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Question Bank
- 1What is the primary effect of ionizing radiation on tissue atoms?
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create ion pairs - 2How quickly do initial interactions with tissue atoms occur?
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extremely fast (~10^-13 sec) - 3How long does it take for DNA damage to be completed?
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within about 1 millisecond - 4Untitled question
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untitled answer - 5What are the cell responses to DNA damage?
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• enzymatic repair • DNA mutation • Cell death - 6Untitled question
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The rate of loss of energy from a particle as it moves along its track through matter (tissue) - 7What is the result of deposition of high-velocity charged particles (α, β, electrons, protons)?
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= high LET (Linear Energy Transfer) densely ionizing, short tissue penetration - 8What type of radiation is released by X-rays and γ-rays?
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= low LET less energy deposited per track length, deeper penetration - 9What kind of radiation leads to deeper tissue penetration?
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X-rays and γ-rays - 10What type of radiation is used to create radiographs?
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ionizing radiation - 11What is the risk of cell damage from radiation during radiographs?
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small but NOT zero - 12What principle should be followed to minimize risks during radiographs?
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ALARA principle - 13What does the acronym ALARA stand for?
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As Low As Reasonably Achievable - 14Which principle does ALARA emphasize?
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Avoiding exposure to radiation that does not have a direct benefit to you, even if the dose is small. - 15Biological effects of ionizing radiation occur through what types of actions
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Direct and Indirect Action - 16What is the direct action of ionizing radiation on DNA?
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• Photons/secondary electrons directly ionize DNA • causing immediate molecular damage - 17What does indirect action of ionizing radiation involve?
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Photons/secondary electrons ionize water molecules → produce free radicals • Free radicals and oxidizing species diffuse → damage DNA indirectly - 18Primary cause of DNA damage in the direct effect of radiation?
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DNA absorbs energy from photons/secondary electrons → ionization of bases or sugar-phosphate backbone - 19WHat happens to oxidized DNA bases and strands
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They break - 20How quickly do free radicals form in the direct effect of radiation?
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within 10^-10 seconds - 21What type of radiation leads to more direct actions in the direct effect?
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High-LET radiation - 22What percentage of DNA damage is direct?
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30% - 23What is the primary substance that absorbs x-ray energy (indirect)?
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Water - 24Which toxic substance is formed as a result of x-ray absorption?
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hydrogen peroxide - 25What type of compounds are formed due to the indirect effects of x-ray absorption?
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free radicals - 26What is the result of the interaction that triggers radiolysis of water?
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reactive chemical species - 27What is the ultimate outcome of the chain of chemical changes in the Indirect Effect?
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indirect DNA damage - 28What does the presence of dissolved oxygen change during water radiolysis?
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the types of free radicals formed - 29Which radical is formed due to the presence of oxygen during water radiolysis?
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(HO2•) radicals and hydrogen peroxide - 30What is the primary cause of x-ray-induced biologic damage according to the slide?
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Hydroxyl radicals - 31How close must radicals be to DNA to cause damage?
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Within ~4 nm of the DNA helix - 32Characteristics of radiolysis products of water?
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Highly reactive with short half-lives - 33What is a free radical?
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An atom or molecule with an unpaired electron, highly reactive. - 34How do free radicals affect DNA?
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Aggressively binds to DNA, causing damage. - 35What happens to free radicals in the presence of oxygen?
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Forms hydroxyl radicals, which are among the most damaging. - 36What is the primary mediator of the indirect effects on DNA?
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free radicals - 37What is the primary cause of: • radiation-induced cell death • carcinogenesis • heritable mutations
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DNA damage - 38Which types of damage can result from direct and indirect actions?
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• base damage • single- and double-strand breaks • DNA/DNA-protein cross-links - 39What type of DNA damage is mostly induced by X-rays?
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base damage - 72% - 40What percentage of X-ray-induced DNA damage is due to single-strand breaks?
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27% - 41Double-strand break frequency?
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1% • rare but highly significant for cell killing and tumorigenesis • 25 times less frequent than SSBs; far more biologically important - 42How much of Xray energy is deposited as spurs
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~95% ~100 eV within 4-nm diameter - 43What are clustered lesions
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Single spur overlapping the 2-nm DNA helix Clustered lesions occur ~3× more frequently than DSB - 44Cell cycle phases
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G1: nuclear components replicated S: synthesis phase (DNA) G2: preparatory stage for cell division M: mitosis - 45Which phase of the cell cycle is most radiosensitive?
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G2 and mitosis phases - 46In which phase of the cell cycle is the cell least sensitive to DNA damage?
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Late S phase - 47What occurs when damage happens before DNA synthesis?
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Chromosome (double-arm) aberration - 48What occurs when damage happens after DNA synthesis?
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chromatid (single-arm) aberration - 49Types of aberrations?
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(A) Ring formation plus acentric fragment (B) Dicentric formation (C) Anaphase bridge formation (D) Translocation (E) deletion - 50Which type of chromosomal aberration involves the formation of two centric chromosomes?
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Dicentric formation - 51What is the process where chromosome segments are exchanged between non-homologous chromosomes?
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Translocation - 52What is the main mechanism of radiation-induced cell killing?
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Mitotic death - 53What type of chromosomal aberrations cause mitotic death?
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lethal chromosomal and chromatid aberrations - 54What is Law of Bergonié and Tribondeau?
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States a cell’s radiosensitivity depends on its mitotic rate and degree of differentiation ie. Rapidly dividing cells are more radiosensitive - 55High to Low - Radiosensitivity
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I. Vegetative inter-mitotic II. Differentiating inter-mitotic III. Multipotent connective tissue IV. Reverting post-mitotic V. Fixed post-mitotic - 56What is the radiosensitivity classification of highly specialized, post-mitotic cells?
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Low, most radioresistant - 57Which of the following cells undergo apoptosis due to radiation?
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Lymphocytes (highly radiosensitive ) - 58What process occurs within hours after radiation exposure?
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Apoptosis - 59Which protein plays a central role in regulating radiation-induced apoptosis?
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p53 - 60What is the bystander effect?
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Nearby non-irradiated cells show radiation-induced responses - 61What mechanism might be involved in the bystander effect?
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Intercellular signaling, chromosome fragments, or diffusible chemokines - 62What is the first phase of radiation damage?
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physical phase ~10^-12 s: ionization - 63What occurs during the chemical phase of radiation damage?
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formation and diffusion of free radicals - 64What happens during the biological phase of radiation damage?
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• seconds: DNA repair • hours: cell death • days: mutations, cell transformation, chromosome aberrations • years: cancer, hereditary effects - 65What are the two main categories of biologic manifestations of ionizing radiation damage?
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stochastic effects and tissue reactions - 66Which type of radiation effect has no dose threshold?
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stochastic effects - 67What type of radiation doses are typically below the threshold for causing tissue reactions?
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Diagnostic radiation doses - 68What causes stochastic effects?
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Sublethal DNA damage - 69What is the threshold dose for stochastic effects?
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None - 70How does the severity of clinical effects relate to dose for stochastic effects?
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Severity is independent of dose all-or-none response - 71What causes tissue reactions?
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Cell killing - 72Does tissue reactions have a threshold dose?
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Yes - 73How does the severity of clinical effects relate to dose for tissue reactions?
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Severity is proportional to dose the higher the dose, the more severe the effect - 74When does Cancer risk increases linearly?
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with doses >0.1 Gy - 75What is the threshold dose for tissue reactions (like mucositis)?
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30 Gy - 76What range of radiation doses is associated with stochastic effects?
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Low-dose range - 77Examples of stochastic effects
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cancer, heritable effects - 78How does the severity of tissue reactions relate to the dose?
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increases with dose - 79Examples of tissue reactions
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salivary dysfunction, cataracts, hair loss, sterility - 80What type of cataracts can radiation induce?
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posterior subcapsular or cortical cataracts - 81What is the threshold for cataract formation?
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~0.5 Gy (ICRP) 1–2 Gy (NCRP) - 82Range of radiation dose from dental radiographs?
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0.02–0.4 mGy - 83Organs with high radiosensitivity?
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• lymphoid organs • bone marrow • testes • intestines • mucous membranes - 84Organs with intermediate radiosensitivity?
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• fine vasculature • growing cartilage • growing bone • salivary glands • lungs • kidney • liver - 85Organs with low radiosensitivity?
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• optic lens • muscle • nerves - 86Effects of therapeutic radiation on oral cavity
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• mucositis • osteoradionecrosis • skin burn and fibrosis - 87Effects on the oral mucous membrane during radiotherapy?
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• mucositis • White to yellow pseudomembrane • Severe discomfort / difficulty to eat • candidiasis • Healing within 2 months - 88What is the 'Golden Window' in relation to radiation therapy?
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lowest risk of osteoradionecrosis (4 mo after Rx. therapy) - 89When is the highest risk of osteoradionecrosis after radiation therapy?
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between 4 and 12 months after Rx. therapy - 90Radiation effect (radiotherapy) on taste buds:
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• 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 - 91Which salivary glands is more radiosensitive?
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parotid glands - 92Effects of radiotherapy on salivary glands?
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• Acute inflammatory repose soon develop • progressive fibrosis, adiposis, loss of fine vasculature, degeneration • salivary flow decreases to zero at 60Gy • Xerostomia - 93When does xerostomia typically subside?
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6-12 months • compensatory hypertrophy of residual s.glands • Beyond a year less likely to show significant return of function - 94What effect does radiation have on the development of teeth?
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Irradiation of teeth during their development retards their growth - 95Radiation effect on tooth bud calcification?
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before calc = may destroy tooth bud After calc = inhibit cellular differentiation → malformation + arresting growth - 96What defect in permanent dentition can be caused by children receiving radiation therapy?
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Retarded root development or missing 1 or 2 - 97Causes of radiation caries?
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• Reduced salivary flow • Decreased pH • Reduced buffering capacity • Increased viscosity - 98Which of the following is NOT a clinical presentation of radiation effect on oral tissue?
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Localized lesions on single buccal surface - 99What is the primary damage to mature bone due to radiation?
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damage of fine vasculature specifically in mandible rather than maxilla - 100What changes occur in marrow tissue due to radiation?
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• becomes hypovascularized, hypoxic, and hypocellular • replacement of normal marrow with fatty marrow of fibrous connective tissue - 101What type of tissue replaces normal marrow in the presence of radiation?
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fatty marrow of fibrous connective tissue - 102What is the typical time frame for the appearance of Osteoradionecrosis (ORN) after radiation?
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6–12 months, but may occur years later - 103What is the incidence of ORN with modern radiotherapy?
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~5–7% - 104In which area is ORN more common?
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mandible Rare below 50 Gy, risk increases 11-fold above 66 Gy. - 105Signs of osteoradionecrosis
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• early = widened PDL space • advanced = patchy radiolucency, sequestra, possible fracture - 106When are extractions recommended before radiation therapy?
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2-3 weeks before radiation - 107What is the preferred method for post-irradiation extraction management?
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Hyperbaric oxygen should include alveolectomy to reduce trauma