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Radiation Biology Flashcards

Introduction to Radiation Biology

  • Radiation Biology Definition: The study of the effects of radiation on living tissue.

  • Ionizing Radiation: X-rays are a form of ionizing radiation, which results in ionization when striking patient tissues. All ionizing radiations can produce biologic changes in living tissue.

What is Radiation?

  • Definition: Energy in the form of waves or particles moving through space (radiant energy).

  • Examples:

    • Warmth from sunlight.

    • Electromagnetic radiation: gamma rays, ultraviolet light, radio waves.

    • Particulate radiation: alpha and beta particles.

Ionizing Radiation

  • Ionization: Atoms lose or gain electrons, altering their chemical state.

  • Definition: Capable of changing the chemical state of matter, causing biological damage, and potentially harmful to human health.

  • Examples: Alpha, beta, and gamma radiation.

Non-ionizing Radiation

  • Definition: Bounces off or passes through matter without displacing electrons.

  • Harmful Effects: Unclear whether harmful to human health.

  • Examples: Visible light and radio waves.

Types of Radiation

  1. Alpha Particle:

    • Composition: Two protons and two neutrons.

    • Characteristics: Heaviest type of radiation particle with a large charge.

    • Penetration: Doesn't travel far; cannot penetrate a sheet of paper or the surface of the skin.

    • Hazards: Harmful if inhaled or ingested.

    • Sources: Naturally occurring radioactive materials like uranium and thorium.

  2. Beta Particle:

    • Composition: An electron not attached to an atom.

    • Characteristics: Small mass and negative charge.

    • Penetration: Travels farther than alpha particles; can be stopped with minimal shielding.

    • Effects: Can enter the body but not pass all the way through

    • Sources: Tritium (produced by cosmic radiation) and Carbon-14 (used in carbon-dating).

  3. Neutron:

    • Composition: Particle with no charge in the nucleus of an atom.

    • Characteristics: Does not interact well with materials, travels a long way.

    • Shielding: Requires large quantities of water or light atom materials to stop.

    • Sources: Nuclear fission in a nuclear reactor (splitting of uranium atoms).

  4. Electromagnetic Radiation (X-rays and Gamma Rays):

    • Characteristics: More energy than sunlight, no mass or charge.

    • Penetration: Can penetrate through the body.

    • Uses: Medical treatments.

    • Energy Levels: Vary from low (dental x-rays) to very high (sterilizing medical equipment).

    • Shielding: Dense materials like concrete and lead.

Radioisotopes

  • Definition: Radioactive isotopes of an element.

  • Isotopes: Same number of protons but differing numbers of neutrons.

  • Characteristics: Unstable combination of neutrons and protons, or excess energy in their nucleus (nuclei are unstable and spontaneously emitting excess energy).

  • Example: Hydrogen isotopes (hydrogen-3/tritium is radioactive).

Radioisotope Occurrence

  • Occur naturally or by artificially altering the atom.

  • Produced in nuclear reactors.

  • Example: Uranium (uranium-238 is most abundant, uranium-235 is more radioactive).

Radioactive Decay

  • Process: Unstable nucleus regains stability by shedding excess particles and energy in the form of radiation.

  • Half-life: Unique time period for each radioisotope to undergo radioactive decay (time it takes for half of the unstable atoms to decay).

  • Medical Value: Used in diagnosis and treatment of disease.

Sources of Radiation

  1. Natural Background Radiation:

    • Sun.

    • Earth.

    • Atmosphere.

  2. Artificial Radiation:

    • Man-made.

    • Medical/dental x-rays.

    • Nuclear sources.

    • Consumer products/activities.

Pathways of Radiation

  • Radioactive materials reach people via various routes.

  • Examples:

    • Airborne radioactive material falling on pasture, eaten by cows, present in milk, consumed by people.

    • Inhalation of radioactive material.

    • Radioactive material in water, exposure through fish consumption or swimming.

Radiation Effects

  • Radiation causes ionization of atoms, which affects:

    • Molecules.

    • Cells.

    • Tissues.

    • Organs.

    • The whole body.

Types of Radiation Injury

  1. Direct Effects:

    • Radiation interacts directly with atoms of the DNA molecule or other critical cellular components.

    • May affect the ability of a cell to reproduce and survive.

    • Infrequent due to the small proportion of critical components in the cell.

    • Direct interaction with an active cell results in cell death or mutation; less effect on dormant cells.

  2. Indirect Effects:

    • Ionizing radiation breaks bonds that hold the water molecule together, producing toxic substances (radicals like hydroxyl OH, superoxide anion O2O_2^{-}$$O_2^{-}$$, etc.).

    • These radicals lead to cell destruction.

    • Frequent occurrence because body cells are mostly water (70-80%).

Free Radical Formation

  • X-ray photons interact with water in cells, leading to ionization and free radical formation.

  • Free radicals also formed by UV light, air pollution, ionizing radiation, inflammation, metabolism, and smoking.

Sequence of Radiation Injury

  1. Prodromal Period:

    • Symptoms: Nausea, vomiting, loss of appetite, possible diarrhea (dose-dependent).

    • Timing: Minutes to days following exposure; symptoms last minutes to days.

  2. Latent Period:

    • Time between exposure and appearance of radiation damage.

    • Varies depending on:

      • Total dose of radiation received.

      • Rate of dose delivery.

    • More radiation + faster dose rate = shorter latent period.

  3. Period of Injury:

    • Cell injuries:

      • Cell death.

      • Changes in cell/tissue/organ function.

      • Breaking or clumping of chromosomes.

      • Formation of giant cells.

      • Abnormal or stopped cell division.

  4. Recovery Period:

    • Not all injuries are permanent.

    • Most low-level radiation damage is repaired within the body's cells.

    • Scatter radiation clears in 24-48 hours.

    • Repeated exposure doesn't allow for adjustment.

Factors Influencing Health Effects

  • Dose Rate: How fast the dose is received. A dose received over time is less severe than the same dose received all at once. High dose rates don't allow time for repair.

  • Dose Location: Impact less severe if only part of the body receives the dose.

  • Sensitivity: Fetus is most vulnerable. Infants, children, elderly, pregnant women, and immunocompromised individuals are more vulnerable. Rapidly dividing cells are more susceptible.

Cumulative Effect

  • Additive effects of radiation exposure; unrepaired damage builds up.

  • Can lead to: Cancer, cataract formation, birth defects.

Short-Term and Long-Term Effects

  • Short Term: High doses over short periods kill cells, leading to death, skin burns, hair loss, sterility, cataracts.

  • Long Term: Low doses over extended periods cause chronic effects that may not be observed for years.

Mutations

  • Germ cells (sperm and ova): Genetic abnormalities in offspring.

  • Somatic cells: Diseases including cancer (carcinogenesis).

  • Oncogenes affect cancer incidence.

Somatic and Genetic Effects

  • Somatic Effects:

    • Occur in all body cells except reproductive cells.

    • Not passed to future generations.

    • Only affect the individual exposed.

    • Primary consequence is cancer.

  • Genetic Effects:

    • Occur in reproductive cells.

    • Passed to future generations.

    • Do not affect the exposed individual.

    • Genetic damage cannot be repaired.

Mitotic Cycle Radiosensitivity

  • Cells most sensitive at or close to M (mitosis).

  • G2 phase as sensitive as M phase.

  • Resistance greatest in the later part of S phase.

  • G1 phase has resistant period early, sensitive period late.

Mechanisms of Cell Death After Irradiation

  1. Mitotic Death:

    • Cells die attempting to divide, primarily due to asymmetric chromosome anomalies.

    • Most common mechanism.

  2. Apoptosis:

    • Programmed cell death.

    • Cell separation in apoptotic bodies.

  3. Bystander Effect:

    • Cells directly affected release cytotoxic molecules, causing death in neighboring cells.

DNA Damage

  • Single-Strand Breaks:

    • Little biologic consequence because repaired readily using the opposite strand as a template.

    • Often repairable.

  • Double-Strand Breaks:

    • Most important lesions produced in chromosomes by radiation.

    • Interaction of two double-strand breaks may result in cell killing.

    • Lethal.

Uses of Radiation

  1. Diagnostic Radiology:

    • Diagnostic.

  2. Radiotherapy:

    • Treatment.

  3. Nuclear Medicine:

    • Diagnostic.

    • Treatment.

    • Lab tests.

Diagnostic Radiology Goal

  • Produce an anatomical or functional patient image (using x-rays) which is clinically useful while delivering as low a radiation dose as possible.

Mammography

  • X-ray picture of the breast.

  • Uses a small dose of ionizing radiation.

  • Detects early signs of breast cancer.

  • Best test for early detection (up to three years before physical detection).

Nuclear Medicine

  • Uses radioactive isotopes.

  • Radioisotope tracer is taken orally, injected, or inhaled.

  • Circulates through the body or taken up by certain tissues.

  • Distribution tracked by emitted radiation.

  • Captured by imaging techniques.

  • Radioisotopes have short half-lives, decay before causing damage.

Radionuclide Angiogram

  • Tells how well the heart pumps and how much blood is pumped with each heartbeat.

  • Radioactive tracer injected into arm vein.

  • Tracer “tags


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Radiation Biology Flashcards

Introduction to Radiation Biology

  • Radiation Biology Definition: The study of the effects of radiation on living tissue.
  • Ionizing Radiation: X-rays are a form of ionizing radiation, which results in ionization when striking patient tissues. All ionizing radiations can produce biologic changes in living tissue.

What is Radiation?

  • Definition: Energy in the form of waves or particles moving through space (radiant energy).
  • Examples:
    • Warmth from sunlight.
    • Electromagnetic radiation: gamma rays, ultraviolet light, radio waves.
    • Particulate radiation: alpha and beta particles.

Ionizing Radiation

  • Ionization: Atoms lose or gain electrons, altering their chemical state.
  • Definition: Capable of changing the chemical state of matter, causing biological damage, and potentially harmful to human health.
  • Examples: Alpha, beta, and gamma radiation.

Non-ionizing Radiation

  • Definition: Bounces off or passes through matter without displacing electrons.
  • Harmful Effects: Unclear whether harmful to human health.
  • Examples: Visible light and radio waves.

Types of Radiation

  1. Alpha Particle:

    • Composition: Two protons and two neutrons.
    • Characteristics: Heaviest type of radiation particle with a large charge.
    • Penetration: Doesn't travel far; cannot penetrate a sheet of paper or the surface of the skin.
    • Hazards: Harmful if inhaled or ingested.
    • Sources: Naturally occurring radioactive materials like uranium and thorium.
  2. Beta Particle:

    • Composition: An electron not attached to an atom.
    • Characteristics: Small mass and negative charge.
    • Penetration: Travels farther than alpha particles; can be stopped with minimal shielding.
    • Effects: Can enter the body but not pass all the way through
    • Sources: Tritium (produced by cosmic radiation) and Carbon-14 (used in carbon-dating).
  3. Neutron:

    • Composition: Particle with no charge in the nucleus of an atom.
    • Characteristics: Does not interact well with materials, travels a long way.
    • Shielding: Requires large quantities of water or light atom materials to stop.
    • Sources: Nuclear fission in a nuclear reactor (splitting of uranium atoms).
  4. Electromagnetic Radiation (X-rays and Gamma Rays):

    • Characteristics: More energy than sunlight, no mass or charge.
    • Penetration: Can penetrate through the body.
    • Uses: Medical treatments.
    • Energy Levels: Vary from low (dental x-rays) to very high (sterilizing medical equipment).
    • Shielding: Dense materials like concrete and lead.

Radioisotopes

  • Definition: Radioactive isotopes of an element.
  • Isotopes: Same number of protons but differing numbers of neutrons.
  • Characteristics: Unstable combination of neutrons and protons, or excess energy in their nucleus (nuclei are unstable and spontaneously emitting excess energy).
  • Example: Hydrogen isotopes (hydrogen-3/tritium is radioactive).

Radioisotope Occurrence

  • Occur naturally or by artificially altering the atom.
  • Produced in nuclear reactors.
  • Example: Uranium (uranium-238 is most abundant, uranium-235 is more radioactive).

Radioactive Decay

  • Process: Unstable nucleus regains stability by shedding excess particles and energy in the form of radiation.
  • Half-life: Unique time period for each radioisotope to undergo radioactive decay (time it takes for half of the unstable atoms to decay).
  • Medical Value: Used in diagnosis and treatment of disease.

Sources of Radiation

  1. Natural Background Radiation:

    • Sun.
    • Earth.
    • Atmosphere.
  2. Artificial Radiation:

    • Man-made.
    • Medical/dental x-rays.
    • Nuclear sources.
    • Consumer products/activities.

Pathways of Radiation

  • Radioactive materials reach people via various routes.
  • Examples:
    • Airborne radioactive material falling on pasture, eaten by cows, present in milk, consumed by people.
    • Inhalation of radioactive material.
    • Radioactive material in water, exposure through fish consumption or swimming.

Radiation Effects

  • Radiation causes ionization of atoms, which affects:
    • Molecules.
    • Cells.
    • Tissues.
    • Organs.
    • The whole body.

Types of Radiation Injury

  1. Direct Effects:

    • Radiation interacts directly with atoms of the DNA molecule or other critical cellular components.
    • May affect the ability of a cell to reproduce and survive.
    • Infrequent due to the small proportion of critical components in the cell.
    • Direct interaction with an active cell results in cell death or mutation; less effect on dormant cells.
  2. Indirect Effects:

    • Ionizing radiation breaks bonds that hold the water molecule together, producing toxic substances (radicals like hydroxyl OH, superoxide anion O2O_2^{-}, etc.).
    • These radicals lead to cell destruction.
    • Frequent occurrence because body cells are mostly water (70-80%).

Free Radical Formation

  • X-ray photons interact with water in cells, leading to ionization and free radical formation.
  • Free radicals also formed by UV light, air pollution, ionizing radiation, inflammation, metabolism, and smoking.

Sequence of Radiation Injury

  1. Prodromal Period:

    • Symptoms: Nausea, vomiting, loss of appetite, possible diarrhea (dose-dependent).
    • Timing: Minutes to days following exposure; symptoms last minutes to days.
  2. Latent Period:

    • Time between exposure and appearance of radiation damage.
    • Varies depending on:
      • Total dose of radiation received.
      • Rate of dose delivery.
    • More radiation + faster dose rate = shorter latent period.
  3. Period of Injury:

    • Cell injuries:
      • Cell death.
      • Changes in cell/tissue/organ function.
      • Breaking or clumping of chromosomes.
      • Formation of giant cells.
      • Abnormal or stopped cell division.
  4. Recovery Period:

    • Not all injuries are permanent.
    • Most low-level radiation damage is repaired within the body's cells.
    • Scatter radiation clears in 24-48 hours.
    • Repeated exposure doesn't allow for adjustment.

Factors Influencing Health Effects

  • Dose Rate: How fast the dose is received. A dose received over time is less severe than the same dose received all at once. High dose rates don't allow time for repair.
  • Dose Location: Impact less severe if only part of the body receives the dose.
  • Sensitivity: Fetus is most vulnerable. Infants, children, elderly, pregnant women, and immunocompromised individuals are more vulnerable. Rapidly dividing cells are more susceptible.

Cumulative Effect

  • Additive effects of radiation exposure; unrepaired damage builds up.
  • Can lead to: Cancer, cataract formation, birth defects.

Short-Term and Long-Term Effects

  • Short Term: High doses over short periods kill cells, leading to death, skin burns, hair loss, sterility, cataracts.
  • Long Term: Low doses over extended periods cause chronic effects that may not be observed for years.

Mutations

  • Germ cells (sperm and ova): Genetic abnormalities in offspring.
  • Somatic cells: Diseases including cancer (carcinogenesis).
  • Oncogenes affect cancer incidence.

Somatic and Genetic Effects

  • Somatic Effects:
    • Occur in all body cells except reproductive cells.
    • Not passed to future generations.
    • Only affect the individual exposed.
    • Primary consequence is cancer.
  • Genetic Effects:
    • Occur in reproductive cells.
    • Passed to future generations.
    • Do not affect the exposed individual.
    • Genetic damage cannot be repaired.

Mitotic Cycle Radiosensitivity

  • Cells most sensitive at or close to M (mitosis).
  • G2 phase as sensitive as M phase.
  • Resistance greatest in the later part of S phase.
  • G1 phase has resistant period early, sensitive period late.

Mechanisms of Cell Death After Irradiation

  1. Mitotic Death:

    • Cells die attempting to divide, primarily due to asymmetric chromosome anomalies.
    • Most common mechanism.
  2. Apoptosis:

    • Programmed cell death.
    • Cell separation in apoptotic bodies.
  3. Bystander Effect:

    • Cells directly affected release cytotoxic molecules, causing death in neighboring cells.

DNA Damage

  • Single-Strand Breaks:
    • Little biologic consequence because repaired readily using the opposite strand as a template.
    • Often repairable.
  • Double-Strand Breaks:
    • Most important lesions produced in chromosomes by radiation.
    • Interaction of two double-strand breaks may result in cell killing.
    • Lethal.

Uses of Radiation

  1. Diagnostic Radiology:

    • Diagnostic.
  2. Radiotherapy:

    • Treatment.
  3. Nuclear Medicine:

    • Diagnostic.
    • Treatment.
    • Lab tests.

Diagnostic Radiology Goal

  • Produce an anatomical or functional patient image (using x-rays) which is clinically useful while delivering as low a radiation dose as possible.

Mammography

  • X-ray picture of the breast.
  • Uses a small dose of ionizing radiation.
  • Detects early signs of breast cancer.
  • Best test for early detection (up to three years before physical detection).

Nuclear Medicine

  • Uses radioactive isotopes.
  • Radioisotope tracer is taken orally, injected, or inhaled.
  • Circulates through the body or taken up by certain tissues.
  • Distribution tracked by emitted radiation.
  • Captured by imaging techniques.
  • Radioisotopes have short half-lives, decay before causing damage.

Radionuclide Angiogram

  • Tells how well the heart pumps and how much blood is pumped with each heartbeat.
  • Radioactive tracer injected into arm vein.
  • Tracer “tags