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Question 1
What is the primary effect of ionizing radiation on tissue atoms?
produce light
form chemical bonds
create ion pairs
generate heat
Question 2
How quickly do initial interactions with tissue atoms occur?
within milliseconds
over hours
in minutes
extremely fast (~10^-13 sec)
Question 3
How long does it take for DNA damage to be completed?
within a few seconds
within about 1 millisecond
within an hour
within a minute
Question 4
Untitled question
untitled answer
Question 5
What are the cell responses to DNA damage?
• enzymatic repair • DNA mutation • Cell death
Apoptosis
Cell division
DNA replication
Question 6
Untitled question
The rate of loss of energy from a particle as it moves along its track through matter (tissue)
Question 7
What is the result of deposition of high-velocity charged particles (α, β, electrons, protons)?
Low-energy electrons
= high LET (Linear Energy Transfer)
densely ionizing, short tissue penetration
X-rays
Gamma rays
Question 8
What type of radiation is released by X-rays and γ-rays?
Alpha particles
Electrons
= low LET less energy deposited per track length, deeper penetration
Protons
Question 9
What kind of radiation leads to deeper tissue penetration?
Protons
Beta particles
X-rays and γ-rays
Alpha particles
Question 10
What type of radiation is used to create radiographs?
ionizing radiation
Sound waves
Heat
Visible light
Question 11
What is the risk of cell damage from radiation during radiographs?
zero
negligible
small but NOT zero
medium
Question 12
What principle should be followed to minimize risks during radiographs?
ALARA rule
ALAPA principle
ALIBRA principle
ALARA principle
Question 13
What does the acronym ALARA stand for?
As Low As Reasonably Acceptable
Always Limit And Reduce Activities
Always Limit And Reduce Amounts
Always Limit And Reduce Amounts
Question 14
Which principle does ALARA emphasize?
Encouraging exposure to all types of radiation
Minimizing exposure to beneficial radiation
Increasing exposure to harmful radiation
Maximizing exposure to beneficial radiation
Question 15
Biological effects of ionizing radiation occur through what types of actions
Direct and Indirect Action
Question 16
What is the direct action of ionizing radiation on DNA?
Photons or secondary electrons ionize water molecules
• Photons/secondary electrons directly ionize DNA • causing immediate molecular damage
Direct action involves free radicals damaging DNA
Ionizing radiation causes DNA replication to stop
Question 17
What does indirect action of ionizing radiation involve?
Production of free radicals from DNA
Immediate molecular damage to DNA
Direct ionization of DNA
Photons/secondary electrons ionize water molecules → produce free radicals • Free radicals and oxidizing species diffuse → damage DNA indirectly
Question 18
Primary cause of DNA damage in the direct effect of radiation?
DNA absorbs energy from photons/secondary electrons → ionization of bases or sugar-phosphate backbone
formation of free radicals
interaction with oxygen molecules
heat absorption by DNA
Question 19
WHat happens to oxidized DNA bases and strands
They break
Question 20
How quickly do free radicals form in the direct effect of radiation?
within minutes
within 10^-10 seconds
within milliseconds
within seconds
Question 21
What type of radiation leads to more direct actions in the direct effect?
beta radiation
High-LET radiation
alpha radiation
low-LET radiation
Question 22
What percentage of DNA damage is direct?
30%
Question 23
What is the primary substance that absorbs x-ray energy (indirect)?
Plastic
Metal
Water
Glass
Question 24
Which toxic substance is formed as a result of x-ray absorption?
chlorine gas
hydrogen peroxide
ozone
carbon monoxide
Question 25
What type of compounds are formed due to the indirect effects of x-ray absorption?
free radicals
metallic ions
stable compounds
inert gases
Question 26
What is the result of the interaction that triggers radiolysis of water?
metals
inert gases
reactive chemical species
stable chemical species
Question 27
What is the ultimate outcome of the chain of chemical changes in the Indirect Effect?
direct DNA damage
indirect DNA damage
cell membrane damage
protein denaturation
Question 28
What does the presence of dissolved oxygen change during water radiolysis?
the types of ions formed
the types of free radicals formed
the types of elements formed
the types of atoms formed
Question 29
Which radical is formed due to the presence of oxygen during water radiolysis?
(HO2•) radicals and hydrogen peroxide
(HO•) radicals
(O2•) radicals
(O•) radicals
Question 30
What is the primary cause of x-ray-induced biologic damage according to the slide?
Gamma rays
Electrons
Ionizing radiation
UV light
Question 31
How close must radicals be to DNA to cause damage?
Within ~1 nm
Within ~4 nm of the DNA helix
Within ~2 nm
Within ~10 nm
Question 32
Characteristics of radiolysis products of water?
Metals
Highly reactive with short half-lives
Stable compounds
Organic molecules
Question 33
What is a free radical?
An atom or molecule with an unpaired electron, highly reactive.
A molecule with a missing proton
A molecule with a double bond only
A compound with no electrons
Question 34
How do free radicals affect DNA?
Promotes DNA replication
Aggressively binds to DNA, causing damage.
Forms protective layers around DNA
Stabilizes DNA structure
Question 35
What happens to free radicals in the presence of oxygen?
Combines with nitrogen
Forms hydroxyl radicals, which are among the most damaging.
Forms hydrogen radicals
Forms carbon radicals
Question 36
What is the primary mediator of the indirect effects on DNA?
free radicals
Question 37
What is the primary cause of: • radiation-induced cell death • carcinogenesis • heritable mutations
Mitochondrial damage
Protein damage
DNA damage
RNA damage
Question 38
Which types of damage can result from direct and indirect actions?
• base damage • single- and double-strand breaks • DNA/DNA-protein cross-links
RNA damage
Protein damage
Mitochondrial damage
Question 39
What type of DNA damage is mostly induced by X-rays?
double-strand breaks
single-strand breaks
base damage - 72%
chromosomal damage
Question 40
What percentage of X-ray-induced DNA damage is due to single-strand breaks?
35%
10%
50%
27%
Question 41
Double-strand break frequency?
as frequent
1% • rare but highly significant for cell killing and tumorigenesis • 25 times less frequent than SSBs; far more biologically important
10 times less frequent
2 times less frequent
Question 42
How much of Xray energy is deposited as spurs
~95% ~100 eV within 4-nm diameter
Question 43
What are clustered lesions
Single spur overlapping the 2-nm DNA helix Clustered lesions occur ~3× more frequently than DSB
Question 44
Cell cycle phases
G1: nuclear components replicated S: synthesis phase (DNA) G2: preparatory stage for cell division M: mitosis
Question 45
Which phase of the cell cycle is most radiosensitive?
Late S phase
G2 and mitosis phases
Early S phase
G1 phase
Question 46
In which phase of the cell cycle is the cell least sensitive to DNA damage?
Mitosis phase
Late S phase
G1 phase
G2 phase
Question 47
What occurs when damage happens before DNA synthesis?
Nucleotide substitution
Chromosome (double-arm) aberration
Chromatid (single-arm) aberration
Gene mutation
Question 48
What occurs when damage happens after DNA synthesis?
chromatid (single-arm) aberration
Question 49
Types of aberrations?
Translocation
Dicentric formation
(A) Ring formation plus acentric fragment (B) Dicentric formation (C) Anaphase bridge formation (D) Translocation (E) deletion
Anaphase bridge formation
Question 50
Which type of chromosomal aberration involves the formation of two centric chromosomes?
Dicentric formation
Translocation
Ring formation plus acentric fragment
Anaphase bridge formation
Question 51
What is the process where chromosome segments are exchanged between non-homologous chromosomes?
Ring formation plus acentric fragment
Translocation
Dicentric formation
Anaphase bridge formation
Question 52
What is the main mechanism of radiation-induced cell killing?
Apoptotic death
Cell fusion
Autophagic death
Mitotic death
Question 53
What type of chromosomal aberrations cause mitotic death?
Single-strand breaks
Gene mutations
lethal chromosomal and chromatid aberrations
Non-lethal chromosomal aberrations
Question 54
What is Law of Bergonié and Tribondeau?
Law of Mendel
States a cell’s radiosensitivity depends on its mitotic rate and degree of differentiation
ie. Rapidly dividing cells are more radiosensitive
Law of Pasteur
Law of Moore
Question 55
High to Low - Radiosensitivity
I. Vegetative inter-mitotic II. Differentiating inter-mitotic III. Multipotent connective tissue IV. Reverting post-mitotic V. Fixed post-mitotic
Cells with low mitotic index
Cells in interphase
Cells in G0 phase
Question 56
What is the radiosensitivity classification of highly specialized, post-mitotic cells?
Moderate
Intermediate
Very Low
High
Question 57
Which of the following cells undergo apoptosis due to radiation?
Muscle cells
Red blood cells
Nerve cells
Lymphocytes (highly radiosensitive )
Question 58
What process occurs within hours after radiation exposure?
Cell division
Cell fusion
Cell differentiation
Apoptosis
Question 59
Which protein plays a central role in regulating radiation-induced apoptosis?
p21
p53
p44
p38
Question 60
What is the bystander effect?
Radiation absorption
Primary effect
Radiation shielding
Cell fusion
Question 61
What mechanism might be involved in the bystander effect?
Chromosome replication
Intercellular signaling, chromosome fragments, or diffusible chemokines
Cell fusion
Direct radiation exposure
Question 62
What is the first phase of radiation damage?
chemical phase
biological phase
physical phase ~10^-12 s: ionization
thermal phase
Question 63
What occurs during the chemical phase of radiation damage?
formation and diffusion of free neutrons
formation and diffusion of free radicals
formation and diffusion of free ions
formation and diffusion of free electrons
Question 64
What happens during the biological phase of radiation damage?
hours
days
minutes
• seconds: DNA repair • hours: cell death • days: mutations, cell transformation, chromosome aberrations • years: cancer, hereditary effects
Question 65
What are the two main categories of biologic manifestations of ionizing radiation damage?
genetic effects and cellular reactions
thermal effects and chemical reactions
acute effects and chronic effects
stochastic effects and tissue reactions
Question 66
Which type of radiation effect has no dose threshold?
tissue reactions
acute effects
stochastic effects
genetic effects
Question 67
What type of radiation doses are typically below the threshold for causing tissue reactions?
Experimental radiation doses
Therapeutic radiation doses
Emergency radiation doses
Diagnostic radiation doses
Question 68
What causes stochastic effects?
Sublethal DNA damage
Radiation-induced burns
DNA mutations
Cell killing
Question 69
What is the threshold dose for stochastic effects?
Low dose
None
Variable
High dose
Question 70
How does the severity of clinical effects relate to dose for stochastic effects?
Dependent on individual tolerance
Random
Proportional to dose
Inversely proportional
Question 71
What causes tissue reactions?
Heritable effects
Radiation-induced cancer
DNA mutations
Cell killing
Question 72
Does tissue reactions have a threshold dose?
No
High dose
Variable
Yes
Question 73
How does the severity of clinical effects relate to dose for tissue reactions?
Random
Inversely proportional
Severity is proportional to dose the higher the dose, the more severe the effect
Independent of dose
Question 74
When does Cancer risk increases linearly?
with doses >0.1 Gy
Question 75
What is the threshold dose for tissue reactions (like mucositis)?
10 Gy
20 Gy
5 Gy
30 Gy
Question 76
What range of radiation doses is associated with stochastic effects?
No specific dose range
High-dose range
Low-dose range
Medium-dose range
Question 77
Examples of stochastic effects
genetic mutations
environmental factors
cancer, heritable effects
hormonal imbalances
Question 78
How does the severity of tissue reactions relate to the dose?
remains constant
fluctuates randomly
increases with dose
decreases with dose
Question 79
Examples of tissue reactions
100 microGy
1 microGy
1 milliGy
salivary dysfunction, cataracts, hair loss, sterility
Question 80
What type of cataracts can radiation induce?
Corneal cataracts
Nuclear cataracts
Anterior cataracts
posterior subcapsular or cortical cataracts
Question 81
What is the threshold for cataract formation?
~0.8 Gy
~0.5 Gy (ICRP) 1–2 Gy (NCRP)
~1.5 Gy
~0.2 Gy
Question 82
Range of radiation dose from dental radiographs?
0.1–0.5 mGy
0.04–0.6 mGy
0.05–0.3 mGy
0.01–0.2 mGy
Question 83
Organs with high radiosensitivity?
Fine vasculature
• lymphoid organs • bone marrow • testes • intestines • mucous membranes
Optic lens
Lymphoid organs
Question 84
Organs with intermediate radiosensitivity?
Growing cartilage
Mucous membranes
• fine vasculature • growing cartilage • growing bone • salivary glands • lungs • kidney • liver
Optic lens
Question 85
Organs with low radiosensitivity?
Mucous membranes
Bone marrow
• optic lens • muscle • nerves
Nerves
Question 86
Effects of therapeutic radiation on oral cavity
Radiation dermatitis
Tooth decay
Osteoradionecrosis
• mucositis • osteoradionecrosis • skin burn and fibrosis
Question 87
Effects on the oral mucous membrane during radiotherapy?
• mucositis • White to yellow pseudomembrane • Severe discomfort / difficulty to eat • candidiasis • Healing within 2 months
Increased salivation
Loss of taste
Numbness
Question 88
What is the 'Golden Window' in relation to radiation therapy?
Period of highest susceptibility to infections
lowest risk of osteoradionecrosis (4 mo after Rx. therapy)
Time during which radiation is administered
Highest risk of osteoradionecrosis (4 mo after Rx. therapy)
Question 89
When is the highest risk of osteoradionecrosis after radiation therapy?
between 4 and 12 months after Rx. therapy
Immediately after radiation therapy
Between 12 and 24 months after radiation therapy
1 year after radiation therapy
Question 90
Radiation effect (radiotherapy) on taste buds:
middle 1/3
base of the tongue
• loss of taste during 2nd and 3rd week of radiotherapy • post. 2/3 of tongue affect bitter/acid • ant. 1/3 affect sweet/salt flavors • Recovery = 60 to 120 days
tip of the tongue
Question 91
Which salivary glands is more radiosensitive?
submandibular glands
sublingual glands
submaxillary glands
parotid glands
Question 92
Effects of radiotherapy on salivary glands?
salivary flow increases
salivary flow remains unchanged
salivary flow increases slightly
• Acute inflammatory repose soon develop • progressive fibrosis, adiposis, loss of fine vasculature, degeneration • salivary flow decreases to zero at 60Gy • Xerostomia
Question 93
When does xerostomia typically subside?
12-24 months
1-3 months
6-18 months
6-12 months • compensatory hypertrophy of residual s.glands • Beyond a year less likely to show significant return of function
Question 94
What effect does radiation have on the development of teeth?
Has no effect on growth
Accelerates their growth
Only affects tooth color
Irradiation of teeth during their development retards their growth
Question 95
Radiation effect on tooth bud calcification?
It strengthens the tooth bud
before calc = may destroy tooth bud After calc = inhibit cellular differentiation → malformation + arresting growth
It changes the tooth bud's shape
It causes the tooth bud to grow faster
Question 96
What defect in permanent dentition can be caused by children receiving radiation therapy?
Enlarged root development
Missing 3 or more
Retarded root development or missing 1 or 2
Additional root development
Question 97
Causes of radiation caries?
Increased fluoride intake
• Reduced salivary flow • Decreased pH • Reduced buffering capacity • Increased viscosity
Increased salivary flow
Enhanced buffering capacity
Question 98
Which of the following is NOT a clinical presentation of radiation effect on oral tissue?
Widespread superficial lesions on all buccal, lingual, incisal and palatal surfaces
Circumferential cervically involving dentine and cementum
Localized lesions on single buccal surface
Dark pigmentation of entire crown and incisor edges may be worn
Question 99
What is the primary damage to mature bone due to radiation?
damage of fine vasculature specifically in mandible rather than maxilla
damage of coarse vasculature specifically in mandible
damage of fine vasculature specifically in maxilla rather than mandible
damage of fine vasculature in both maxilla and mandible equally
Question 100
What changes occur in marrow tissue due to radiation?
• becomes hypovascularized, hypoxic, and hypocellular • replacement of normal marrow with fatty marrow of fibrous connective tissue
becomes hypovascularized, normoxic, and hypercellular
becomes hypervascularized, normoxic, and hypercellular
becomes hypervascularized, hypoxic, and hypocellular
Question 101
What type of tissue replaces normal marrow in the presence of radiation?
nerve tissue
muscle tissue
fatty marrow of fibrous connective tissue
cartilage
Question 102
What is the typical time frame for the appearance of Osteoradionecrosis (ORN) after radiation?
6–12 months, but may occur years later
12–24 months
3–6 months
2–5 years
Question 103
What is the incidence of ORN with modern radiotherapy?
~2–4%
~8–10%
~5–7%
~1–2%
Question 104
In which area is ORN more common?
skull
mandible Rare below 50 Gy, risk increases 11-fold above 66 Gy.
maxilla
cervical spine
Question 105
Signs of osteoradionecrosis
• early = widened PDL space • advanced = patchy radiolucency, sequestra, possible fracture
Question 106
When are extractions recommended before radiation therapy?
2-3 weeks before radiation
4-6 weeks before radiation
1-2 weeks before radiation
immediately before radiation
Question 107
What is the preferred method for post-irradiation extraction management?
Corticosteroids
Topical creams
Antibiotics
Surgical debridement