OMFPR 3: Radiation Safety and Protection Selection Criteria - Radiographic Prescription Guidelines

Naturally occurring background radiation

Main source of exposure for most people

3

Average exposure from background radiation is ___ mSv/yr

Radon (73%)

Main source of background radiation

2

Dose (mSv) of radon per year

Radon

Gas released from ground that enters home and buildings - largest source of background radiation

Alpha particles

Radioactive decay products of radon emit _____ _________ that affect cells in the lung

1980s: 83% background, 15% medical

2006: 50% background, 48% medical

1980s vs. 2006 breakdown of exposure

1980s: 68% conventional, 3% CT

2006: 11% conventional, 49% CT

Compare medical exposures of patients in the 1980s vs. 2006.

0.26%

Dental imaging accounts for what % ?

50 mSv annual effective dose limit

Occupational dose limit: relative to stochastic effects

150 mSv annual equivalent

500 mSv annual equivalent

Occupational dose limit: relative to deterministic effects

5 mSv annual effective dose limit for infrequent exposure

Nonoccupational dose limit: relative to stochastic effects

50 mSv annual equivalent

Nonoccupational dose limit: relative to deterministic effects

0.5 mSv equivalent dose/month

Occupational dose limit: embryo-fetus

1. Principle of justification

2. Principle of optimization

3. Dose limitation

3 guiding principles in radiation protection

Principle of justification

Dentist should identify situations where the benefit from diagnostic radiation exposure likely exceeds the risk of harm

Reduce unnecessary radiographic examinations

Most effective way to reduce unnecessary exposures is to...

In the dentist's judgement, it is reasonably likely that the patient will benefit by the discovery of clinically useful information in the radiograph

Radiographic exposures are only necessary when...

Principle of optimization

Dentists should use every reasonable means to reduce unnecessary exposure to their patients and themselves

ALARA (as low as reasonably possible)

The principle of optimization is often referred to as...

Dentists and their staff (not patients!)

Who does dose limitation apply to?

True

T/F: There are no dose limits for individuals exposed for diagnostic purposes.

No

Do patients have dose limits?

Posterior bitewings with panoramic exam or

Posterior bitewings and selected periapical images

ADA guidelines for new patient radiographs

Posterior bitewings at 6-12 month intervals (child)

Posterior bitewing exam at 6-18 month intervals (adult)

ADA guidelines for recall patient with increased risk for caries radiographs

Posterior bitewing at 12-24 month intervals (child)

Posterior bitewing exam at 24-36 month intervals (adult)

ADA guidelines for recall patient with no increased risk for caries radiographs

Evaluate patient and see

ADA guidelines for recall patient with periodontal disease

E

Receptor selection - film of a speed slower than _ speed should not be used for dental radiographs

F

Which speed is 20-50% less exposure than E-speed?

True

T/F: Rare-earth intensifying screens combined with high speed screen film is recommended (extraoral imaging).

False; significant dose reduction is already achieved with intensifying screen-screen film combination

T/F: A significant dose reduction for extraoral imaging is seen with digital sensors compared to screen films.

Length of position indicating device (PID) of x-ray tube

How is source-to-skin or focal spot to film distance (FFD) controlled?

Less

Do we want the beam to be more or less divergent?

Increases (sharpness, fog)

Reduction in exposed tissue volume as the x-ray beam is less divergent _________ image quality.

Rectangular

____________ collimation decreases radiation dose.

60% (five fold)

Dose reduction achieved with a rectangular collimator vs. round is almost __%.

Rectangular PID

What limits the size of the x-ray beam to the size of intraoral sensor reducing unnecessary exposure?

Filtration

Removes low energy x-ray photons from the x-ray beam

Increase patient dose without contributing to image formation

What do low energy photons do?

Al

3mm of __: 80% reduction in exposure

1.5, 2.5

Federal requirements:

___ mm Al: 50-70 kVp

___ mm Al: > 70 kVp

If all NCRP recommendations are followed

When are aprons not necessary?

Yellow tab, yellow ring, bent rod with yellow prongs

Posterior PA appearance

White tab, blue ring, bent rod with blue prongs

Anterior PA appearance

Blue tab, red ring, straight rod

Bitewing appearance

PID

Reference marks for aligning ___ of x-ray tube to prevent cone-cuts

60 and 80

Operating potential of dental x-ray machines must range between 50 and 100 kVp but should range between what kVP?

High (reduces patient dose)

Is high or low kVp better? Why?

High: pass through

Low: absorbed by patient

What will happen to the x-ray beams with high vs. low kVp?

kVp: quality (power of penetration)

mA: amount (amount of photons)

kVp vs. mA

mA-s

Amperage and time settings for optimal quality radiographs that controls radiographic density

6 feet, 90-135 degrees

If no barrier, what is the position and distance rule for operators?

True

T/F: Operator should not hold sensor receptor holder during exposure.

False; neither

T/F: Either the operator or patient can hold the radiographic tube housing during exposure.

Film badges

Which personal monitoring device:

Special type of sensitive film in a special holder with metallic filters

Attached to external area

Reasonably accurate

Not for periods of longer than 1 month

TLD (thermoluminescent dosimeter)

Which personal monitoring device:

Lithium fluoride crystal

Absorb energy which will be read by a special reader

Reusable

More sensitive and accurate

True

T/F: Quality assurance protocols for x-ray machines, imaging receptors, film processing, and lead aprons should be developed and implemented in every dental practice.