Radiation Effects, Dose Response, and Protection in Medical Imaging

Protraction

Continuous dose given at lower dose rate.

Biological effects of radiation

Potential impacts on living organisms due to exposure to radiation.

Factors affecting dose response

Elements that influence the relationship between radiation dose and biological response.

Dose response relationship

A relationship between different radiation doses and the magnitude of the observed response.

Skin Erythema

Skin reddening; also known as a radiation burn.

Desquamation

Drying and flaking of skin.

Epilation

Hair loss that may occur anywhere on the body where radiation hits.

Hematologic Depression

Early, threshold somatic whole-body effect characterized by a decrease in circulating blood cells.

Lymphocytes

White blood cells that are most sensitive to radiation.

Thrombocytes and granulocytes

Blood cells that are moderately sensitive to radiation.

Erythrocytes

Red blood cells that are least sensitive to radiation.

Cytogenetic Effects/Chromosomal Aberrations

Early, threshold somatic effect seen at the next mitosis, with changes to cells.

Acute Radiation Syndrome

Early threshold whole body somatic effect that often results in death.

Mean survival time

Time between exposure and death, which decreases with increasing dose.

Gonadal Dysfunction

Early, threshold local tissue somatic effect causing delayed menstruation or decreased sperm count.

Temporary sterility

Short-term inability to reproduce, which can occur in either sex.

Permanent sterility

Long-term inability to reproduce, which can occur in either sex.

Threshold Doses

Specific doses at which certain effects begin to manifest.

Cataracts

Late, threshold local somatic tissue effect.

Hereditary Effects

Late, non-threshold, local tissue genetic effect.

Genetic Effects

Caused by damage to sperm or egg (one cell).

Doubling Dose

The dose that produces twice the number of genetic mutations that would normally occur.

Linear Energy Transfer (LET)

The average amount of energy transferred from ionizing radiation to tissue per unit distance.

Relative Biological Effect (RBE)

A method to compare how damaging different types of radiation are, given the same dose.

RBE of Diagnostic X-ray

1

Radiation Weighting Factor (WR)

Specific for each radiation type and accounts for biological effectiveness.

Fractionation

Dose divided up into fractions with time in between.

Oxygen Effect

Radiation + oxygen = increase radiosensitivity.

Oxygen Enhancement Ratio (OER)

The difference in biological harm for each radiation type.

Tissue Weighting Factor (Wt)

Different body tissues have different radio-sensitivities relative to each other.

Exposure Area

Radiation has less effect when only part of the body is exposed vs. whole body.

Ionizing Radiation

Can cause excitation or ionization.

Non-Ionizing Radiation

Can cause excitation only.

Primary Radiation

Useful beam produced in x-ray tube.

Scatter Radiation

Produced in part being imaged and travels in all directions.

Remnant/Exit Radiation

The remainder of the x-ray beam after it passes through matter.

Radiation Hormesis

The concept that low doses of radiation may be beneficial.

Target Theory

Radiation is most harmful when it hits the critical target (DNA).

Direct and Indirect Action

The study of how ionizing radiation affects biological systems at the molecular level.

Molecular Radiobiology

Focuses on understanding the molecular mechanisms by which radiation causes damage to cells.

Cell death

One of the three principal observable effects resulting from irradiation of DNA.

Mutation

One of the three principal observable effects resulting from irradiation of DNA.

Chromosomal aberrations

One of the three principal observable effects resulting from irradiation of DNA.

Radiolysis of Water

When water interacts with radiation, water molecules dissociate into other molecular products.

Free radical

An ion or molecule that has unpaired electrons, making it highly reactive and unstable.

Tissue Radiosensitivity

The susceptibility of tissues to damage from radiation exposure.

Law of Bergonie and Tribondeau

A principle stating that radio-sensitivity increases with decreased cell maturity, decreased age of tissues or organs, increased metabolic activity, and increased proliferation rates.

Somatic Effects

Effects of radiation that affect the individual exposed, not passed to offspring.

Stochastic Effects

Effects of radiation that occur by chance and have no threshold, such as cancer.

Deterministic Effects

Effects of radiation that have a threshold and increase in severity with increased dose, such as skin burns.

Exposure

A measure of the number of ionizations in air, with units of Coulombs/Kilogram (C/kg) or Gray (Gy).

KERMA

Kinetic Energy Released in Mass, measuring the energy of ionizations in air, with units of Joules/Kilogram (J/kg) or Gray (Gy).

Air Kerma

A measure of the energy of ionizations in air, commonly used to assess scatter radiation and tube leakage.

Absorbed Dose

A measure of energy absorbed in the body, with units of Gray (Gy) or milligrays (mGy).

Equivalent Dose

Accounts for the type of radiation and its biological effect, calculated using the formula: Equivalent Dose (H) = Absorbed Dose (D) × Radiation Weighting Factor (Wᵣ).

Effective Dose

A measure used to compare biological harm based on radiation and tissue type, calculated using the formula: Effective Dose (E) = ∑(Equivalent Dose × Tissue Weighting Factor Wt).

Sievert (Sv)

The unit of measure for equivalent dose and effective dose, reflecting biological effect rather than just energy absorbed.

Milligray (mGy)

A subunit of Gray, commonly used in clinical practice to measure absorbed dose.

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