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Doses of ionizing radiation

Doses of ionizing radiation - is the energy of radiation, which should be or was transferred to the substance, calculated for 1 g of the mass of this substance.

The physical dose of ionizing radiation is the energy of X-ray or gamma radiation absorbed in 1 cm 3 of air and estimated by the ionization produced in the air. A more modern term - the exposure dose - has roughly the same meaning. The unit of this dose is x-ray, p (see item 3, table "Units of Measurement"). Universal is the concept of absorbed dose - the amount of energy absorbed in the irradiated object, calculated for 1 g of the mass of its substance. For unit of the absorbed dose, a rad is accepted (see item 3, table "Units of measurement").

The amount of absorbed dose depends on a number of factors: the type of radiation, its energy, the properties of the irradiated object, etc. The absorbed dose of x-ray and gamma radiation, as a rule, is not equal to the exposure dose and is different for different tissues. For example, at an exposure dose of 1 p of x-ray radiation with an energy of 180-250 kV (see X-ray radiation ) or Co-60 gamma radiation (see Cobalt, radioactive), the absorbed dose in bone tissue is 0.84 rad, in muscle - 0 , 93 rad, in fatty tissue - 0.97 rad. The obsolete term tissue dose is close in meaning to the concept of absorbed dose. Sometimes the tissue dose is the absorbed dose, which is created in the tissues of the radioactive isotopes contained in them (see Isotopes , radioactive).

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In the radiological practice, often, especially earlier, the exposure dose was used. To judge the absorbed dose at different points of the irradiated object, use a set of values ​​that determine by measuring the doses in special models (phantoms) made from so-called tissue-like materials (see Phantoms dosimetric ). By placing dosimeters at different points in the phantom, the distribution of the dose of ionizing radiation is determined - the dose field (see Isodoses), according to which the distribution of the absorbed radiation energy is judged. Doses of ionizing radiation, created in the depth of the irradiated object, is called the depth dose. It is composed of a dose created by a direct beam, more or less attenuated, depending on the depth, and the dose of scattered radiation. The latter depends on the radiation energy, the size of the object and the irradiated part of it, the distance from the radiation source to the surface of the object, and so on.

Surface dose - the dose created on the surface of the irradiated object. Due to the backscattering of radiation, the surface dose can be 20-25% higher than the exposure dose measured at the same point in the absence of the object. Focal dose - the dose in the outbreak to be irradiated (for example, a tumor).

In the case of multiple (fractionated) irradiation in radiation therapy, a single dose, i.e., a dose per session, is distinguished, and the total dose for the entire course of treatment is the total dose. The same terms can be applied to any other cases of repeated exposure to ionizing radiation.

When evaluating the biological effect of radiation, the integral dose may be important. In the case of uniform irradiation of the whole body, the integral dose is found by multiplying the exposure dose by the body weight. In case of uneven exposure, the average dose value is used - medium-tissue dose.

There is a term indicator dose. However, it should be considered unsuccessful, since it characterizes not the dose of ionizing radiation, but the activity of a drug labeled with a radioactive isotope, introduced into the body for radioisotope diagnostics (see).

The dose of ionizing radiation, calculated per unit time, is called the dose rate. For the dose rate unit, an x-ray or rad was taken for 1 second. (p / sec, rad / sec) and its derivatives (for example, rad / min, rad / hr, micro / sec, etc.). In the case of continuous chronic irradiation, the dose rate in p / day or rad / day is called the daily dose.

  • Biological dose of ionizing radiation