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MED 107- MEDICAL PHYSICS II > 13. RADIATION HEALTH EFFECTS: DOSE LIMITS > Flashcards

13. RADIATION HEALTH EFFECTS: DOSE LIMITS Flashcards

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1
Q
  1. Fill in the empty spaces in the table.
A
  1. 20 mSv in a year averaged over 5 years
  2. 1 mSv in a year
  3. 20 mSv
    (milliSilvert)
  4. 500 mSv
  5. 500 mSv
  6. 50 mSv
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2
Q
  1. What is meant by Occupational?
A
  • people who work with radiation
  • such as nurses, doctors and staff
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3
Q
  1. In terms of Absorbed Energy, what can be said about Ionising Radiation?
A
  • Ionising Radiation is much more harmful than chemical
    or other physical agents
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4
Q
  1. What happens when ionisation occurs?
A
  • it results in a small cluster of ion pairs
  • each of these clusters represent a very small amount
    of energy
  • this energy is highly localised
  • it has around 100 eV per cluster
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5
Q
  1. What happens when small radiation exposures occur?
A
  • these are known as Dental Exposures
  • they will create millions of ion pairs in the exposed
    tissue
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6
Q
  1. What can be said about energy deposition at the Bimolecular Level?
A
  • the energy deposition is highly localised
  • it is non-uniform
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7
Q
  1. Which parts of the organism receive no energy at all?
A
  • relatively large volumes of each cell and the
    macromolecules within it
  • they receive no energy at all
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8
Q
  1. What happens in the regions where Ionisation occurs?
A
  • the energy deposited is very high
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9
Q
  1. How much energy does an ionising radiation event produce?
A
  • it produces approximately 70 times more energy than
    the energy required to break a hydrogen bond in DNA

NB:
- this means that even small doses of (mGY) of Ionising
Radiation will produce a large number of random sub-
molecular events in cells

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10
Q
  1. What happens to the sensitive macromolecules when they are exposed to ionising radiation?
A
  • they may be damaged
  • this can happen without raising the temperature of the
    cell outside of the normal range

NB:
- this unique form of Radio-sensitivity only happens with
ionising radiations

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11
Q
  1. What percentage of Ionisation levels are potentially harmful?
A
  • 1%
  • this is because the energy absorption events rarely
    occur close to important cellular macromolecules
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12
Q
  1. What is the most abundant cellular molecule?
A
  • water
  • this means that radiation absorption mostly ionises
    H2O molecules
  • this occurs within nanoseconds during exposure
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13
Q
  1. What happens when the Radiolysis of water molecules occurs?
A
  • transient free radicals (+OH°) (hydroxyls)
    and +H° (Hydrogens)
    and Hydrated Electrons are formed
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14
Q
  1. What are Hydrated Electrons?
A
  • these are extra electrons that are solvated in liquid
    water
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15
Q
  1. What can be said about the Transient free radicals, the +H° and the Hydrated electrons?
A
  • they are highly reactive
  • they usually recombine within milliseconds to re-form
    water molecules
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16
Q
  1. What happens if these radicals are formed within a few nanometers of larger biological macromolecules or cell membranes?
A
  • they may interact with these cellular components

THIS INDIRECT ACTION MAY INITIATE:
- a chain of sub-cellular events
- these will produce temporary or permanent
microscopic and detectable changes in the cells

17
Q
  1. What can happen even if Free Radicals are made due to low radiation doses?
A
  • the Free Radical effects may lead to delayed and
    increased risks of cancer in the exposed individual
  • it may cause genetic changes in the future
18
Q
  1. What happens if the Free Radicals are made due to high radiation doses?
A
  • the microscopic damage due to the Free Radical Attack
    is more severe
  • it is more likely to kill the cells
  • this would lead to the temporary or permanent
    changes in normal tissue functions
19
Q
  1. Which is the most damaging of the Free Radicals?
A
  • the Hydroxyls
  • the +OH°
  • it is believed to initiate about ⅔ of all the effects of the
    external exposure of the body to X and Y Rays
20
Q
  1. In which two ways can radiation attack the DNA?
A
  1. Indirect Route
  2. Direct Route
21
Q
  1. What is meant by the Indirect Route?
A
  1. Radiation
  2. Water molecules are ionised by the radiation
  3. Free Radicals are formed
  4. These attack the DNA
  5. This causes damage
22
Q
  1. What is meant by the Direct Route?
A
  1. Radiation
  2. Damage

NB:
- this route is very high in energies
- it can attack the DNA directly due to this

23
Q
  1. What attacks the DNA through the Indirect Route?
A
  • the Free Radicals that are surrounding the cellular DNA
    attack it
  • this attack produces most of the known high or low
    dose effects of Ionising Radiation
24
Q
  1. Other than the Free Radicals, what else can cause damage directly to the DNA?
A
  • the relatively smaller free electrons
  • these are negatively charged
  • heavier and more densely ionising charged particles
    are much more likely to cause direct DNA damage
  • EG: alpha particles
    : such as Radionuclides
25
Q
  1. Does this diagram make sense?
A
  • yes
26
Q
  1. What is Base Modification or Deletion?
A
  • it is a type of radiation damage to the DNA
  • it causes genetic defects
  • it increases the mutation rates in the reproductive cells
27
Q
  1. What happens if the damaged DNA Bases are not repaired or eliminated?
A
  • it increases the risk of malignant cell transformation
28
Q
  1. What is Bond Breakage?
A
  • this facilitates the loss of a base
  • it changes the molecular shape and structure
29
Q
  1. What is Single Strand Breakage?
A
  • this can occur at random
  • it happens in either strand along the DNA double helix
30
Q
  1. What are Double Strand Breaks?
A
  • these are due to a single event
  • they can also be caused by the random coincidence of
    two single events that occur at the same time on the
    complementary DNA strands

NB:
- this process becomes more probable the higher the X-
Ray dose and Dose rate are

31
Q
  1. What is Cross-Linkage?
A
  • this potentially inhibits the replication of the DNA

MED 107- MEDICAL PHYSICS II (108 decks)

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