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Radiology > Biological Effects Of Ionising Radiation > Flashcards

Biological Effects Of Ionising Radiation Flashcards

1
Q

Two types of ionising radiation

A

By-products of radioactive decay
Artificially produced EM radiation

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2
Q

3 by-products of radioactive decay

A

Alpha particle
Beta particle
Gamma ray

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3
Q

What is the result of ionising radiation

A

Free electron and positively charged ion (Ion Pair)

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4
Q

3 steps of radiation interaction

A
  1. When radiation passes through matter it ionises atoms in path
  2. Each ion pair deposits around 35ev of energy in air and tissue
  3. This energy is greater than energy involved in atomic bonds
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5
Q

Most significant effect of ionising radiation

A

Damage to DNA
E.g. large radiation dose> faulty repair of chromosome breaks>abnormal cells>cancer

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6
Q

Two types of DNA damage

A

Direct
Indirect

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7
Q

Direct DNA Damage

A

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

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8
Q

Indirect effect

A

Radiation interacts with water in cell> H2O becomes ionised> free radical formed> two join forming hydroxyl radical causing DNA damage

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9
Q

DNA damage to one strand of helix vs both strands

A

One strand reads, held in place by other> easily fixed

Both strands break, two remaining ends will seek to rejoin other free ends, not necessarily right ones (DSB)

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10
Q

4 factors affecting biological effect of radiation

A

Type of radiation DSB usually alpha
Amount of radiation (dose)
Time over which dos is received (dose rate)
Tissue or cell type irradiated

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11
Q

Dose effect

A

Low doses>less damage
Linear relationship for alpha particles which kill more cells than a similar dose of X-rays would
N.b WEIGHTING FACTOR

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12
Q

Dose Rate Effect

A

Low dose rate> less damage
Cells can repair less serious DNA damage before further damage occurs
High dose rate, DNA repair capacity of cell likely to be overwhelmed

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13
Q

Organ cancer risks

A

After large radiation exposures, higher incidence of cancer in certain tissues
Depends on organ receiving highest dose

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14
Q

What is tissue radiosensitivity dependent on

A

The function of the cells that make up the cells
If cells are actively dividing

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15
Q

Two types of cells and their radiosensitivity

A

Stem cells
Produce cells for another cell population
Divide frequently
Very radiosensitive

Differentiated cells
Do not exhibit mitotic behaviour
Less sensitive to radiation damage

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16
Q

High radiosensitive tissues

A

More rapid cell division>greater sensitivity to radiation

Bone marrow, lymphoid, GI, gonads, embryonic

17
Q

Moderately radiosensitive tissues

A

Skin, vascular endothelium, lung, lens of eye

18
Q

Least radiosensitive tissues

A

CNS, bone and cartilage, connective tissue

19
Q

Possible outcomes when radiation hits cell nucleus

A

No change

                       - Mutation repaired > viable cell DNA mutation - Cell Death > Unviable cell
                       - Mutated cell > Cancer?
20
Q

Three different types of dose quantities

A

Absorbed Dose (Gy)
Equivalent Dose (Sv)
Effective Dose (Sv)

21
Q

Absorbed Dose

A

Measures the energy deposited by radiation
E.g. IO X-ray typical entrance skin dose at colllimator tip is 2mGy

22
Q

Equivalent dose

A

Is the absorbed dose multiplied by radiation weighting factor depending on radiation
Beta, gamma and X-rays - weighting factor 1
Alpha particles - 20

23
Q

Effective Dose

A

Is the EQUIVALENT DOSE multiplied by tissue weighting factor
Is probability of cancer induction
Typical intra oral X-ray is 5uSv

24
Q

What does LNT model do

A

Estimates long term damage from radiation
Assumes always harmful with no safety threshold and several small exposures have same effect as one large

25
Q

Two types of radiation effects

A

Deterministic- tissue reactions, only occur above threshold dose, severity of effect related to dose received

Stochastic- probability of occurrence related to dose received, no threshold to the effect and severity of not dependent on dose. Basis of LNT model

26
Q

Deterministic effects of ionising radiation

A

Unusual to see in radiology
Effects wont show immediately but several days after
Certain things happen at certain values e.g. hair loss at 3Sv, lethal dose at 6Sv
Typical io xray 5uSv (0.000005Sv)

27
Q

Stochastic effects of ionising radiation

A

Have no known thresholds
Cannot predict if they will happen or how severe they will be
Effects can develop years after exposure
Can be somatic (resulting in disease or cancer) or genetic (resulting in abnormalities of descendents)

28
Q

Effect of radiation during pregnancy

A

Doses for any abnormalities to occur are 1000 times greater than that of an IO xray
Dose to foetus is so low (0.01uSv and 8uSv which is less than background dose received)

29
Q

what must not happen when taking radiograph of pregnant woman

A

Foetus must not be irradiated inadvertently nor should X-ray Bea, be directed towards abdomen

30
Q

Examples of natural background radiation

A

Cosmic rays
Radionuclides from diet
Radionuclides in air e.g. radon
External gamma radiation e.g. soil, rocks
Estimated UK background radiation 2.2mSv

31
Q

Lifetime risk of cancer from IO xray

A

From one in 10m to one in 100m

32
Q

Guidance for X-ray use

A

Guidance notes for dental practitioners on safe use of X-ray equipment by college of general dentistry

33
Q

IRMER 2017 protecting patient

A

Justification- must have sufficient benefit to individuals or society in order to offset detriment
Optimisation- individual doses and number of people exposed should be kept As Low As Reasonably Practicable (ALARP)

34
Q

How do we keep pt dose ALARP

A

Using E speed film or faster
Using kV rang 60-70kV
Focus to skin distance > 200mm

35
Q

Diagnostic Reference Levels in patients

A

Established dose levels for typical exams on standard sized pts
Enables identification of units giving higher doses

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

36
Q

What can we do to improve image quality and therefore reduce pt dose

A

Reduce damage by inserting CR plates between two plastic sheets
Replace/clean damaged detectors
Save images with minor artefacts, can be referred to and used in training

Radiology (4 decks)

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