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Types of the radiations used in medical practice. The biological effect|act| of ionizing radiation on a healthy and pathologically changed cell|cell|.

Radiotherapy is the branch|division| of medical radiology, which|what| studies|learns| the application of ionizing radiations for treatment of illnesses.

Radiotherapy is conducted at radiological departments of oncologic dispensaries|clinics| and scientific evalvulation institutes (SRI)|. For the treatment of malignant tumours|swelling| radiotherapy is used almost in 80% patients in the combination with surgical one or chemotherapeutical| methods and almost in 40% patients radiotherapy is conducted as an independent radical method of treatment.

In medical practice there are used both ionizing (alpha-|, beta-|, gamma-|, x-ray, neutron and proton) and nonionizing (ultrasound, infra-red, laser, resonance radio frequency) radiations.

Sources of |springs,sources| ionizing radiations.They distinguish natural sources|springs| - the space radiation and natural radio nucleides of the Earth and artificial sources|springs,sources| of ionizing radiation - non-nuclear and nuclear.

Non-radionucleid sources|springs,sources| are the technical devices which|what| do not contain radionuclides, but under certain conditions are |definite| able to generate ionizing radiation due to acceleration and braking of the charged particles. These are generators of x-ray (x-ray short-| and far-distant apparatuse|), braking and corpuscular radiations of high energies (linear accelerators of electrons, betatrons, synchrophasotrons, synchro-cyclophasotrons| and others).

Radionuclear sources|springs,sources| ionizing are sources|springs,sources|, in which|what| the radioactive material is continuous effect|act|. Depending on the technological setting|purpose| distinguish the closed and opened sources|springs,sources| ionizing.

The closed source|spring| is a radioactive radiant|spring,source| ionizing, the equipment of which|what| eliminates|dismisses,removes| the hit of radioactive material, that in him is contained|maintained|, in an external environment|Wednesday|, this: radioactive preparations (needles, marbles and other) and gamma-therapy device for the static and dynamic|run-time| radiation exposure.

The opened source|spring| is a radioactive radiant|spring,source| at the use of which|what| possible hit in the external environment|Wednesday| of radioactive material, that in him is contained|maintained| are the real|authentic,this| solutions and suspension| of radioactive material.

Physical properties|virtues| and penetrable ability|power| of some|certain| ionizing radiations are represented|presented| in tabl.2.1

Table 2.1 Physical properties|virtues| and penetrable ability|power| of some|certain| types of ionizing radiations

Biological effect|act| of ionizing radiations

Under biological effect|act| of ionizing radiations understand their ability|power| to cause|calls| the functional, anatomic and metabolic changes|changing| at all levels of biological organization. Biological effect|act| of ionizing radiations is predefined by energy; wich is passed by the radiations to different|diverse| tissues and organs.

In basis|foundation| of biological effect|act| of ionizing radiations lie:

- absorption of radiation energy by biosubstratum|;

- ionization and excitation of atoms and molecules, radiolysis| of water with formation of free radicals H⁺ OH- and hydrogen peroxid - H₂O₂, formation of active free radicals, and development of primary radiation-chemical reeffects and damage of high molecular connections|halving,compounds,junctions,joints,coupling|.

Primary effect|act| of radiation can be a line and no|un| line. There are excitation and ionization molecules of tissues and organs at the direct radiation influence.

Transmission of energy of ionizing radiation to the material short space|term| is carried out in strong (see|q.v.| tabl|.2.2):

Table 2.2 Stages of radiodefect

Ionization and excitation of the exposed to the rays tissue atoms and molecules is|appears| a primary physical process, the starting mechanism of the biological effect|act| of ionizing radiation, that is why|that is why| it is called the direct effect|act|. Thus there is the break of molecular associations| with the formation of free radicals with the high chemical activity. They interact with surrounding intact| atoms and molecules (molecules of the organic materials dissolved|opened| in water: proteins, nucleoproteides|, lipids|, enzymes and others), as a result of which there occurs their splitting with the formation of following free radicals which|what| interact with the molecules unexposed to the rays and predetermine the indirect effect|act| of ionizing radiation, that is changes|changing| of molecules arise up not from the got|received| energy of ionizing radiation, but|but| from the energy of the changed molecules (during the radiation exposure a very insignificant part|portion| of molecules of the exposed organism to the rays found themselves under the direct effect|act|).

The basic|main| biosubstance| of oxidizing reeffects caused by free radicals are biolipids and nucleoproteides|. As a result of the radiation influence the structure of tissues and cells|cells| is damaged|excited|.

Ionization of atoms and molecules leads to the change|changing| of molecules structure, which results in|to| the violation of biochemical processes in organs and tissues and displays in disorders|discord| of the tissue breathing, change|changing| |act| in the fermentative| systems action, violation of proteins synthesis and others.

Ionizing radiation always has a destructive|causes,calls| |effect|act| on a living organism. The reeffects of the organism to the radiation exposures are variable and determined by both the character of radiation and the condition|virtues| of the organism itself.

The degree of radiodefects correlates distinctly with the partial pressure of oxygen in tissues — the less is the partial pressure of oxygen, the less is the radiodefect (the so-called «oxygen effect»)||lesser,small. In the conditions of hypoxia, the | radiosensitivity| of the organism can go down by 2 – 3 times.

Features of the radiations biological effect|act|:

1. A biological effect depends upon the |value| absorbed dose and power of|capacity| the radiations dose (the linear dependence) – the effect increases|aggravated| with the growth of the dose and its power|capacity|. Pathological changes|changing| arise up at all the levels of the organism integration – molecular, cellular, organ, and in the organism as a whole|whole|.

2. The effect of radiation exposure is related|tied| to the distribution of the dose in time, that with the speed of the energy absorption. The disintegration of the same total dose into separate fragments leads to the diminishing of the radiodefect degree. The processes of renewal begin at once|immediately| after radiation exposure and are able to coADLnsate, |clever| at least partly, the violations which arose up.

3. The degree and the form|shape| of the radiodefect are determined by the radiation |distributing| energy distribution about the organism. The greatest destruction is caused by the radiation exposure of the whole organism, which is the general radiation exposure. The less|lesser,smaller| changes|changing| are caused|called| by the influence of the same dose on separate parts|portions| of the organism which is called the local radiation exposure.It is important which parts|portions| of the organism are exposed to the rays. The greatest consequences are caused|called| by the radiation exposure of the stomach, and|but| the least by the radiation exposure of extremities|endings,limbs|.

4. The biological effect|act| depends upon the type of radiation (see|q.v.| the section|division| “Interaction of ionizing radiation with the material”).

Consequently|so,thus|, all types of ionizing radiations, either themselves or indirectly,|or| cause|calls| the excitation or ionization of atoms or molecules of the biological system. However, at the radiation exposure of objects by different|diverse| types of ionizing radiations in even|equal| doses there emerge quantitavely|quality|, and|but| sometimes qualitatively|quality| various|various| biological effects. That is why|that is why| there was introduced the concept|notion| about the relative biological efficiency (RBE|) of ionizing radiations (see|q.v.| the section|division| “Interaction of ionizing radiation with the material”).

5. The presence of the latent period of the radiation effect|act|. The latent period is |the interval|space| of time, which covers|embraces| the period from the moment of radiation exposure to|by| the appearance of changes|changing| which are registered clinically. The duration of this period is inversely proportional to the absorbed dose. The greater the dose, the shorter the latent period is. It is necessary to bear in mind that the latent period is|appears| a|notion| conventional, purely clinical concept, because actualy the reeffect of the radiation exposure develops persistantly.

6. The ability|virtue| of accumulation. If one exposes an area of the skin by the dose of 1 Gy|, no visual changes|changing| will be present. If one repeates radiation exposure for a few|a little| days successively|in succession,in a row|, erythema will develop. If radiation exposure is given every day|every d for 2-3 months|moon| - there is necrosis. It takes place because small changes accumulate gradually in tissues|changin, which|what| are caused|called| by every radiation exposure which eventually result in || great damages.

In the formation of the biological effect, a special role belongs to the function of the systems, which|what| integrate the organism – the nervous system, the endocrine system and humoral| system (which transports toxic products about the organism being formed in tissues as a result of radiation exposure).

Nervous receptors experience the influence of toxic products, which results in|to| the violation of the nervous regulation processes|adjustment,regulation|, and|but| the origin of chain self-accelerating| reeffects in the organism exposed to the rays, predetermines the development of the radiodefect the at subsequent |consequent| stages with characteristic|character,typical| periodicity of the pathological process development.

Two important statements are the derivatives|rules| from the aforesaid:

First – the interaction of ionizing radiation with the living material takes place after the laws of physics and is accompanied by excitation and ionization of atoms and molecules and primary radiochemical processes (reeffects). But this is only the primary effect|act| of radiation.

Second - ionization of atoms and molecules is|appears| only the starting mechanism for secondary|secondary| processes which further|what| develop in a living organism after biological laws. That is why the |that is why| efficiency of the biological effect|act| of ionizing radiations is estimated|evaluated| from the point of view of the severety of these second|secondary| damages.