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Dental Radiography > Radiation sources & measurement > Flashcards

Radiation sources & measurement Flashcards

1
Q

What percentage of death is radiation responsible for?

A

1%

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2
Q

What percentage of cancer deaths is due to radiation?

A

4%

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3
Q

How many people are killed by radiation in the UK per year?

A

6588

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4
Q

What percentage NUMBER of medical radiographic examination are dental?

A

30%

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5
Q

What of radiation is environmental or artificial?

A

17% - environmental

83% - artificial

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6
Q

What percentage of medical exposures are due to dental?

A

3-9%

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7
Q

What percentage of medical and dental doses are avoidable?

A

45-50%

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8
Q

What affect does additional doses have on the human population?

A

Additional doses increase the number of cases seen.

Not likely to result in new disease and malformations as we have been exposed to radiation since the beginning.

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9
Q

Why is it important to measure radiation dose?

A

Hazards result from radiation doses, thus need to assess risk planned doses against benefit from the dose.

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10
Q

What properties of x-rays allow use to measure dose?

A
  • Excitation

- Ionisation

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11
Q

Name the dose meters that measure via the amount of ionisation?

A
  • Free ionisation chamber
  • Thimble ionisation chamber
  • Chemical conversion (Frickes’ Dose Meter)
  • Photographic ionisation
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12
Q

How does a Thimble ionisation chamber work?

A

Measures the amount of discharge due to ionisation.

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13
Q

How does a chemical conversion (Frickes Dose Meter) work?

A

Measures chemical changes due to ionisation.

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14
Q

What does a photographic density dose meter work?

A

Assesses dose through level of black caused by ionisation of Silver Bromide.

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15
Q

How doses a calorimetry dose meter work?

A

Measures heating due to excitation

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16
Q

Name the dose meters that measure exitation?

A
  • Calorimetry

- Thermoluminescent dose meter

17
Q

In a sentence how does a free air ionisation chamber measure dose?

A

Collects electrons and measures charge.

18
Q

In a sentence how does a thermoluminescent dose meter measure dose?

A

Assesses dose by measuring released stored energy, modified type on excitation.

19
Q

How does a freer air ionisation chamber work?

A

-Arrangements of the plates producesa measurable volume between plates
-Free electrons are liberated from air by ionising radiation
- Liberated electrons are allows to pass through the plate to a meter
-Measuring how many electrons shows how many ionisation events have occurred
Thus able to calculate the total energy transferred to the sample

20
Q

Why is the free air ionisation chamber not used to measure dose in practice?

A

Not practical as the machine is too large to be used everyday

It is a primary standard laboratory method.

21
Q

What can used to record personal dose?

A

Thermoluminescent dose meter (TLD)

22
Q

How does a thermoluminescent dose meter work?

A

-Work on modified type of excitation
-Electrons do not return directly to their original positions but are suspended in a state of increased energy
-Exposure of radiation raises the energy levels of electrons (excitation) from valency band
-These electrons are trapped by energy anomalies
-Electrons remain here until released by heating they then fall giving off light that can be measured.
Intensity of light is proportional to the dose received.

23
Q

What are the advantages of TLDs?

A
  • Tissue equivalent so dose reading is direct
  • Can be reused
  • Measures HP7 and HP10 (surface, deep)
  • Relatively inexpensive
  • Widely dynamic range
  • Reading can be recorded as effective dose
  • Can be produced in a wide variety of sizes
24
Q

What are the disadvantages of TLDs?

A
  • No permanent dose record

- Sensitive to extreme environments

25
Q

What is radiation exposure?

A

Number of ionisation events (C/kG) - off little use

26
Q

What is absorbed dose?

A

Total energy absorbed (J/kg- Grays Gy) - most common but not very informative.

27
Q

What is equivalent dose?

A

Weighted by radiation hazard but adds little in terms of x-ray assessment. (Sieverts -Sv)

28
Q

What is effective dose

A

Absorbed (Gy) x Radiation weighting factor (WR) x Tissue weighting factor (Sum of WT)
Most important but has little use in practice.
Measure in Sieverts (Sv)

29
Q

Why is effective dose an important measurement?

A

It is the only measurement that gives a realistic assessment of potential harm.

30
Q

What are the 15 tissue weighting factors?

A
  • Bone marrow
  • Colon
  • Lung
  • Stomach
  • Breast
  • Gonads
  • Bladder
  • Oesophagus
  • Liver
  • Thyroid
  • Brain
  • Salivary glands
  • Skin

Dental Radiography (6 decks)

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