Radiation Biology and Protection Study Guide

Chapter 3 – Radiation Biology (18 Questions)
Main Topics

  • Biologic changes

  • Dose-response curve

  • Cellular injuries

  • Dose types

  • Somatic/genetic effects

  • Units of measurement

  • Free radicals

  • Patient protection

Mechanisms of Injury

  • Ionization:

    • Definition: X-ray photons strike tissue and eject electrons, forming ions which lead to cell damage.

  • Free Radical Formation:

    • Process: X-rays interact with water molecules, producing free radicals such as H• and OH•.

    • Result: These free radicals combine to form toxins (e.g. H₂O₂) that can damage cells.

  • Direct Theory:

    • Explanation: Radiation directly hits DNA or critical areas, leading to direct damage to the cellular structures.

  • Indirect Theory:

    • Explanation: Radiation interacts with water, producing free radicals that cause damage through toxins. This is the most common mechanism of injury.

Dose-Response Curves

  • Linear, Non-Threshold Curve:

    • Definition: Suggests that tissue response is proportional to the dose received; there is no safe amount of radiation.

  • Threshold Curve:

    • Definition: There exists a dose threshold below which no biological response occurs.

Types of Effects

  • Stochastic Effects:

    • Definition: The probability of occurrence increases with the dose; however, the severity of the effect remains unchanged (e.g., cancer, genetic mutations).

  • Nonstochastic (Deterministic) Effects:

    • Definition: These effects have a defined threshold; severity of the effects increases with the dose (e.g., skin erythema, hair loss, cataracts).

Radiation Injury Sequence

  1. Latent Period:

    • Definition: The duration of time between exposure to radiation and the appearance of any signs.

  2. Period of Injury:

    • Occurrence of cell death, mitotic delay, and chromosomal damage.

  3. Recovery Period:

    • Most damage is repaired during this time, but cumulative effects may occur.

Short- vs. Long-Term Effects

  • Short-term Effects:

    • Definition: Result from a large dose of radiation received over a short period of time (e.g., nausea, hair loss, Acute Radiation Syndrome - ARS).

  • Long-term Effects:

    • Definition: Result from small doses of radiation received over a long duration (e.g., cancer development, genetic defects).

Somatic vs. Genetic Effects

  • Somatic Effects:

    • Definition: Effects that occur in body cells, impacting the individual only, not passing to offspring.

  • Genetic Effects:

    • Definition: Effects that occur in reproductive cells and can be passed down to future generations.

Units of Measurement

  • Exposure:

    • Measured in Coulombs/kg (C/kg) or roentgen (R).

  • Dose:

    • Measured in Gray (Gy) or rad.

  • Dose Equivalent:

    • Measured in Sievert (Sv) or rem.

Risk Estimates

  • Dental X-ray Dose:

    • Extremely low, with Full Mouth X-ray (FMX) estimated at approximately 35 μSv, which is equivalent to about 4 days of background exposure.

  • ALARA Principle:

    • Definition: Stands for "As Low As Reasonably Achievable"; emphasizes minimizing patient exposure to radiation as a fundamental principle of safety.

Chapter 4 – Radiation Protection (10 Questions)
Main Topics

  • Filtration

  • Position-Indicating Devices (PIDs)

  • Collimator

  • Guidelines for radiation exposure

  • Legislation and safety cases

Filtration

  • Definition:

    • The process of removing low-energy (long-wavelength) x-rays that do not aid in diagnosis.

  • Types of Filtration:

    • Inherent Filtration:

    • Components: Tube glass, oil, and tubehead seal, with typical values of approximately 0.5–1.0 mm of aluminum.

    • Added Filtration:

    • Involves aluminum disks placed between the collimator and tubehead; contributes to total filtration.

  • Required Total Filtration:

    • Less than 70 kVp: Minimum of 1.5 mm aluminum required.

    • Greater than or equal to 70 kVp: Minimum of 2.5 mm aluminum required.

Collimator

  • Definition:

    • A lead plate that has a central hole to shape the x-ray beam and limit its size.

  • Beam Sizes:

    • Round beam: Maximum diameter of 2.75 inches (7 cm) at skin.

    • Rectangular beam: Can reduce patient exposure by approximately 60%.

Position-Indicating Device (PID)

  • Definition: A device that guides the x-ray beam during exposure.

  • Shapes:

    • Types include cone, rectangular, or round shapes.

  • Lengths:

    • Longer lengths (e.g., 16 inches) are preferred, as they result in less x-ray beam divergence and reduced dose exposure to the patient.

Guidelines for Prescribing Radiographs

  • Determined by the dentist following the ADA/FDA (2012) guidelines.

  • Based on patient’s age, risk factors, and dental history.

  • Avoids preset intervals; each patient evaluated individually.

Legislation & Safety

  • Federal standards regulate:

    • Equipment filtration

    • Collimation

    • Exposure limits

  • Maximum Permissible Dose (MPD):

    • Occupational: Limited to 50 mSv/year (5 rem).

    • Public: Limited to 1 mSv/year (0.1 rem).

  • ALARA Principle Reiterated:

    • Continued emphasis on minimizing radiation exposure.

Chapter 30 – Introduction to Image Interpretation (2 Questions)
Main Topics

  • Understanding who diagnoses and the reasons behind it.

  • Interpretation:

    • Definition: Reading and understanding what is visible on the radiographic image.

  • Diagnosis:

    • Definition: The identification of disease; a process that can only be performed by a licensed dentist.

  • Dental Radiographer’s Role:

    • May interpret and describe findings based on the images (must not diagnose).

    • Can educate patients about normal and abnormal findings observed in their radiographic images.

Chapter 31 – Descriptive Terminology (10 Questions)
Main Topics

  • Importance of language in radiology

  • Types, shapes, and locations of lesions

Purpose

  • Provides a universal language for accurately describing radiographic findings.

  • Facilitates clear communication among professionals and contributes to legal documentation purposes.

Radiolucent Lesions (Dark)

  • Appearance:

    • Categories: Unilocular (one area), multilocular (comprising many lobes).

  • Location Terms:

    • Periapical: Located around the apex of a tooth.

    • Interradicular: Situated between the roots of adjacent teeth.

    • Pericoronal: Found surrounding the crown of a tooth.

    • Edentulous zone: Present in the area where a tooth is missing.

    • Alveolar bone loss: Positioned below the cementoenamel junction (CEJ).

Radiopaque Lesions (Light)

  • Patterns:

    • Focal opacity, target lesion, multifocal confluent lesions, irregular/ill-defined shapes, ground glass, mixed lucent-opaque, and soft tissue opacity.

  • Location Terms:

    • Same as those used for radiolucent lesions, adaptable for clear differentiation.

Shape & Borders

  • Corticated:

    • Definition: Exhibits a well-defined white border.

  • Noncorticated:

    • Definition: Presents as fuzzy or poorly defined borders.

Landmark Descriptions for Intraoral and Panoramic Images

  • Detailed radiographic appearances and descriptions of various anatomical landmarks are documented throughout the outline, including:

    • Maxillary Landmarks

      • Incisive Foramen: A small, ovoid or round radiolucent area seen between maxillary central incisors.

      • Superior Foramina: Two small radiolucent dots above the central incisors' apices.

      • Maxillary Sinus: A large radiolucent area located above the apices of maxillary posterior teeth.

      • Zygomatic Process: A J- or U-shaped radiopaque area often superior to the maxillary first molar region.

      • Maxillary Tuberosity: A radiopaque bulge distal to the most posterior maxillary molar.

      • Hamulus: A small, hook-like radiopaque projection extending from the sphenoid bone, often seen posterior to the maxillary tuberosity.

      • Nasal Cavity/Fossa: A large radiolucent area divided by the nasal septum, superior to the anterior teeth.

      • Soft Tissue of the Nose: A faint radiopaque outline seen in periapical radiographs of the incisor region.

    • The document concludes with clear descriptions of the Mandibular Landmarks and their identities when viewed radiographically, facilitating an enhanced understanding of radiological anatomy.

      • Mental Foramen: A small, ovoid radiolucent area often seen near the apex of the mandibular premolars.

      • Mental Ridge: A thick, radiopaque band extending from the premolar region to the incisor area, inferior to the apices of the anterior teeth.

      • Mandibular Canal: A radiolucent band outlined by two thin radiopaque lines, extending from the ramus to the mental foramen.

      • Lingual Foramen: A small, round radiolucent dot located inferior to the apices of the mandibular central incisors.

      • Mandibular Torus: A radiopaque protrusion often found on the lingual aspect of the mandible, commonly in the premolar region.

      • Mylohyoid Ridge (Internal Oblique Ridge): A radiopaque line running diagonally downwards and forwards from the molar region on the lingual aspect of the mandible.

      • External Oblique Ridge: A radiopaque line running diagonally downwards and forwards from the coronoid process on the buccal aspect of the mandible.

  • Air spaces and soft tissues are also delineated specifically for panoramic imaging, ensuring clarity in interpreting complex anatomical features during examination.