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MED-107 Medical Physics II: Medical Imaging and Radiotherapy > 3.1/3.2 radiation health effects I&II > Flashcards

3.1/3.2 radiation health effects I&II Flashcards

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1
Q

to describe the health effects of exposure to ionizing radiation, what 3 things must we define?

A
  • absorbed dose
  • equivalent dose
  • effective dose
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2
Q

what is the largest man-made source of radiation exposure to general population worldwide?

A

the radiation exposure from diagnostic X-rays

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3
Q

man-made exposure contributes ___% of total annual exposure from all sources

A

14

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4
Q

why is the concept of exposure significant?

A

because although diagnostic x-rays provide great benefits, their use involves some small risk of developing cancer

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5
Q

what is exposure (or exposure dose)?

A
  • the method of measuring the amount of ionization in air
  • measures the ratio of the total charge produced (of, electrons for example) in a small volume of air
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6
Q

what is the unit of exposure for air?

A
  • Coulombs per kilogram (C/kg)
  • Röntgen
    (1R = 2.58 x 10^-4 C/kg)
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7
Q

what does exposure ONLY apply to?

A

X-rays and γ-rays (photons)

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8
Q

as a measure of radiation damage, exposure has been superseded by the concept of

A

absorbed dose

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9
Q

what is absorbed dose?

A

a quantity that better describes the effects on radiation on materials/human beings

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10
Q

what is the SI unit of absorbed dose?

A

the gray (Gy)

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11
Q

what is absorbed dose equivalent to?

A
  • the absorption of one joule of energy in a kilogram of a substance by ionizing radiation
  • (or amount of energy that is absorbed to the mass (matter) to the human body)
  • (1 Gy = 1 J/kg)
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12
Q

since the Gray is a large unit, for radiation protection purposes, it is more common to use ____ and ____

A
  • microgray (μGy) - (1 x 10^-6)
  • milligray (mGy) - (1 x 10^-3)
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13
Q

what is KERMA?

A
  • KINETIC ENERGY RELEASED IN MEDIUM
  • when a photon beam interacts with a medium, the photon interactions release electrons with KE into the medium
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14
Q

the energy deposited by these electrons per unit mass is the?

A

absorbed dose

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15
Q

what is the unit for KERMA?

A
  • joule per kilogram (same as absorbed dose)
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16
Q

when is KERMA dose equal to absorbed dose, and when is it different?

A
  • different doses at high energies (up to 1 MeV)
  • doses are roughly equal at low energies
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17
Q

_____ is energy released, and _____ is energy absorbed

A

KERMA, absorbed dose

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18
Q

what allows the effect of radiation exposure on human tissue to be determined?

A

equivalent dose

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19
Q

what do we use equivalent dose for?

A

to relate the absorbed dose in human tissue to the effective biological damage of ionizing radiation

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20
Q

explain why we might not get the same biological effects of the same amounts of absorbed doses?

A
  • not all types of radiation has the same biological effect, even for the same amount of absorbed dose
  • example: if we have equal amounts of absorbed dose of both X-rays and another organ that absorbed an α-particle, there won’t be equal biological effects of each
  • since α-particles are much heavier, they cause more damage to cells
  • it is important to take into account the type of radiation
21
Q

in what cases do we use equivalent doses in?

A

when we need to take into consideration the different types of radiation

22
Q

what is the SI unit of equivalent dose? what does it represent?

A
  • the Sievert (Sv)
  • it represents the stochastic biological effect (i.e. cancer)
23
Q

the Sievert is also a large unit, for normal radiation protection levels, it is more common to use _____ and _____

A
  • microSievert (μSv)
  • milliSievert (mSv)
24
Q

what equation do we use to determine equivalent dose?

A

HT = Σ WR x D

  • HT - equivalent dose
  • WR - radiation weighting factor
  • D - absorbed dose
25
Q

what is the use of radiation weighting factor (WR)?

A

it takes into account the type of radiation when making a calculation

(that some kinds of radiation are more dangerous to biological tissue)

26
Q

how do we determine the dose in Sieverts from the dose in Grays?

A

multiply by the WR

27
Q

what is the relationship between absorbed Sieverts in a unit of time and exposure intensity?

A

the more Sieverts absorbed in a unit of time, the more intense the exposure
(higher dose=higher intensity)

28
Q

what is it called to express exposure as an amount over a specific amount of time?

A

dose rate
(ex: 5 mSv per year)

29
Q

which dose quantity shows that the probability of a harmful effect from radiation exposure depends on the part(s) of the body exposed?

A

the effective dose

30
Q

give an example that shows that some organs are more sensitive to radiation than others

A

bone marrow is a more dense organ compared to skin, so it can be damaged more easily than skin for the SAME amount of radiation

31
Q

what equation do we use to determine effective dose?

A

E = Σ WT x HT

  • E - effective dose
  • WT - tissue weighting factor
  • HT - equivalent
32
Q

what is the use of tissue weighting factor (WT)?

A

it takes in account the sensitivity of each organ tissue when making a calculation

33
Q

what is the SI unit of effective dose?

A

the Sievert (Sv)
(since equivalent and effective dose both use Sv, identify which you have used when calculating)

34
Q

the higher the value of WT, the _____?

A

the higher the sensitivity of the organ tissue

35
Q

list the 3 dose quantities

A

(1) absorbed dose: energy “deposited” in a kg of a substance by the radiation

(2) equivalent dose: absorbed dose weighted for harmful effects of different radiations (WR)

(3) effective dose: equivalent dose weighted for susceptibility to harm of different tissues (WT)

36
Q

what are the annual dose limits for (1) occupational workers and (2) the public?

A

occupational workers - 20mSv
public - 1 mSv

37
Q

what are the annual equivalent doses of
- lens of the eye
- skin
- hands & feet

A
  • 20 mSv
  • 500 mSv (occupational), 50 mSv (public)
  • 500 mSv
38
Q

why is ionizing radiation much more harmful than chemical or other physical agents?

A
  • each ionization results in a small cluster of ion pairs
  • each of these clusters represent a very small amount of energy (≈100eV per cluster)
  • even small radiation exposures will create millions of ion pairs in the exposed tissues
  • at the bimolecular level, the energy deposition is highly localized and non-uniform
39
Q

relatively large volumes of each cell will receive ____ while, smaller volumes receive ____ when exposed to radiation

A

large volumes receive no energy at all while smaller volumes receive a higher dose

40
Q

what happens to the location where ionization occurs?

A

the energy deposited is very high

41
Q

how could a macromolecule become damaged by ionizing radiation without raising the temperature of the cell outside normal range?

A
  • even very small doses (mGy) of ionizing radiation will produce a large number of random sub-molecular events in cells
  • any one of these may damage a sensitive macromolecule
42
Q

only about ___% of the ionization events are potentially harmful, because there are enough mechanisms of DNA repair

A

1%

43
Q

what are the two ways radiation can attack DNA?

A
  • direct route
  • indirect route
44
Q

describe the direct route of radiation attacking DNA

A
  • in very high energies, radiation (photons) can directly attack DNA
  • the relatively small negatively charged electrons can also cause damage by direct interaction with DNA
  • heavier, more densely ionizing charged particles (α-particles) are much more likely to cause direct damage
45
Q

describe the indirect route of radiation attacking DNA

A
  • since the most abundant cellular molecule is water, radiation will mostly ionize H2O molecules
  • this results in the formation of FREE RADICALS (hydroxyl, hydrogen)
  • they are highly reactive and will re-combine to reform water
  • however, if these radicals are formed within a few nm of large biological macromolecules/cell membranes/ cellular DNA, they could interact with them
  • this indirect action, could initiate a chain of sub cellular events that will produce detectable changes in cells
  • after low doses, free radical effects may lead to delayed but increased risks of cancer
  • with higher doses, microscopic damage is even more severe
46
Q

which radical is the most damaging of the free radicals?

A

the +OH˚radical
- it initiates about 2/3 of all the effects of external exposure of the body to X- or γ- rays

47
Q

what are some effects of radiation exposure on DNA?

A
  • single-stand break
  • double-strand break
  • base loss / base change
  • cross-linkage
  • DNA cross-linkage
  • protein cross-linkage
48
Q

what are the two categories of effects due to radiation?

A
  • stochastic effects
  • deterministic effects
49
Q
A

MED-107 Medical Physics II: Medical Imaging and Radiotherapy (16 decks)

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