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000 Radiobiology > RADIOBIOLOGY COPY > Flashcards

RADIOBIOLOGY COPY Flashcards

1
Q

Describe what occurs in the Compton Effect, and what impact does it have on the radiograph?

A
  • the incident X-ray photon collides with an outer shell electron of an atom, and is scattered with resulting energy loss.
  • creates fog on radiograph
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2
Q

Describe what occurs in the Photoelectric Effect, and what is it responsible for on the radiograph?

A
  • the incident X-ray photon collides with an inner shell electron and is totally absorbed.
  • is responsible for the white areas on a radiograph representing bone.
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3
Q

What determines the probability of the Photoelectric Effect?

A

-probability of it occurring increases as:
kvp decreases
atomic number increases

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4
Q

What interactions occur above the diagnostic energy range?

A

-pair production and photodisintegration

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5
Q

Define pair production:

A
  • when a high energy photon interacts with the nucleus of the atom, creating one positive and one negative charged atom.
  • only occurs at energy levels of 1.02 MeV or above
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6
Q

What are the three local tissues that will exhibit an immediate response to radiation?

A

–skin, gonads and bone marrow.

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7
Q

Define erythema:

A
  • reddening of the skin following high doses of radiation.

- threshold DRR

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8
Q

What is the most radiosensitive phase of the male germ cell?

A

-spermatagonia (stem cell)

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9
Q

Describe the response of the hemopoietic system:

A
  • there is a decrease in the # of circulating blood cells.
  • the initial damage takes place on the stem cell level.
  • effects vary depending on blood cell maturity rate and lifetime in peripheral blood system
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10
Q

Which is more damaging: a chromosome hit or DNA hit?

A

-chromosome hit

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11
Q

What are the four major long-term effects of radiation?

A
  • local tissue effects
  • life span shortening
  • carcinogenesis
  • embryological effects
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12
Q

What kind of DRR does cataractogenesis follow?

A

-threshold DRR
-does: acute 200 rads
fractionated 1000 rads

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13
Q

What is easiest to link to radiation exposure and what kind of DRR does it follow?

A
  • leukemia
  • linear non-threshold DRR
    ex. A-Bomb survivors, radiologists, ankylosing spondylitis pts, children irradiated in utero.
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14
Q

What is the fetal dose limit?

A

.5 rems

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15
Q

What are the five basic interactions with matter?

A
  1. classical scattering/coherent effect
  2. compton effect
  3. photoelectric effect
    ^ occur in diagnostic range
  4. pair production
    5.photodisintegration
    ^ occur above diagnostic range
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16
Q

Describe classical scattering:

A
  • the incident X-ray photon bumps into the atom and is deflected from its path with no loss of energy.
  • occurs in low energy ranges- below 70 kvp
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17
Q

Describe back scatter and when does it occur?

A
  • photons which are reflected 180 degrees back in the same direction of origin.
  • occurs if the incident photon strikes the electron head on, or if the electron it strikes has a high binding energy.
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18
Q

What determines the probability of the compton effect occurring?

A

-chances go down as kvp increases

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19
Q

Define local tissue damage:

A

-specific tissue or organ response from partial body doses of radiation exposure

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20
Q

What do chromosomes consist of?

A
  • DNA and protein
  • cell nucleus contains 23 pairs of chromosomes
  • chromosomes are visualized during metaphase and replicated during S phase
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21
Q

What kind of DRR does radiation induced chromosome damage follow?

A

-non threshold DRR

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22
Q

When is a single hit chromosome aberration observed and what does it result in?

A
  • observed following a low dose of radiation
  • results in chromosomes with missing genetic material at the end of the cycle
  • linear DRR
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23
Q

When does a multi hit chromosome aberration occur and what does it result in?

A
  • chromosome sustains more than one hit
  • occurs as radiation doses approach 100 rads
  • results in severe chromosome damage/latent effects
  • follows non-linear DRR
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24
Q

Define roentgen (R):

A
  • unit of radiation exposure
  • measures radiation as it passes thru air
  • SI unit= air kerma
25
Q

Define rad:

A
  • radiation absorbed dose
  • measures absorbed energy into the tissue
  • SI unit= gray
26
Q

Define rem:

A
  • radiation equivalent man
  • dose equivalent of effective dose
  • expresses occupational & population dose
  • SI unit=sievert
27
Q

Define radiation weighting factor:

A

-ability of radiation to cause biologic damage

28
Q

Define tissue weighting factor:

A

-accounts for the relative radio sensitivity of various tissues and organs

29
Q

Define Curie (Ci):

A
  • unit of measurement for radioactivity

- SI unit= becquerel

30
Q

Define ionization:

ionizing radiation:

A

-the removal or addition of an orbital electron from or to an atom
-radiation which is capable of causing ionizing of atoms which it interacts with
2 types: particulate and electromagnetic

31
Q

Define particulate radiation:

A
  • composed of subatomic particles in motion at high speeds.

- types include alpha, beta, fast neutrons and electrons

32
Q

Describe alpha radiation:

A
  • positive +2 charge
  • large, massive and sluggish
  • looses energy quickly
  • highly ionizing internally (inhalation, absorption, ingestion)
  • absorbed by one sheet of paper
33
Q

describe beta radiation:

A
  • negative charge, light weight -1 charge
  • electron in motion
  • travels fast
  • more penetrating than alpha
  • absorbed by several sheets of paper
34
Q

Define electromagnetic radiation:

A
  • consist of photons or bundles of energy traveling through space at the speed of light
  • no charge and no weight
35
Q

Which forms of electromagnetic radiation are capable of ionization?

A
  • x rays: originate from electron shells

- gamma rays: originate from the nucleus

36
Q

What accounts for the sources of ionizing radiation?

A
  • natural background=accounts for 50%

- manmade radiation=accounts for 50%

37
Q

Define radioisotope:

A
  • an atom with an unstable nucleus
  • proton to neutron ratio is unbalanced
  • it spontaneously emits particles from nucleus to become stable
38
Q

Define isotope:

A

-an atom of the same element which has the same atomic number (number of protons) but different atomic mass numbers.

39
Q

Define radioactive decay:

A

-radiation being emitted from the nucleus of a radioisotope, which are either alpha, beta or gamma

40
Q

Define radioactive half life:

A

-the length of time required for one half of any amount of radioactive material to decay to stability

41
Q

Define somatic and genetic cells:

A
  • somatic= all functioning body cells (except reproductive)

- genetic=germ or reproductive cells

42
Q

Define mitosis:

A
  • mitosis=somatic cell division
  • 4 phases: prophase, metaphase, anaphase, telephase
  • metaphase most radiosensitve
43
Q

Define meiosis:

A

-genetic cell division

44
Q

Define linear:

A

-indicates that the biologic response is directly proportional to the radiation dose

45
Q

Define nonlinear:

A

-indicates that the biologic response is not directly proportional to the radiation dose

46
Q

Define threshold and give examples:

A
  • indicates that a certain level of radiation is needed to cause a certain biological effect to occur.
  • below that level of radiation there will be no biologic response
  • intersects the graph at a point ABOVE zero
  • points of intersection indicate the threshold dose of radiation
  • Ex. cataracts, erythema, epilation, sterility
47
Q

Define non threshold and give examples:

A
  • indicates that there is no safe level of radiation
  • a biologic response is always present even at zero levels of radiation
  • intersects the graph at zero or BELOW
  • ex. leukemia, chromosome abberations, genetic effects
48
Q

Define linear quadratic DRR:

A
  • a curve that indicates at low doses of radiation, biologic response is not as great as indicated by the linear graph
  • as doses are increased, the biologic response increases significantly
  • indicates how humans really respond to low and high levels of radiation
49
Q

Define main chain scission-

A

-a break in the backbone of the molecule chain

50
Q

Define cross-linking:

A

-radiation causes spurs on side of chain causing molecules to stick together

51
Q

Define point leisions:

A

-disruption of a single chemical bonds along molecules, causing chemical changes and late effects from the radiation.

52
Q

Define radiolysis:

A
  • the interaction of radiation and water molecules in the body
  • represents the principle interaction since the body is mostly made up of water
  • results in the formation of two major by products=ion pair and free radical pair
  • ion pair is harmless and can exist as a free agent with no ill effects
53
Q

Describe the free radicals produced from radiolysis:

A
  • uncharged molecules containing a single electron in the outermost shell
  • very unstable and quick to react with other molecules
  • in order to become stable, they may do one of three things:
    1. transfer excess energy to other molecules
    2. travel to distant points causing damage
    3. bond with other free radicals resulting in production of toxic agents (hydrogen peroxide or another type of free radical)
54
Q

Direct effect versus indirect effect:

A
  • direct effect: when a critical molecule such as DNA is directly hit by the ionizing radiation photon
  • indirect effect: occurs when a critical molecule is affected by a free radical produced through radiolysis of water (accounts for 95% of radiation damage)
55
Q

What is the target theory?

A
  • assumes that cells have a critical or target molecule which must be hit and inactivated by radiation in order for the cell to die
  • high LET radiation causes more direct hits
  • low LET more apt to cause indirect hit
56
Q

Describe the single target-single hit model:

A
  • applies to singe celled organisms which only have one target
  • chances of target being struck ^ with ^ radiation doses
57
Q

Describe the multitarget-single hit model:

A
  • complex cells have two targets, and in order for the cell to be inactivated both targets must be hit
  • at low doses of radiation chances of both targets being hit is unlikely, therefore cell survival will be nearly 100%
58
Q

What is cell recovery dependent on?

A
  • cell cycle when irradiated
  • time between doses
  • the percentage of radiation damage that is repairable is 90%
59
Q

When is the first most sensitive cell phase? Second? Least sensitive?

A
  • mitosis
  • G1-S transition
  • late S-phase

000 Radiobiology (52 decks)

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