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Biological effects of radiation Flashcards

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1
Q

T or F - with regards to absorbed dose.
A. Is a measure of energy deposition per unit mass of tissue by radiation
B. Is the dose averaged over an organ or tissue
C. Takes account of differences in biological effectiveness for different types of radiation
D. When measured in air, the value is similar to air kerma
E. Entrance surface dose from a radiograph is a measurement of this quantity

A

A. True. B. False. C. False. D. True E. True

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2
Q

T or F - with regards to absorbed dose. A. It is the dose averaged over an organ or tissue
B. It is measured in gray
C. It takes account of differences in biological effectiveness for different types of radiation
D. It is derived from the absorbed dose multiplied by the radiation weighting factor
E. It is related to the uniform whole body dose with the same health detriment

A

A. True. B. False. C. True. D. True. E. False

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3
Q

What is the units for absorbed dose?

A

Gray

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4
Q

What is the units for equivalent dose?

A

sievert

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5
Q

T or F - with regards to effective dose.
A. It is the dose quantity related to the risk of health effects in man
B. It is derived from the sum of doses to radiosensitive organs weighted according to risk of health detriment
C. It is different for each type of radiation
D. It is related to the uniform whole body dose with a similar health detriment
E. It is measured in sievert

A

A. True B. True C. False. D. True. E. True

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6
Q

What is the units for effective dose?

A

sievert

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7
Q

What is the minimum energy needed to ionise any atom?

A

12eV

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8
Q

What is the typical amount of energy released when an atom is ionised?

A

35eV

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9
Q

What are the 2 main ways ionising radiation damages biological molecules?

A

The release of energy from an ionisation event is sufficient to break molecular bonds directly. Damage may also be induced by the interaction of free radicals produced by the ionisation. Eighty percent of tissue is made up of water. When water molecules ionise H+ ions and OH* free radicals are formed. The OH* radical is thought to be responsible for initiating about two-thirds of all the damage produced by exposure of the body to x-rays

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10
Q

is Alpha radiation or Xrays more likely to damage DNA and why?

A

an α-particle would produce several ionisation events as it passed through aDNAmolecule. The production of many ionisation events close together increases the potential for α-particles to damage cells and tissues.

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11
Q

What is a gray?

A

1 gray = 1 joule per kg A gray represents a high radiation absorbed dose and doses of this order are used in radiotherapy for killing malignant cells.

Doses in diagnostic medical radiation procedures are of the order of milligray (mGy) or microgray (μGy).

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12
Q

What is the risk associated with DNA damage with radiation?

A

Nearby breaks in the two strands of a DNA molecule are particularly important in terms of biological damage. Damage to DNA is involved in both acute tissue injury after moderate and high radiation doses and an increased risk of developing cancer after low dose exposure.

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13
Q

What is the linear energy transfer of a particle?

A

The density of energy deposition along the track of a photon or particle is a useful quantity for assessing the potential biological consequences of different types of radiation

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14
Q

What is target theory?

A

target theoryin which two or more hits are required within a sensitive target on the scale of aDNA moleculein order to kill a cell. The model predicts that fewer cells are killed per unit dose by lower doses ofx-rays. As the dose increases there is more chance of a target that has already been hit receiving a second hit which damages or kills the cell.

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15
Q

What is a radiation weighting factor?

A

defined for each type of radiation in order to provide an approximate indicator of their effectiveness in producing damage to biological tissue

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16
Q

How are radiation weighting factors used?

A

used to calculate an equivalent dose (HR), which is measured in sievert (Sv), from the absorbed dose (DR) measured in gray

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17
Q

What is the weighting factor for x-rays, γ-rays and β-particles used in most medical applications?

A

1

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18
Q

What is the weighting factor for alpha radiation?

A

20

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19
Q

What is the weighting factor for neutrons?

A

5-20 depending on neutron energy

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20
Q

Why do alpha particles not present much of an external hazard?

A

α-particles interact strongly and deposit energy quickly, they do not penetrate very far into tissue. Thus an α-particle is stopped by the outer layer of skin, so it does not present much of an external hazard

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21
Q

How do neutrons cause molecular damage?

A

Neutrons will readily bounce off heavier atoms without dislodging them. However, in any material that contains hydrogen atoms, such as tissue, the neutrons will transfer energy to thehydrogen atomsorprotonsin collisions. The protons will then interact with other atoms.

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22
Q

What is the effect of dose rate on molecular damage from radiation?

A

At low dose rates, cells are able to repair less serious DNA damage, so that recovery can occur, before further damage is produced. The accumulation of further damage might not be repairable. At higher dose rates, damage accumulates more rapidly, the DNA repair capacity of the cell is more likely to be overwhelmed and more cells are killed per unit dose.

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23
Q

What is the effect of fractionation of dose on molecular damage from radiation?

A

Similar to lower dose rate if a high dose of x-rays or γ-rays is delivered in several fractions at intervals of 12 hours or more. Damage such as single strand breaks in DNA molecules can be repaired between exposures. Thus when another dose of radiation is given, all the remaining cells have been fully repaired and are essentially undamaged

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24
Q

How long do cells need to recover damage from previous radiation exposure?

A

Any time over 18-24 hours should allow sufficient time for the cells to repair most of the damage from the previous exposure.

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25
Q

What cells are most sensitive to DNA damage?

A

Cells that are dividing are particularly sensitive to damage when in the G2and mitosis phases.

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26
Q

What types of tissue are most sensitive to radiation?

A

Organs that need to maintain a high level of cellular proliferation tend to be more sensitive to radiation damage. Examples are the skin, the bone marrow, and the gastrointestinal tract.

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27
Q

What are the 2 ways a cell population can be protected from genetic damage?

A

Repairof DNA damage to keep the cell alive. Removal of damaged cells. If there are breaks in both strands of the DNA molecule, which cannot be repaired, a cell may: Be prevented from progressing to mitosis, the delay may give the cell time to repair the damage
Be removed by apoptosis

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28
Q

How is apoptosis different to necrosis?

A

In apoptosis, the cell is packaged to prevent spillage of contents and so it differs from necrosis in which there is uncontrolled lysis.

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29
Q

What is radiation induced genomic instability?

A

a phenomenon whereby radiation exposure appears to induce a type of genetic instability in individual cells, which is transmitted to their progeny. The cell genome starts to rearrange during clonal expansion. This leads to an enhanced rate at which genetic changes arise in the descendants of the irradiated cell. Thus radiation may induce instability in cells that enhances the rate at which malignant transformation may occur in descendants of the irradiated cells.

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30
Q

What is the bystander effect in relation to DNA damage to radiation?

A

The bystander effect refers to the transmission of damage signals from irradiated to non-irradiated cells in a population. This can lead to biological effects in cells that have not themselves been directly exposed to radiation.

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31
Q

What are the common chromosome aberrations produced by radiation?

A

Translocations, dicentric chromosomes, ring chromosomes

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32
Q

How do chromosome abnormalities arise with radiation?

A

If breaks in DNA strands are repaired and joined together incorrectly, this will result in the formation of imperfect chromosomes when the cells are preparing for mitosis.

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33
Q

How are dicentric aberrations used in real practice?

A

The number of chromosomal aberrations formed increases with radiation dose. Scoring of dicentric aberrations in peripheral blood lymphocytes can be used as a retrospective biological radiation dosimeter to evaluate doses received. The technique is only sensitive enough to detect changes after doses over 100 mSv which is five times the annual dose limit for radiation workers. Therefore this would only be used in accident situations where it is suspected that a person has received a high dose.

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34
Q

What are the three possible outcomes for a cell after exposed to radiation?

A

Damage repaired, cell transformation, cell death/apoptosis

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35
Q

What are proto-oncogenes?

A

Alterations in certain genes may increase the risk of malignant transformation of a cell. These genes are called proto-oncogenes and they control cellular growth, proliferation and differentiation. Through mutation, radiation can convert proto-oncogenes into oncogenes, which may lead to inappropriate gene expression and a malfunction of cellular regulation

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36
Q

Why are subtle changes in genes sometimes worse than major changes?

A

Subtle changes in genes are less likely to be picked up by the check-point responses, and may be important in development of cancer.

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37
Q

What role in cancer development can radiation exposure play?

A

Radiation plays an important role as the initiating event in cancer development, and may also be involved in promotion and progression of tumours initiated by radiation or other means.

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38
Q

T or F - Concerning the effects of x-rays on cells:

A. Effects are less severe if the radiation dose is protracted
B. Once a chromosome mutation has occurred the cell will eventually develop into a cancer
C. Effects are less severe in cells with a high turnover
D. Sub-populations of damaged cells may incur further mutations to be transformed into a malignant state
E. Small acute doses of radiation are less damaging to cells per unit dose than high acute doses
F. Cells are able to repair almost all radiation damage at low dose rates
G. Adaptive responses protect cells at doses of a few mSv
H. Biological effects of radiation are less severe if dose is fractionated

A

A. True. Cells have more time to repair non-fatal damage.

B. False. Most chromosome mutations are unrelated to cancer development.

C. False. Effects are more severe in cell populations that are proliferating and tend to be more sensitive in the G2 and mitosis phases.

D. True. Malignant transformation of a cell is not a simple one stage process, it may require several mutations. The promotion and progression of the disease may be enhanced by radiation or other environmental carcinogens.

E. True. If there is a smaller amount of damage distributed across the cells, the cells are likely to be able to repair it.

F. True. Cells have to repair damage continually and do so successfully.

G. False. Studies on cell cultures have shown that the protective mechanisms are enhanced after doses of 50-200 mSv.

H. True. Cells that have been damaged but not fatally are able to repair the damage. Thus the cell is able to return to a healthy, undamaged state before the next dose fraction is delivered.

39
Q

Where does terrestrial radiation come from?

A

natural radionuclides - e.g. radon (from the decay of uranium) gives 50% of annual dose

40
Q

What sort of radiation does radon emit?

A

alpha - therefore more dangerous if inhaled or ingested through water.

41
Q

What is the average effective dose of background radiation?

A

The average effective dose received by persons in the United Kingdom is 2.7 mSv each year, of which 2.3 mSv per year is from natural sources or 0.006 mSv per day. Persons within the UK receive another 0.4 mSv from medical exposures.

42
Q

What is the effective dose from a chest X-ray?

A

0.02 mSv

43
Q

What is the effective dose from a lumbar spine X-ray?

A

1 mSv

44
Q

What is the effective dose from an abdominal CT?

A

10 mSv

45
Q

How can the effects of radiation on the body be divided?

A

deterministic effects/tissue reactions and stochastic effects

46
Q

When do deterministic effects of radiation occur?

A

result from high doses when the cumulative effects on cells in the body are sufficient to produce a measurable clinical response. occur within hours, days or weeks of exposure

47
Q

When do stochastic effects of radiation occur?

A

not apparent until many years after an exposure if they occur at all. The likelihood of these effects occurring is very small but the probability increases with the radiation dose received

48
Q

What can happen with acute whole body radiation?

A

radiation syndromes, which produce the symptoms associated with radiation sickness, including haemorrhage, infection, low blood cell count, diarrhoea and vomiting and may lead to the death of the individual.

49
Q

What are the most radiation sensitive cells in the skin?

A

basal stratum of epidermis

50
Q

At what dose do the earliest deterministic effects occur in the skin?

A

2 Gy (transient erythema)

51
Q

other than radiotherapy when can skin effects occur with radiation?

A

fluoroscopy especially in complex IR/cardiology procedures with oblique angles as beams need higher energy as more tissue to pass through

52
Q

Which part of the eye is mot susceptible to radiation?

A

The lens of the eye is susceptible to radiation damage

53
Q

Is it acute or chronic exposure to radiation of the eye that causes problems?

A

Both although the damage is cumulative, so such opacities may result from exposure over many years - with doses of greater than 0.1Gy/year causing detectable opacities.

54
Q

What are stochastic effects?

A

ones whose occurrence is determined by the laws of chance. The frequency of the effect increases with radiation dose but the severity does not change. It is thought that there is no threshold below which the risk of the effect is zero, because a single ionisation event can damage a DNA molecule and even diagnostic x-rays result in millions of ionisations.

55
Q

What are the 2 types of stochastic effect?

A

induction of cancer and the production of genetic changes in the offspring of the individual or in subsequent generations.

56
Q

What is the annual whole body effective dose limit for radiation workers?

A

20mSv a year

57
Q

What is the annual equivalent dose limit for the lens of the eye for radiation workers?

A

20mSv

58
Q

What is the annual equivalent dose limit for the skin/extremities or radiation workers?

A

500mSv

59
Q

T or F - Regarding stochastic or non-deterministic effects of radiation:
A. Effects only occur above a threshold dose
B. The chance of the effect occurring increases with dose
C. The severity of the effect varies with dose
D. Leukaemia is an example of a stochastic effect
E. Loss of fertility is an example of a stochastic effect

A

A. False. It is thought that there is no threshold below which the risk of the effect is zero, because a single ionisation event can damage a DNA molecule and even diagnostic x-rays result in millions of ionisations.

B. True.

C. False. The frequency of the effect increases with radiation dose but the severity does not change.

D. True.

E. False. It is a deterministic effect.

60
Q

T or F - Concerning deterministic tissue reactions:

A. Effects only occur above a threshold dose
B. The likelihood of the effect occurring increases with dose
C. The severity of the effect increases with dose
D. Skin cancer is an example of a deterministic effect
E. Cataract formation is an example of a deterministic effect

A

A. True.

B. True.

C. True.

D. False. It is an example of a stochastic effect.

E. True.

61
Q

What is the relationship between higher radiation dose and solid tumours?

A

The data showed that the risk increases with dose. The data for solid tumours shows a near linear rise in the number of excess cancers with dose.

However, the smallest doses at which there is a statistically significant increase in risk of cancer are 100-200 mSv.

62
Q

What is the relationship between higher radiation dose and leukaemia?

A

a curve with a proportionately lower risk at low doses. This type of relationship can be described by a linear-quadratic equation which contains terms proportional to ‘dose’ and ‘dose2’.

63
Q

What model is used to extrapolate dose vs cancer risk?

A

A linear no-threshold (LNT) extrapolation model

64
Q

What is the issue with the LNT model for cancer risk and radiation dose?

A

it sends out a message that no radiation dose is safe, no matter how small.

65
Q

What is the difference between absolute and relative risk with regards to excess cancer risk with radiation?

A

The absolute risk model assumes a constant excess risk after a latent period, while projections for the relative risk model are based on the background age-specific death rates for the different cancers in the particular population.

66
Q

why is the dose and dose rate effectiveness factor applied to the LNT for modelling cancer risk and radiation?

A

It is known that the cells’ repair mechanisms would be able to provide some protection at lower dose levels, but it is difficult to predict quite how large this effect would be. As a best estimate, a reduction factor of two is employed.

67
Q

Is the time between exposure to radiation and occurrence of cancer the same for all tumours?

A

No - Among the Japanese atomic bomb survivors, there was an excess of leukaemia between 5 and 14 years after exposure. However, the risk of solid tumours does not increase above normal levels until 10 years after the exposure, and for most types of cancer this period is much longer.

68
Q

What is a tissue weighting factor?

A

The sum of the weighting factors is 1.0, so that they represent a weighted sum of doses to radio-sensitive organs.

69
Q

How is effective dose calculated?

A

Effective dose = sum of wT x HT summed over 28 organs and tissues within the body.

70
Q

Why is the tissue weighting factor for gonads high?

A

A weighting factor for the gonads is included, relating to hereditary effects, although its significance will vary with the individual patient since there is no risk of these effects for those who have passed the reproductive age.

71
Q

Can effective dose be measured?

A

No - it can only be computed

72
Q

How is effective dose computed?

A

Conversion coefficients have been derived to allow organ doses to be calculated based on measured dose quantities such as entrance surface dose or dose-area product for x-ray procedures, or administered activity for radionuclide investigations.

73
Q

What is the purpose of effective dose?

A

To provide a dose quantity related to risk

74
Q

Is the effective dose of radio iodine thyroid imaging higher or lower than for abdominal CT?

A

Lower (4mSv vs 10)

75
Q

Based on the LNT model, what is the excess risk of developing fatal cancer per Sievert?

A

5% excess risk of developing cancer per Sv (1 in 20 000 per mSv)

76
Q

What are the standard terminologies regarding risk and at what effective dose?

A

<0.1 mSv Negligible
0.1-1 mSv Minimal
1-10 mSv Very low
10-100 mSv Low

77
Q

How can you explain radiation risk to patients?

A

Numerical estimates of radiation risks have a high level of uncertainty and are more likely to be confusing to the patient or give the wrong impression. Comparisons with other risks in everyday life can also be useful in helping to calibrate you perception.

78
Q

How should effective dose be changed regarding age?

A

The effective dose should be multiplied by an adjustment factor for age when determining the risk category. A simple option is to multiply it by a factor of 2 for those under 20 and divide by 2 for those over 70 years.

79
Q

When ae the risks of deterministic effects with radiation in pregnancy highest?

A

if the exposure occurs during organogenesis (day 8 - end of week 8)

80
Q

is radiation exposure in the first 8 days significant?

A

In the early stages of development, when the embryo only contains a few cells that are not specialised, radiation exposure could damage or kill enough of the cells for the embryo to be resorbed. Lethal effects can be induced by doses of the order of 100 mGy before or immediately after implantation of the embryo into the uterine wall. However, since the cells are still undifferentiated at this stage, if enough cells survive and continue to reproduce, the only effect would be a delay in development. Risks of effects appearing in a pregnancy that goes to term following radiation exposure during this period are therefore considered to be minimal.

81
Q

When is there the highest risk to the brain from radiation in pregnancy?

A

There is a rapid increase in the number of neurons during the period lasting from the 8th to the 15th week, which migrate to their functional site in the cerebral cortex

82
Q

What is the biggest risk of low doses of radiation in pregnancy?

A

The most significant effect of foetal exposure at low doses is an increased risk of cancer, especially leukaemia.

83
Q

What is the 10 day rule?

A

There is no evidence that there is an increased risk to the foetus during the first ten days of the menstrual cycle from radiation exposures at diagnostic levels.

Therefore the risk to the foetus from higher dose procedures can be reduced by restricting such procedures to the first 10 days of the menstrual cycle.

84
Q

When is the risk greatest for radioiodonhe in pregnancy for the foetus?

A

If 131I is administered during the middle or later stage of pregnancy, there is an increased risk of hypothyroidism in the infant with the possibility of mental deficiency if it is not detected and treated. However, no increased risk of spontaneous abortion or foetal abnormalities has been observed.

If iodine is administered at an earlier stage in pregnancy, a proportion will be retained by the maternal thyroid and released gradually. Iodine released at a later stage when the foetal thyroid is developing may also be taken up.

85
Q

What advice is given to women taking radionuclides?

A

female patients are advised to avoid conception for several months following therapies involving some radionuclides. Female patients are generally advised to avoid conception for 4 months following any administration of 131I.

86
Q

What is the risk in infants for developing cancer related to X-rays?

A

similar to that for the foetus. Risks projected from the models dare about 1 in 1000 lifetime risk of fatal cancer from a 10 mSv exposure for a child under 10 years old.

87
Q

What is advised to breastfeeding mothers taking radionuclides?

A

store pre-expressed milk or if long half-life stop breastfeeding (e.g. radio iodine)

88
Q

There is evidence of a risk of childhood cancer from foetal exposures above what dose?

A

10 to 20 mGy

89
Q

There is a risk of a measurable decrease in IQ in a small proportion of children after exposure as a foetus to what dose?

A

> 200 mGy

90
Q

T or F - Concerning the effects of antenatal exposure to radiation
A. Risks to the foetus are greater because more foetal cells are dividing
B. Risks of induction of childhood cancer are higher during the first 8-10 days of pregnancy
C. There is a high risk of foetal death following a radiation exposure during the first half of pregnancy
D. Risk of abnormalities in foetal development are likely to occur following irradiation during organogenesis, between the 2nd and 8th week post conception

A

A. True.

B. False. The risk of childhood cancer is greatest during the foetal period (9th to 38th week after conception). This is the time when foetal organs are growing.

C. False. There are risks during the pre-implantation period, but the risk falls during organogenesis.

D. True. However, effects only occur above doses of about 250 mGy.

91
Q

T or F - Concerning the effects of antenatal exposure to radiation:
A. The risk of Down’s syndrome is increased by irradiation in the first trimester
B. Risks of intellectual disability are greatest during the late stages of pregnancy
C. Irradiation of the foetus twith a dose of 500 mGy at 6 weeks after conception carries a higher risk of organ malformation than in the later stages of pregnancy
D. There is a risk of intellectual disability in a foetus if a mother is given an abdominal CT scan between 8 and 15 weeks after conception
E. Risks of induction of childhood cancer are likely to be lower during the early stages of pregnancy
F. The risk of hypothyroidism is higher if 131I is administered to the mother at any stage during pregnancy

A

False. There is no conclusive evidence that exposure to radiation causes Down’s syndrome.

B. False. They are greatest during the period 8th-15th week after conception.

C. True.

D. False. The dose from a CT scan would be 10-20 mGy, but the threshold for intellectual disability is 200 mGy.

E. True.

F. True.

92
Q

When is uptake of radio-iodine by the foetal thyroid significant?

A

10 weeks

93
Q
A
94
Q
A

R-ITI physics (2 decks)

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