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ne262 > midterm2 > Flashcards

midterm2 Flashcards

1
Q

different types of ionizing radiation

A

hpc, neutrons, electrons, photons

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2
Q

define absorbed dose

A

measure of deposited energy in material
D = E/m

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3
Q

units of dose

A

1 Gy = 1 J/kg = 100 rad

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4
Q

what does absorbed dose depend on

A

(1) energy/type of radiation
(2) depth within material
(3) elementary constitution of material

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5
Q

define exposure

A

amount of energy transferred from photon/x-ray to unit mass of air

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6
Q

units of exposure

A

1 R = 2.58E-4 C/kg

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7
Q

define kerma

A

measure of all the energy transferred from uncharged particles to primary ionizing particle per unit mass

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8
Q

absorption of energy from radiation may lead to:

A

(1) excitation
(2) ionization

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9
Q

depending on incident e energy, a molecule in water can undergo:

A

(1) ionization (~13 eV)
(2) excitation (~7.4 eV)
(3) thermal transfer

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10
Q

what happens during the initial physical events in water during irradiation

A

(1) excitation: H2O -> H2O*
(2) ionization: H2O -> H2O+ + e-

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11
Q

what species are created during the initial physical events in water during irradiation

A

H2O*, H2O+, e-

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12
Q

what timeframe do the initial physical events of water irradiation occur

A

1E-16 s

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13
Q

what species are created in the prechemical events in water after irradiation

A

H3O+, OH, H, H2, eaq

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14
Q

what timeframe do the prechemical events occur in water after irradiation

A

1E-16 s - 1E-12 s

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15
Q

give examples of radicals produced in water

A

H, OH

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16
Q

what happens during the chemical stage in water after irradiation

A

H3O+, OH, H, H2, eaq react until stabilize

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17
Q

what is the timeframe for chemical stage in water after irradiation

A

1E-6 s

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18
Q

what are the three phases of water irradiation

A

(1) initial physical events
(2) prechemical events
(3) chemical stage

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19
Q

define G-value

A

species produced per 100 eV of energy loss by charged particle & secondaries in water

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20
Q

define direct action

A

energy deposition directly in biological molecule

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21
Q

what is the dose response of direct action

A

linear

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22
Q

indirect action

A

relies on ionization of intermediate solvent molecules

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23
Q

what is the dose response of indirect action

A

complicated

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24
Q

do high LET rad have primary indirect or direct action

A

direct

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25
Q

how is radiation damage repaired in DNA

A

(1) recombination: DNA radical reacts w nearby radical to regenerate original DNA (~1E-11 s)
(2) restitution: chemical restoration of DNA (~1E-3 s)
(3) repair: cellular enzyme repair (min - hr)

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26
Q

define scavengers

A

chemicals that react w reactive species (radicals like OH) and block indirect action of radiaiton

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27
Q

% cell damage caused by low LET OH radicals

A

~60-70%

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28
Q

irradiation of the cell causes:

A

(1) cell killing
(2) mutagenesis

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29
Q

what are two types of repair

A

(1) error-free: restores DNA to original state
(2) mis-repair: non-lethal errors passed down to daughter

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30
Q

what are the four different types of radiation damage to DNA?

A

(1) SSB
(2) DSB
(3) base damage
(4) DNA crosslinks

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31
Q

what are two ways to repair SSB

A

(1) base excision repair (BER)
(2) nucleotide excision repair (NER)

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32
Q

what are two ways to repair DSB

A

(1) nonhomologous end joining (NHEJ)
(2) homologous recombination (HR)

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33
Q

what is the most lethal form of radiation damage

A

DSB

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34
Q

how are DSB repaired in early phase

A

nonhomologous end joining (NHEJ)

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35
Q

how are DSB repaired in late phase

A

homologous recombination (HR)

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36
Q

what will lead to chromosome aberrations?

A

radiation induced breakage & incorrect rejoining in prereplication

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37
Q

what will lead to chromatid aberrations

A

radiation induced breakage & incorrect rejoining in postreplication

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38
Q

define death for cells that do not proliferate

A

loss of function

39
Q

define death for cels that proliferate

A

loss of reproductive ability

40
Q

define clonogenic

A

cell that is able to proliferate indefinitely

41
Q

what is a cell survival curve?

A

describes relationship between dose and proportion of cells that survive

42
Q

what is the mean lethal dose for loss of reproductive capability

A

~ 2 Gy

43
Q

define plating efficiency

A

PE = (# colonies)/(# cells seeded) x 100

44
Q

define surviving fraction

A

SF = (# colonies)/(# cells seeded x (PE/100))

45
Q

define D0

A

dose that leads to 37% of population left (SF = 0.37)

46
Q

define D10

A

dose that leaves 10% of population left (SF = 0.1)

47
Q

what are the survival curves of high LET rad

A

linear (w slope = D0 = 1/alpha)
exp(-D/D0) = exp(-alpha D)

48
Q

what are the two general survival models

A

(1) linear-quadratic model
(2) multi-target model

49
Q

what are the two components of the linear quadratic model

A

(1) cell killing proportional to dose, single lethal event: exp(-alpha D)
(2) cell killing proportional to dose^2, accumulation of sublethal events: exp(-beta D^2)

50
Q

what does the survival curve for low LET look like?

A

has shoulder

51
Q

what are the four components of the cell cycle?

A

(1) G1: growth
(2) S: DNA synthesis
(3) G2: growth and prep for mitosis
(4) M: mitosis

52
Q

what are the 3 classifications of radiation damage

A

(1) lethal damage
(2) potentially lethal damage
(3) sublethal damage

53
Q

define lethal damage

A

damage thats irreversible/irreparable and will lead to cell death

54
Q

define PLD

A

component of rad damage that can be modified by post-irradiation environment conditions

55
Q

define SLD

A

repaired in hours

56
Q

PLD survival increased when

A

(1) cells prevented from dividing for > 6hrs (in vitro)
(2) cells kept in G0 phase for > 6hrs (in vitro)
(3) delay after irradiation and before assay (in vivo)

57
Q

PLD repair is good/bad for which types of rad

A

good: x-ray/photon
bad: n/high LET rad

58
Q

the 3 Rs of radiation biology

A

(1) repair: of sublethal damage
(2) reassortment: progression of survivors through cell cycle
(3) repopulation: if interval between fractions > cell cycletime
(4) reoxygenation

59
Q

define oxygen enhancement ratio

A

OER: D0(hypoxic cells)/D0(oxygenated cells)

60
Q

what is OER at high/low doses

A

high D: OER ~ 3
low D: OER ~2

61
Q

OER ____ as LET ____

A

OER decreases as LET increases because fraction of damage from direct action increases

62
Q

in order for oxygenation to work…

A

O2 must be present during irradiation

63
Q

define radiosensitizers

A

agents that enhance the cells response to radiation

64
Q

define radioprotectors

A

agents that decrease the cells response to radiation (-SH) - scavenge free radicals

65
Q

when are cells most sensitive to irradiation

A

during G2 and M phase

66
Q

when are cells most resistant to irradiation

A

during S phase

67
Q

define MI

A

MI = Tm/Tc

68
Q

define LI

A

LI = Ts/Tc

69
Q

define growth fraction

A

GF = ratio of proliferating cells to total # cells ~30-50%

70
Q

what does tumor doubling time (Td) depend on

A

(1) Tc
(2) GF
(3) cell loss fraction

71
Q

define potential doubling time

A

Tpot = Tc/GF = Ts/LI

72
Q

what is cell loss due to

A
  • inadequate nutrition
  • apoptosis
  • immunological surveillance
  • metastasis
  • exfloliation
73
Q

define cell loss factor

A

cell loss factor = 1 - (Tpot/Td)

74
Q

what type of ionizing radiation has track avg = energy avg

A

x-rays/photons

75
Q

define LET

A

energy transferred per unit length of track [keV/um]

76
Q

how does LET depend on E

A

as E increases, LET decreases

77
Q

define relative biological effectiveness

A

RBE = dose [Gy] of 250 kV x-rays/dose [Gy] of other radiation with same biological effect

78
Q

how does RBE depend on dose

A

as dose increases, RBE decreases

79
Q

how does RBE depend on LET

A

as LET increases, RBE increases

80
Q

what is the optimal LET

A

100 keV/um

81
Q

what are 5 factors that influence RBE

A

(1) radiation quantity
(2) radiation dose
(3) # dose fractions
(4) dose rate
(5) endpoint

82
Q

how does OER depend on LET

A

as LET increases, OER decreases

83
Q

define equivalent dose

A

equivalent dose = absorbed dose x Wr

84
Q

define effective dose

A

effective dose = SUM(absorbed dose x Wr x Wt)

85
Q

what are fractionation advantages

A

(1) spare normal tissue (allows SLD repair)
(2) increases tumor damage (reoxygenation between fractions)

86
Q

early responding tissues have what dominate factor, and how does that affect the SF curve

A

alpha factor dominate - SF curve does not bend until higher energies

87
Q

late responding tissues have what dominate factor, and how does that affect the SF curve

A

beta factor dominate - SF more curved and curved at lower doses –> more sensitive to fewer and larger doses

88
Q

define biologically effective dose

A

BED = relative effectiveness = E/alpha = nd(1+d/(alpha/beta))

89
Q

define somatic effects

A

related to body health of individual

90
Q

define genetic effects

A

related to offspring/future generations

91
Q

what are 3 characteristics of deterministic effects

A

(1) threshold
(2) severity proportional to dose
(3) early effects

92
Q

what are 2 characteristics of stochastic effects

A

(1) no threshold
(2) late effects

93
Q

define LD50

A

dose required to kill 50% of population (~3-4 Gy in humans)

ne262 (2 decks)

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