Chapter 3 Radiation Biology – Flashcards

A comprehensive set of flashcards covering mechanisms of radiation injury, dose-response concepts, cellular effects, tissue and organ sensitivity, measurement units, exposure sources, and dental radiography risk considerations.

What are the two main mechanisms of radiation injury?

Ionization and free radical formation.

How is ionization produced in tissue when exposed to x-rays?

Through the photoelectric effect or Compton scatter, resulting in a positive atom and a dislodged electron.

What happens when an atom becomes ionized?

It becomes a positive atom with a dislodged electron, leading to chemical changes that can cause biologic damage.

What is free radical formation in radiation biology?

Free radicals are formed when x-ray photons ionize water; they are highly reactive and unstable and can damage cellular components.

What is the Direct Theory of radiation injury?

Cell damage results when ionizing radiation directly hits critical targets within the cell; it is less frequent (often involves DNA).

What is the Indirect Theory of radiation injury?

X-ray photons are absorbed by water, producing free radicals that combine to form toxins that damage cells.

What does the Dose-Response Curve illustrate?

The relationship between the amount of tissue damage and the dose of radiation received.

What does a linear, nonthreshold dose-response relationship imply?

Tissue response is directly proportional to dose; some biologic damage occurs at any dose, no matter how small.

What are stochastic (random) effects?

Effects that are a direct function of dose with no threshold; examples include cancer and genetic mutations.

What are nonstochastic (deterministic) effects?

Somatic effects with a threshold; severity increases with higher absorbed dose (e.g., erythema, hair loss, cataracts, decreased fertility).

What is the latent period in radiation injury?

The time between exposure and appearance of observable clinical signs; depends on total dose and dose rate.

What is the period of injury in radiation exposure?

A period during which cellular injuries manifest; a variety of injuries may occur.

What is the recovery period in radiation injury?

The time during which cells may repair damage caused by radiation, depending on several factors.

What are cumulative effects in radiation exposure?

Effects are additive; unrepaired damage accumulates in tissues.

What are the determining factors for radiation injury?

Total dose, dose rate, amount of tissue irradiated, and cell sensitivity.

How does age affect radiation sensitivity?

Children are more sensitive to radiation than adults.

What does radiosensitive mean? What does radioresistant mean?

Radiosensitive: a cell easily damaged by radiation; radioresistant: a cell more resistant to radiation damage.

What cellular characteristics influence radiosensitivity?

Mitotic activity, cell differentiation, and cell metabolism.

Name examples of radiosensitive tissues.

Lymphoid tissue, bone marrow, testes, and intestines.

Name examples of radioresistant tissues.

Salivary glands, kidneys, and liver.

What are the critical organs exposed during dental radiographic procedures?

Skin, thyroid gland, lens of the eyes, and bone marrow.

What were the traditional units of radiation measurement?

Roentgen (R) for exposure, rad for absorbed dose, rem for dose equivalent.

What is a rad?

Radiation absorbed dose—the amount of energy absorbed by tissue.

What is a rem?

Roentgen equivalent man—the dose equivalent used to compare biologic effects.

What are the SI units for radiation dose and dose equivalent?

Coulombs/kilogram (C/kg) for exposure, Gray (Gy) for absorbed dose, Sievert (Sv) for dose equivalent.

How are Gy and rad related?

1 Gy = 100 rad.

How are Sv and rem related?

1 Sv = 100 rem.

What is the difference between dose and dose equivalent?

Dose is energy absorbed by tissue; dose equivalent accounts for the biological effect and is expressed in rem/Sv.

What are natural background radiation sources?

Cosmic radiation and terrestrial radiation; they contribute to natural background exposure.

What is the typical range of background radiation exposure in the United States per year?

Approximately 150–300 mrad per year.

What are artificial (human-made) sources of radiation?

Medical radiographic procedures (including dental imaging), fallout from weapons, weapons production, and the nuclear fuel cycle.

What are the dental exposure risk estimates for thyroid, bone marrow, and eyes?

Thyroid cancer ~6000 mrad; bone marrow leukemia ~5000 mrad; eyes cataracts ~200,000 mrad.

What are Acute Radiation Syndrome (ARS) symptoms?

Nausea, vomiting, diarrhea, hair loss, and hemorrhage.

What distinguishes short-term from long-term radiation effects?

Short-term: large doses over a short time (ARS); long-term: small doses over long periods (cancer, birth abnormalities, genetic defects).

What is the difference between somatic and genetic effects?

Somatic effects occur in the irradiated person; genetic effects occur in future generations and are seen in reproductive cells.