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202 MEDIMAGE > 2. Radiation Biology > Flashcards

2. Radiation Biology Flashcards

1
Q

what are the 2 types of ionising radiaiton

A

electromagnetic and particulate

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2
Q

what is electromagnetic radation

A

oscillating electric fields which self propagate

wave form

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3
Q

what is particulate radiation

A

particles or photons rather than waves

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4
Q

low frequencies have long/short wavelengths

A

long

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5
Q

where does the split between ionising and non ionising radiation fall between

A

anything above UV light is ionising

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6
Q

what is an isobar

A

atom with the same mass of nucleons/same mass number

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7
Q

what is an isotope

A

atom with the same number of protons/same atomic number

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8
Q

what are the 2 forces holding and breaking the subatomic particles of an atom

what are these forces like in a stable atom

A

strong nuclear force holds atom together

electromagnetic force splits it apart

balanced forces in stable atom

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9
Q

what is radioactivity

A

activity is the number of disintergrations that occur per second

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10
Q

what is radioactivity measured in

A

becquerel (Bq)

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11
Q

what is alpha decay

A

2neutrons and 2 protons are emitted

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12
Q

what is beta decay

A

convert neutron to proton and ejects an e-

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13
Q

what is gamma decay

A

gamma particle like a photon is emitted

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14
Q

what is the radioactive decay law

A

number of atoms decaying per unit time is proportional to the total number of radioactive nuclei

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15
Q

what is the half life

A

time for activity to reduce to 1/2 its initial value

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16
Q

what is the equation for the radioactive decay law

A

N(t) = Noe^-(decay constant x t)

N = number of nuclei
No = number of nuclei at time t = 0
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17
Q

what is the biological half life

A

time takes for body to excrete half of it (how quickly it clears it from the body)

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18
Q

what model does the radioactive decay follow

A

exponential

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19
Q

what is the physical 1/2 life

A

time for activity to reduce to 1/2 its initial value

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20
Q

what is the effective 1/2 life

A

time to reduce radioactivity level of internal organ/whole body to 1/2 its initial value due to both elimination and decay

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21
Q

effective half life is larger/smaller than the physical and biological 1/2 life for what reason

A

smaller

both act to reduce overall activity so 1/2 life overall should be smaller and quicker

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22
Q

what are the 2 types of photon interactions

A

compton scattering

photoelectric effect

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23
Q

what is compton scattering

is the atom ionised

A

incident photon impart some energy to outer shell e- of the atom

compton e- is ejected from atom

scattered photon loses energy and continues on a different path

atom is ionised so potential for biological harm

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24
Q

what is photoelectric effect

A

incident photon is completely absorbed by inner shell e-

photoelectron is ejected from atom

vacancy is filled by outer shell e-

secondary photon is produced releasing lower amounts of energy

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25
Q

what is exposure

A

any incident ionising radiation produces ion pairs

exposure is the amount of charge produced per mass of air

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26
Q

what is the unit for exposure

A

colombs per kg (C/kg)

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27
Q

what is the equation for exposure

A

X = Q/m

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28
Q

radiation particle interacts with nuclei to ionise them and produce what?

A

produces a charged pair

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29
Q

what is absorbed dose

A

as radiation is incident on tissue it imparts energy to that tissue

energy deposited in tissue per unit mass

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30
Q

what are the 2 units of absorbed radiation

A

joules per kilogram (J/Kg)

Gray (Gy)

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31
Q

what is the equation of absorbed dose

A

D = E/m

D = absorbed dose (Gy)
E = energy (J)
m = Mass (kg)
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32
Q

does absorbed dose indicate anything about biological harm

A

no, only how much energy is imparted on the tissues

33
Q

what is kerma

A

kinetic energy released in matter

kinetic energy transferred to charged particles by indirectly ionising radiation per unit mass

34
Q

what is air kerma

A

measure of tube output

35
Q

what is the unit used for air kerma

A

mGy per 100mAs

36
Q

what is entrance skin kerma

A

dose absorbed by skin at beam entrance

37
Q

what is the unit of ESK

A

Gy

38
Q

what are the 4 factors that effect the ESK

ESK are proportional to __

A

SSD
tube current
Length of exposure
square of kVp

39
Q

does ESK say anything about how it interacts with tissue

A

no just at the surface, says nothing about biological harm

40
Q

how do e- differ from alpha particles in the way that they interact and travel through tissue

A

e- = scatter through material and interact with an atom to produce ion pair

alpha = travels shorter distance but larger so deposits more energy in one place so can do alot of damage to the tissue they encounter

41
Q

what is the path length

A

total distance particle travels

42
Q

what is the range

A

penetration depth in the tissue

43
Q

what is the specific ionisation

A

number of ion pairs produced per unit length

44
Q

what is the linear energy transfer

A

energy transferred per unit length in tissue

product of average energy per ion pair and specific ionisation

(how much energy its depositing over the path it travels)

45
Q

is the path length of e- or alpha particles greater

A

e-

46
Q

is the range of the e- or alpha particles greater

A

about the same for both of them

47
Q

do e- or alpha particles have a greater specific ionisation

A

e- travel trough longer path for same # of ion pairs but alpha produces lot more ion pairs in short distance so SI is higher than e-

48
Q

for an e- is which is greater the path length or the range

A

path length

49
Q

for an alpha particle is which is greater the path length or the range

A

both are equal

50
Q

for an e- does it have high or low specific ionisation

A

low

51
Q

for an alpha particle does it have high or low specific ionisation

A

high

52
Q

for an e- does it have high or low average energy

A

low

53
Q

for an alpha particle does it have high or low average energy

A

high

54
Q

does an e- have high or low LET radiation

A

low

55
Q

does an alpha particle have high or low LET radiation

A

high

56
Q

what is a bragg peak

A

for heavy charged particles (Eg alpha, protons) specific ionisation increases as the particle loses energy

it carries charge but loses energy to neighbouring tissue so slows down resulting in an increased level to a certain point

57
Q

when we talk about average energy of e- and alpha particle tissue interactions what do we mean that as

A

the average energy per ion pair

58
Q

what characteristic of the x-ray beam and radiation determines what shielding it needs and how much energy it imparts

A

range

59
Q

the range for alpha is small/large and e- and gamma can travel further/less distance

A

small

further

60
Q

what is the equation for relative biological effectiveness

A

RBE = Dose of 250kV x-rays required to produce effect ‘X’/dose of test radiation required to produce effect ‘X’

could be at a different kV

61
Q

what does RBE depend on

A

LET

62
Q

what is biological effectiveness

A

how effective it is at producing biological harm for tissues

63
Q

what is overkill

A

Even though high LET, low RBE

A single particle deposits much more energy than is required to kill a cell. Therefore, it kills less cells per absorbed dose

produce more harm than alpha particles so they’re damaging tissue but not going to penetrate the tissue anyways so lower bio effectiveness

64
Q

what is the relative biological effectiveness

A

The ratio of the doses required by two radiations to cause the same level of effect. Thus, the RBE depends on the dose and the biological endpoint

65
Q

what is direct interaction of ionising radiation with tissue

A

photons or e- directly ionise DNA molecules by removing atoms or breaking bonds

damages tissues as tissue cells replicate depending on DNA

66
Q

what are the 2 ways that radiation interacts indirectly with tissue

A

incident photons and scatter e- produce free radicals

free radicals induce damage to DNA

67
Q

what is the equation of H2O’s and radiation’s indirect interaction with tissue

what is its process of interaction

A

H2O + xray -> H2O+ +e-
this can then take 2 pathways

1/ e- + H2O -> H2O- and then H2O- -> OH- + H’ (hydrogen radical)

2/ H2O+ + H2O -> H3O+ +OH’ (hydroxyl radical)

photons interact with water molecule and ionises water to produce free radicals that then damage DNA

68
Q

what is a product of the radicalisation of water by x-rays that can also cause tissue damage

A

H2O2

69
Q

why are free radicals dangerous and harmful

A

They are highly reactive as they have an unpaired e- and can react with anything

As they react they tend to break down other bonds so will bind and damage DNA molecule

70
Q

what is the equivalent dose

A

absorbed dose weighted for relative biological effectiveness

71
Q

what is the unit of equivalent dose

A

Sievert (Sv)

72
Q

what is the equation for equivalent dose

A

Ht = sum (WrDtr)

for xrays only:
Ht = Dt

Ht = equivalent dose (Sv)
Wr = radiation weighting factor (Sv/Gy)
Dtr = absorbed dose (Gy)
73
Q

what is the equation for equivalent dose when only x-rays are concerned

A

Ht = Dt

Ht = equivalent dose (Sv)
Dtr = absorbed dose (Gy)
74
Q

how do you calculate the equivalent dose if you have different types of radiation coming in

A

If you have different radiation types coming in, take dose for each one and multiple by radiation factor and add them all up

75
Q

equivalent dose and absorbed dose have the same value just different units true/false

A

true

76
Q

what is the effective dose

A

equivalent dose weighted for biological sensitivity of tissues

77
Q

what is the unit of effective dose

A

Sieverts (Sv)

78
Q

what is the equation for effective dose

A

E = sum (WtHt)

E = effective dose (Sv)
Wt = tissue weighting factor
Ht  = equivalent dose in tissue (Sv)
79
Q

Why is the effective dose not always useful

why is it useful or what is it useful for

whys is it not useful or in what ways is it not useful

A

Effective doses are for a generic patient so while its useful to make comparisons, different people have different amounts of tissue types based on risk factors, gender, race, shape etc

Can’t use effective dose to describe individuals

While useful to say you get more dose here than there, you can’t use it to say anything about the risk/dose to an individual as there is too much variability

Useful for comparisons between examinations but not useful for assessing individual risk to a particular patient

202 MEDIMAGE (18 decks)

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