Radiation Biology Review

Comprehensive practice flashcards covering basic radiation concepts, units, macromolecules, biological principles, and deterministic/stochastic effects based on the lecture transcript.

Ionizing Radiation

Higher energy electromagnetic waves (gamma) or heavy particles (beta and alpha) with sufficient energy to pull electrons from orbit.

Non-Ionizing Radiation

Lower energy electromagnetic waves that do not have enough energy to pull electrons from orbit but can excite them.

Radon

The natural background radiation source that contributes the highest individual dose equivalent per year to the general population ($200\,mrem/year$).

Cosmic Radiation

Radiation from outer space consisting of $80\%$ protons and $10\%$ alpha particles that interact with Earth's atmosphere.

Internal Radiation

Radiation from radioactive elements within the body, including $K-40$, uranium, thorium, $H-3$, and $C-14$.

Diagnostic X-rays

The single largest contributor to human exposure from man-made ionizing radiation.

Radiation Exposure

A quantity indicating the amount of ionization in air produced by X-rays or gamma rays; the SI unit is Coulomb per kilogram ($C/kg$) and the old unit is the Roentgen.

Absorbed Dose

A measure of the energy deposited in a mass of material; the SI unit is the Gray ($Gy$), defined as $1\,J/kg$, and the old unit is the rad ($1\,Gy = 100\,rad$).

Equivalent Dose ($H$)

A measure used to compare biological effects of different types of radiation, calculated as absorbed dose multiplied by a radiation weighting factor ($W_R$); measured in Sieverts ($Sv$).

Effective Dose ($E$)

The sum of weighted equivalent doses for all irradiated tissues or organs, accounting for specific tissue radiosensitivity ($W_t$); measured in Sieverts ($Sv$).

Linear Energy Transfer (LET)

A measure of the rate at which energy is transferred from ionizing radiation to soft tissue, expressed in units of $keV/\mu m$.

Relative Biologic Effectiveness (RBE)

The ratio of the dose of standard radiation ($250\,kVp$ X-rays) to the dose of test radiation needed to produce the same biological effect.

Oxygen Enhancement Ratio (OER)

The ratio of the dose necessary to produce a given effect under anoxic conditions to the dose necessary under aerobic conditions.

Law of Bergonie and Tribondeau

A principle stating that radiosensitivity is a function of the metabolic state of the tissue being irradiated, with stem cells and younger tissues being more sensitive.

Deterministic Effect

A radiation response that increases in severity with increasing dose, exhibits a dose threshold, and typically occurs shortly after exposure (e.g., skin erythema).

Stochastic Effect

A radiation response where the probability of occurrence increases with dose, has no threshold, and follows a linear non-threshold model (e.g., cancer, leukemia).

Linear Non-Threshold (LNT) Model

The dose-response model used to establish radiation protection guidelines, indicating that no level of radiation is completely safe.

Target Theory

The concept that for a cell to die after radiation exposure, its target molecule (DNA) must be inactivated by a 'hit'.

$$D_{37}$$

A measure of radiosensitivity in the single-target, single-hit model that represents the dose sufficient to kill $63\%$ of the cells, leaving $37\%$ surviving.

$$D_0$$

The mean lethal dose in the multi-target, single-hit model, representing a constant related to the radiosensitivity of the cell.

$$LD_{50/60}$$

The whole-body radiation dose that causes $50\%$ of the irradiated subjects to die within $60$ days; for humans, this is approximately $3.5\,Gy_t$.

Hematologic Syndrome

A component of Acute Radiation Syndrome occurring at doses of $2-10\,Gy_t$, characterized by depletion of blood cells.

Gastrointestinal (GI) Syndrome

A component of Acute Radiation Syndrome occurring at doses of $10-50\,Gy_t$, where death occurs due to damage to the intestinal lining.

Central Nervous System (CNS) Syndrome

A component of Acute Radiation Syndrome occurring at doses above $50\,Gy_t$, resulting in death within hours to $3$ days due to fluid buildup in the brain.

Skin Erythema

A sunburn-like reddening of the skin occurring after a threshold dose of approximately $2\,Gy$ ($200\,rad$).

Epilation

Loss of hair (alopecia) following a radiation threshold dose of approximately $3\,Gy$ ($300\,rad$).

Thorotrast

A colloidal suspension of thorium dioxide ($ThO_2$) used as a contrast agent for angiography between 1925 and 1945, later identified as carcinogenic.

Mitosis (M phase)

The most radiosensitive phase of the cell cycle.

S phase

The most radioresistant phase of the cell cycle.

Hormesis

The theory that a little bit of radiation may be beneficial to humans.