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RT 206 > 4.2 Fundamental Principles of Radiobiology > Flashcards

4.2 Fundamental Principles of Radiobiology Flashcards

1
Q

if the dose is delivered continuously but at a lower dose rate, it is
said to be _____
-When 6 Gyt is delivered at the rate of 10 mGyt/hr for a total time of 600
hours, the mouse will survive

A

protracted

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2
Q

If the 6-Gyt dose is delivered at the same dose rate, but in 12 equal fractions
of 500 mGyt, all separated by 24 hours, the mouse will survive. In this
situation, the dose is said to be _____

A

fractionated

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3
Q 
Six gray (600 rad) delivered in 3 -minutes at a dose of 2 Gyt/min is \_\_\_\_ for
a mouse
A

lethal

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4
Q

The response of biologic tissue to radiation is ____ when irradiated in the oxygenated, or aerobic, state than when irradiated in anoxic or hypoxic conditions.

A

greater

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5
Q

OER (oxygen enhancement ratio)=

A

OER= dose necessary under anoxic conditions to produce a given effect / dose necessary under aerobic conditions to produce the same effect

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6
Q

is defined as the
dose of radiation that produces a given biologic response under
anoxic conditions divided by the dose of radiation that produces the
same biologic response under aerobic conditions.

A

oxygen enhancement ratio (OER)

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7
Q

It is theorized that
oxygen is needed in order for free radicals to form during ionization
of water. Without the free radicals, hydrogen peroxide is not formed,
and thus cell damage is _____

A

reduced

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8
Q

OER depends on ____

A

LET

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9
Q

The OER is most pronounced for ___

LET radiation, and is less effective with __ LET radiation

A

most - low,

less - high

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10
Q

Because of the physical differences between high and low LET radiation, the quantity of damage done by high LET radiation would
be beyond repair. Thus, having oxygen present would not _____
the response to radiation to the same magnitude, as would be the case with low LET radiation

A

intensify

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11
Q

Humans are most _____
before birth and are most
____ during
maturity

A

sensitive,

radioresistant

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12
Q

With old age, humans again tend to become more _____

A

radiosensitive

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13
Q

Tissue is more sensitive to radiation when irradiated in the oxygenated state than when irradiated under anoxic (without oxygen) or hypoxic (low-oxygen) conditions.
This characteristic of tissue radiation response is called
the _____ and is described numerically by the
_____

A

oxygen effect,

oxygen enhancement ratio (OER)

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14
Q

without oxygen

A

anoxic

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15
Q

low-oxygen

A

hypoxic

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16
Q

high-pressure

A

Hyperbaric

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17
Q

has been used in radiation oncology in an attempt to enhance the radiosensitivity of nodular, avascular tumors, which are less radiosensitive than tumors
with an adequate blood supply

A

Hyperbaric (high-pressure)

oxygen

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18
Q

The OER is highest for low-LET radiation, with a maximum value of approximately __ that decreases to approximately __ for high-LET radiation

A

3,

1

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19
Q

a decrease in the size of a tissue or organ due

to cellular shrinkage

A

cell atrophy

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20
Q

In vitro experiments show that if dose is not sufficient to induce interphase death, then cell will be able to _____

A

recover

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21
Q

occurs when the cell dies before replicating

A

Interphase death

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22
Q

At the whole-body

level, this recovery from radiation damage is assisted through _____ by surviving cells

A

repopulation

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23
Q

If a tissue or organ receives a sufficient radiation
dose, it responds by shrinking. This is called ____, and it occurs because some cells die and disintegrate,
and are carried away as waste products

A

atrophy

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24
Q

Recovery =

A

Recovery = Intracellular repair + Repopulation

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25
Q

agents that enhance the effect of radiation

A

Radiosensitizers

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26
Q

halogenated pyrimidines, methotrexate, actinomycin D, hydroxyurea,
and vitamin K

A

Radiosensitizers

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27
Q

become incorporated

into the DNA of the cell and amplify the effects of radiation on that molecule

A

halogenated pyrimidines

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28
Q

include molecules that

contain a sulfhydryl group (sulfur and hydrogen bound together), such as cysteine and cysteamine

A

Radioprotectors (Radioprotective compounds)

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29
Q

have not found human application because, to be effective, they must be administered at toxic levels. The protective agent can be worse than the radiation

A

Radioprotective agents

30
Q

A separate and small body of radiobiologic evidence suggests that a
little bit of radiation is good for you

A

Hormesis

31
Q

Interactions with Radiation

A
  • Radiolysis of Water
  • Irradiation of Macromolecules
  • Single-Hit Chromosome Aberrations
  • Multi-Hit Chromosome Aberrations
  • Reciprocal Translocations
32
Q

When an atom of water is irradiated this ionizes the water, and produces a free radical

A

Radiolysis of Water

33
Q

an uncharged molecule that contains a single unpaired

electron in its outermost or valence shell, which makes it chemically unstable and highly reactive

A

Free Radical

34
Q

Reactions of water include:

A
  1. H2O + radiation = HOH+ + e-
  2. H2O + e- = HOH–
  3. HOH+ = H+ + OH*
  4. HOH- = OH- + H*
  5. OH* + OH* = H2O2
  6. H* + O2 → HO*2
  7. HO2 + HO2 → H2O2 + O2
35
Q

occurs when an atom has an extra electron, or has had an electron removed

A

Ionization

36
Q

If an ion has more electrons than it does protons, it is designated with a _____ sign. If an ion has more protons than electrons, it is designated with a ____ sign

A

negative,

positive

37
Q

The occurrence of molecular derangements or lesions may be classified as either effects on _____ or effects on _____

A

macromolecules,

water

38
Q

If macromolecules are exposed to ionizing radiation ___, a significant dose
of radiation is needed to produce a measurable effect

A

in vitro

39
Q

Irradiating macromolecules ___ shows that when cells

are in their natural conditions, they are much more radiosensitive

A

in vivo

40
Q

The three primary effects of irradiating macromolecules in vitro include

A

main-chain scission, cross-linking, and point lesions

41
Q

occurs when the thread

or backbone of the long-chain molecule is broken

A

Main-Chain Scission

42
Q

This results in the long-chain molecule being reduced
to numerous smaller molecules, which can still be
macromolecular in nature. Not only is the size of the
macromolecule reduced, but its viscosity is also
reduced

A

Main-Chain Scission

43
Q

Some macromolecules have small, spur-like side
structures that extend off the main chain. Others
produce these spurs as a consequence of irradiation

A

Cross Linking

44
Q

Others develop these spurs after being irradiated.
After being irradiated, these spurs can act as if they had sticky material on their ends. These spurs can attach to neighboring macromolecules or to another segment of the same molecule. This stickiness causes the macromolecule to
connect to another macromolecule, or to another section of the same
molecule

A

Cross Linking

45
Q

is increased by

radiation-produced molecular cross-linking

A

Viscosity

46
Q

Radiation interaction with macromolecules also can
result in disruption of single chemical bonds,
producing ____

A

Point Lesions

47
Q

may cause slight molecular changes,

which in turn cause the cell to function incorrectly

A

Point Lesions

48
Q

At low doses of radiation, _____ are regarded to be the cellular
radiation damage that is responsible for the late radiation effects,
which are observed at the whole-body level

A

Point Lesions

49
Q

are not detectable, but they can cause a minor modification of
the molecule, which in turn can cause it to
malfunction within the cell.

A

Point Lesions

50
Q

its radiosensitivity is midway between that of DNA and protein macromolecules

A

RNA

51
Q

These molecular genetic mutations are termed _____, and are common with low LET radiations

A

Point mutations

52
Q

may be either of minor or major significance to the cell. A very major
effect of these point mutations would be the genetic code being
incorrectly transferred to daughter cells.

A

Point mutations

53
Q

When chromosomes are irradiated, the interaction can be either direct or indirect. The result of either interaction is called a __

A

hit

54
Q

Chromosome hits cause a
____ chromosome change. Such a hit would mean that numerous molecular bonds had been interfered with, and that several chains of DNA had been severed

A

visible

55
Q

breakage of a chromatid

A

chromatid deletion

56
Q

can occur in G1 phase and G2 phase of cell cycle

A

Single-Hit Chromosome Aberrations

57
Q

During the S-phase of the cell cycle, the deletion and the remaining chromosome are replicated. The chromosome abnormality
that is seen during metaphase is a normal-appearing chromosome
with material missing from the ends of two sister chromatids and two
acentric fragments. Such fragments are called _____

A

isochromatids

58
Q

There is a ___ probability that ionizing radiation will pass through
sister chromatids to produce isochromatids

A

low

59
Q

A single chromosome can sustain more than one hit

A

Multi-Hit Chromosome

Aberrations

60
Q

are not uncommon,

A

Multi-Hit Chromosome

Aberrations

61
Q

During the G1 phase of the cell cycle, if two hits occur on one chromosome, _____ are produced

A

ring chromosomes

62
Q

When neighboring chromosomes each suffer one hit and then recombine, this produces ____

A

dicentrics

63
Q

a chromosome with two centers or two centromeres

A

dicentric

64
Q

The quality of the _____ present at the severed chromosome is the determining factor for the joining of the chromatid

A

stickiness

65
Q

During the __ phase of the cell cycle, similar chromosomal abnormalities can occur. These types of aberrations are rare, as they
require that the same chromosome is hit two or more times, or that
neighboring chromosomes are hit and join together

A

G2

66
Q

are representative of major

cell damage

A

Multi-Hit Chromosome

Aberrations

67
Q

are multi-hit chromosomal aberrations

A

Reciprocal translocations

68
Q

If chromosomes experience this type of alteration, they do not lose
any genetic material, but instead the genes become rearranged. This
results in all genetic codes being available, but sequenced incorrectly

A

Reciprocal translocations

69
Q

At the doses received in diagnostic radiology, only _____ types of chromosomal aberrations are seen

A

single-hit

70
Q

If the radiation dose is not known, the approximate chromosomal aberration frequency will be:

A

-two single-hit aberrations/rad/1,000 cells,
-one multi-hit aberration/
10 rad/1,000 cells

RT 206 (9 decks)

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