radiation biology test 2

Radiation Biology and Protection

Introduction

  • Instructor: Lindsey Farris, RDH, MA
  • Institution: Kellogg Community College
  • Course: DEHY 123
  • Term: Spring

Goals

  • To become familiar with:
    • Effects of ionizing radiation on the human body and living tissue
    • Patient education concepts related to risks associated with radiation
    • Ways to minimize risks from radiation exposure

Sources of Radiation

  • Natural Background Radiation:
    • Accounts for the majority of exposure to the U.S. population
Natural Radiation Types
  • Cosmic Radiation:
    • Originates in outer space, including sources such as stars and the sun
  • Terrestrial Radiation:
    • Comes from the earth, including soil, rocks, concrete, and granite
    • Includes radon gas as a significant contributor
Artificial Radiation
  • Radiation in the Healing Arts:
    • Largest source of artificial radiation in the U.S.
    • Includes both diagnostic and therapeutic radiation
    • Diagnostic Radiation:
    • The largest component of artificial radiation exposure

Radiation Injury

  • Not all x-rays reach the sensor; many are absorbed by patient tissues.
  • Ionization Process:
    • Occurs when x-rays strike patient tissues, resulting in:
    • Formation of a positive atom
    • Dislodgement of a negative electron
    • The dislodged electron interacts with other tissues, causing further effects

Theories of Tissue Damage

  • Direct Theory:
    • Involves critical damage to critical areas, for example:
    • An x-ray strikes the DNA of a cell, leading to mutations or immediate cell death
    • This occurrence is infrequent and referred to as a direct hit.
  • Indirect-Action Theory:
    • Involves the ionization of water; x-rays produce free radicals.
    • This can lead to the formation of new toxic chemicals, such as hydrogen peroxide, resulting in cellular dysfunction.
Indirect Theory of Tissue Damage from Radiation
  • X-ray photons interact with water in cells, resulting in:
    • Ionization, which leads to free radical formation:
    • products include H⁺, OH⁻, and O⁻
  • Free Radical Formation:
    • Free radicals can combine to form toxins, such as H₂O₂ (hydrogen peroxide).

Antioxidants

  • Role of Antioxidants:
    • Antioxidants help in eliminating free radicals from the body.

Safety Considerations

  • No Safe Level of Radiation:
    • There is no safe level of radiation exposure; all ionizing radiations are harmful and produce biologic changes in tissues.
  • Terminology Caution:
    • It is discouraged to use the term "safe" in reference to x-rays.

Radiation Effects

Stochastic Effects
  • Definition:
    • The probability of occurrence increases with dose but is not dose dependent (e.g., cancer).
    • Radiation may lead to cancer, but it does not guarantee more severe forms of cancer.
Non-Stochastic Effects
  • Definition:
    • Severity of damage is dependent on the dose.
    • Examples include burns and erythema of skin.

Dose-Response Curve

  • Correlation between the damage (response) of tissue and the amount (dose) of radiation.
Types of Dose-Response Curves
  • Linear Response Curve:
    • Response is proportional to the dose.
  • Threshold Curve:
    • Below a certain level, no response is seen.
  • Linear Non-Threshold Response:
    • Response is seen at any dose.

Radiation Injury Progression

  • Phases of Radiation Injury:
    • Latent Period: Time from exposure to appearance of clinical signs.
    • Period of Injury: Observable effects occur.
    • Recovery Period: Cellular damage repairs to a certain extent.
  • Cumulative Effects:
    • Damaging effects accumulate over time.
Radiation Amounts in Dentistry
  • The concept of ALARA (As Low As Reasonably Achievable):
    • Emphasizes minimal exposure and longer healing times before repeat x-rays are taken.
    • Utilizes less radiation and allows more time for tissue repair due to lengthened latent periods.

Somatic vs. Genetic Effects

  • Somatic Effects:
    • Directly impact the individual exposed to radiation.
  • Genetic Effects:
    • Involve changes to genetic material, potentially passed to future generations (e.g., ovum and sperm).

Radiosensitivity of Tissues

  • High Radiosensitivity:
    • Bone marrow, reproductive tissues, lymph tissue, intestines, skin, and mucous membranes.
Medium Radiosensitivity
  • Examples of Medium Radiosensitivity:
    • Growing cartilage/bone, salivary glands, thyroid, kidney/liver.
Lesser Radiosensitivity Tissues
  • Examples:
    • Nerve tissue, mature skeletal tissue, heart, muscle.
Cell Sensitivity Factors
  • Mitotic Activity:
    • Rapid division leads to greater sensitivity.
  • Metabolism:
    • High metabolic rates correspond to high sensitivity.
  • Cell Differentiation:
    • Immature cells are more sensitive to radiation.

Radiographs During Pregnancy

  • Traditionally, it was advised to provide emergency treatment anytime.
  • Current understanding indicates the 2nd trimester is optimal for procedures.
  • Research supports that preventive, diagnostic, and restorative dentistry (including radiography) is safe at any stage of pregnancy.

Measuring Radiation Exposure

  • Three Different Measurements:
Radiation Measurements
  • Exposure in Air:
    • Defined as the quantity of ionization in air around x-rays.
    • Traditional Unit: Roentgen
    • SI Unit: None (expressed in Coulombs/Kilograms).
Radiation Absorbed Dose
  • Definition:
    • Amount of radiation absorbed by tissues.
    • Traditional Unit: RAD (radiation absorbed dose)
    • SI Unit: Gray (1 Gy = 100 RAD).
Radiation Equivalent Dose
  • Definition:
    • Adjusted absorbed dose based on biological damage potential.
    • Traditional Unit: REM (Roentgen equivalent in man)
    • SI Unit: Sievert (1 Sv = 100 REM).
Conversion Equivalents
  • Equivalent Conversion:
    • 1 Gy = 1 Sv
    • 100 RAD = 100 REM.

Units of Measurement Overview

  • Measurement: Exposure in Air
    • Traditional Unit: Roentgen
    • SI Unit: None (Coulomb/Kg)
  • Measurement: Absorbed Dose
    • Traditional Unit: RAD
    • SI Unit: Gray (Gr.)
  • Measurement: Dose Equivalent in Man
    • Traditional Unit: REM
    • SI Unit: Sievert (Sv)

Maximum Permissible Dose (MPD)

  • Occupational Exposure Limits:

    • Traditional Unit: 5 rem/year (5000 mrem)
    • SI Unit: 0.05 Sv/year (50 mSv)

  • Non-Occupational Exposure Limits:

    • Traditional Unit: 0.1 rem/year (100 mrem)
    • SI Unit: 0.001 Sv/year (1 mSv)

  • Pregnancy Radiation Limits:

    • Limit: 0.5 mSv per month during the 9-month pregnancy, as the fetus is considered non-occupational.

ALARA Principle

  • Operation of ALARA:
    • Stands for "As Low As Reasonably Achievable"
    • Focuses on achieving minimal radiation exposure while employing good techniques and safety through good equipment usage.

Dose - Response Curve Analysis

  • Dose-response curves depict two types of effects:
    • Stochastic Effects:
    • Cancer induction and genetic mutations, nonthreshold.
    • Non-Stochastic Effects:
    • Somatic effects with a threshold; severity increases with dose leading to outcomes like erythema, loss of hair, cataracts, and decreased fertility.

Sample Questions

  • Question: Which of the following is the SI unit equivalent to absorbed dose?

    • A. Roentgen
    • B. Sievert
    • C. Gray
    • D. Coulomb/kg

  • Question: Which option offers the BEST protection from excess radiation for the patient?

    • A. Inherent filtration
    • B. Collimation
    • C. Lead apron
    • D. Digital receptors

    Note: The question regarding protection methods is repeated multiple times, indicating its importance in understanding safe practices surrounding the use of radiation in medical settings.