedures for all exposures. Referrers, Practitioners and Operators have specific roles and must perform their specific duties.
• All medical exposures must be justified
• All doses must be kept as low as reasonably practicable
• Clinical audit must be undertaken
• Equipment must be checked for safety and an inventory must be maintained.
• Operators and Practitioners must have received adequate training.
• Operators and Practitioners must undertake continuing education to keep their knowledge up-to-date.

Question 6

What is the name of the body that gathers research data and provides recommendations to governments around the world regarding radiation dose limits?

Answer 6

International Commission on Radiological Protection (ICRP)

Question 7

What are the three principles of the ICRP?

Answer 7

1. JUSTIFICATION - positive net benefit
2. OPTIMISATION - ALARP as low as reasonably practicable
3. LIMITATION - dose does not exceed limits

Question 8

Which legislation introduced the annual dose limits?

Answer 8

Ionising radiation regulations (IRR) 1999

Question 9

Outline the 3 categories that physical and practical methods of dose limitation can be divided into

Answer 9

1. Equipment used - x-ray generating equipment, image receptors
2. Clinical judgement - decide whether a patient is exposed, how frequently and how much radiation is used
3. Practical radiographic techniques employed

Question 10

At what kV should dental equipment operate at?

Answer 10

70kV

Question 11

What filter should be built in to dental equipment?

Answer 11

In-built aluminium filtration

Question 12

What should be adjustable on dental radiography equipment?

Answer 12

kV, mA, time

Allows for short exposure times

Question 13

What generator should dental radiography equipment have?

Answer 13

DC generator/constant potential unit

Question 14

Should the focus to skin distance be short or long in dental radiography?

What shape should the beam be collimated into?

Answer 14

Long.

Rectangular shape.

Question 15

Who needs to test the radiography equipment prior to clinical use?

What 2 tests need to be done?

Answer 15

Installers and medical physicists.

TESTS: critically examined, acceptance tested

Question 16

Outline the ideal image receptors used in:

1. film radiography
2. extra-oral radiography
3. Digital imaging

Answer 16

1. E or F speed
2. Rare earth intensifying screens
3. Solid-state and phosphor plates (these require even less radiation than film)

Question 17

How does a higher kV result in a lower physical dose to the patient?

Answer 17

A higher kV produces more high energy photons.

If kV is increased, the penetrating power of the beam is increased, so less photons stop in the patient.

Question 18

How does aluminium filtration reduce the dose to the patient?

Answer 18

It removes the lowest energy photons from the beam.
The potentially most harmful photons cannot pass through the aluminium filtration, so the skin dose to patient is dramatically reduced

Question 19

What is the benefit of being able to adjust the exposure factors, the kilovoltage, the mA and the time?

Answer 19

The benefit is that you are able to optimise the dose to the patient, and increase the diagnostic yield by being able to vary contrast and the degree of film blackening

Question 20

How does DC or constant potential unit of radiography equipment lower the dose to patients?

Answer 20

It ensures that x-ray productions is kept at peak throughout the exposure. The overall energy of the photon beam is higher and exposure times are shorter.

Question 21

What is the benefit of a rectangular collimator?

Answer 21

It reduces the size of the film so that it is the same size as film packets.
They produce a much smaller beam than those from other devices.

Question 22

What is the benefit of long focus-to-skin distance (fsd)?

Answer 22

Reminder: fsd is the distance between the focal spot in the tubehead and the end of the spacer cone

The emerging beam is much narrower, there is less divergence so this reduces the area of the patient that is irradiated.

Question 23

What is the recommended measurement of aluminium filtration in radiographic equipment?

Answer 23

1.5mm of aluminium filtration

Question 24

What is the recommended focus to skin distance?

Answer 24

200mm

Question 25

How is the switch designed so that accidental exposure is prevented?

Answer 25

Timer switch has to be continuously depressed by the operator (dead man’s switch)

Question 25

How is the switch designed so that accidental exposure is prevented?

Answer 25

Timer switch has to be continuously depressed by the operator (dead man’s switch)

Question 26

What is the benefit of using faster films?

Which film is fastest- D, E or F?

Answer 26

The benefit is that shorter exposure times are required = the patient dose is lower

D-speed films are the slowest and is no longer recommended. E and F are faster.

Question 27

What is the benefit of using rare-earth intensifying screens with indirect action film?

Answer 27

Fewer photons are required to produce the green light which affects the green sensitive emulsion to create a visual image.
Rare earth screens are much faster than traditional calcium tungstate screens.

Question 28

What is the benefit of using digital image receptors (solid-state or phosphor plates)?

Answer 28

Increased sensitivity resulting in shorter exposure times with the resultant reduction in patient dose, particularly with solid-state type receptors.

Question 29

What book was published to assist dentists in making a clinical judgement as to whether an x-ray is needed?

Answer 29

Selection Criteria for Dental Radiography

by the Faculty of General Dental Practitioners of the Royal College of Surgeons England (2004, prev. 1998)

Question 30

What is the definition of selection criteria?

Answer 30

• Description of clinical conditions derived from patient signs, symptoms and history that identify patients who are likely to benefit from a particular radiographic technique
• Evidence-based recommendations (not rigid) on why radiographs should be taken, when they should be taken and how frequently

Question 31

What are the general recommendations for taking radiographs?

Answer 31

1. Use of image receptor holders with beam-aiming devices to produce geometrically accurate images.
2. Take minimum number of images
3. Avoid re-takes by trying to get it right first time
4. Chemically processing films under optimum conditions (manually or automatically)
5. Optimise digital images to maximise diagnostic yield
6. Strict quality assurance procedures should be adhered to
7. Use appropriate protective lead apron

Question 32

Are lead aprons currently recommended to be used in dental radiography

Answer 32

Current recommendations say there is no justification for the routine use of lead aprons in dental radiography, the use is also discouraged when taking panoramic radiography.
It is regarded as the least important method of reducing dose to patients - it is regarded as unnecessary.

Question 33

Why is the lead apron not considered necessary in dental radiography?

Answer 33

In most dental radiography, the main beam is aimed at the face, which will receive the maximum dose and will be at maximum risk.

The other reduction techniques and equipment has a far greater influence on reducing the dose than the aprons.

Question 34

What is one type of lead protection that is considered necessary?

Answer 34

Use of thyroid shield - thyroid has it’s own tissue weighting factor as it is a particularly radio sensitive structure and is very close to area irradiated when conducting dental radiography.

Question 35

In what scenario may you x-ray a pregnant or possibly pregnant woman?

Answer 35

If a clinical procedure needs to be carried out that requires x-ray evidence.

This is outside of routine care that could potentially wait

Question 36

When is the use of a lead apron a legal requirement?

Answer 36

If a pregnant or possibly pregnant patient is having a radiograph that is aimed at the pelvic region (so highly unlikely in dental practice)

Question 37

Why may you offer a lead apron to a pregnant patient?

Answer 37

For potential psychological benefit - dentistry should be seen as a caring profession

Question 38

What are the golden rules for staff? (3)

Answer 38

1. 2m away from x-ray machine and patient or behind lead screen; never stand in line with main beam and always stand outside the controlled area. (the exclusion zone for most equipment is 1.5m so if you stand 2m away then you are definitely outside of the controlled area)
2. Never hold x-ray packet in patient’s mouth
3. Never hold x-ray tube head during an exposure

Question 39

What are the ‘specific duties of employees’ laid out by IRR 1999 (that also applies to students) listed in the guidance notes? (3)

Answer 39

• All employees and students should not knowingly expose themselves or any other person to x-rays to a greater extent than necessary for the purposes of their work.
• Employees and students must exercise reasonable care when working with any aspect of dental radiology.
• employees and students must immediately report to their employers or a member of staff whenever they have reasonable cause to believe that an incident or accident may have occurred leading to an over exposure.

Question 40

How could the members of the dental team measure the radiation dose they have received?

Answer 40

Yellow thermoluminescent dose meter
Blue film badges
Electronic personal dosemeter

Question 41

Why are dental team members not HAVE to monitor the radiation dose they receive?

Answer 41

Because they are unclassified workers

Question 42

Who else may the ‘golden rules’ apply to in a dental practice? (3)

Answer 42

Other people in clinical area e.g. waiting rooms
People who work in reception
People walking in corridors

Question 43

Why may you need to consider walls when designing a surgery/where to position an x-ray beam?

Answer 43

If a stud partition wall made of timber, x-rays could pass through and irradiate someone on the other side

May need lead protection or perhaps a layer of barium plaster to reduce amount of radiation passing through

This requires a physicist to measure radiation through the wall.