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Oral Radiography > Radiation Biology > Flashcards

Radiation Biology Flashcards

1
Q

Dose Units
for
Radiation Measurement
(4)

A
  1. Exposure Dose
  2. Absorbed Dose; RAD vs. Gray (G)
  3. Equivalent Dose; REM vs. Sievert (Sv)
  4. Effective Dose; REM vs Sievert
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2
Q

Terms: Exposure
Definition
Traditional
SI unit
Conversion

A

ionize air
R
air kerma
1 R= 2.58 x 10-4
Coul./kg

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3
Q

Terms: Absorbed dose
Definition
Traditional
SI unit
Conversion

A

energy absorbed by tissue
rad
Gy
1Gy = 100 rads

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4
Q

Terms: Equivalent dose
Definition
Traditional
SI unit
Conversion

A

modified by radiation weighting factor
rem
Sv
1 Sv= 100 rem

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5
Q

Terms: effective dose
Definition
Traditional
SI unit
Conversion

A

modified by tissue weight factor
rem
Sv
1 Sv= 100 rem

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6
Q

Exposure
* A measure of the

A

capacity of radiation to ionize air

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7
Q

skipped
Exposure
Traditional unit:

A

roentgen (R) = produce 2.08x109 ion
pairs in 1.0 cc of air at standard temperature and
pressure

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8
Q

Exposure
Metric equivalent unit (S.I.) :

A

air kerma (kinetic energy
released in matter) = sum of the kinetic energy of all
liberated charged particles/mass (Coulomb/kg)

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9
Q

Exposure
Conversion:

A

1 R= 2.58 x 10-4 Coulomb/kg
1 Coulomb/kg=3.88x103 R

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10
Q

Roentgen (R) -

A

unit of radiation exposure that
produces 2.08 x 109 ion pairs in 1.0 cc of air at
standard temperature and pressure

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11
Q

Metric equivalent (S.I.)-

A

Coulomb/kg
Conversion; 1 Coulomb/kg=3.88x103 R
»2.58 x 10-4 Coulomb/kg=1R

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12
Q

RAD - acronym for

A

Radiation Absorbed Dose

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13
Q

100 ergs or radiation energy in

A

1 gram of
absorbed material

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14
Q

Metric equivalent (S.I.) - Gy (gray) is Joule/Kg
Conversion;

A

1 Gy=100 RAD
0.0 1 Gy= 1 RAD

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15
Q

1R =

A

0.903 RAD

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16
Q

Equivalent Dose (I)
* To compare the

A

biological effects of different types of radiation

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17
Q

Radiation weighing factor (WR) depends on the

A

type and energy of the radiation involved

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18
Q

QF
❖X-ray =
❖High energy radiations=

A

1
>1
- high energy protons = 5
- alpha particles = 20

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19
Q

Quality Factor(Q.F)-

A

is a measure of the
biological effectiveness of a radiation to ionize
matter

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20
Q

the QF for x-radiation =

A

1

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21
Q

REM-
(2)

A

acronym for Roentgen Equivalent
in Man
* equivalent to RAD x Q.F.

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22
Q
  • Since the QF for X-radiation = 1;
  • RAD units for x-radiation are equivalent to
A

REM units

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23
Q

Equivalent Dose
S.I. unit =

A

Sv (sievert)

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24
Q
  • S.I. unit = Sv (sievert)
  • Conversion: 1 rem =
A

0.01 Sv
1 Sv = 100 rem

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25
Q

Diagnostic x-radiation is usually measured in

A

millirems (mRem)

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26
Q

Since 1 R ~= 0.903 RAD = 0.903 REM
therefore

A

1 mR ~ 1 mRad = 1 mRem
0.01mGy = 0.01 mSv
10 μGy = 10 μSv

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27
Q

E = Σ WT x HT
WT –
HT -

A

Tissue weight factor
Dose equivalence to tissue

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28
Q

Effective Dose
* This measure is used to specifically
calculate

A

risks of radiation to human
tissues on a common scale.

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29
Q

Effective Dose
* This measure is used to specifically
calculate risks of radiation to human
tissues on a common scale.
* The calculation is a product of the

A

sum
of dose equivalence to the specific
tissues or organs exposed and the
biological tissue weighting factor.

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30
Q

Effective Dose
* Use of the effective dose allows
comparisons of

A

different imaging
techniques to be made on a common
scale.

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31
Q

Effective Dose
* Use of the effective dose allows
comparisons of different imaging
techniques to be made on a common
scale.
* The value is an estimated measure of all

A

somatic and genetic radiation-induced risk
even if the entire body is not uniformly
exposed.

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32
Q

Effective Dose
Used to assess risk of non-uniform radiation to
localized part of body and degree to which this
would increase a person’s “whole body” risk of
(2)

A
  1. cancer induction and/or
  2. induction of genetic mutations
    i.e., Stochastic effects
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33
Q

AREA EXPOSED is related to the

A

maximum size of the beam

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34
Q

Ionization:

A

Interactions of X-radiation
with Matter

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35
Q

RADIATION
INJURY

A

Mechanisms of Injury
from x-ray interaction with matter

………….(i.e., ionization)

36
Q

Ionization form exposure sets of
a multiple direct and indirect
molecular reactions in

A

< 1 sec.

37
Q

Enzymatic repair or further
deleterious molecular changes
occur in

A

minutes to hours

38
Q

Determinsitic and stochastic
effects take place over time from

A

months, to decades, to
generations

39
Q

Interactions of X-radiation
with Matter
1. No interaction ~
2. Photoelectric effect ~
3. Compton Scatter ~
4. Coherent (Thomson) Scatter ~

A

9%
27 - 30%
57 - 62%
7%

40
Q

No Interaction

A
  • X-ray photon enters object (eg. patient
    or other biologic tissues) and exits with
    no change in its energy
41
Q

Photoelectric Interaction

A
  • Accounts for 30% of all interactions
  • X-ray photon collides with an orbital
    electron and loses its energy
  • Ejected photoelectron loses it energy
  • Results in an atom with an altered
    electric state, i.e., “+” charge
  • (similar orbital electron reaction to characteristic
    radiation production but no x-radiation is produced)
    (5)
42
Q

Photoelectric Interaction
* The ionized matter is unstable and seeks a more stable configuration.
* The new configuration may include new ionic bonds, different covalent bonding, etc…
* If the degree of photoelectric effect is significant,

A

this may affect, biologic structure, function or both.
* These effects are often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc…

43
Q

Compton Interaction/Scatter
(4)

A
  • accounts for 62% of interactions
  • X-ray photon collides with an outer
    orbital electron losing some energy
  • X-ray photon continues in different
    direction with less energy creating more
    scatter until all the energy is lost
  • results in an atom with an altered
    electric state, i.e., “+” charge
44
Q

Compton Interaction/Scatter
* The ionized matter is unstable and seeks a more stable configuration.
* The new configuration may include new ionic bonds, different covalent bonding, etc…
* If the degree of photoelectric effect is significant,

A

this may affect, biologic structure, function or both.
* These effects are often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc…

45
Q

Coherent Interaction
(4)

A
  • accounts for 8% of all interactions
  • X-ray photon of low energy interacts
    with an outer orbital electron and
    changes direction
  • no photoelectron produced
  • no ionization occurs
46
Q

Mechanisms of Injury
from x-ray interaction with matter
………….(i.e., ionization)
(2)

A
  • Direct
  • Indirect
47
Q
  • Direct
  • Indirect
    both… (3)
A

– Both effects occur quickly
– Both effects take hours to
decades to become evident
– Both are a result of
ionization

48
Q

Direct effect
(2)

A

➢ Directly ionizes biologic maromolecules
➢ Contributes to 1/3 of biologic effects

49
Q

Indirect effect
(2)

A

➢ X-ray photons absorbed by H2O →
free radicals →biologic damages
➢ Contributes to 2/3 of biologic effects

50
Q

Outcome of
Direct Effect of
UV Light
on Skin DNA
(3)

A
  1. Repair (healed)
  2. Inaccurate repair (mutation)
  3. No repair (death)
51
Q

Indirect Effect
* Primary method of

A

cell damage from
radiolysis of water caused by x-radiation

52
Q

Indirect effect
equaiton

A

Photon + H2O H2O* OH + H

53
Q

Free radical:

A

a free atom or molecule
carrying an unpaired orbital electron
in the outer shell

54
Q

Free Radical Formation
(2)

A
  • Highly reactive and unstable
  • Lifetime = 10-10 seconds
55
Q

Toxins from Free Radicals

A

Free radicals seek a more stable
configuration which results in formation of
toxic substances

56
Q

Dose-Response Curves
(2)

A
  • Dose (amount) of radiation is correlated with the
    response or damage
  • Curves are theoretical for diagnostic x-radiation
57
Q

Threshold Non-Linear Curve
(3)

A
  • Small exposures do a
    substance do not
    produce measurable
    changes
  • A threshold must be
    reached before
    changes are observed
  • Most biologic effects
    are non-linear
58
Q

Linear Non-Threshold Curve
(2)

A
  • Dose is proportional to the response
  • No matter how small the dose, there is some
    damage or risk
59
Q

Nonlinear Nonthreshold Curve
(2)

A
  • No threshold
  • Minimal damage at first with increased rate
    of damage with increased dose
60
Q

Deterministic risk/effect
(2)

A
  • Have a threshold
  • severity is proportional to
    the dose
61
Q

Deterministic risk/effect
examples (7)

A

Erythema
●xerostomia
●cataract
●osteoradio-
necrosis
●fertility
●fetal devel-
opment
●alopecia

62
Q

radiation Erythema

A
  • Side-effect of head &
    neck cancer treatment
63
Q

Stochastic effects
(3)

A
  • Have no dose threshold
  • Probability of occurrence
    is proportional to dose
  • Severity of effects does not
    depend on dose
64
Q
  1. To somatic cells -genetic mutations cause
A

malignancy

65
Q
  1. To germ cells - genetic mutations cause
A

heritable
effects

66
Q

Genetic Injury
(2)

A

– no affect on parent
– affects future
generation

67
Q

Somatic Injury
(2)

A

– affects parent
– no affect on
future generation

68
Q

Somatic effects/mutations
(3)

A

– Somatic cells –all those except reproductive cells
– Seen in the person irradiated
– NOT transmitted to future generations
* Induction of cancer, leukemia, cataracts

69
Q

Genetic effects/mutations
(2)

A

– NOT seen in the person irradiated
– Passed on to future generations

70
Q

Sequence of Radiation Injury
(3)

A
  • Latent period
  • Period of injury
  • Recovery period
71
Q

Latent Period
definition
* May be short or long depending on: (2)
* Shorter latent period if: (2)
* Genetic effects –

A
  • Time that elapses between exposure and appearance of clinical signs

– Total dose
– Dose rate

– Increased amount of radiation
– Faster dose rate

may be generations before clinical effects are seen

72
Q

Period of Injury
(6)

A
  • Cell death
  • Changes in cell function
  • Breaking or clumping of chromosomes
  • Giant cell formation
  • Cessation of mitotic activity
  • Abnormal mitotic activity
73
Q

FACTORS MODIFYING EFFECTS
OF X-RADIATION
(6)

A
  1. Total dose
  2. Dose rate
  3. Oxygen
  4. Area exposed
  5. Cell type and function
  6. Age
74
Q
  1. Total dose
A

increase Total dose → increase damage

75
Q
  1. Dose rate
A
  • Describe the frequency of dose delivery
  • increase Dose rate = decrease cellular repairs = increase damages
76
Q
  1. Oxygen
A

increase Oxygen content = increase radiosensitivity
= increase tissue damage

77
Q
  1. Area exposed
  2. Cell type
    Cell Type vs. Radiosensitivity
    (CASARETT CLASSIFICATION)
    Radiosensitive –
    Radioresistant –
A

young, immature, rapidly growing
and dividing, least specialized
mature, specialized cells

78
Q

Cell Type vs. Radiosensitivity
(3)

A

Species
Intrinsic resistance
Cells

79
Q

Species

A

◦ Mammals more sensitive than reptiles, insects, bacteria

80
Q

Cells

A

◦ Mitotic activity
 increased frequency of cell division = ↑ sensitivity
◦ Mitotic activity
 Immature cells/not highly specialized = ↑ sensitivity
◦ Cell metabolism
 increased metabolism = ↑ sensitivity

81
Q

High sensitivity to radiation
Least radioresistant
(6)

A

Blood cells
Small lymphocyte –most sensitive
Bone marrow
Reproductive cells
Intestinal mucosa
Mucous membrane

82
Q

Intermediate sensitivity to radiation
(5)

A

Connective tissue
Breast (women)
Small blood vessels
Growing bone and cartilage
Salivary gland

83
Q

Fairly low sensitivity to radiation
(2)

A

Thyroid gland
Skin

84
Q

Low sensitivity to radiation
Most radioresistant
(3)

A

Muscle
Nerve
Mature bone

85
Q
  1. Age
    Pediatric Patients at risk
    (2)
A
  • Rate of cellular and organ growth puts tissues
    at greatest level of radiosensitivity
  • Greater life expectancy puts children at 2-10
    greater risk of being afflicted with a radiation
    induced cancer

Oral Radiography (24 decks)

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