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Flashcards in chapter 7 EXAM 3 Deck (141):
1

what is the goal of radiobiologic research

the accurate description of the effects of radiation on humans so that radiation can be used more safely in diagnosis and more effectively in therapy

2

generalizations about radiation effects on living organisms
#1

the interaction of radiation in cells is a probability function or a matter of chance
ionizing radiation does not seek out certain cells.

3

generalizations about radiation effects on living organisms #2

the initial deposition of energy occurs very rapidly

4

generalizations about radiation effects on living oragnisms #3

radiation interaction in a cell is nonselective
energy is deposited randomly

5

generalizations about radiation effects on living organisms #4

the visible changes in the cells, tissues and organs due to ionizing radiation are not unique. They can't be distinguished from damage produced by other types of trauma
cancer is cancer

6

generalizations about radiation effects on living organisms #5

the biologic changes in cells and tissues resulting from radiation occur only after a period of time. The length of time depends on the initial dose and varies from weeks or even years

7

3 radiation energy transfer determinants

1. Linear energy transfer (LET)
2. relative biologic effectiveness (RBE)
3. oxygen enhancement ratio (REO)

8

characteristics of ionizing radiation

charge
mass
energy

9

Linear Energy Transfer (LET)

the measure of the rate at which energy is transferred from ionizing radiation to soft tissue

10

LET is expressed in

kiloelectronvolts per micrometer

11

the LET of diagnostic xrays is

3 KeV/micrometer
considered Low LET

12

LET is a factor in

assessing potential tissue and organ damage from exposure to ionizing radiation

13

when LET increases,

the likelihood of biologic response increases

14

T or F
LET helps determine radiation weighting factors

true

15

radiation is divided into 2 categories according to LET

1. low LET
2. high LET

16

Low LET

xrays and gamma rays
electromagnetic radiation is sparsely ionizing therefore it is Low LET

17

when interacting with biologic tissue Low LET causes damage primarily

through indirect action which involves the production of free radicals

18

free radicals

a solitary atom or a combo of atoms that behave as extremely reactive single entities as a result of the presence of an unpaired electron

19

Low LET radiation generally causes what kind of damage to the DNA

sublethal damage
repair enzymes revers the damage

20

direct action means

it will hit the nucleus of a cell

21

indirect action means

it will hit water

22

high LET includes

particles that possess large mass and charge

23

high LET causes

dense ionization along its length of track and more likely to interact with biologic tissue
way more destruction

24

examples of high LET radiation

alpha particles
ions of heavy nuclei
low energy neutrons
charged particles released from interactions between neutrons and atoms

25

T or F
high LET loses energy more rapidly than low LET

True

26

why does high LET lose energy more rapidly than low LET

high LET produces more ionization per unit of distance traveled
they exhaust their energy in a shorter length of track and cannot travel as far

27

the higher the LET the greater

the biologic response

28

relative biologic effectiveness definition

RBE
a term relating the ability of radiations with different LETs to produce a specific biologic response

29

RBE describes

the ratio of the dose of a reference radiation to a dose of radiation of the type in question that is necessary to produce the same biologic reaction in a given experiment

30

RBE =

dose in Gy from 250 kvp xrays / dose in Gy of test radiation

31

RBE is used to refer to

experiments with specific cells or animal tissues

32

RBE is not practical for

specifying radiation protection dose levels in humans

33

as LET increas so does

RBE

34

high LET radiations such as alpha partices has a high

RBE

35

low LET radiations such as xrays and gamma rays have a low

RBE

36

xrays have an RBE of

1

37

oxygen effect

biologic tissue is more sensitive to radiation when irradiated in an oxygenated (aerobic) state than when it is exposed to radiation under anoxic or hypoxic conditions

38

t or f
The oxygen enhancement ratio (OER) describes the oxygen effect numerically

true

39

Oxygen enhancement ratio (OER) definition

the ratio of dose required to produce a given biologic response in the absence of oxygen to the dose required to produce the same response in the presence of oxygen

40

OER =

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

41

xrays and gamma rays have an OER of what when radiation dose is high

3

42

when radiation doses are lower than 2 Gy the OER may be

less (about 2)

43

OER values for high let radiations are what and why

1
because the high LET radiations are so effective in producing damage, the presence or absence of oxygen doesn't matter

44

radiation induced damage is observed on 3 levels

1. molecular
2. cellular
3. organic

45

T or F
any visible radiation induced injuries to cells or the organism always begin with damage at the molecular level

true

46

molecular damage results in

the formation of structurally changed molecules that may impair cellular functioning

47

organic level:
when a sufficient number of somatic cells are affected,

the entire body processes could be adversely affected

48

organic level:
if germ cells are damaged,

the damage may be passed onto future generations in the form of genetic mutations

49

when ionizing radiation interacts with a cell,

ionizations and excitations are produced in vital macromolecules (such as DNA) or in the nedium in which the cellular organisms are suspended (water)

50

direct action (effect)

biologic damage occurs when any type of radiation ionizes master or key molecules such as DNA causing them to become inactive or functionally altered

51

what could the damages of direct action lead to

inappropriate chemical reactions
essential biochemical processes may not occur in the cell

52

indirect action (effect)

occurs when the radiation interacts with water in the cell causing the formation of free radicals

53

when the water molecule is irradiated through indirect action

a free radical is formed and can migrate tot eh master or key molecule (DNA) and can result in cell death

54

direct effect may result after exposure to.....
but is much more likely to happen after exposure to ...

any type of radiation
high LET radiation than Low LET radiation

55

since the human body is 80% water and less than 1% DNA it's assumed that

most of the effects of radiation in you result from the indirect effect

56

the primary mechanism for indirect action is

the radiolysis of water

57

radiolysis of water definition

when water is irradiated, it dissociates into other molecular products

58

for every molecule of DNA in the cell there are how many molecules or water

1.2 x 10^7

59

when a water molecule is irradiated it absorbs energy and dissociates into

a positive water ion and an electron

60

t or f
after the initial ionization of a water molecule, many reactions can happen

true

61

type of reaction that can happen from ionization of a water molecule

the ion pair AKA positive water molecule and electron may rejoin into a stable water molecule
no damage occurs

62

type of reaction that can happen from ionization of a water molecule

if the ions do not rejoin the electron can attach to another water molecule and produce another type of reaction (a negative water ion)

63

t or f
the HOH+ (positive water molecule) and the HOH- (negative water molecule) are unstable and can break apart into smaller molecules

true

64

HOH+ becomes

a hydrogen ion (H+) and a hydroxyl radical (OH+)

65

HOH- becomes

a hydroxyl ion (OH-) and a hydrogen radical (H*)

66

the ultimate result of the interaction of radiation with water is

the formation of an ion pair and 2 free radicals (H* and OH+)

67

the free radicals can also produce

other products that are poisonous to the cell and act as toxic agents

68

the OH+ (hydroxyl radical) can join with a similar molecule and form

hydrogen peroxide
toxic to the cell
can kill

69

the H* (hydrogen radical) can interact with molecular oxygen to form

hydroperoxyl radical
can kill the cell

70

free radicals are believed to be a major factor in

the production of damage via indirect action in the cell

71

2 points that are considered about the effects of radiation on DNA

1. much of the damage in DNA can be, and is repaired by the cell
2. all types of DNA damage are not equal in terms of their biologic significance

72

5 effects of ionizing radiation on DNA

1. single strand break
2. double strand break
3. double strand break in the same rung of DNA
4. mutation
5. covalent cross links

73

single strand breaks (SSB)

the ionizaiton of a DNA macromolecule resulting in a break of one of its chemical bonds.
it severs one of the sugar phosphate chain side rails.

74

single strand break type of injury is also called a

point mutation

75

point mutations commonly occur with what kind of radiation

low LET radiation

76

can single strand breaks be repaired?

yes
repair enzymes can reverse the damage
no long term consequences to the cell

77

double strand breaks

ionization of a DNA macromolecule resulting in the rupture of one or more of its chemical bonds
creates one or more breaks in each of the 2 sugar phosphate chains

78

double strand breaks occur most commonly with what type of radiation

high LET radiation

79

can double strand breaks be repaired?

yes, but not as easily as SSB

80

double strand break in the same rung of DNA

if both strands of DNA are broken at the same nitrogenous base or rung resulting in complete breakage of DNA

81

can double strand breaks in the same rung of DNA be repaired ?

no it results in death or impaired functions of the new daughter cells

82

mutation

changes in genes caused by the loss or change of base in the DNA chain

83

mutation may not be

reversible and cause acute consequences for the cell

84

covalent cross links can occur in

many different patterns
all are potentially fatal to the cell if not properly repaired

85

intrastrand cross link

cross link formed between 2 places on the same DNA strand

86

interstrand cross link

cross link formed between complementary DNA strands or between entirely different DNA molecules

87

3 effects of ionizing radiation on chromosomes

1. radiation induced chromosome breaks
2. chromosomal fragments
3. chromosome anomalies

88

radiation induced chromosome breaks may be viewed microscopically during

metaphase and anaphase of cell division

89

the effects of radiation induced chromosome breaks is

the visible difference in the structure of the chromosome

90

chromosome fragments

2 or more fragments are produced after chromosomal breakage
each has a fractured extremity and broken ends appear sticky and can adhere to another sticky end

91

2 types of chromosome anomalies observed at metaphase

1. chromosome aberrations
2. chromatid aberrations

92

1. chromosome aberrations

lesions that result when irradiation occurs early in interphase before DNA synthesis takes place

93

2. chromatid aberrations

lesions that result when irradiation of an individual chromatid occurs later in interphase after DNA synthesis has taken place

94

4 consequences to the cell from structural changes in biologic tissue

1. restitution
2. deletion
3. broken end rearrangement
4. broken end rearrangement without visible damage to the chromatids

95

1. restitution

a process in which chromosome breaks rejoin in their original configuration with no visible damage

96

2. deletion

part of the chromosome or chromatid is lost at the next cell division creating an aberation known as an acentric fragment

97

3. broken end rearrangement

where a grossly misshapen chromosome may be produced

98

4. broken end rearrangement without visible damage to teh chromatids

where the chromatids genetic material has been rearranged even though the chromatid appears normal

99

target theory

a concept that the cell dies if inactivation of the master or key molecule occurs as a result of exposure to ionizing radiation

100

damage to cell's nucleus can result in various types of ways (7 types)

1. instant death
2. reproductive death
3. apoptosis or programmed cell death
4. mitotic or genetic death
5. mitotic delay
6. interference with function
7. chromosome breakage

101

instant death can occur when

the cells are irradiated with a high 1000 gray dose of xrays or gamma rays over a period of a few secs or mins
well above diagnostic range

102

instant death affects

vital functions of cytoplasmic organelles , the cell membrane, the nucleus and DNA

103

reproductive death

permanent loss of cells ability to reproduce because of exposure to doses of 1-10 gray
cell will function normally just won't reproduce

104

apoptosis

cell that dies from radiation exposure before it attempts division

105

t or f
radiosensitivity of the cell governs the dose required to induce apoptosis

true

106

mitotic or genetic death

ionizing radiation affect cell division by retarding or by permanently inhibiting the mitotic process
can happen at small doses

107

mitotic delay

failure of a cell to divide on time
can occur when exposed to as little as 0.01 gray
after the delay the cell functions normal

108

interference of function

permanent or temporary interference of cell function independent of the cell's ability to divide

109

chromosomal breakage

breaking of one or both sugar phosphate chains of DNA

110

cell survival curves

method of displaying the radiation sensitivity of a particular type of cell

111

vertical axis on cell survival curve

surviving fraction

112

horizontal axis on cell survival curve

radiation dose

113

immature cells

nonspecialized
more radiosensitive
undergo rapid cell division

114

mature cells

specialized
more radioresistant
divide at a slower rate or don't divide at all

115

t or f LET affects cell radiosensitivity

true

116

hyperbaric oxygen

sometimes used in conjunction with radiation to treat certain types of cancers

117

law of bergonie and tribondeau formed when? and why?

1906
theorized and observed that radiosensitivity was a function of the metabolic state of the tissue being irradiated

118

law of bergonie and tribondeau states

the radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation

119

hematologic depression is caused by how much dose delivered within a few days

0.25 Gyt

120

time necessary for bone marrow cells to recover depends on amount of radiation received
below 1 Gy =

repopulation occurs within weeks of irradiation

121

time necessary for bone marrow cells to recover depends on amount of radiation received
1-10 Gy or more =

severely depletes the # of bone marrow cells and require a longer recovery period

122

time necessary for bone marrow cells to recover depends on amount of radiation received
very high doses =

permanent decrease in number of stem cells

123

t or f
erythrocytes are among the most radiosensitive of human tissues

true

124

whole body doses in excess of 5 Gy

may die within 30-60 days

125

lethal dose of radiation for humans is specified as

LD 50/60

126

lethal dose of radiation for animals is specified as

LD 50/30

127

the lethal dose for humans in grays is

3-4 grays

128

what are the most radiosensitive blood cells in the human body

lymphocytes manufactured in bone marrow

129

a dose of what does what to neutrophils

a dose of 0.5 gray can cause a reduction in # of neutrophils present in blood

130

a dose of waht can do what to lymphocytes

a dose of .25 gray decreases the number of lymphocytes, but they can recover quickly

131

epithelial tissue is highly radiosensitive or radioinsensitive

radiosensitive

132

muscle tissue is highly radiosensitive or radioinsensitive

radioinsensitive

133

nerve tissue is highly radiosensitive or radioinsensitive

radioinsensitive

134

spermatogenia (germ cells) are highly radiosensitive or radioinsensitive

radiosensitive
mature = insensitive
immature = sensitive

135

radiation dose of 2 Gy to reproductive cells can cause

temporary sterility for as long as 12 months

136

radiation dose of 5 or 6 Gy to reproductive cells can cause

permanent sterility

137

radiation dose of 0.1 Gy to reproductive cells may

depress male sperm population

138

male reproductive cells exposed to dose of 0.1 Gy or more

may cause genetic mutations in future generations

139

radiation dose of 2 Gy to the ovaries may cause

temporary sterility

140

radiation dose of 5 Gy to the ovaries may cause

permanent sterility

141

small doses as low as 0.1 Gy to the ovaries may cause

menstrual irregularities