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BDS3 Radiology > Biological Effects of Ionising Radiation > Flashcards

Biological Effects of Ionising Radiation Flashcards

1
Q

ionising radiation can be divided into (2)

A

by products of radioactive decay

artificially produced electromagnetic radiation

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2
Q

by products of radioactive decay

divides into (3)

A

alpha particles

betal particles

gamma rays

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3
Q

alpha particles

A

2 protons/2 neutrons

large particle

20um in water

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4
Q

beta particles

A

electron

very small particle

less than 1cm in water

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5
Q

gamma rays

A

high energy

travels long distances

10s of cm in water

also electromagnetic radiation

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6
Q

artificially produced electromagnetic radiation is

A

X-rays for radiographic imaging

high or low energy

travels 10s of cm in water

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7
Q

X rays and gamma rays

A

are identical

only differ in source

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8
Q

atoms Vs Ions

A

atoms have equal numbers of proton and electrons

ions do not

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9
Q

ionising radiation energy

A

is enough to turn atoms into ions

Does this by ‘knocking away’ electrons orbiting the nucleus of an atom

single photon of radiation can carry enough energy to ionise an atom

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10
Q

ion pair =

A

negative electron and positive atom

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11
Q

interaction of radiation

A

When radiation passes through matter it will ionise atoms along it’s path

Following each ionisation process, each ion pair, will deposit a certain amount of energy locally, approximately 35eV for air and tissue
- This energy is greater than the energy involved in atomic bonds e.g. ionic and covalent bonds in molecules involve approximately 4eV

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12
Q

how does density of ionisation differ

A

Density of ionisation occurs differs for radiation

Gamma and electrons are sparsely ionising

Alpha particles, protons and neutrons and heavy ions are densely ionising

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13
Q

ionising potential for gamma and electrons

A

sparsely ionising

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14
Q

ionising potential for alpha particles, protons and neutrons

A

heavy ions are densely ionising

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15
Q

effect of ionising process on structure of organic molecules

A

Cells of basic building elements

DNA in cell nucleus

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16
Q

most significant effect of ionising radiation

A

damage to DNA

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17
Q

evidence of DNA damage by radiation

A

can be seen in the faulty repair of chromosome breaks, leading to development of abnormal cell populations and the development of cancer

The majority of damage is easily repaired, depending on the category of damage

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18
Q

evidence of faulty DNA repair

A

Faulty repair of breaks is seen in individuals who are exposed to large radiation doses

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19
Q

is DNA damage repairable?

A

The majority of damage is easily repaired, depending on the category of damage

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20
Q

2 types of DNA damage

A

direct effect

indirect effect

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21
Q

direct effect of DNA damage

A

radiation interacts with the atoms of a DNA molecule or another important part of cell

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22
Q

indirect effect of DNA damage

A

Radiation interacts with water in the cell (75% water)

when water molecule becomes ionised a highly reactive free radical ion is formed
- 2 of these can combine to form a hydroxyl radical which can diffuse short distances and cause DNA damage

Free radicals are unstable, highly reactive molecules
- these damage DNA

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23
Q

free radicals

A

unstable, highly reactive molecules

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24
Q

DNA damage when no radiation

A

can occur

frequency of more than 50 thousands per cell per day

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25
Q

DNA damage and repair - advantage of structure

A

An advantage of DNA being a double helix is that if only one strand of the helix breaks, the DNA is still held in place by the second and so it can be easily fixed

However, if both strands break it becomes far more difficult to piece the DNA back together
- The 2 remaining ends will seek to re-join with other free ends, not necessarily the correct matching end

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26
Q

what if both strands of DNA double helix break

A

However, if both strands break it becomes far more difficult to piece the DNA back together
- The 2 remaining ends will seek to re-join with other free ends, not necessarily the correct matching end

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27
Q

single strand DNA break

A

can usually be repaired

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28
Q

double stranded breaks (DSB)

A

more difficult to repair

Usually occur as a result of alpha radiation
- The increase of DNA damage complexity with ioniation density

If the DSB is misrejoinined, then this can lead to mutations which can affect cell function

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29
Q

increase of DNA damage is with

A

ionisation density

  • alpha
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30
Q

biological effect depends on (4)

A

Type of radiation

Amount of radiation (dose/ energy absorbed)

Time over which the dose is received (dose rate)

The tissue or cell type irradiated

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31
Q

low doses of radiation produces

A

less damage compared to higher density doses

e.g. X rays less damage compared to alpha particles

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32
Q

alpha particles Vs X-rays in damage

A

there is a linear relationship for alpha particles which in turn kills more cells than a similar dose of X-rays would

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33
Q

dose rate of radiation on damage effect

A

Radiation delivered at a low dose rate is less damaging
- Cells can repair less serious DNA damage before further damage occurs

At high dose rates, the DNA repair capacity of the cell is likely to be overwhelmed

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34
Q

organ cancer risks of radiation

A

Following large radiation exposures, there has only been higher incidence of cancer in certain tissues

Most medical exposures do not irradiate the body uniformly

Risk will vary depending on the organ that receives the highest dose

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35
Q

tissue radiosensitivity

dependent on (2)

A

the function of the cells that make up the tissue

if the cells are actively dividing

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36
Q

stem cells radiosensitivity

A

Stem cells exist to produce cells for another cell population
-Divide frequently

Very radiosensitive

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37
Q

differentiated cells radiosensitivity

A

Do not exhibit mitotic (dividing) behaviour

Less sensitive to radiation damage

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38
Q

the more rapidly the cells is dividing the…

A

greater the sensitivity to radiation

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39
Q

highly radiosensitive tissues (5)

A 
bone marrow
lymphoid 
gastrointestinal
gonads
embryonic
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40
Q

moderately radiosensitive tissues

A

skin
vascular endothelium
lung
lens of the eye

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41
Q

least radiosensitive tissues

A

CNS
bone and cartilage
connective tissue

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42
Q

tissue weighting factors related to

A

Tissue radiosensitivity leading to tissue weighting factors

- The more rapidly a cell is dividing, the greater the sensitivity to radiation

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43
Q

tissue weighting factor for:

bone marrow, colon, lung, stomach, breast

A

0.12

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44
Q

tissue weighting factor for:

gonads

A

0.08

45
Q

tissue weighting factor for:

bladder, oesophagus, liver, thyroid

A

0.04

46
Q

tissue weighting factor for:

bone surface, skin, brain, salivary glands

A

0.01

47
Q

tissue weighting factor for:

remaining tissues

A

0.12

48
Q

sum of all tissue weighting factors

A

1.00

49
Q

what are the possible outcomes after radiation hits a cell

A

radiation hits cell nucleus

  • no change
  • DNA mutation (3 outcomes)
50
Q

3 outcomes of DNA mutation

A

mutation repaired -> viable cell

cell death -> unviable cells

cell survives but is mutated -> cancer?

51
Q

experiments of ionising radiation on cell cultures

A

Doses from heavily ionising particle radiations are more damaging than similar doses of X-rays

Affected cells may be able to repair damage

Dividing cells are more susceptible to damage

Heavily damaged cells may be programmed to die

52
Q

ionising radiation transfer of energy

A

Ionising radiation has the ability to transfer energy from one medium to another

e.g. X-ray tube to a pt

53
Q

dose is

A

measure of the amount of energy that has been transferred and deposited in a medium

has units
- defined in order to quantify the level of biological damage and the overall effect of the dose

54
Q

dose units defined to

A

defined in order to quantify the level of biological damage and the overall effect of the dose

55
Q

what does dose not take into account

A

dose takes no account of the variations in the potential damage that different types of radiation produce, or the different sensitivities of tissues

56
Q

absorbed dose (Gy)

A

a quantity that can be measured

absorbed dose measures the energy deposited by radiation

for example, for an intra-oral X-ray the typical Entrance Skin Dose at the collimator tip is around 2mGy

57
Q

equivalent dose (Sv)

a derived quantity

A

equivalent dose is the absorbed dose multiplied by a radiation weighting factor depending on the type of radiation

for beta, gamma and X-rays the weighting factor is 1

for alpha particles it is 20

58
Q

effective dose (Sv)

a derived quantity

A

Equivalent dose to each organ, multiplied by the tissue weighting factor and summed.

Represents the stochastic health risk to the whole body,
- which is probability of cancer induction

A typical intra-oral X-ray effective dose is 5uSv

59
Q

linear no threshold model (LNT)

A

effect of radiation on the population

Current practical radiation theory assumes that the coefficient for risk against dose remains constant no matter how small the dose
- It assumes that the Linear No Threshold (LNT) model is valid

The LNT model estimates the long term biological damage for radiation

  • it assumes that radiation is always harmful with no safety threshold
  • several small exposures would have the same effect as one large exposure
60
Q

LNT assumes

A

it assumes that radiation is always harmful with no safety threshold

The LNT model estimates the long term biological damage for radiation

  • several small exposures would have the same effect as one large exposure
61
Q

LNT

the effective dose is directly proportional to

A

the risk of cancer (the damage)

62
Q

associated lifetime risk of 1mSv dose

A

associated lifetime risk of cancer of 1 in 20,000

63
Q

associated lifetime risk of an intra oral X-ray

A

less that 1 in 10,000,000

64
Q

error bars on LNT at high dose end

A

tight
compared to large at low dose end

means several curves can be drawn through data points

65
Q

error bars on LNT at low dose end

A

large

means several curves can be drawn through data points

66
Q

why has the ICRP opted for linear no threshold (LNT) model

A

cautious approach to radiation reduction

67
Q

aim for public radiation exposure

A

maintained the doses to public to As Low As Reasonable Practicable

accepted that exposures to natural low levels of radiation are inevitable

68
Q

2 types of radiation effects

A

deterministic effects

stochastic effects (statistical approach)

69
Q

deterministic radiation effects

A

tissue reactions

only occur above a certain (threshold) dose

the severity of the effect s related to the dose received

70
Q

stochastic radiation effects (statistical approach)

A

the probability of occurence is related to the dose received
- basis of LNT model

no threshold to the effect and severity of that effect is not dependent on dose

71
Q

deterministic effects

seen when

A

unusual to see in radiology but possible in high dose areas (e.g. interventional radiology)

often the effects will not show immediately, but rather several days after exposure

72
Q

threshold dose for deterministic effects on

bone marrow blood cell depletion

A

> 0.5Sv

73
Q

threshold dose for deterministic effects on

cataracts

A

> 0.5Sv

74
Q

threshold dose for deterministic effects on

sterility

A

> 3Sv

75
Q

threshold dose for deterministic effects on

hair loss

A

> 3Sv

76
Q

threshold dose for deterministic effects on

skin damage/erythema

A

> 5Sv

77
Q

threshold dose for deterministic effects on

lethal dose

A

6 Sv to whole body

For comparison, a typical intra-oral X-ray effect dose is 5uSv (0.000005 Sv)

78
Q

stochastic effects threshold

A

no known threshold for stochastic effects

- there is no dose below which the effects will not occur

79
Q

able to predict stochastic effects?

A

cannot predict if these effects will occur in an exposed individual or how severe they will be
- the likelihood of the effect occurring increases as the dose increases

80
Q

stochastic effects devlop

A

years after exposure

81
Q

stochastic effects categories (2)

A

somatic - results in disease or disorder e.g. cancer

genetics - abnormalities in descedents

82
Q

somatic stochastic effect

A

results in disease or disorder e.g. cancer

83
Q

genetic stochastic effect

A

abnormalities in descendants

84
Q

effect of radiation during preganancy

A

doses for any abnormalities to occur are moe than 1000 times greater than that of an intra-oral X-ray

pregnancy does not need to be taken into account for dental X-rays because the dose to the foetus is so low

  • between 0.01 uSv and 8 uSv
  • this is usually less than the estimated daily natural background dose received by the foetus

in early pregnancy, radiation exposure above 100 mGy could damage or kill enough of the cells for the embryo to undergo resorption

lethal effects can be induced by doses of the order of 100 mGy before or immediately after implantation of the embryo into the uterin wall

during organogenesis (2 – 8 weeks post conception) when the organs are not fully formed, doses >250 mGy could lead to growth retardation

85
Q

effect of radiation on pregnancy

  • dental X-rays
A

doses for any abnormalities to occur are moe than 1000 times greater than that of an intra-oral X-ray

pregnancy does not need to be taken into account for dental X-rays because the dose to the foetus is so low

  • between 0.01 uSv and 8 uSv
  • this is usually less than the estimated daily natural background dose received by the foetus
86
Q

childhood cancer and radiation

A

a number of studies have examined the risk of childhood cancer before the age of 15 years, following exposure in utero

the natural incidence of childhood cancer is low – 1 in 650 up to age of 15

the risk of cancer induction is 1 in 13,00 per 1mGy exposure in utero

the risk of fatal cancer from a 1mGy exposure is 1 in 40,000 up to age 15
- risk from a dental X-ray would be a million times less if beam is not directed towards abdomen

87
Q

sources of natural background radiation (4)

A

cosmic rays, 320 uSv/yr at sea level 9 mSv/yr at 6000m
- round trip to Mars 0.6 Sv

internal radionuclides from diet 300 uSv annually

radionuclides in the air e.g. radon

external gamma radiation
- e.g. soil, rocks, the decay of uranium, building materials

88
Q

estimated annual UK natural background radiation dose is

A

2.2mSv

can increase to 10mSv in some regions due to radon

89
Q

sources of radiation exposure UK from highest to lowest

A

NATURAL (84%)

  • radon gas from ground (50%)
  • gamma rays from ground/buildings (13%)
  • cosmic rays (12%)
  • food and drink (9.5%)

ARTIFICIAL (16%)

  • fallout (0.2%)
  • occupational (0.2%)
  • discharges (<0.1%)
  • products (<0.1%)
  • medical (15%)
90
Q

effective doses for examination

intra oral X-ray

A

0.005mSv

lifetime risk of cancer, 1 in 10 million – 1 in 100 million
- negligible risk

91
Q

effective doses for examination

lumbar spine X-ray

A

1 mSv

Lifetime risk of cancer, 1 in 10,000 – 1 in 100,000
- Very low risk

92
Q

effective doses for examination

abdominal CT

A

10 mSv

Lifetime risk of cancer, 1 in 1,000 – 1 in 10,000
- Low risk

93
Q

cumulative exposure from several X-rays

A

can be significant

94
Q

radiation protection

guidance notes for dental practitioners on safe use of X-ray equipment 2nd edition

A

IRMER (pts)
- Duty holders, employer’s procedures, accidental and unintended exposures, MPE, training

IRR17 (staff and public)
- Safety and warning systems, risk assessment, controlled areas, personal dose monitoring, local rules, RPS, RPA

QA programme for X-ray equipment, image processing, viewing, image quality

95
Q

dose limits IRR17

employee

A

body: 20mSv

skin, extremities: 500mSv

eye: 20mSv

96
Q

dose limits IRR17

trainee <18y

A

body: 6mSv

Skin, extremities: 150mSv

eye: 15mSv

97
Q

dose limits IRR17

other

A

body: 1mSv

skin, extremities: 50mSv

eye: 15mSv

98
Q

controlled areas IRR17

A

Should extend at least 1.5m from the X-ray tube and pt

The X-ray beam should always be directed away from staff

99
Q

radiation protection philosophy from IRMER17 protecting the pt

A

justification
- Practices must have sufficient benefit to individuals or society in order to offset the detriment

optimisation
- Individual does and the number of people exposed should be kept as low as reasonably practicable (ALARP)

100
Q

dose optimisation

A

is legal requirement

We need to make sure the dose to the patients is ALARP
- Still maintain adequate image quality

Rectangular collimators should be used
- Circular collimators have been shown to increase dose by 40%

101
Q

3 ways patient doses can be reduced

A

Use E speed film or faster (fewer X-ray photons required)

Use a kV range of 60kV to 70kV

The focus to skin distance should be >200mm

102
Q

diagnostic reference levels DRLs

A

Not appropriate to apply dose limits to medial exposure as there is a direct benefit to the pt

Quantitive guidance available – clinical audit tools to identify poor practice

Legislation requires employers to have established dose levels for typical examinations for standard sized patients

They are comparative standard that is used in optimisation
- They are compared to national reference levels

Individual X-ray units are compared to DRLs and national reference levels
- Enable identification of units giving higher doses

103
Q

current DRLs for adult intra-oral examinations

A
  1. 9mGy (digital sensor)

1. 2mGY (phosphor plates and film)

104
Q

current DRLs for child intra-oral examinations

A
  1. 6mGy (digital sensor)

0. 7mGy (phosphor plates and film)

105
Q

image quality needs to be

A

Sufficient for clinical purpose

Not justified exposure if there is no adequate image quality attained

106
Q

CR plates damage

A

CR plates are prone to damage by teeth marks
- Reduce damage by inserting the plates between 2 plastic sheets

Damaged detectors should be cleaned or replaced if necessary

107
Q

images with minor artefacts and non-uniformities

A

should be saved

Refer to these images if there is a suspected artefact in a clinical image

Can also be used for training

108
Q

CR plates artefacts due to:

A

fingerprints

scratches

109
Q

radiation risk assessment

A

by the employer

identify all hazards with a potential to cause a radiation accident

Evaluate the risks of arising from the hazards

BDS3 Radiology (14 decks)

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