From Big Medical Encyclopedia

CRITICAL BODY — the body, fabric, a part of a body or all body, radiation to-rogo in the corresponding conditions causes the greatest damage to health of this person or his posterity. To. lakes divide into the groups differing on radio-sensitivity. In decreasing order of radio sensitivity marginal doses are established for three groups K. lake: The I group — all body, gonads and red marrow; The II group — muscles, a thyroid gland, fatty tissue, a liver, kidneys, a spleen, went. - kish. a path, lungs, lens and other bodies, except for those which concern to I and III groups; The III group — a bone tissue, an integument, brushes, forearms, anklebones and feet.

At uniform radiation of all body (see. Radiation ) those bodies and fabrics most of which radiochuvstvitelna are critical (see. Radiochuvstvitelnost ) and which functions are most important for life activity of an organism. In these cases all body, red marrow and gonads are considered critical. At action of neutrons (see. Neutron emission ) and corpuscular radiation from high linear power transmission (see). To. the lake can become also lens. At the same time both the direct, and remote effects of a radiation effect are taken into account: for gonads — disturbance of ability to reproduce posterity, for a crystalline lens — developing of a cataract (see. Cataract, beam ), for marrow — development of leukoses (see. Leukoses ).

At external radiation of a limited part of a body critical can appear that body, damage to-rogo will influence most life activity of an organism. So, e.g., at massive radiation of a breast in a role To. islands act lungs (see. Pneumosclerosis, beam ), at radiation of lumbar area — kidneys (see. Nephrosclerosis, beam ). At impact of the ionizing radiation having small getting to a component (see. Alpha radiation , Beta radiation , Proton radiation , X-ray emission , Electronic radiation ), To. the lake can be skin (see. Burns, beam ).

In some areas of specific activity of the person special requirements to functioning of this or that system or body are imposed. So, at assessment of radiation hazard of space flight, in conditions to-rogo normal functioning of a vestibular analyzer of the astronaut is especially necessary, To. the lake can be considered vestibular analyzer (see).

Biol, effect of beam influence depends on attenuation range of energy fabric at a different depth. For determination of size of the dose of radiation absorbed To. the lake, it is necessary to know topography and a depth of this body. At assessment of influence of external radiation it is considered to be that a sensory layer of skin 100 mg/cm thick 2 it is located under a covering layer 7 mg/cm thick 2  ; thickness of the shielding layer of lens is accepted equal 300 mg/cm 2  ; men's gonads — 500 mg/cm 2 , red marrow — on average 5 g/cm 2 .

If spacing of ionizing radiation in body is heterogeneous, then an average value physical. doses (see. Doses of ionizing radiation ) will not characterize its potential danger for fiziol, functions of body and an organism in general. In such cases in body it is accepted to consider any limited volume, in Krom the absorbed dose appears the greatest and to estimate a share of the structures irradiated with this dose in relation to the others.

It is considered that the accepted marginal dose (see. Marginal doses of radiation ) in relation to the general external irradiation of an organism it is equal to the dose of radiation received by marrow. For others To. lakes are defined coefficients of transition and levels of doses, various depending on category of the irradiated groups. For the I group K. the island coefficient of transition is equal to unit, for the II group — 3, for the III group — 6. Annual marginal doses are respectively established. For category A (the person constantly or temporarily working with sources of ionizing radiation) marginal doses of the specified groups K. lakes are equal 5, 15 and 30 rem/year; for category B (persons who do not work directly with sources of radiation, but under the terms of accommodation or placement of jobs are affected by radioactive materials and other sources of radiation) — 0,5, 1,5 and 3 rem/year.

Thus, the limit exposure dose will be defined To. lake. Possible effects of radiation of all other bodies or fabrics in which the dose is lower than the individual limit doses provided for them are not considered.

For radioactive nuclides (see. Isotopes ), got into a human body, the bodies which are selectively accumulating them, napr for radioisotopes of strontium — bones, for carbon — fatty tissue, for iodine — a thyroid gland are critical. In this case radiation To. the lake occurs continuously during a certain time term which first of all depends from effective period (see) removal of radionuclide from an organism. Dynamics of accumulation of a dose of radiation in To. the lake depends hl. obr. from a type of radionuclide (table 1). E.g., when To. the lake is a bone, a dose of radiation for the first 4 days after hit in an organism 89Sr and 90Sr makes respectively 7,2 and 1,8% of an annual absorbed dose, in 10 days — 19,2 and 5,1%, in 20 days of 34 and 9,3% and is caused by accumulation of a total dose of radiation. If nuclides it is long are in an organism, manifestation a wedge, symptoms perhaps during a wide interval of time, and sometimes and all human life as the total dose of radiation constantly increases.

For diagnosis use various radionuclides and drugs taking into account the features of their distribution in an organism connected with chemical structure of drug or way of its introduction. Exposure doses To. lakes at radio diagnostic testings are presented in table 2. E.g., at single introduction to an organism 1 mkyur 131 I, 125 I, 133 I, 132 I, 123 I in To. the island (thyroid gland) is created a dose of radiation respectively 2000,0; 1200,0; 430,0; 25,0; 20,0 rem. At treatment of diseases apply various amounts and ways of administration of radionuclides. In all cases it is necessary to compare the single and total doses of radiation created collecting in To. the lake radionuclides, with the accepted marginal sizes specified in standards of radiation safety and not to allow their exceeding.


Table 1. DYNAMICS of ACCUMULATION of the DOSE of RADIATION IN CRITICAL BODIES WITHIN a YEAR AT SINGLE RECEIPT of the RADIOACTIVE NUCLIDE (as a percentage, the total dose in a year is taken for 100%)


  • In standards of radiation safety (NRB-76) data are absent

Bibliography: Protection of the patient at radio isotope researches, the lane with English, M., 1974; Standards of radiation safety (NRB — 76), M., 1978; Standards of radiation safety for patients during the use of radioactive materials with the diagnostic purpose, M., 1974; Radiation protection, Recommendations of the International commission on radiological protection, the lane with English, M., 1967; Radio sensitivity and spacing of a dose, the lane with English, M., 1974.

Yu. G. Grigoriev.