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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
how is radiation damage repaired in DNA
(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)
26
define scavengers
chemicals that react w reactive species (radicals like OH) and block indirect action of radiaiton
27
% cell damage caused by low LET OH radicals
~60-70%
28
irradiation of the cell causes:
(1) cell killing (2) mutagenesis
29
what are two types of repair
(1) error-free: restores DNA to original state (2) mis-repair: non-lethal errors passed down to daughter
30
what are the four different types of radiation damage to DNA?
(1) SSB (2) DSB (3) base damage (4) DNA crosslinks
31
what are two ways to repair SSB
(1) base excision repair (BER) (2) nucleotide excision repair (NER)
32
what are two ways to repair DSB
(1) nonhomologous end joining (NHEJ) (2) homologous recombination (HR)
33
what is the most lethal form of radiation damage
DSB
34
how are DSB repaired in early phase
nonhomologous end joining (NHEJ)
35
how are DSB repaired in late phase
homologous recombination (HR)
36
what will lead to chromosome aberrations?
radiation induced breakage & incorrect rejoining in prereplication
37
what will lead to chromatid aberrations
radiation induced breakage & incorrect rejoining in postreplication
38
define death for cells that do not proliferate
loss of function
39
define death for cels that proliferate
loss of reproductive ability
40
define clonogenic
cell that is able to proliferate indefinitely
41
what is a cell survival curve?
describes relationship between dose and proportion of cells that survive
42
what is the mean lethal dose for loss of reproductive capability
~ 2 Gy
43
define plating efficiency
PE = (# colonies)/(# cells seeded) x 100
44
define surviving fraction
SF = (# colonies)/(# cells seeded x (PE/100))
45
define D0
dose that leads to 37% of population left (SF = 0.37)
46
define D10
dose that leaves 10% of population left (SF = 0.1)
47
what are the survival curves of high LET rad
linear (w slope = D0 = 1/alpha) exp(-D/D0) = exp(-alpha D)
48
what are the two general survival models
(1) linear-quadratic model (2) multi-target model
49
what are the two components of the linear quadratic model
(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
what does the survival curve for low LET look like?
has shoulder
51
what are the four components of the cell cycle?
(1) G1: growth (2) S: DNA synthesis (3) G2: growth and prep for mitosis (4) M: mitosis
52
what are the 3 classifications of radiation damage
(1) lethal damage (2) potentially lethal damage (3) sublethal damage
53
define lethal damage
damage thats irreversible/irreparable and will lead to cell death
54
define PLD
component of rad damage that can be modified by post-irradiation environment conditions
55
define SLD
repaired in hours
56
PLD survival increased when
(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
PLD repair is good/bad for which types of rad
good: x-ray/photon bad: n/high LET rad
58
the 3 Rs of radiation biology
(1) repair: of sublethal damage (2) reassortment: progression of survivors through cell cycle (3) repopulation: if interval between fractions > cell cycletime (4) reoxygenation
59
define oxygen enhancement ratio
OER: D0(hypoxic cells)/D0(oxygenated cells)
60
what is OER at high/low doses
high D: OER ~ 3 low D: OER ~2
61
OER ____ as LET ____
OER decreases as LET increases because fraction of damage from direct action increases
62
in order for oxygenation to work...
O2 must be present during irradiation
63
define radiosensitizers
agents that enhance the cells response to radiation
64
define radioprotectors
agents that decrease the cells response to radiation (-SH) - scavenge free radicals
65
when are cells most sensitive to irradiation
during G2 and M phase
66
when are cells most resistant to irradiation
during S phase
67
define MI
MI = Tm/Tc
68
define LI
LI = Ts/Tc
69
define growth fraction
GF = ratio of proliferating cells to total # cells ~30-50%
70
what does tumor doubling time (Td) depend on
(1) Tc (2) GF (3) cell loss fraction
71
define potential doubling time
Tpot = Tc/GF = Ts/LI
72
what is cell loss due to
- inadequate nutrition - apoptosis - immunological surveillance - metastasis - exfloliation
73
define cell loss factor
cell loss factor = 1 - (Tpot/Td)
74
what type of ionizing radiation has track avg = energy avg
x-rays/photons
75
define LET
energy transferred per unit length of track [keV/um]
76
how does LET depend on E
as E increases, LET decreases
77
define relative biological effectiveness
RBE = dose [Gy] of 250 kV x-rays/dose [Gy] of other radiation with same biological effect
78
how does RBE depend on dose
as dose increases, RBE decreases
79
how does RBE depend on LET
as LET increases, RBE increases
80
what is the optimal LET
100 keV/um
81
what are 5 factors that influence RBE
(1) radiation quantity (2) radiation dose (3) # dose fractions (4) dose rate (5) endpoint
82
how does OER depend on LET
as LET increases, OER decreases
83
define equivalent dose
equivalent dose = absorbed dose x Wr
84
define effective dose
effective dose = SUM(absorbed dose x Wr x Wt)
85
what are fractionation advantages
(1) spare normal tissue (allows SLD repair) (2) increases tumor damage (reoxygenation between fractions)
86
early responding tissues have what dominate factor, and how does that affect the SF curve
alpha factor dominate - SF curve does not bend until higher energies
87
late responding tissues have what dominate factor, and how does that affect the SF curve
beta factor dominate - SF more curved and curved at lower doses --> more sensitive to fewer and larger doses
88
define biologically effective dose
BED = relative effectiveness = E/alpha = nd(1+d/(alpha/beta))
89
define somatic effects
related to body health of individual
90
define genetic effects
related to offspring/future generations
91
what are 3 characteristics of deterministic effects
(1) threshold (2) severity proportional to dose (3) early effects
92
what are 2 characteristics of stochastic effects
(1) no threshold (2) late effects
93
define LD50
dose required to kill 50% of population (~3-4 Gy in humans)

ne262 (2 decks)

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