Module 4 Flashcards by Valicia Ruparelia

Define radiation dose

Amount of radiation received by patients from different X-ray exams

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Define reference dose

Dose level which is set for every radiographic exam.

It shouldn’t be exceeded.

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Define radiation dose limits

Maximum levels of radiation to patients (only if clinically necessary)

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Define Natural background radiation dose

Naturally occurring radiation from foods, radon gas, rocks, earth’s crust and space.

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What is the natural background radiation dose calculated as in the UK per year?

2.23 mSv

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What are the 3 main dose units in radiation?

Radiation absorbed dose (D)
Equivalent dose (Ht)
Effective dose (E)

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What is the unit for Radiation absorbed dose?

Gray (or milligrays)

- measured in Joules/kg

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What is the unit for Equivalent dose?

Sievert (or millisievert)

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What is the unit for Effective dose?

Sievert (or millisievert)

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How can you calculate the Radiation absorbed dose?

Dosimeter

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How can you calculate the Equivalent dose?

H(t) = D x W(r)

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How can you calculate the Effective dose?

E = H(t) x W(t)

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Define Radiation absorbed dose

Measure of the amount of energy absorbed from the radiation beam per unit mass of tissue

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Define Equivalent dose

Measure that indicates the different radio-biological effectiveness of different types of radiation.

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Define Effective dose

Measure that allows doses from different investigations of different parts of the body to be compared.

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What does W(t) stand for?

Tissue weighting factor

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What is the W(t) for bone marrow?

0.12

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What is the W(t) for salivary glands?

0.01

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What is the W(t) for gonads?

0.08

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What is the W(t) for breast?

0.12

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What is the W(t) for lungs?

0.12

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What is the W(t) for thyroid?

0.04

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What is the W(t) for skin?

0.01

What is the W(t) for oesophagus?

0.05

What is the W(t) for bone surface?

0.01

What is the W(t) for brain?

0.01

What is the W(t) for oral mucosa?

0.12

What is the effective dose for a bitewing/PA radiograph?

0.0003-0.022 mSv

What is the effective dose for an OPG?

0.0027-0.038 mSv

What is the effective dose for an upper standard occlusal?

0.008 mSv

What is the effective dose for a lateral cephalometric radiograph?

0.0022-0.0056 mSv

What is the effective dose for a skull radiograph (PA)?

0.02 mSv

What is the effective dose for a skull radiograph (lateral)?

0.016 mSv

What is the effective dose for a head CT?

1.4 mSv

What is the effective dose for a mandible/maxilla CT?

0.25-1.4 mSv

What is the effective dose for a barium swallow?

1.5 mSv

What is the effective dose for a barium enema?

2.2 mSv

What is the effective dose for a CBCT (dento-alveolar)?

0.01-0.67 mSv

What is the effective dose for a CBCT (craniofacial)?

0.03-1.1 mSv

How can the dose be reduced?

- Change speed of film to faster speed. - Use 70kV equipment. - 200mm fsd. - Rectangular collimator to produce rectangular beam.

What % of X-rays taken each year are dental?

40%

What should the reference dose be of a mandibular molar PA for an adult?

4 mGy per millimeter

What should the reference dose be for an adult OPG?

65 mGy per millimeter

How does the reference dose aim to protect patients?

Identifying high dose equipment that can be adjusted or taken out of service.

True or false: The effective dose takes into account the part of the body being irradiated?

True

What statements are true of: | 'the risks of ionising radiation' ?

- If 1 million patients had an OPG radiograph, approximately one excess cancer would be expected. - The risk of radiation-induced cancer is increased as radiation dose increases.

What number of patients can be expected to get cancer per year for intra-oral radiographs?

1 in 2 million exposures = cancer. 1 in 20 million exposures = cancer (with modern 70kV, fast E speed films = lower dose).

What are some examples of radiation dosimeters?

- Thermo-Luminescent Dosimeters (TLD) or film badges. | - Electronic dosimeter.

What does justification, optimisation and limitation mean?

- Justification = benefit of radiograph must outweigh the risks (only if clinically necessary). - Optimisation = ALARP. - Limitation = Dose shouldn't exceed appropriate limits.

What are the 3 groups that the population is divided into?

- Patients - Radiation workers - Public

What are the dose limits for patients?

No set dose limit

What are the dose limits for radiation workers?

Classified workers (those in nuclear power industry) = 20 mSv. Non-classified workers (dental) = 6 mSv

What are the dose limits for the general public?

1 mSv

What is the estimated number of fatal malignancies per year in the UK associated with dental radiography?

10-12

What is the estimated number of genetic stochastic effects (dental radiography) in the UK?

1 congenital abnormality every 3 years

Who is more at risk with radiographs: younger or elderly patients?

Younger