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oral radiology > radiation biology > Flashcards

radiation biology Flashcards

1
Q

why do we learn radiation bio?

A

protecting the public and to have knowledge for controling risk

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2
Q

Dose Units for
Radiation Measurement

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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3
Q

exposure dose

A

amount produced by machine

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4
Q

absorbed dose

A

amount absorbed by tissue (about the same as exposed dose)

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5
Q

equivalent dose modified by?

A

modified by radiation weighing factor

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6
Q

effective dose modified by what factor?

A

modified by tissue weight. factor

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7
Q

expsoure

A
  • A measure of the capacity of radiation to ionize air
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8
Q

units of exposure:
traditional unit and metric equivalent

A

Traditional unit: roentgen (R)
Metric equivalent unit (S.I.) : air kerma

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9
Q

Absorbed Dose
* acronym?
* Metric equivalent (S.I.)? Conversion?

A

Absorbed Dose
* RAD - acronym for
Radiation Absorbed Dose
* 100 ergs or radiation energy in 1 gram of absorbed material
* Metric equivalent (S.I.) - Gy (gray) is Joule/Kg
Conversion; 1 Gy=100 RAD
0.0 1 Gy= 1 RAD
* 1R = 0.903 RAD

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10
Q

used for? weighing factor? calculation?

equivalent dose

A
  • To compare the biological effects of different types of radiation
  • Radiation weighing factor (WR) depends on the type and energy of the radiation involved
    ❖X-ray = 1
    ❖High energy radiations >1 - high energy protons = 5 - alpha particles = 20
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11
Q

quality factor of equivalent dose

A
  • Quality Factor(Q.F)- is a measure of the biological effectiveness of a radiation to ionize matter
  • the QF for x-radiation = 1;
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12
Q

calculated how? xrays value/conversion?

REM?

A
  • REM- acronym for Roentgen Equivalent in Man
  • equivalent to RAD x Q.F.
  • Since the QF for X-radiation = 1;
  • RAD units for x-radiation are equivalent to REM units
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13
Q

equivalent dose SI unit and conversion

A
  • S.I. unit = Sv (sievert)
  • Conversion: 1 rem = 0.01 Sv
    1 Sv = 100 rem
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14
Q
  • Diagnostic x-radiation is usually measured in?
A
  • Diagnostic x-radiation is usually measured in
    millirems (mRem)
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15
Q

used to measure? calculation?

effective dose

A
  • This measure is used to specifically calculate risks of radiation to human tissues on a common scale.
  • The calculation is a product of the sum of dose equivalence to the specific tissues or organs exposed and the biological tissue weighting factor.
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16
Q

Use of the ________ dose allows
comparisons of different imaging
techniques to be made on a common
scale.

A

Use of the effective dose allows
comparisons of different imaging
techniques to be made on a common
scale.

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17
Q

does the whole body need to be exposed for effective dose

A
  • The value is an estimated measure of all somatic and genetic radiation-induced risk even if the entire body is not uniformly exposed.
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18
Q

effective dose used for?

A

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
1. cancer induction and/or
2. induction of genetic mutation

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19
Q

what tissue have high weight factors

A

gnads and hematopoetic

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20
Q

low weight factor tissues

A

skin and cortical bone

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21
Q

what benefit do solid state sensors have with effective dose?

A

much lower than film and PSPP

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22
Q

area exposed related to?

A

size of beam (affected by collimination)

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23
Q

possible interactions of xrays with matter

A
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24
Q

examples?

stochastic effects?

A

sublethal DNA damage
gene mutation
replication of mutated cells
Examples: leukemia, thyroid cancer, salivary gland tumors and heritable disorders

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25
Q

examples?

deterministic effects?

A

Lethal DNA damage
cell death
decreased tissue/organ function
examples: xerostomia, osteoradionecrosis, cataracts, etc.

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26
Q

Mechanisms of Injury
from x-ray interaction with matter

A
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27
Q

what interactions produce secondary electrons

A
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28
Q

what is the majority of xrays interaction with matter

A

compton scattering which can cause biological changes

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29
Q

no interaction by x rays

A

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

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30
Q

Photoelectric Interaction
% interaction?
mechanism?

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)
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31
Q

Photoelectric Interaction consequences
unstable/seeks?
new configuration?
if the degree of the effect is significant what can be altered?
alterations often cause?

A
  • 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, this may affect, biologic structure, function or both.
  • These effects are often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc…
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32
Q

compton scatter
mechanism?
%interactions?

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
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33
Q

compton scatter consequences
unstable/seeks?
new configuration?
if effect significant what can be altered?
alteration often lead to?

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

SAME AS PHOTOELECTRIC

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34
Q

Coherent Interaction
* accounts for __% of all interactions
* mechanism

A

Coherent Interaction
* 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

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35
Q

direct and indirect xray injury similarites

A

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

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36
Q

direct effect

A

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

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37
Q

indirect effect

A

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

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38
Q

direct DNA damage flow chart

A
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39
Q

Outcome of Direct Effect of UV Light on Skin DNA

A
  1. Repair (healed)
  2. Inaccurate repair (mutation)
  3. No repair (death) 1
    2
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40
Q

Indirect Effect Primary method of cell damage from?

A
  • Primary method of cell damage from
    radiolysis of water caused by x-radiation
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41
Q

radiolysis of indirect effect

A
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42
Q

toxins from free radicals

A

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

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43
Q

Dose-Response Curves

A
  • Dose (amount) of radiation is correlated with the
    response or damage
  • Curves are theoretical for diagnostic x-radiation
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44
Q

Threshold Non-Linear Curve

A

Threshold Non-Linear Curve
* 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

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45
Q

Linear Non-Threshold Curve

A
  • Dose is proportional to the response
  • No matter how small the dose, there is some damage or risk
    XRAYS BELIEVED TO BE THIS
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46
Q

Nonlinear Nonthreshold Curve

A
  • No threshold
  • Minimal damage at first with increased rate of damage with increased dose
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47
Q

threshold? severity proportional to? curve?

Deterministic risk/effect

A
  • Have a threshold
  • severity is proportional to the dose
    *ex: Erythema, xerostomia, cataract ,osteoradio-necrosis, fertility, fetal devel-opment, alopecia
48
Q

Radiation Erythema

A

Radiation Erythema
* Side-effect of head &
neck cancer treatment

49
Q

dose threshold? severity of effects depends on? somatic/germ cells?

Stochastic effects

A
  • Have no dose threshold- Probability of occurrence is proportional to dose
  • Severity of effects does not depend on dose
    1. To somatic cells -genetic mutations cause malignancy
    2. To germ cells - genetic mutations cause heritable effects
50
Q

stoichastic effects potential curves

A
51
Q

genetic vs somatic effects

A
52
Q

examples?

somatic effects/mutations

A

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

53
Q

Genetic effects/mutations

A

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

54
Q

sequence of radiation injury

A
  • Latent period
  • Period of injury
  • Recovery period
55
Q

Latent Period
* Time?
* May be short or long depending on:
* Shorter latent period if:
* Genetic effects?

A

atent Period
* Time that elapses between exposure and appearance of clinical signs
* May be short or long depending on:
– Total dose
– Dose rate
* Shorter latent period if:
– Increased amount of radiation
– Faster dose rate
* Genetic effects –may be generations before clinical effects are seen

56
Q

Period of Injury potential events
cells?
cell function?
chr?
what can form?
what cellualr activity can be impacted? how?

A

Period of Injury
* Cell death
* Changes in cell function
* Breaking or clumping of chromosomes
* Giant cell formation
* Cessation of mitotic activity
* Abnormal mitotic activity

57
Q

FACTORS MODIFYING EFFECTS
OF X-RADIATION

A
  1. Total dose
  2. Dose rate
  3. Oxygen
  4. Area exposed
  5. Cell type and function
  6. Age
58
Q

dose effect on damage

A

increased dose= increased damage

59
Q

dose rate and damage

A
60
Q

oxygen and damage

A
61
Q

area exposed and damage

A

increased area=increased damage

62
Q

radiosensitive and radioresistant cells

A

Radiosensitive –young, immature, rapidly growing
and dividing, least specialized
Radioresistant –mature, specialized cells

63
Q

spp and radiosensitivty

A

◦ Mammals more sensitive than reptiles, insects, bacteria

64
Q

cellular activity and radiosensitivity

A

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

65
Q

least radioresistant tissues

A
66
Q

most radioresistant tissues

A
67
Q

Pediatric Patients at risk

A

Pediatric Patients at risk
* 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

68
Q

ACUTE RADIATION SYNDROME

A
  • A collection of signs and symptoms
    following acute whole-body radiation
    exposure
69
Q

acute radiation syndrome radiation level exposure

A
70
Q

higher doses effect on latent period and symptoms

A

shorter latent with severe symptoms

71
Q

sAcute radiation syndrome
syndromes/ tissues involved

A
  1. Prodromal period
  2. Hematopoietic syndrome
  3. Gastrointestinal syndrome
  4. Central nervous system and
    cardiovascular syndrome
    (CNS/CVS syndrome)
72
Q

prodromal period dose

A

<200R; <2Gy

73
Q

hematopoetic syndrome dose

A

(200- 1,000R; 2-10 Gy)

74
Q

Gastrointestinal syndrome dose

A

(1,000 – 10,000R; 10 – 100Gy)

75
Q
  1. Central nervous system and
    cardiovascular syndrome dose
A

> 10,000R; 100Gy

76
Q

PRODORMAL SYNDROME

A
  • Shortly after exposure to whole-body
    radiation, an individual may develop
    nausea; vomiting;
    diarrhea; anorexia;
    Causes general malaise, fatigue,
    drowsiness and listlessness
    Symptoms resolve after several weeks
77
Q

ACUTE RADIATION SYNDROME lethal and sublethal exposure ranges

A
78
Q

injury to? infection? hemmorhage? anemia? death?

HEMOPOIETIC SYNDROME

A
  • irreversible injury to the proliferative capacity of the spleen and bone marrow with loss of circulating peripheral blood cells
  • infection from the lymphopenia and
    granulocytopenia
  • hemorrhage from thrombocytopenia
  • anemia from the erythrocytopenia
  • Death within 10 - 30 days.
79
Q

GASTROINTESTINAL SYNDROME
damage to what systems?
injury to what cells? leads to?
loss of?
signs?
death in?

A
  • extensive damage to the GI system (in addition to the hemopoietic system)
  • There is extensive injury to the rapidly proliferating basal epithelial cells of the intestinal villi which leads to atrophy and ulceration
  • loss of plasma and electrolytes
  • hemorrhage and ulceration
  • diarrhea, dehydration, weight loss
  • Infection
  • Death in 3 - 5 days
80
Q

CARDIOVASCULAR
and
CENTRAL NERVOUS SYSTEM
SYNDROME

A
  • radiation induced damage to neurons and fine vasculature of brain
  • Intermittent stupor, incoordination, disorientation, and convulsions from extensive CNS damage
  • irreversible damage with death in a few minutes to 48 hours
81
Q

RADIATION TREATMENTS TO THE
ORAL CAVITY

A
  • Combined surgical, radiation and chemotherapy often provides the optimum treatment for cancers
    • Oral tissues are subjected to high doses of
      radiation during the treatment of malignant
      tumors of the soft palate, tonsils, floor of the
      mouth, nasopharynx, and hypopharynx
82
Q
  • Total radiation doses to treat malignanttumors ranges from ______Rads. Or
    _____ G
A
  • Total radiation doses to treat malignant
    tumors ranges from 6,000 - 8,000 Rads. Or
    60 -80 G
83
Q

fractionation of radiation doses for cancer tx

A
  • Fractionation of the total dose into multiplesmall doses provides greater tumor destructionthan a single large dose
  • Fractionation also increases cellular repair of the normal tissues
84
Q

RADIATION EFFECTS ON THE ORAL CAVITY
* Mucosa
* Taste Buds:
* Salivary Glands:
* Teeth:
* Bone:
* Muscle:

A

RADIATION EFFECTS ON THE ORAL CAVITY
* Mucosa: - mucosits (2 infections)
* Taste Buds: - loss of taste
* Salivary Glands: - xerostomia
* Teeth: - lack of or retarded development
- radiation caries with stronger adhered plaque
* Bone: - osteoradionecrosis (decreased angiogenesis)
* Muscle: - fibrosis

85
Q

what can casue this? when is onset? recovery?

hypoguesia of radiation

A
  • Epithelial atrophy, xerostomia and
    mucositis all result in loss of taste
    (hypoguesia) by the 2nd- 3rd week of treatment
  • recovery of taste sensitivity will occur in 2 - 4 months followingtreatment
86
Q

adult teeth and radiation

A
  • Adult teeth are very resistant to the directeffects of radiation exposure
  • There is no discernible effect on the crystallinestructure of enamel, dentin, or cementum
  • Radiation does not increase the solubility ofteeth
87
Q

developing teeth and radiation

A
  • When teeth are irradiated during the
    developmental stage, their growth may beseverely retarded
  • If the radiation precedes calcification, thetooth bud may be destroyed
  • Irradiation after initiation of calcification,teeth may demonstrate malformations and arresting general growth
88
Q

xerostomia and radiation
if a portion spared?
can it persist?

A
  • Generally, if some portion of the salivary gland has been spared, the dryness of the mouth subsides in 6 month to 1 year
  • However, xerostomia may persist without any significant return of salivation
89
Q

when could these be exposed? what makes this tissue so susceptiable?

major salivary glands exposed

A
  • Major salivary glands are often exposed unavoidably to radiation during treatment for carcinoma of the oral cavity or oropharynx
  • Parenchymal cells (especially of the parotid glands) are very sensitive to X-rays and are replaced by fibrosis and adiposis with parenchymal degeneration and loss of fine vasculature
90
Q

makes mouth? pH? buffering capacity?

scanty saliva with radiation

A
  • The scanty saliva makes the mouth dry (xerostomia) and tender. Swallowing is difficult and painful
  • The residual saliva has a lowered pH (from 6.5 to 5.5), which is acidic enough to initiate decalcification of enamel
  • The buffering capacity of saliva is reduced 40 -45%
91
Q

A dose as low as ____ R at the age of 5 monthshas been reported to cause hypoplasia of the enamel

A

A dose as low as 200 R at the age of 5 months has been reported to cause hypoplasia of the enamel

92
Q

radiation and tooth eruption

A
  • Although irradiation may retard or abort toothformation, the eruptive mechanism is much more radiation resistant
  • Irradiated teeth with altered root formation will still erupt
93
Q

radiation caries

A
  • A rampant form of decay that may affect individuals who received a course of radiation therapy that include exposure of the salivary glands
94
Q

osteoradinecrosis

A
  • The primary damage to bone is from
    irradiation to
    – fine vasculature
    – marrow – affecting vascular and hemopoieticelements.
95
Q

radiation effect on oral masculature

A
  • Inflammation and fibrosis – results in contracture and trismus in the muscles
96
Q

where can ionizing radiation be encountered

A

everywhere

97
Q

mrem, rem, mSv

Maximum Permissible Doses

A
98
Q

medical and dental exposure make up what fraction of exposure to ionizing rad

A

1/6

99
Q

why was there a scare with radiation expsoure not long ago

A

too many CT scans given and nuclear med
avg was above 5mSv for everyone

100
Q

cancers associated with dental xrays

A
  • Leukemia and thyroid cancer have the highest risk from dental radiographic exposure
101
Q

Artificial/Manmade Radiation Sources
– %?

A

– 2%
* Consumer products
– Televisions, wristwatches, computers
* Airport scanners
* Nuclear fuel cycle
* Weapons production
* Fall-out from atomic weapons

102
Q

how to airport scanners work

A

use of compton scatter to find metal objects

103
Q

compared to PAs? whole body?

Radiation Erythema dosage levels

A
  • 250 Rads – Threshold radiation Erythema Dose (TED)
  • 500 Rads – Average radiation Erythema Dose
  • 750 Rads – Maximum radiation Erythema Dose
  • all of these much more than normal PA
  • not a whole body exposure (would be fatal)
104
Q

current imaging and TED

A

At a 16” focal distance 1/3 of the TED is delivered with ~473 intraoral dental exposures

105
Q

risk for congenital defects in pregnant women with imaging

A
  • Studies show risk for congenital defects is negligible at 50 mSv or less
106
Q

absorbed doses of 50mSv/mGy and risk of deterministic effects on fetus

A

virtually none, almost all intraorla techniques are considerably less than 50mSv (CBCT can be more)

107
Q

what dosage can increase risk of childhood cancer? by how much?

stoichastic risks to the fetus

A

absorbed doses >25mSv doubles the childhood cancer rate, cn occur with film, pano, CBCT

108
Q

radiographs of a new pt who is pregnant

A
  • Radiographs of pregnant patients as part of any new patient or recall exam must be postponed until post-partum.
109
Q

when should pregnant pts be imaged

A
  • If urgent care dental treatment is required during pregnancy, radiographs may be necessary as the standard of care to treat and diagnose a condition that threatens the health of the mother and the unborn child. The clinician must assure that the primary beam is not directed toward the child-bearing area.
    any infection/condition that threatens the mother or child
110
Q

why take radiogrpahs if there is a risk

A

for diagnostic benefit

111
Q

R to Gy conversion

A

100R=1Gy

112
Q

x rays believed to have what dose response curve?

A

linear non-threshold

113
Q

photoelectric vs compton scatter effect

A

In the photoelectric effect, all of the photon energy is absorbed in the ionization process as this usually involves an inner shell electron.. In the Compton effect, the ionization is with an outer shell electron with low binding energy. So with respect to the original x-ray photon, it loses some kinetic energy, but there is still enough energy to ionize other atoms especially if the ionization is with peripheral electrons.

114
Q

metric and standard units conversions

A

One metric unit = 100 standard units

1 Gy = 100 Rads; 1 Rad = 0.01 Gy

1 Sv = 100 Rems; 1Rem = 0.01 Sv

115
Q

stochastic vs deterministic effects

A

deterministic – dose dependent
stochastic risks - incident dependent -each incident of exposure to ionizing radiation

116
Q

examples?

stochastic effects?

A

sublethal DNA damage

oral radiology (22 decks)

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