Ch. 9 Key Terms

Air Kerma

SI quantity used to measure energy transferred from radiation to matter, which may be at the surface of a patient’s or radiologic and imaging sciences professional’s body

ALARA

Mnemonic meaning to keep all radiation exposure as low as reasonably achievable

Becquerel (Bq)

Unit of radioactivity in the International System of Units, equal to one disintegration per second.

Classic Coherent Scattering

Interaction with matter in which a low-energy photon (below 10 kiloelectron volts) is absorbed and released with its same energy, frequency, and wavelength but with a change of direction

Compton Scattering

Interaction with matter in which a higher energy photon strikes a loosely bound outer electron, removing it from its shell, and the remaining energy is released as a scattered photon.

Exposure (X)

The amount of radiation delivered to a point. Measured in coulomb per kilogram (AirKerma)

Germ Cells

Cells of an organism whose function is to reproduce the organism (e.g., ovum, spermatozoa)

Gray (Gy)

Unit in the International System used to measure the amount of energy absorbed in any medium; 1 Gy= 100 radiation absorbed doses

International System (SI) of Units

System of units based on metric measurement developed in 1948 and having units used to measure radiation

Kiloelectron Volts (keV)

Units of energy equal to 1000 electron volts

Photoelectric Interaction

Interaction with matter in which a photon strikes an inner shell electron, causing its ejection from orbit with the complete absorption of the photon’s energy

Radiation

Forms of energy emitted and transferred through matter

Sievert (Sv)

Unit in the International System used to measure the dose equivalence, or biologic effectiveness, of differing radiations; 1 Sv =100 rem

Somatic Cells

All of the body’s cells except germ cells

X-rays

Form of electromagnetic radiation traveling at the speed of light, possessing the ability to penetrate matter

Thermionic emission

Boiling off electrons by the applied electric current (mA) on the filament of a cathode

Heterogeneous

Many energies

Primary or useful beam

X-rays directed toward the patient

Photoelectron

A released electron of an atom

Characteristic radiation

X-rays originating within the body as a result of the photoelectric effect are collectively known as _________, and are the source of secondary radiation

Thomson, unmodified scattering, Rayleigh

Other name for Classic Coherent Scattering

Modified, Compton effect

Other name for Compton Scattering

Because the original photon possesses less energy AFTER the interaction

Why is the interaction of the Compton effect also referred to as Modified Scattering?

Sievert (Sv)

Expressed as the product of absorbed dose and the quality factor

The Center for Devices and Radiological Health (CDRH) under the direction of the US Food and Drug Administration

Who sets the rules and regulates standards for radiation-producing equipment

Photoelectric absorption/interaction

The greatest hazard to patients in diagnostic radiography is

The National Council on Radiation Protection and Measurements (NCRP)

Not-for-profit organization formed by Congress in 1964 to collect and distribute information regarding radiation awareness and safe practice to the public

Nuclear Regulatory Commission (NRC)

Who enforces the standards of radiation’s safe practice

50 mSv

Annual whole body effective dose limit for the occupational worker

Nonthreshold

Indicates that no dose exists below which the risk of damage does not exist

Nucleus (Chromosomes, Genes, DNA)

Which molecule is at risk when exposed to ionized radiation

Direct hit theory

Any type of radiation transfers its energy directly to the key molecule it has struck, resulting in the formation of ion pairs or elevation to an increased, excited energy state.

Indirect hit theory

Key molecules are affected by radiation depositing its energy elsewhere in the cell, occurs when water molecules are ionized.

Acute Radiation Syndrome

Total body response at a particular dose. Occurs when the organism is exposed fully (total body) to an external source of radiation given in a few minutes.

Prodromal Stage

Nausea, vomiting, and diarrhea stage

Latent Stage/Period

The organism feels well, but body is undergoing biological changes

Manifest Stage

The organism feels the full effects of the exposure, leading to either recovery or death

Somatic effects

Late effect of radiation exposure developed in the individual exposed

Genetic effects

Late effect of radiation exposure that occurs in future generations as a result of damage to the germ cells.

Lens of the eye, breasts, and the thyroid gland

Areas of the body that should be shielded

Distance

The best measure of protection for an occupational worker is

Dose required for Biologic Response to Ionizing Radiation; Hematopoietic (Bone Marrow) Syndrome

2-10 Gy

Dose required for Biologic Response to Ionizing Radiation; Gastrointestinal Syndrome

10-50 Gy

Dose required for Biologic Response to Ionizing Radiation; Central Nervous System Syndrome

50+ Gy

Positive Ion

Knocking out electrons creates a

Natural (background) Ionizing radiation

Radioactive substances present on Earth, such as uranium, radium, radon, are examples of?

Medical and Dental exposures (Imaging)

Constitutes the greatest source of human-made radiation.

Kiloelectron Volts (keV)

Energy measurement directed toward the patient. Also known as the primary or useful beam.

Compton scattering and Photoelectric interaction/Absorption

Which Interaction directly influences patient and occupational worker exposure?

Exposure

The measure of ionization in air

Coulomb

A quantity of electric charge

Absorbed Dose (Gray)

The radiation energy per unit mass, has unit of J/kg or Gyt

Effective Dose (Sievert)

The best measure of the overall risk of exposure to humans from ionizing radiation

Activity

The measure of the rate at which a radionuclide decays

Becquerel (Bq)

The units of quantity of radioactive material, not the radiation emitted by that material. Commonly employed in nuclear medicine and radiotherapy

Cumulative whole body dose

10 mSv x age

Lens of eyes Annual Dose limits for Occupational workers

150 mSv

Skin, Hands, and feet Annual Dose limits for Occupational workers

500 mSv

Most Radioresistant cells

Nerve Cells, muscle, and brain cells

Most Radiosensitive cells

Lymphocytes, blood cells, basal cells of the skin, crypt cells of the small intestine, and germ cells

Indirect hits (Indirect hit theory)

The vast majority of cellular damage is the result of

Manifest Symptoms of Hematopoietic Syndrome (Bone Marrow)

Infection, hemorrhage, anemia

Manifest Symptoms of Gastrointestinal (GI) Syndrome

Massive diarrhea, nausea, vomiting, fever

Manifest Symptoms of Central Nervous System (CNS) Syndrome

Seizures, coma, eventual death

Cataract Formation and Carcinogenesis

Most frequently induced somatic late effect of radiation exposure

Photoelectric effect

Lead shields absorb x-rays through the process of

Aluminum

Most common material used in filtration

Optically Stimulated Luminescence Dosimeter (OSL)

Consists of a strip of aluminum oxide, a copper filter, an open window, a tin filter, and an imaging filter. Can detect X-rays and gamma radiation in the range of 5 keV to 40 MeV.

Thermoluminescent Dosimeter (TLD)

Consists of a plastic holder containing crystals that absorb a portion of the energy they receive from a radiation exposure. The crystal most commonly used is lithium fluoride. Provides readings as low as 0.05 mSv.

Pocket Direct Ion Storage Dosimeter (DIS)

Small ionization gas-filled dosimeter connected to a solid-state device with electrically erasable programmable read-only memory (EEPROM). Provides instant access to data.

Geiger-Muller counter

A field survey instrument that detects radiation. Exposure is displayed in a special meter and determines exposure in coulombs per kilogram.