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Radiology > Biological Effects of Ionising Radiation & Risk Assessment > Flashcards

Biological Effects of Ionising Radiation & Risk Assessment Flashcards

1
Q

What is the difference between atoms and ions?

A

Atoms have equal numbers of protons and electrons, ions do not.

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2
Q

What can ionising radiation do to atoms?

A

has enough energy to turn atoms into ions. It does this by “knocking away” electrons orbiting the nucleus of an atom.

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3
Q

What charge do ions have?

A

+

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4
Q

What are the 4 main types of ionising radiation?

are they high/low energy and how far do they travel?

A

Alpha particle (2 protons / 2 neutrons)
Large particle, travels a few inches
Beta particle (electron)
Very small particle, travels a few feet
Gamma ray (electromagnetic radiation)
High energy, travels long distances
X-rays
High or low energy, travels long distances

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5
Q

How much energy locally will each ionisation process deposit, and what is this energy greater than?

A

Each ionisation process will deposit a certain amount of energy locally, approximately 35eV
This energy is greater than the energy involved in atomic bonds e.g. ionic and covalent bonds involve approximately 4eV

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6
Q

What happens when radiation passes through matter?

A

it will ionise atoms along it’s path

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7
Q

What is the most significant effect of ionising radiation?

A

Damage to DNA is the most significant effect of ionising radiation
Evidence of DNA damage can be seen in the faulty repair of chromosome breaks

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8
Q

What is the direct effect of radiation on DNA damage?

A

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

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9
Q

What is the indirect effect of radiation on DNA damage?

A

Radiation interacts with water in the cell, producing free radicals which can cause damage
Free radicals are unstable, highly reactive molecules

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10
Q

What type of strand break can usually be repaired?

A

A single strand break in DNA can usually be repaired

Double strand breaks are more difficult to repair
Usually occur as a result of alpha radiation
If the repair is faulty then this can lead to mutations which can affect cell function

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11
Q

What do double strand breaks usually occur due to?

A

alpha radiation

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12
Q

What if the repair is faulty, what can this lead to?

A

mutations which can affect cell function

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13
Q

What is the biological effect of DNA damage dependant on?

A

Type of radiation
Amount of radiation (dose)
Time over which the dose is received (dose rate)
The tissue or cell type irradiated

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14
Q

What do low doses of radiation produce?

why?

A

produce less damage
- radiation delivered at a low dose rate is less damaging - this is because cells can repair less serious DNA damage before further damage occurs.
- at high does rates, the DNA repair capacity of the cell is likely to be overwhelmed.

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15
Q

What disease has a high incidence following large radiation exposures?

what does the risk depend on?

A

cancer

depends on the organ that receives the highest dose

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16
Q

What is the radiosensitivity of tissues dependent on?

2 factors

A

function of the cells that make up the tissues
if the cells are actively dividing

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17
Q

What is the radiosensitivity of the stem cells?

A

Divide frequently
Very radiosensitive

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18
Q

What is the radiosensitivity of differentiated cells?

A

do not exhibit mitotic behaviour
less sensitive to radiation damage

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19
Q

What tissues are highly radiosensitive and why?

A

Bone marrow, lymphoid tissue, gastrointestinal, gonads, embryonic tissues

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

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20
Q

What tissues are moderately radiosensitive?

A

Skin, vascular endothelium, lung, lens of the eye

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21
Q

What tissues are the least radiosensitive?

A

Central nervous system, bone and cartilage, connective tissue

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22
Q

What are the several possible DNA mutations that could occur when radiation hits cell nucleus?

what is the effect on the cell

A

mutation repaired - viable cell
cell death - unviable cell
cell survives but is mutated - cancer

23
Q

What is dose?

A

Dose is a measure of the amount of energy that has been transferred and deposited into a medium.

24
Q

What does ionising radiation has the ability to do?

A

to transfer energy from one medium to another e.g. an X-ray tube to a patient

25
Q

What does the absorbed dose measure?

A
  • Absorbed Dose (Gy) = Measures the energy deposited by radiation.
    • e.g. for an intra-oral X-ray the typical entrance skin dose at the collimator tip is around 2 mGy
26
Q

What is the equivalent dose? - What is it for beta, gamma, x-rays and alpha?

what units does it have?

A
  • Equivalent Dose (Sv) = Absorbed dose multiplied by a weighting factor depending on the type of radiation.
    • For beta, gamma and X-ray the weighting factor is 1
    • For alpha particles the weighting factor is 20
27
Q

What is the LNT model and what does it estimate?

A

Linear No Threshold (LNT) Model
The LNT model estimates the long term biological damage from radiation It assumes the damage is directly proportional (linear) to radiation dose
It assumes that radiation is always harmful with no safety threshold

28
Q

What would several small exposures have the same effect as?

what is this called?

A

Several small exposures would have the same effect as one large exposure This is known as response linearity

29
Q

What does a dose of 1mSv have an associated lifetime risk of cancer?

A

1 in 20,000

30
Q

What is the risk from an intra oral x-ray?

A

less than 1 in 10,000,000

31
Q

What are the two types of radiation effects?

A

Deterministic Effects
Tissue reactions
Only occur above a certain (threshold) dose
The severity of the effect is related to the dose received
Stochastic Effects
The probability of occurrence is related to the dose received

32
Q

When will deterministic effects show and where are they possible?

A

Unusual to see in radiology although are possible in high dose areas such as interventional radiology
Often the effects will not show immediately, but rather several days after exposure

33
Q

What is the threshold for stochastic effects?

A

No known threshold for stochastic effects
There is no dose below which the effects will not occur

34
Q

When do stochastic effects develop?

A

can develop years after exposure

35
Q

Can stochastic effects be predicated and what increases their likelihood?

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

36
Q

What are the two categories of stochastic effects?

A

Somatic – results in disease or disorder e.g. cancer Genetics – abnormalities in descendents

37
Q

What are the effects of radiation during pregnancy?

what are the required doses for these abnormalities

A
  • Radiation exposure 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 100mGy before or immediately after implantation of the embryo into the uterine wall
  • During organogenesis (2 – 8 weeks post conception) when the organs are not fully formed, doses >250mGy could lead to growth retardation

Doses for these abnormalities are more than 1000 times greater than that of an intra-oral X-ray

38
Q

What is the guidance for pregnant patients for dental x-rays?

A

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

The foetus must not be irradiated inadvertently nor should the X-ray beam be directed towards the patient’s abdomen

39
Q

What are the sources of natural background radiation?

A

Cosmic rays
Internal radionuclides from diet
Radionuclides in the air e.g. radon
External gamma radiation e.g soil, rocks and building materials
Air travel

40
Q

What is the estimated annual background radiation?

A

2.2mSv

41
Q

What are the effective doses of intra-oral, lumbar spine, abdominal CT?

what is the lifetime risk of cancer for each?

A
  • Intra-oral X-ray = 0.005 mSv
    • negligible lifetime risk of cancer
  • Lumbar spine X-ray = 1mSv
    • very low lifetime risk of cancer
  • Abdominal CT = 10mSv
    • Low lifetime risk of cancer
42
Q

How far should the controlled area extend and where should it be directed?

A

The controlled area should extend at least 1.5m from the X-ray tube and patient
The X-ray beam should always be directed away from staff members

43
Q

What is the dose limitation?

A

System of individual dose limits so that the risks to individuals are acceptable

44
Q

What is optimisation and why is it important?

A

Individual doses and the number of people exposed should be kept as low as reasonably practicable (ALARP), taking into account economic and social factors

Dose optimisation is a legal requirement

45
Q

What increases the dose by 40% and what should be used instead?

A

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

46
Q

How can the patient does be reduced?

various ways

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
Use rectangular collimation

47
Q

What are the diagnostic reference levels?

what are they compared to?

A

Legislation requires Employers to have established dose levels for typical examinations for standard sized patients
They are a comparative standard that is used in optimisation
They are compared to national reference levels
Individual X-ray units are compared to the DRLs and national reference levels

48
Q

What do DRLS enable?

A

Enables identification of units giving higher doses

49
Q

What are the current DRLs for intra-oral examinations?

adult and child

A

Adult: 0.9mGy (digital sensors) and 1.2mGy (phosphor plates and film)
Child: 0.6mGy (digital sensors) and 0.7mGy (phosphor plates and film)

50
Q

What are CR plates prone to?

A

damage by teeth marks

51
Q

How should damage be reduced in CR plates and what should happen to damaged detectors?

A

Reduce damage by inserting the plates between two plastic sheets
Damaged detectors should be cleaned or replaced if necessary

52
Q

Why should images with minor artefacts or non uniformities be saved?

A

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

Can also be used for training purposes

53
Q

Apart from biting, how can CR plates be damaged?

A

fingerprints
scratches

Radiology (15 decks)

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