Irradiation

Exposure - exposure to radiation. Exposure can be carried out from sources of infrared, ultraviolet and ionizing radiation see ionizing Radiation, Infrared radiation, Ultraviolet radiation). People are subject to continuous exposure from natural sources of radiation (see Cosmic radiation, Radioactivity). A significant part of the population periodically exposed to radiation in medical examinations (see Radioisotope diagnostics, x-Ray examination) or therapeutic procedures (see Radiation therapy). A small contingent of people associated with periodic radiation in the professional conditions when working with radiation sources. Radiation sources may be located outside of the irradiated object, and thus to carry out external external irradiation of the body. Some sources α-, beta - and gamma-radiation (see alpha particles, Beta, Gamma radiationand Isotopes) when introduced directly into the blood, and when released through the mouth , or respiratory tract into the body and determine its internal irradiation. Sources, distributed with the blood flow throughout the body (for example, Na24)create almost uniform O., in which the values of absorbed doses (see Doses of ionizing radiation) at all points of the body are the same. At selective accumulation of radioactive radiation sources in any of the organs or tissues is created preferential their exposure. For example, radioactive isotopes of strontium (see), phosphorus (see), as well as stable isotopes of these elements, focusing mainly in the bones, radioactive iodine isotopes (see) in the thyroid gland, caesium (see) in the muscles. Radiation therapy is mainly malignant tumors of the use of unilateral, bilateral or multilateral Acting from multiple sources penetrating emission or of one such source that moves around the body. The most often for these purposes use of high-energy gamma radiation (for example, With60) or x-ray radiation (see Cobalt, radioactive, X-rays). Ultraviolet, infrared, as well as alpha radiation absorbed only superficial layers of the skin, beta-radiation of different isotopes penetrate on average, to a depth of several millimeters. Area of application is the treatment of inflammatory, skin, nervous diseases. In contrast to the overall (total) irradiation of the whole body is used very rarely in practice, the partial radiation capture only large part of it (for example, a basin, a limb), and local (local) radiation - a small area of the body affected by the disease process. Total irradiation always has on the body stronger effect than any version of partial and local irradiation. For example, x-g-irradiation hands in a dose of 600 R causes less serious changes than the total irradiation of the body in the same dose.
Radiation can be distributed as evenly over the entire depth of tissues and uneven. When equal doses uniform Acting more potent than the uneven exposure.
Biological effect depends not only on the spatial distribution of radiation in the body, but also from the so-called time factor exposure. Under the factor of time to understand the dependence of the biological effect of the temporary distribution of radiation, i.e. from the multiplicity and rhythm of exposure and the dose of ionizing radiation. Radiation can be performed once for a short period of time (single short-term exposure). If the irradiation of the body is exposed to in the high dose speak about acute irradiation. Acute irradiation of the person may be in wartime, in case of use of nuclear weapons, as well as in time of peace, in case of accidents in industries associated with the use of ionizing radiation sources. Acute exposure of the body lead to acute radiation sickness (see).
Exposure can be carried out in several fractions with different time horizons (fractionated, or fractional, irradiation). Local fractionated irradiation is used in a clinic for radiotherapy patients mainly malignant diseases. When used in these cases, large doses of radiation (several thousand CT scans) in patients may experience different reactions, typical of radiation sickness mild.
Irradiation of the body may be continuous for a long time (continuous or extensive, irradiation). It can meet in the professional conditions in violation of rules of safety. Such exposure sometimes lead to development of chronic radiation sickness. Both acute and chronic radiation sickness occur when the effects on the body radiation with a high penetrating ability. Little penetrating radiation in external influence can cause pronounced radiation damages (see) surface tissues without the development of radiation sickness.
One of the most difficult problems in radiobiology is regularities under irradiation with different capacities doses of radiation. In General, it is established that the biological effect with the increase of dose rate in the majority of cases increases. It is established, for example, that when a local x-ray irradiation with a dose of 500 R/min erythema (see) in humans occurs when 500-600 R, and when exposed to a dose of 0.5 R/min the same skin reaction develops only when the dose of 2250 R. the Revealed law is taken into account in oncological practice.

Radiation - natural or artificial, which is controlled by a person of radiation effects on living and non-living objects (the use of the term "irradiation" this is wrong).
In natural conditions the irradiation is performed by means of visible light, heat rays, ultraviolet radiation, cosmic radiation, gamma-radiation of the earth's crust, radiation radon air and radioactive elements, scattered in nature and included in the tissues of living organisms (see ionizing Radiation, Cosmic radiation).
In the result of human activity are aimed Acting with various natural and man-made radiation. For the purposes of O. create artificially ultraviolet radiation - shortwave (KOF) and far (DUF), heat rays, ultrashortwave radiation (VHF), x-rays, as well as the use of alpha, beta, gamma radiation of radioactive substances, electron, proton and neutron radiation generated by particle accelerators and nuclear reactors.
Irradiation is widely used in hygienic and therapeutic purposes, in agriculture and industry. Exposure to sunlight, KOF, DUF, VHF, heat rays and partly ionizing radiation are used in physiotherapy. Microbiologists applied radiation sterilization. X-ray, beta, gamma, neutron, electron and proton O. are of value in the treatment of various diseases, especially cancer. These exposure are the subject of radiation therapy - radiation therapy, telecommuter, electronic therapy (see Electron radiation), proton therapy (see Proton radiation), neutron capture therapy (see Neutron therapy). O. using sources of ionizing radiation is also experimental-biological purpose.
You have the following options to classify radiation used in medical science and practice: 1) O. experimental facilities; 2) sanitary O.; 3) Acting with the purpose of sterilization of dressings (bandages, cotton wool), bacterial preparations and utensils, medicines; 4) therapeutic O.
The nature of radiation distinguish external O. - from external natural or artificial sources and internal O. implemented in the result of radioactive decay directly in the exposed environment, for example in tissues and body fluids. An example of internal O. serves radiation impacts during the decay of radioactive trace elements contained in the tissues of living organisms. Internal exposure can occur in inclusion in the biological chain (soil - plants - animals - man) radioactive isotopes (mainly Sr90) - products of nuclear decay, falling on the ground after testing or use of nuclear weapons. Internal O. medical reasons are using input per os or parenteral radioactive isotope of phosphorus, iodine and others In therapeutic practice used also intracavitary and interstitial Acting by typing in the cavity and tissues of open and closed drugs - sources of beta - and gamma-rays (see x-Ray therapy.
In natural conditions, professional practice in clinical and experimental radiology may be different spatially, the Acting Radiation impact on the entire object is called total (or General) O., the impact on part - partial exposure. Exposure of body parts, randomly selected within, are called local. An example of local O. serve radiation exposure the pathological focus in radiotherapy using limited external beam radiation, interstitial or intracavitary injection of radioactive drugs. An example of a strictly local About. can serve effects in experimental purposes at the cellular structure of thin beams of protons. Internal O. depending on the nature of the distribution of radioactive isotope in the tissues may be total (for example, with the introduction of Na24) or localized in the electoral accumulation in the body (for example, J131 in the thyroid gland, Sr90 in the bones). Uniformity Acting is determined by the peculiarities of interaction of radiation with matter (see ionizing Radiation).
In quantitative terms, O. characterized by exposure radiation dose. There are Acting in low -, moderate-and high doses. These quantitative determination are not absolute values. No specific ranges of small, medium and large doses for all biological consequences of O. This is explained primarily by the different radiosensitivity of biological objects. In addition, the effects of radiation depends not only on the dose of radiation, but also on the relative biological effectiveness (RBE) of this type of radiation and temporal distribution of radiation (see Radiobiology).
When assessing the importance of Acting for the population it is characterized by a dose compared with the level of dose of natural radiation (see Doses of ionizing radiation), the average level of which is 100 millirem per year.
Ranges of doses taken for groups of population with a professional attitude to the Acting, are assessed in accordance with the maximum permissible dose (MPD) radiation. The level of Acting in a professional practice, determined according to the following dependence: 5(N-18), where 5 - PDD for the year (in REMS), and the difference enclosed in parentheses is the number of years worked in conditions of the Acting-For-age N is the maximum value because the persons under 18 years, work in conditions of the Acting is prohibited.
In the practice of radiation therapy assess the impact on the lesion (Acting in a sufficient dose), and the degree of O. healthy tissue. Therefore take into account the dose in the lesion, integral dose, absorbed the whole body, and especially the dose received by the tissues surrounding the lesion. In practice, anti-inflammatory radiation therapy is used single dose in the range from a few up to 100-150 happy with limited exposure. When the number of non-neoplastic diseases single dose increased to 150-200 happy, and total up to 2000-3000 happy. Treatment of malignant tumors requires the use of single doses in 200-250 glad, often in 2-4 times larger daily doses, and the total dose for a course of treatment (6-8 weeks) can reach 6000-8000 happy and more. Data about the maximum O. tissues in the conditions of radiation therapy are given in table.



The maximum dose of various organs and tissues (according to the Institute of Russi, France)
Irradiated organ or tissue The nature of the reaction Dangerous dose, pleased
Skeletal muscle
Heart
Bones
Cartilage
Bone marrow
Leather
Intestine
Nervous tissue (neuron)
Urinary bladder
Light
Kidney
The lens of the eye
Egg
Ovary
Atrophy
Violations, defined on ECG
Osteoporosis, fractures
Developmental delay
Anaemia, lakopenia
Acute radioceramic
Diarrhea
Violations conductivity
Cystitis
Violation ventilation
Interstitial nephritis
Cataract
Azoospermia
Castration
7000
5000
5000
500
500
6000
1500
4000
6000
3000
3000
4000
1500
3500
Note: an exposure for 6-8 weeks; fields O. widely include the irradiated body.

Striking action O. characterized minimum lethal dose (MRD), the dose-half-survival (SD) and absolutely minimal lethal dose (IADI). For a person FFM - 200 glad SD-400 glad IADI-600 glad (in a single total irradiation) (see Doses of ionizing radiation).
Dose dependence of biological action of radiation fair considering RBE this type of radiation. It is commonly characterized by the Acting through the exposure dose in the biological equivalent of x-rays (REM). To Express the dose in REMS, multiply dose in x-rays by a factor of RBE. Dose dependence may characterize the radiation at the account of his time parameters. In this respect it is necessary to distinguish first single (one-time) and a fractional (fractionated) O. Each this is About. can be done with different dose R. depending on the values of the P exposure - long (the terms "potraviny, protagorean" not recommended) or intensive. Prolonged low-intensity R.H. called chronic. Intensive irradiation is carried with the River on the order of tens R/min and above the long - units or shares of unit R/min O. intermittent done with alternation of radiation pulses and pauses between them, described as pulse, or ultraprecision. Such nature are, for example, bremsstrahlung and electron radiation produced by betatron or linear accelerator.
O. characterized by physical and artificially created radiation - also and technical parameters. The main physical characteristic is the amount of energy used radiation (energy rays or particles), usually measured in kiloelectronvolt (Kev) or megaelectronvolt (MeV). X-ray radiation, applied in therapy and diagnostics, characterized by energy generation. For therapeutic exposures using x-rays with energy generation: 7-9 kV (Bucky tray-therapy), 30 to 60 kV, sometimes more (close-focus radiotherapy), 60-120 kV (surface radiotherapy), 150 kV (polukrovka radiotherapy), 180-250 kV (deep radiotherapy). Since the spectrum of x-ray radiation depends not only on energy generation, but also from the stress curve generated by this device, from the material of the anode material and the thickness of the filter, usually characterized by x-ray irradiation for layer half of weakening (E), expressed in mm of aluminum or copper. When the characteristic x-ray O. indicate the amount of current flowing through the tube (in mA)that, together with energy and a focal length guides in relation to the strength Acting In diagnostic practice, the use of x-rays with energy generation from 30 to 110 square
As with therapeutic and diagnostic applications of radiation are of great value accounting and valuation of unused radiation. The radioprotective measures of protection can limit radiation exposure in accordance with the rules of traffic rules adopted for professional conditions. Of particular importance is limited Acting in radiological studies (mostly contingents of people in the reproductive period of life). Done in x-ray diagnostic practice, exposure can result in additional to natural radiation exposure in size, reaching 0.2 to natural background radiation. This value due to various organizational, technical and methodical measures tends to decrease.