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PHYS853: Radiation Protection in Medicine > Biological Effects of Ionising Radiation > Flashcards

Biological Effects of Ionising Radiation Flashcards

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1
Q

Describe the 3 biological effects of cell exposure to ionising radiation

A
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2
Q

How can ionising radiation cause cell damage?

A

Ionising radiation is capable of ejecting an atomic electron. This electron can cause further ionisation or free radical production within the cell, resulting in either indirect or direct action.

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3
Q

How does indirect action cause cell damage?

A

Radiation interacts with other molecules in the cell, producing free radicals which causes chain reactions until there is damage to critical cell structures. This is the dominant process in low LET interactions.

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4
Q

How does direct action cause cell damage?

A

Radiation damages critical cell structures. This is the dominant process in high LET interactions.

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5
Q

What are LET interactions?

A

The linear energy transfer of a charged particle in a medium is the average energy locally imparted to the medium by a charge particle of specified energy when passing through a given distance (the average energy deposited per unit track length).

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6
Q

Does high LET give up energy more or less readily than low LET?

A

More readily

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7
Q

Does high LET have a shorter or longer radiation stopping distance than low LET?

A

A shorter stopping distance

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8
Q

Is high LET easier or harder to shield than low LET?

A

Easier to shield

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9
Q

What is the threshold for high LET?

A

> 10 keV/µm

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10
Q

What is the threshold for low LET?

A

< 10 keV/µm

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11
Q

Are 250 kVp X-rays high or low LET?

A

Low LET: 2 keV/µm

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12
Q

Are 3 MeV X-rays high or low LET?

A

Low LET: 0.3 keV/µm

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13
Q

Are 1 MeV electrons high or low LET?

A

Low LET: 0.25 keV/µm

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14
Q

Are alpha particles high or low LET?

A

High LET: > 130 keV/µm

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15
Q

What are the 9 possible cell outcomes following irradiation?

A

1) No effect
2) Division delay
3) Apoptosis (cell dies before division)
4) Reproductive failure (cell dies during subsequent mitosis)
5) Genomic instability (reproductive issues transferred to daughter cells)
6) Mutation (cell survives but with a mutation)
7) Transformation (cell survives but mutation leads to possible carcinogenesis)
8) Bystander effects (irradiated cell induces genetic damage in nearby cells)
9) Adaptive response (irradiated cell is primed for more radiation damage and is potentially more resistant)

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16
Q

What are the two types of DNA repair?

A
  • Complete repair (error free)
  • Partial repair (especially prone in double strand breaks)
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17
Q

What are the possible consequences of cells with altered DNA?

A
  • Cell is non-viable (dies)
  • Cell is unable to divide (reproductive death)
  • Gives rise to a colony of mutated cells
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18
Q

What are cell survival curves?

A

Graphs that plot the fraction of cells that maintain reproductive integrity against the irradiated dose.

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19
Q

Cell survival when exposed to high LET radiation demonstrates a _______ relationship with dose, but low LET radiation results in a _______ _________ response.

A

Linear
Linear quadratic

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20
Q

What is the equation for the linear quadratic model of cell survival

A

D = dose

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21
Q

What are the benefits and limitations of in vitro studies to learn about the effects of radiation?

A

+ Easy to perform
- Cells are not complex organ systems, meaning they don’t account for factors like oxygen supply to tissue

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22
Q

What is the bystander effect?

A

The radiation induced effects that occur in cells adjacent to irradiated cells, despite not being exposed to radiation themselves.

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23
Q

What damage can be caused by the bystander effect?

Study These Flashcards
A
  • DNA damage
  • Chromosomal instability
  • Mutation
  • Apoptosis (cell death)
24
Q

What are parallel organs?

Study These Flashcards
A

Organs whose sub-structures can be considered to be working alongside one another, so damage to one sub-structure reduces the overall function of the organ.

25
Give an example of a parallel organ
The kidneys
26
What are serial organs?
Organs whose sub-structures are considered to be dependent on one another, so damage to one sub-structure can prevent the entire organ from functioning.
27
Give an example of a serial organ
The spinal cord
28
Give an example of an organ that is simultaneously parallel and serial
The lungs are parallel at the parenchyma level (gas exchange) but serial at the higher level (the bronchi).
29
Why is cancer considered a rare event?
Because cells experience billions of mutations in their life time and interact with background radiation quadrillions of times per year, however, the large majority of these interactions do not result in cancer because DNA is continuously monitored and repaired.
30
What is a deterministic effect?
Effects of ionising radiation that are only apparent above a 'threshold dose'. Above the threshold dose, the severity of the effect increases with dose.
31
What is the typical cause of deterministic effects?
Cell death, as organ function is relatively unaffected until a certain number of cells are lost. As absorbed dose increases, more cells die until tissues, organs, or even the individuals dies.
32
Give an example of a deterministic effect
Erythema (sun burn)
33
Why do deterministic effects depend on dose and dose rate?
The severity of harm relates to whether cells can repair and repopulate. This means that, for a high dose or a high dose rate, effects may not be reversible as the cells cannot recover.
34
Are all deterministic effects immediate?
No, they can occur months to years after exposure
35
What is a stochastic effect?
Effects of ionising radiation where the chance of developing the condition is related to the quantity of dose received. The severity of the condition is independent of the dose received.
36
Give an example of a stochastic effect
Cancer
37
How does the probability of getting radiation induced cancer change at very high doses?
The probability may reduce as the cells become sterilised rather than mutating.
38
What is the induction effect of cancer due to ionising radiation?
~ 5%/Sv
39
What factors influence cancer induction?
- Sex - Age at exposure - Elapsed time - Dose distribution - Genetic factors - Environmental factors - Lifestyle factors
40
Define excess absolute risk (EAR)
The absolute difference in risk between two populations (e.g. an irradiated and non-irradiated population).
41
How is excess absolute risk expressed?
EAR per 1000 person-years per Gy (or Sv) 1 EAR means that for every Gray irradiated in a population, 1 cancer will be observed for every 1000 people per year.
42
Define relative risk (RR) or excess relative risk (ERR)
The increased probability of seeing an event occur compared to another population (e.g. if 75/100 people experience an event in one group and 25/100 experience it in another, the relative risk is 3 and the excess relative risk is 2).
43
Give the equation for excess relative risk
ERR = RR - 1
44
How is relative risk or excess relative risk expressed?
As a fraction or % per Gy (or Sv)
45
What high dose exposure data is used to analyse the impacts of ionising radiation on humans?
- Atomic bombs - Radiotherapy applications - Early radiology - Nuclear accidents
46
What are life span studies?
Studies that study the lifespan and health impacts of a large exposed population following incidents like Hiroshima and Nagasaki. These studies use estimated doses to individuals of all ages and sexes to understand the biological impacts of radiation.
47
What were the 3 main findings about cancer induction from life span studies?
Solid tumours follow a linear dose response and leukaemias follow a linear quadratic response. Leukaemias appear within a few years of exposure, but solid tumours have a longer latent period (10-15 years). Solid tumours make up the majority of cancer deaths over a long period.
48
What are the 4 main types of occupational exposure that are used to study radiative effects?
1) Early radiation workers 2) Radium workers 3) Uranium miners 4) Classified/registered radiation workers
49
What is the radiation protection dilemma?
There is lots of robust data for the effects of radiation at high and intermediate doses, but very little at low levels (which is the majority of exposures).
50
What are the 4 potential models for human response to low levels of radiation?
1) Supralinear/hypersensitive 2) Linear no threshold 3) Threshold 4) Hormetic
51
Describe the linear no threshold model
The assumption that there is no threshold for radiation induced damage. This assumption states that there is no 'safe' level of radiation, just a reduced likelihood of cancer induction. This model assumes that there is an increased risk of 5% per Sv. Radiation protection is built around this framework
52
What is the risk of using the linear no threshold model?
- The risk may be underestimated: they might not be approriately justified - The risk may be overestimated: may be spending too many resources on ALARP and causing psychological damage - Hormesis: small amounts of radiation may actually be curative
53
State the 5 ways in which cancer risk is typically quantified
1) Risk of developing cancer (incidence) 2) Risk of dying from cancer (mortality) 3) Loss of life expectancy 4) Morbidity from non-fatal cancers 5) Risk to offspring (hereditary detriment)
54
Epidemiology studies typically focus on ________ or ________ when considering cancer risk.
Incidence Mortality
55
What are hereditary effects of radiation?
The irradiation of gonads can damage germline cells. These mutations could cause hertiable diseases, development abnormalities, or reduce the likelihood of foetal survival.
56
What is embryo irradiation?
The irradiation of an in utero embryo, which can increase the risk of childhood cancer development (particularly during early development).
57
Why is it important to identify pregnancy when working with radiation?
Because foetal doses significantly increase the risk of childhood cancer and reduced IQ.

PHYS853: Radiation Protection in Medicine (19 decks)

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