threshold dose

dose (dōs) the quantity to be administered at one time, as a specified amount of medication or a given quantity of radiation.

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absorbed dose  that amount of energy from ionizing radiations absorbed per unit mass of matter, expressed in rads.

air dose  see under exposure.

booster dose  a dose of an active immunizing agent, usually smaller than the initial dose, given to maintain immunity.

divided dose  fractionated d.

effective dose  (ED) that quantity of a drug that will produce the effects for which it is given.

erythema dose  the amount of radiation which, when applied to the skin, causes temporary reddening.

fatal dose  lethal d.

fractionated dose  a fraction of the total quantity of a prescribed drug or radiation to be given at intervals.

infective dose  that amount of pathogenic organisms that will cause infection in susceptible subjects.

infinitesimal dose  see under principle.

lethal dose  that quantity of an agent that will or may be sufficient to cause death.

maximum dose  the largest dose consistent with safety.

maximum permissible dose  (MPD) the largest amount of ionizing radiation that one may safely receive in a specified period according to recommended limits in radiation protection guides.

median curative dose  (CD50) a dose that abolishes symptoms in 50 per cent of test subjects.

median effective dose  (ED50) a dose that produces the desired effect in 50 per cent of a population.

median immunizing dose  the dose of vaccine or antigen sufficient to provide immunity in 50 per cent of test subjects.

median infective dose  (ID50) the amount of pathogenic microorganisms that will cause infection in 50 per cent of the test subjects.

median lethal dose  (LD50) the quantity of an agent that will kill 50 per cent of the test subjects; in radiology, the amount of radiation that will kill, within a specified period, 50 per cent of individuals in a large group or population.

median toxic dose  (TD50) the dose that produces a toxic effect in 50 per cent of the population.

minimum dose  the smallest dose that will produce an appreciable effect.

minimum lethal dose  (MLD)

1. the smallest amount of toxin that will kill an experimental animal.

2. the smallest quantity of diphtheria toxin that will kill a guinea pig of 250 g weight in 4 to 5 days when injected subcutaneously.

skin dose  (SD)

1. the air dose of radiation at the skin surface, comprising primary radiation plus backscatter.

2. the absorbed dose in the skin.

threshold dose  the minimum dose of ionizing radiation, a chemical, or a drug that will produce a detectable degree of any given effect.

threshold erythema dose  the single skin dose that will produce in 80 per cent of those tested a faint but definite erythema within 30 days, and in the other 20 per cent, no visible reaction. Abbreviated T.E.D.

tolerance dose  the largest quantity of an agent that may be administered without harm.

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threshold dose

Etymology: AS, therscold + Gk, dosis, giving

1 a measure of a dose of radiation exposure defined in terms of conditions needed to produce a visible erythema in a given proportion of people exposed. Also called minimal erythema dose, skin erythema dose, threshold erythema dose.

2 the minimum dose of a drug needed to produce a measurable response. Administration of drugs at dosages of intervals that do not maintain concentration about the threshold level wastes the medication and, in cases such as antibiotic treatment or cancer chemotherapy, can have additional adverse consequences resulting from the selective growth of cancer cells or microorganisms that are more resistant to the medication.

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dose,

n 1. the quantity of drug necessary to produce a desired effect.
n 2. the total radiation delivered to a specified area or volume or to the whole body. See also dose, radiation-absorbed.

dose, absorbed (D),

n the amount of energy imparted by ionizing particles to unit mass of irradiated material at a place of interest. The unit of absorbed dose is the rad (100 ergs/Gm).

dose, air,

n a radiographic dose delivered at a point in free air; expressed in roentgens. It consists only of the radiation of the primary beam and the radiation scattered from surrounding air; does not include backscatter from radiated matter (e.g., tissue).

dose, booster,

n the portion of an immunizing agent given at a later time to stimulate the effects of a previous dose of the same agent.

dose, cumulative

(kū´myltiv),
n the total accumulated dose resulting from a single or repeated exposure to radiation of the same region or of the whole body. If used in area monitoring, it represents the accumulated radiation exposure over a given period.

dose, depth,

n the absorbed dose of radiation imparted to matter at a particular depth below the surface, usually expressed as “percentage depth dose.” See also dose, percentage depth.

dose, distribution,

n a representation of the variation of dose with position in any region of an irradiated object. The dose distribution may be measured using detectors small enough to avoid disturbing the distribution, or it may be calculated and expressed in mathematical form.

dose, doubling,

n the amount of ionizing radiation, absorbed by the gonads of the average person in a population over a period of several generations, that will result in a doubling of the current rate of spontaneous mutations.

dose, effect curve,

n See curve, dose effect.

dose, equivalent (DE),

n the product of absorbed dose and modifying factors, namely the quality factor (QF), distribution factor (DF), and any other necessary factors. The unit of dose equivalent is the rem (rads times qualifying factors).

dose, erythema

(erthē´m),
n the dose of radiation necessary to produce a temporary redness of the skin. This dose varies with the quality of radiation.

dose, exit,

n the absorbed dose delivered by a beam of radiation at the surface through which the beam emerges from a phantom or patient.

dose, exposure,

n See exposure.

dose, fractionation,

n a dose given by a number of shorter exposures over a longer period than would be required if the dose was given by a continuous exposure in one session at the same dose rate.

dose, gonadal,

n the dose of radiation absorbed by the gonads.

dose, integral (integral absorbed dose, volume dose),

n the total energy absorbed by a part or object during exposure to radiation. The unit of integral dose is the gram rad (100 ergs/gm).

dose, lethal,

n 1. the amount of a drug that would prove fatal to the majority of persons.
n 2. the amount of radiation that will be or may be sufficient to cause the death of an organism.

dose, maintenance,

n the quantity of drug necessary to sustain a normal physiologic state or a desired blood or tissue level of drug.

dose, maximum permissible (MPD),

n the maximum relative biologic effect dose that the body of a person or specific parts thereof shall be permitted to receive in a stated period. In most instances, for the roentgen rays used in dental radiography, it is satisfactory to consider the RBE dose in rems numerically equal to the absorbed dose in rads and the absorbed dose in rads numerically equal to the exposure dose in roentgens. See also dose, weekly permissible.

dose, median effective (ED50),

n a dose that, under standard conditions, is effective in 50% of a randomly selected group of subjects.

dose, median lethal (LD50),

n the amount of ionizing radiation required to kill, within a specified period, 50% of the individuals in a large group or population of animals or organisms.

dose, minimum lethal (MLD),

n the minimal amount of a drug that will kill an experimental animal.

dose, percentage depth,

n the ratio (expressed as a percentage) of the absorbed dose at a given depth in an irradiated body, to the absorbed dose at a fixed reference point on the central ray, usually the surface-absorbed dose.

dose, priming,

n a quantity several times larger than the maintenance dose; used at the initiation of therapy to rapidly establish the desired blood and tissue levels of the drug.

dose, protraction

(prōtrak´shn),
n a method of radiation administration delivered continuously over a relatively long period at a relatively low dosage rate.

dose, radiation,

n the amount of energy absorbed per unit mass of tissue at a site of interest. Note: This definition limits the use of “dose” to conform with the 1962 recommendations of the International Commission on Radiological Units and Measurements (ICRUM). The following terms therefore become obsolete but will be found in this dictionary under the general heading of exposure: air dose, cumulative dose, exposure dose, and threshold dose.

dose, radiation-absorbed (rad),

n the unit of absorbed dose, with a value of 100 ergs per gram.

dose, rate,

n the time rate at which radiation dose is applied, expressed in either roentgens per unit time or rads per unit time.

dose, safely tolerated (STD),

n the dose that can be safely tolerated without producing serious acute toxicity.

dose, skin,

n See dose, surface-absorbed.

dose, subantimicrobial

n the quantity of medication to be taken at one time for purposes other than the elimination of disease-causing microorganisms.

dose, surface-absorbed,

n the absorbed dose delivered by a radiation beam at the point where the central ray passes through the superficial layer of the phantom or patient.

dose, therapeutic,

n a quantity several times larger than the maintenance dose; used in vitamin therapy in which a marked deficiency exists.

dose, threshold,

n the minimum dose that will produce a detectable degree of any given effect.

dose, tissue,

n the dose absorbed by a tissue or tissues in a region of interest.

dose, tolerance,

n See dose, maximum permissible.

dose, toxic,

n the amount of a drug that causes untoward symptoms in the majority of persons.

dose, transit,

n a measure of the primary radiation transmitted through the patient and measured at a point on the central ray at some point beyond the patient.

dose, U.S.P,

n See dose, median effective (ED50); dose, lethal.

dose, volume,

n See dose, integral.

dose, weekly permissible,

n a dose of ionizing radiation accumulated in 1 week and of such magnitude that, in view of present knowledge, exposure at this weekly rate for an indefinite period of time is not expected to cause appreciable bodily injury during a person's lifetime.

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threshold (thresh´ōld),

n the lowest limit of stimulus capable of producing an impression on the consciousness or evoking a response in irritable tissue.

threshold dose,

n See dose, threshhold.

threshold, high pain,

n higher than average capacity to withstand pain; exceptional pain tolerance.

threshold, low pain,

n lower than average capacity to withstand pain; minimal pain tolerance.

threshold, swallowing,

n the minimal stimulation required to initiate the reflex action of deglutition.