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Radiation biology > Radiobiology: PP2 > Flashcards

Radiobiology: PP2 Flashcards

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1
Q

Human Radiation response is what?

A

The effects of ionising radiation on humans and other living tissue is the result of interactions at the atomic level.
- Can result in the transfer of heat in tissue and changes to the atoms chemical binding properties.

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2
Q

When were x-rays discovered?

A

1895

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3
Q

Classification of Biologic Effects

A
  • Stochastic

- Deterministic

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4
Q

Stochastic Effect:

A

At random, effects normally take a long time to appear. Probability of event occurring increases with dose.
-NO minimum safe threshold dose

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5
Q

What are examples of Stochastic effect?

A

Radiation induced cancers and hereditary effects

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6
Q

Latent period

A

The delay in effect of radiation becomes apparent

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7
Q

Explain the Deterministic Effect

A

Radiation response following high dose exposure.

  • Appears in a short period of time and effects are deliberate and known
  • High dose to skin could cause radiation burns
  • Severity increases (rather than probability) with increased dose
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8
Q

Describe Somatic effects

A

Effects appear on the exposed individual

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9
Q

Describe Genetic effects of radiation

A

Effects are on the offspring of the exposed individuals - Pre Conception

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10
Q

What are Teratogenic effects

A

Effects are on offspring of the exposed individual.

- Exposed during (foetal) gestational period

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11
Q

What is the target molecule?

A

DNA as it is the most sensitive molecule in the human body

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12
Q

what are examples of DETERMINISTIC EFFECT

A

Skin erythema, cataracts and acute radiation sickness are examples of deterministic effect.

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13
Q

What are Direct interaction of radiation on the body?

A

The result of ionisation or excitation of DNA, RNA or Protein molecules

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14
Q

What is Indirect interactions?

A

Refers to effects as a result of interactions within the surrounding medium e.g. cytoplasm of the cell, which in turn interact with the target molecule (DNA).

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15
Q

What causes the creation of free radicals?

A

The ionisation or excitation of water molecules

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16
Q

What are some of the radiation related factors that determine the biologic response to radiation exposure?

A
  • Absorbed dose (quantity) and dose rate
  • Type and energy of the radiation (quality)
  • Conditions on how the dose was delivered
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17
Q

Biology related factors that determine the biologic response to radiation exposure?

A
  • Condition of the cells at the time of irradiation

- The cells or organs affected and their radio-sensitivity

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18
Q

Define Cell sensitivity

A
  • Not all living cells are equally sensitive to radiation

- Those cells which are actively reproducing are more sensitive than those which are not

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19
Q

When are cells most sensitive?

A

During Mitosis (m-phase)

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20
Q

When are cells less sensitive?

A

G1 and G2

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21
Q

When are cells least sensitive?

A

During S phase

22
Q

Why factors make specific cells more sensitive than others?

A
  • Have a high division rate
  • Have a high metabolic rate
  • Are of a non specialised type
  • Are well nourished
23
Q

What cells are most sensitive?

A
  • Lymphocytes (white blood cells) and cells which produce blood are constantly regenerating, and therefore the most sensitive.
24
Q

What cells are least or not very sensitive to radiation?

A
  • Reproductive and GI cells do not regenerate as quickly, so are slightly less sensitive.
  • Nerve and muscle cells are the slowest to regenerate and are therefore the least sensitive.
25
Q

What are the types of DNA mutations?

A
  • MAIN-CHAIN SCISSION: This is the breakage of the backbone of a molecule or DNA strand. In DNA it can sever one or both side rails of the strand.
  • CROSS LINKING: When the side rail on a DNA strand is broken, it may slip and cross link
  • POINT LESSIONA: disruption of a single chemical bond which is not detectable but can cause malfunction within the cell.
26
Q

Describe cell repair:

A

The ability to either repair or cope with damage. As a result not all radiation effects are irreversible. Cells are able to completely repair any damage and function normally

27
Q

Organ sensitivity is what?

A

The sensitivity of the various organs of the human body correlate with the relative sensitivity of the cells from which they are composed.

28
Q

What are some factors that affect organ sensitivity?

A
  • Rate of Reproduction

- Oxygen Supply (increased O2 supply leads to increased production of free radicals)

29
Q

What organs are the most sensitive and insensitive to radiation?

A

SENSITIVE: Blood forming cells because of their rapid regeneration rate
INSENSITIVE: Brain, nerve cells and muscles

30
Q

What medical imaging procedure could be an example of the deterministic effect and why?

A

Fluro -could cause skin burns

Acute radiation changes were the first radiation effects seen on skin soon after x-rays began being used.

31
Q

What is regeneration?

A

is replacement of damaged cells in the organ by cells of the same type. Full functionality of the organ.

32
Q

What is the difference between regeneration and repair?

A
  • Repair is replacement of the damaged cells by fibrotic scar tissue. Function of the organ is compromised.
  • Regeneration returns the full functionality of the organ
33
Q

Repair of a cell:

A

Replacement of damaged cell by different cell type e.g. fibrosis so function of the organ is compromised.

34
Q

What are Anoxic cells?

A
  • A = without: Oxy = oxygen
  • Cells with insufficient oxygen:

e.g. Malignant tumour: removed by shrinking method

35
Q

Shrinking method or “FRACTIONATION”

A

e.g. Malignant tumour:
As the tumour is exposed to radiation, the outer layer of rapidly dividing cells is destroyed, causing it to “shrink” in size. Rather than one massive dose the tumour is given a small dose over a period of time, which gives the healthy tissue a chance to recover from any damage, while gradually shrinking the highly sensitive tumour.

36
Q

Name and explain what the Five R’s of Fractionation are?

A
  1. REPAIR: allowing the cells time to recover in between doses of radiation.
  2. REDISTRIBUTION: different cells react in different ways at different times. Some cells might be radioresistant to begin with but more sensitive if given additional doses.
  3. RE-OXYGENATION: anoxic cells are more resistant than normal cells. By dividing the dose into small amounts more oxic cells are available.
  4. REPOPULATION: the increase in cell division that occurs at some time after radiation is given. In general this occurs at about four (4) weeks.
  5. RADIOSENSITIVITY: the general sensitivity of all cells to radiation.
37
Q

What is “a special case” in regards to the Five R’s of Fractionation?

A

Embryos: An embryo would suffer consequences of exposure to radiation that differ.
As it also is comprised of rapidly dividing cells with a good blood supply and lots of oxygen (like a tumour).

38
Q

What relates to the most sensitive organs which in turn relates to the most sensitive cells.

A

Whole body sensitivity

39
Q

Factors affecting Whole Body Sensitivity

A
  • Total dose
  • Type of cell
  • Type of radiation
  • Age of the individual
  • Stage of cell division
  • Part of the body exposed
  • General state of health
  • Tissue volume exposed
  • Time interval over which the dose is received
40
Q

Biological effects of radiation are typically divided into two categories.
What are these categories?

A

High exposure levels:
consists of exposure to high doses of radiation over brief intervals of time producing acute or short term effects.

Low exposure levels:
consists of exposure to low doses of radiation over an extended period of time producing chronic or long term effects.

41
Q

What is the difference between high and low exposure levels?

A
  • High doses tend to kill cells

- Low doses tend to damage or change cells

42
Q

What is acute radiation sickness?

A

full body response rather than just an organ or cell response.
ARS is a group of sub-syndromes occurring at different stages over the period of hours to weeks, after exposure.
Each manifestation occur in a predictable sequence of events.

43
Q

What are the stages of ARS

A
  1. PRODROMAL: Dose dependent and can begin within minutes to hours after exposure.Symptoms: Anorexia, nausea, vomiting, diarrhoea, increased salivation, abdominal cramps and dehydration.
  2. LATENT or ASYMPTOMATIC The prodromal symptoms subside. Like an incubation period during which the organ system damage is progressing. Stage which may last days to weeks.
  3. MANIFEST ILLNESSAbrupt onset of moderate to severe symptoms relevant to the underlying organ system damage.
  4. Death or RECOVERYwhich may take weeks to months.
44
Q

What is a lethal dose to humans and what are the complications?

A

Dose excess of 50 Gy or more invariably die within 24 – 48 hours from complications of neurovascular syndrome.

45
Q

A dose exposure between 0.5-10 Gy will cause what syndrome?

A

Go through prodromal and latent periods before they begin to exhibit hematopoietic syndrome symptoms.

-Symptoms.
Haemorrhage, ulceration, infection due to the destruction of both red and white blood cells. Also epilation (hair loss). Most will also show GI symptoms due to damage to the mucosal barrier.

46
Q

A dose exposure between 10- 50 Gy will cause what syndrome?

A

Will often go through prodromal and latent periods before they exhibit gastrointestinal syndrome symptoms.

  • Generally GI syndrome leads to death within 3 – 10 days if no medical care given or as long as 2 weeks if intensive medical support is given.
47
Q

Healthy adults with proper medical care almost always recover from doses lower than

A

2 Gy

48
Q

What is the whole body response to the following exposure levels:
20Sv, 10Sv, 5sv, 1Sv

A
  • 20 Sv. Death in hours due to severe damage to central nervous system .
  • 10 Sv. Death in days due to damage to lining of the GI tract. Infection enters blood. Patient dies of septicaemia or haemorrhage as a result of the breakdown of the gut lining.
  • 5 Sv. Death within weeks due to bone marrow failure (unless medical intervention).
  • 1 Sv. Survival with low blood count.
49
Q

Death due to ARS is an Example of…

A

DETERMINISTIC EFFECT

50
Q

What does this stand for:

The LD50/60

A

The lethal dose which will kill 50% of an exposed population in 60 days.

51
Q

The LD50/60 for humans is _____ when delivered rapidly.

A

3 - 5 Sv

52
Q

The LD50/60 for humans may extend to____ with supportive medical care such as transfusions and antibiotics and possibly as high as _____ in an intensive care system

A
  • 6 Sv

- 6 – 8 Sv

Radiation biology (19 decks)

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