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imaging science > X-ray radiation dose > Flashcards

X-ray radiation dose Flashcards

1
Q

What is radiation?

A

Radiation is a means by which energy is transported through space or through matter

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2
Q

What are some examples of radiation?

A

Light, X-rays and radio waves are all forms of electromagnetic radiation

They exhibit both wave and particle like behaviour

There is no mass associated with the transfer of energy

Particles (with mass) can be viewed as radiations as they carry energy

Sound can be also viewed as a form of radiation as it has the properties of waves and carries energy

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3
Q

Radiation Ionising &
Non-ionising

A

Ionising
X-rays, g-rays, a-particles, b-particles, neutrons, cosmic rays

Non-ionising
Light, ultraviolet, infra-red, radio waves, microwaves, ultrasound

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4
Q

X-ray Radiation Dose Risk

A

Different measures of radiation dose
Absorbed dose
Equivalent dose
Effective dose

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5
Q

Absorbed Dose

A

Only absorbed energy can cause biological damage
A starting point for understanding such damage is to describe & quantify the absorbed dose

X-rays photons transfer energy into a material as kinetic energy of charged particles (electrons)
These electrons deposit their energy along ionization tracks
The energy per unit mass deposited by

Absorbed Dose
The primary physical quantity used in dosimetry is called the absorbed dose
It is defined as the energy absorbed per unit mass from any kind of ionizing radiation in any target
The SI unit of absorbed dose is called the gray and has SI base units of J kg-1

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6
Q

Measures of Radiation Dose: Equivalent Dose

A

Appropriate weighting factors can be applied to the absorbed dose reflecting the different relative biological effects of different types of radiation

This is termed the equivalent dose

Measure of the radiation dose to tissue where an attempt has been made to allow for the different relative biological effect of different types of ionizing radiation
Equivalent dose is therefore a less fundamental quantity than radiation absorbed dose but is more biologically significant.
Equivalent dose has SI units called sieverts and has SI base units of J kg-1

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7
Q

Equivalent dose (HT)
equation

A

Calculated by multiplying the average absorbed dose to the organ or tissue (DT) by a weighting factor (wR)
The weighting factor is selected for the type and energy of the radiation incident on the body

H,T,R= W,R x D,T,R

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8
Q

Measures of Radiation Dose: Different tissues of the body respond differently to radiation

A

The probability for stochastic effects that result from a given equivalent dose will generally depend upon the particular tissue or organ irradiated

A tissue weighting factor (wT) is introduced to account for this, giving rise to the concept of effective dose

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9
Q

Effective Dose (E)

A

Effective dose, E, is proportional to the stochastic health effects of radiation in humans
It takes into account the radio-sensitivity of different organs and also the equivalent dose to each organ

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10
Q

In radiography the only way to estimate effective dose is to

A

Measure the Entrance Surface Dose (ESD) or DAP for a specific examination (e.g. chest exam)
Lookup the effective dose for that examination in a published table
These tables are compiled using mathematical models to estimate internal organ doses

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11
Q

More commonly, diagnostic reference levels are used to gauge radiation received from a particular examination..?

A

National Diagnostic Reference Levels
Dose measurement audits for specific examinations can be undertaken within your department
ESD or DAP levels can be compared to the published diagnostic reference levels
They can also be used to estimate effective dose (risk) for specific examinations

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12
Q

Practical patient dose measurements in radiography

A

Entrance Surface Dose measured with:
Dosimeter
Directly
Phantom
TLD
Dose Area Product (DAP)

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13
Q

Entrance Surface Dose

A

The entrance surface dose (ESD) is equivalent to the absorbed dose in air at the surface of skin on the central beam axis at the position of the patient or phantom surface
Backscattered radiation from the patient is included in the measurement
It is also referred to as the entrance air kerma or the entrance surface air kerma (kerma - kinetic energy released in the medium)

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14
Q

Entrance Surface Dose Measurement

A

Can be measured with an ionisation chamber (dosimeter) close to the patient’s skin – this is generally not practical
Can be measured using a suitable test phantom – but may not represent the patient or spread of patients accurately

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15
Q

Dose Area Product (DAP)

A

DAP is a quantity that is becoming more common in assessing diagnostic reference levels in radiography
It is defined as theabsorbed dose(in air) multiplied by the area irradiated, expressed inGy·cm2
Sometimes theprefixedunits mGy·cm2or cGy·cm2are also used

DAP reflects not only the dose within the radiation field but also the area oftissueirradiated
Therefore, it may be a better indicator of the overall risk of inducing cancer than the dose within the field
Effective dose (risk) can be estimated from DAP
It also has the advantages of being easily measured, with the permanent installation of a DAP meter on the X-ray set

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16
Q

Radiation Dose Risk: Deterministic Effects

A

There are definable threshold doses for these effects below which no damage, in terms of measurable clinical response, can be detected

Above the threshold, the severity of effect increases with dose in a way that can be predicted
Such effects are referred to as deterministic effects

17
Q

Radiation Dose Risk: Stochastic Effects

A

A stochastic effect is one that is governed by the laws of chance
Since a single ionising event may cause radiation damage to the DNA it is usual to assume that there is no threshold dose for stochastic effects of ionising radiation
No radiation dose, no matter how small, is safe!

Effects of multiple doses are additive
Frequency of stochastic damage increases with dose - but severity does not
The degree of malignancy of radiation-linked cancer is not related to the dose

There is extensive evidence that ionising radiation increases the risk of malignant disease in humans
Carcinogenesis (including leukaemias, sarcomas and other rare tumour types)
This evidence comes from many sources

18
Q

Stochastic Effects: Key Points from Data

A

The risk of cancer is not the same for all parts of the body. Many organs are affected, but not all to the same degree

There is a long latent period before cancer develops- excess leukaemia occurred between 5-14 years but the risk of solid tumours was still increasing 40 years after the bombs

There is no evidence of a threshold dose for most tumour types

In terms of relative risk, cancer was highest in those under 10 years of age at the time of exposure

19
Q

Radiation Dose Risk: Heritable Effects

A

Less clear evidence
Strong circumstantial evidence
Plants, bacteria, fruit flies and mice
For the purposes of risk estimation the dose of radiation that would double the natural incidence of germ line mutation is estimated from animal work to be approximately 1 Sv

20
Q

Models of radiation cancer risk

A

Risks of very low doses are uncertain, as they are based on relatively few studies
The smallest dose that has provided clear evidence of an increased cancer risk is approximately 200 mSv
Breast cancer after multiple lung radiographs of patients with tuberculosis
Japanese atom bomb survivors

There are however ways to extrapolated from the higher dose data down to the much lower doses, typically 1-2 mSv used for many radiological procedures
Currently the ICRP recommends a linear no-threshold (LNT) extrapolation method
However other models may also be valid

21
Q

Radiation Risk to Individuals

A

Medical exposures deliver radiation doses to individuals or members of specific groups (men vs women, young vs old)
In some cases, average risk factors based on the total population will be misleading

22
Q

The risk of long-term stochastic effects

A

The health effects of radiation to be considered when deciding whether a diagnostic examination should be carried out are the stochastic effects:
Cancer and hereditary disease

For stochastic effects, the chance that any one person will be affected is very small
BUT the implications for an individual who is affected will be very great

23
Q
  1. The effects of large radiation doses that become apparent within days are often referred to as
    a. random effects
    b. mixed effects
    c. deterministic effects
    d. stochastic effects
    e. Compton effects
A

c. deterministic effects

24
Q
  1. The effect of increasing the risk of developing an illness such as cancer as a result of being exposed to ionizing radiation is often referred to as
    a. random effects
    b. mixed effects
    c. deterministic effects
    d. stochastic effects
    e. Compton effects
A

stochastic effects

25
Q
  1. A simple model relating the increase in the chance of developing cancer resulting from an exposure to ionizing radiation and recommended by the International Commission on Radiological Protection (ICRP) is called the
    a. Linear no-threshold model
    b. Non-linear threshold model
    c. Non-linear no-threshold model
    d. Cancer production model
    e. Sievert model
A

Linear no-threshold model

26
Q
  1. Which of the following best describes radiation of all kinds?
    a. Radiation is a means of transporting matter through space
    b. Radiation is a means of transporting energy in a vacuum
    c. radiation is a means by which energy is transported through space or matter
    d. Radiation is a means of transporting electrons through space
A

radiation is a means by which energy is transported through space or matter

27
Q
  1. Which form of radiation is the most penetrating through matter?
    a. X-ray radiation
    b. a-particle radiation
    c. neutron radiation
    d. y-ray radiation
    e. b-particle radiation
    article radiation
A

neutron radiation

28
Q
  1. Which of the following is not a form of ionising radiation?
    a. X-ray radiation
    b. a-particle radiation
    c. neutron radiation
    d. microwave radiation
    e. b-particle radiation
A

microwave radiation

29
Q
  1. Which of the following percentages best approximates the dose received by the UK population from medical sources?
    a. 1%
    b. 15%
    c. 25%
    d. 75%
    e. 80%
A

15%

30
Q
  1. X-ray photons that interact with matter transfer their energy as
    a. kinetic energy of photons
    b. potential energy of electrons
    c. kinetic energy of electrons
    d. potential energy of the atom’s nucleus
    e. electron volts
A

kinetic energy of electrons

31
Q
  1. Absorbed dose may be defined as the
    a. electrons absorbed per unit mass from any source of non-ionizing radiation of any kind in any target
    b. energy absorbed per unit density from any kind of ionizing radiation in any target
    c. energy absorbed per unit mass from any kind of ionizing radiation in any target
    d. energy absorbed per unit mass from only X-ray radiation in any target
A

energy absorbed per unit mass from any kind of ionizing radiation in any target

32
Q
  1. What is the SI unit or absorbed dose and what are the SI base units?
    a. Sieverts, Joules.kilograms-1
    b. Grays, kilograms/Joules
    c. Grays, Joules.kilograms-1
    d. Sieverts, kilograms/Joules
A

Grays, Joules.kilograms-1

33
Q
  1. What is the SI unit of equivalent dose and what are the SI base units?
    a. Sieverts, Joules.kilograms-1
    b. Grays, kilograms/Joules
    c. Grays, Joules.kilograms-1
    d. Sieverts, kilograms/Joules
A

Sieverts, Joules.kilograms-1

34
Q
  1. Which radiation dose metric of the following best estimates the stochastic health effects of radiation in humans
    a. entrance surface dose
    b. dose area product
    c. absorbed dose
    d. effective dose
    e. equivalent dose
A

effective dose

35
Q
  1. Which of the following radiation dose metrics best accounts for the biological effects of different types of radiation
    a. effective dose
    b. equivalent dose
    c. entrance surface dose
    d. dose area product
    e. absorbed dose
A

equivalent dose

36
Q
  1. Which one of the following is closest to the threshold of absorbed dose that will give rise to early transient erythema of the skin from a brief exposure of ionizing radiation?
    a. 0.5 Gy
    b. 0.5 Sv
    c. 2 Gy
    d. 20 Sv
    e. 200 Gy
A

2 Gy

37
Q
  1. An effective dose of 1 mSv is associated with a risk of an adult developing a fatal cancer (all types) of approximately
    a. 1 in 10,000
    b. 1 in 1 million
    c. 1 in 20,000
    d. 1 in 3
    e. 1 in 10,000
A

1 in 20,000

38
Q
A

imaging science (9 decks)

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