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Dose and dose rate are used to measure different quantities [1] in the same way that distance and speed are used to measure different quantities. When considering stochastic radiation effects, only the total dose is relevant; each incremental unit of dose increases the probability that the stochastic effect happens. [4]
Therapeutic doses of radiation therapy are often given and tolerated well even at higher doses to treat discrete, well-defined anatomical structures. The same dose given over a longer period of time is less likely to cause ARS. Dose thresholds are about 50% higher for dose rates of 20 rad/h, and even higher for lower dose rates. [4]
As of 2012, the risk of low dose radiation in medical imaging was unproven. [7] It is difficult to establish risks associated with low dose radiation. [7] One reason why is that a long period of time occurs from exposure to radiation and the appearance of cancer. [7] Also, there is a natural incidence of cancer. [7]
Recognized effects of higher acute radiation doses are described in more detail in the article on radiation poisoning.Although the International System of Units (SI) defines the sievert (Sv) as the unit of radiation dose equivalent, chronic radiation levels and standards are still often given in units of millirems (mrem), where 1 mrem equals 1/1,000 of a rem and 1 rem equals 0.01 Sv.
The public information dose chart of the USA Department of Energy, shown here on the right, applies to USA regulation, which is based on ICRP recommendations. Note that examples in lines 1 to 4 have a scale of dose rate (radiation per unit time), whilst 5 and 6 have a scale of total accumulated dose.
Counts is the number of events detected, but dose rate relates to the amount of ionising energy deposited in the sensor of the radiation detector. The conversion calculation is dependent on the radiation energy levels, the type of radiation being detected and the radiometric characteristic of the detector.
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The definition was refined in 1950 as "that dose of any ionizing radiation which produces a relevant biological effect equal to that produced by one roentgen of high-voltage x-radiation." [ 19 ] Using data available at the time, the rem was variously evaluated as 83, 93, or 95 erg /gram. [ 20 ]