Qessions for self-control:

1. History of radioactivity opening: basic|main| stages of radiology development.

2. Nature and properties|virtues| of ionizing radiations: α-|, β-|, γ-|, x-rays, neutrons and protons.

3. The radioactivity, units of radioactivity. Types of radioactive disintegration.

4. Isotopes. Basic|main| descriptions of radioactive isotopes. Description of radioactive isotopes: ⁶⁰Co, ³²P, ^{123, 125, 131}I, ^99mTc_; ¹⁹⁸Au, ^113mIn.

5. Methods of dose determination|definition|. Types of dosimeters.

6. Description of ionization and scintilation| methods of dose determination|definition|.

7. Chemical methods of dose determination|definition|. Mode and principle of action|act| of photochemistry dosimeter.

8. Biological and calculations|computations| methods of dose determination|definition|.

9. Methods of determination|definition| of radioactivity. Types of radiometers.

Section 2. 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

Radiation|	Energy of radiation of МeV|	Speed of distribution in the vacuum of km/c	Length of run in mid air	Length of run in tissues	Ionizing ability|power| (closeness of ionization on unit of way of run)
Alpha	1-10	20 000	to 20 sm|	to 50mkm |	10 000-20 000 pair|couples|/mm|
Beta	0,1-2	270 000	to 15 m	to 1 sm|	5-10 pair|couples|/mm|
Gamma	0,1-20	300 000	hundreds meters	ten of centimetres	1 pair|couple|/sm |
Neutrons	0,5-10	0,001-1000000	hundreds meters	centimetres, meters	Hundreds, ten of thousands of pair|couples| on mm|

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

Time	Stage of defect	Level of the biological organization
10-12 sec|	Physical co-operation, absorption of energy, ionization and excitation of molecules.	Molecular
10-9-10-3 sec|	Primary radiochemistry reeffects formations of radicals. Changes|changing| of molecules, violation of biochemistry of cells|cells|.	Subcellular
Seconds-minutes	Defect of cells|cells|: violation of structures which provide|secures| a function and heredity of cells|cells|.	Cellular
Minutes-hours	Violation of morphology of cells|cells| and their death	Tissue, organ
Minutes-months|moons|	Defect of integral|whole| organism: violation of functions of organs and systems; morphological changes|changing| in organs and systems; death of organism	Whole|whole| organism
Right through life personal	Remote|distant| somatic effects (decline|lowering| of resistance|, reduction|abbreviation,shortening| of life-span, development of cancer or leucosis, dystrophic changes|changing| of tissues)
Indefinitely long time	Genetic consequences of radiation exposure	Public|

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.

The effect|act| of ionizing radiations on a cell|cell| and organism of warm-blooded animals

As a result of radiation exposure in a cell|cell| it is possible to register the great number of most various reeffects - delay of division, supression of the DNA synthesis|, damage of membranes and others. The degree of expression of these reeffects depends on the stage of a life cycle of cell|cell| the radiation exposure took|happened,finished| place.

It is known that the synthesis of DNA| in a cell|cell| takes place in the interphase|, which|what| is divided into 3 periods – the period of synthesis of DNA| (S is a period), before - (G1) and postsynthetic| (G2) periods||spac, the fourth period - mitosis| (М). The duration of the mitotic| cycle varies|modifies| in time|value|, being disposed as follows: M < G2 - S - G1. The shortest|brief| period – mitosis -| - is over within 30-60 minutes.

Some|certain| radio-reeffects are easily born by a cell|cell|, as the result of structures damage, the loss of which|what| is very quickly restored. The most universal reeffect is the temporal delay (supression) of cellular division that is often named|called| the radiation blocking|locking,deadlock| of mitoses|. For the majority of cells cultures |cells| the delay of division is equal to approximately 1 hour per every 1 Gy|. The duration of the delay time depends also on the stage of a cellular cycle, in which|what| cells|cells| are at the moment of radiation exposure. It is the longest |prolonged| in those cases when the radiation influence is experienced|felt| by cells|cells| at the stage of the DNA synthesis|, and|but| the shortest|brief| - at the radiation exposure in mitosis|. One should distinguish the reeffect of division from the complete supression of mitosis|, which sets in after the influence of greater doses, when a cell|cell| continues to live for a considerable time, but completely|wholly| loses the ability to|to| division.

Lethal reeffects of cells|cells|. The forms|shapes| of cellular death

Under cellular death or lethal effect of radiation exposure one understands the loss by a cell|cell| the ability to|to| proliferation|. The survived cells |cells|are those ones, which preserved the ability to|to| unlimited reproduction|duplication|, which is cloning|. Thus|on this grow|, the question is about the reproductive| death of a cell|cell|. This form|shape| of radio-inactivation| of cells|cells| is most widespread in nature.

Another type of the reproductive| death of the exposed cells descendants |cells| is the formation of the so-called giant cells|cells|, which arise up as a result of the confluence of two neighbouring|nearby|, “sisterly” cells|cells|. Such cells|cells| are able to 2-3 divisions|clever|, after which they perish.

The principal reason for the reproductive| death of cells|cells| is|appears| structural interaction|conversions| of DNA| as the so-called chromosomal alterations|realignments| or aberations|. The basic|main| types of aberrations are|: fragmentation of chromosomes, forming of chromosomal bridges, dicentrics|, circular chromosomes, the appearance of intra-| and interchromosomal exchanges, and others.

Some|certain| aberration, for example bridges, mechanically|mechanics| hinder|prevents| the division of cells|cell|. The exchange inside chromosomes and between them results in|to| the uneven division|distributing| of chromosomes, |by| the loss of the genetic material|fabric| that causes|calls| the death of a cell|cell| as a result of metabolites deficite|, the synthesis of which|what| was encoded by the DNA| of the lost part|portion| of the chromosome.

Still another form|shape| of radiation of cells inactivation| |cells| - the interphase| death – sets at the cells|cells| entering mitosis|. At the radiation exposure doses 10 Gy| death can set in “under a ray|beam|” or soon|before long| after radiation exposure. At the radiation exposure dose up to 10 Gy| death sets in within first hours after radiation exposure and can be registered as the varied|various| degenerative changes|changing| of cells|cell| - more frequent piknosis or fragmentation of chromatin|.

The nature of the cells radiation death|cells|

The sensitiveness of a cell|cell| nucleus is approximately six orders higher than the sensitiveness of protoplasm. Of all intranuclear structures DNA| is accountable for the viability of a cell|cell||appears|. The latter takes part in forming chromosomes and the transfer of the genetic information. Radiation exposure causes|calls| varied|various| interaction|conversions| in DNA|: breaks of a DNA molecule|, the formation of alkali-labile associations|, the loss of bases|grounds| and change|changing| of their composition|syllable,storage|, changes|changing| of nucleotides| sequences, sewings together of DNA|-DNA| and DNA|-protein, violations of DNA| complexes with other molecules.

One distinguishes single breaks of DNA|, when the associations | between separate atomic groupments is violated|excited| in one of the filaments|threads,strings| of a bi-spiral| molecule of DNA| and double, when the break takes place at once|immediately| near the closely|near| located areas of two chains, that results in|to| the disintegration of a molecule. At any|some| break, reading the information from a molecule of DNA and spatial structure of chromatin are violated|excited|||.

Single breaks do not result in|to| breakages of a molecule of DNA|, because the torn filament|thread,string| is firmly|tightly| kept |retained,maintained,deducted| in place by hydrogen, hydrophobic| and other types of interaction and the opposite filament|thread,string| of DNA|. In addition, the structure is restored well enough |restored| by the powerful system of reparation|. Single breaks themselves are|appears| not the reasons for cells destruction|cells|.

With the increase of the radiation exposure dose the probability of transition of single breaks into double ones grows as well. Rare-ionising| radiations (gamma, x-ray, fast|quick,fast| electrons) per 20-100 single breaks cause one double break. Densly-ionising| radiations cause the|calls| much greater|far more| number of double breaks of DNA| and chromosomes aberations| immediately|immediately| after radiation exposure.

Alongside with the formation of breaks, the structure of bases|grounds| in the exposed DNA|, foremost|first and foremost,first off| of thimine is violated |, that increases the number of genes mutations|excited|. The formation of sewings together between DNA| and proteins of a nucleoprotein| complex is marked|noted|.

Finally, the important sequence of radiation exposure is the change|changing| of epigenomic| (unconnected with the enuclear material|fabric|) heredity of a cell|cell| the transmitters|carriers| of which|what| are|appears| varied|various| cytoplasmic| organels||appears|. Thus, the functional activity of the exposed cells descendants |cells| goes down. Probably, exactly it can be one of the reasons|causes| for remote|distant| consequences of radiation exposure. However, the main|head,leading| reason of the cells reproductive| death |cells| at radiation exposure is|appears| the damage of their genetic apparatus.

The post-radiation renewal (reparatiion|) of cells|cells|

A lot of radiation damages recommence|restored|. Such damages are named|calls| potential. Their fate|stake,share| may be relateed to two ways: they are repaired| and then a cell|cell| survives, or realized and then a cell|cell| perishes.

After the time of realization, one distinguishes the pre-replicative|, post-replicative | and replicative | reparations|.

The pre-replicative| reparatiion| (before the |by|stage of DNA doubling|) can take place by the reunion of breaks, and also with the help of exclusion|withdrawal,exclusion| (excision|) of the damaged bases|grounds|. In the uniting of single breaks there take part the enzymes: ligase|, endo-|, exonuclease|, DNA-ligase|, which|what| provide|secures| the eventual|end,final| act of reparation| - the ligasion| reunion.

The post-replicative | reparatiion| is the process at which|what| a cell|cell| keeps its |saves,stores| viability, inspite of the presence of DNA defects |.

The replicative | reparatiion| (DNA renewal | in the process of its reparation|) is carried out by eliminating during reparation| of damages in the area|zone| of chain growth point|heig, or by elongation|, passing the damage.

Non-stochastic and stochastic consequences of radiation influence

The non-stochastic are those|calls| effects for which|what| there exists the threshold of radiation exposure and the |but| probability of their emerging and the degree of severity depend on the dose of radiation exposure.

The stochastic are those|calls| effects for which there are no the threshold of radiation exposure.

The genetic and carcinogenic consequences of the radio influence are the |appears| basic|main| stochastic effects.

In the table 2.3 the |pointed|structure of pathological violations as a result of the |because of,owing to| radiation influence on the organism of the man is presented.

Tabl. 2.3 The structure of pathological violations as a result of the |because of,owing to|radiation influence on the organism of the man.

Radiation influence
Direct|immediate| effects	Remote|distant| effects
	Somatic	Teratogenic	Genetic
Acute radiation illness	Growth|height| of common somatic| diseases	Mental|cogitative| retardation	Dominant|leit-motifs| mutations
Chronic radiation illness	Leucosis	Congenital defects	Resulted|pointed| genetic effects
Hyperplasia|, destruction of thyroid	Cancer of the thyroid gland	Blastomatic effects	Defects related|tied| to the effect|act| on chromosomes
Cataract	Cancer of mammary|suckling| gland
Radio traumas	Cancer of lungs
Psychoemotional disorders|discords|	Other types of tumours|swelling|
	Pathology of pregnancy and delivery|
	Reduction|abbreviation,shortening| of life-span

Somatic consequences of the radiation influence

Among the non-stochastic consequences, except for radiation illness, hypoplastic| and dystrophic states|figures,camps,mills| disfunctions of ductless glands can develop. The functional and organic changes|changing| are|appears| the most typical|models| consequences from the side of the nervous, cardio-vascular|, immune haemopoietic systems|.

Genetic consequences of the radiation influence

Genetic consequences of radiation exposure appear|shown,turned,displayed| in the first and next generations. Under the influence of ionizing radiations in small doses genes mutations develop most frequently, which in the greatest degree affect the human heredity. Different|diverse| forms|shapes| of inherited illnesses as a result of damaging the genetic apparatus of gametes|cages,cells| nuclei belong to the genetic effects of the radiation exposure action. The factors which condition changes|changing| of the genetic information are named|called| mutagens|, and|but| this phenomenon - mutagenesis|.

At damaging the somatic cells|cells| chromosomal apparatus under the influence of ionizing radiations there can develop different|diverse| no|un|n-tumours|swelling| illnesses (somatic, teratogenic effects).

At the ionizing radiations action on gametes|cages,cells| (gonades|) there can appear changes|changing| in the number and the structure of chromosomal apparatus, which cause|calls| the inheritedly predefined forms|shapes| of pathology:

• The change|changing| of the inner structure of separate genes can predetermine mortinatality, spontaneous abortion, birth of non-viable children|kids|; mutations which are characterized|described| by structural alteration|realignment| of one or a few|a little| chromosomes and predetermine severe pathological syndromes;

• The change|changing| of the chromosomes number in a set can predetermine the severe |difficult| forms|shapes| of inherited pathology and be the reason|cause| for the most widespread chromosomal illnesses.

• Genetic violations as a result of|because of,owing to| radiation exposure of parental sexual glands are|fathers| divided|divided| into dominants|leit-motifs| and recessions.

The effect|act| of radiation on the embryo and the fetus

The prenatal development of a child takes place within three periods —the pre-implantation period, organogenesis| and fetogenesis|.

The pre-implantation| period lasts until the 9^th day after impregnation. The most sensitive|sensitive| embryos are until 5^th day of the development. Radiation exposure by the dose of 1 – 1,5 Gy| causes the death of 70 – 80% embryos. The radiation exposure of embryoson the 6^th – 10^th days of the development predetermines the emerging of the following innate vices: morpho-functional violations of the brain, defect of the heart, skeleton and others.

Organogenesis| lasts|proceeds| from the 9^th day to the 6^th week after conception. Radiation exposure by the dose of 0,2 Gy| in this period can entail the delay of the fetus growth|height||, severe |rude| anomalies of its|its| development and the neonatal| death.

Fetogenesis | begins from the 7^th week after impregnation. In this period relatively|in relation to| large|great,big| doses of radiation exposure predetermine the stable legging behind of the organism growth|height|.

They estimate|evaluates| the biological effect|act| of radiations also after radiosensitivity| (the appearance of physiological reeffects to radiation exposure) and radiolethality| (radiolethality|: ML50/30 causes|calls| the death of 50% animals during 30 days; ML100/30 – causes the |calls| death of 100% exposed to the rays).

A radio defect depends on personal sensitiveness to|by| ionizing radiation and general|common| reactivity of the organism during radiation exposure. There are specific differences in sensitiveness at mammals. A mortal dose for a man is more than|more than| 6 Gy|, for a dog – 6 Gy|, for a guinea-pig - 5 Gy|, for a rat - 8 Gy|, for a bird - 8-10 Gy|, for a rabbit| - 12 Gy|, for the simplest (amoeba) - 1000 Gy|, bacteria - hundreds of thousands of Gy| (Mіcrococcus radіodurens lives and reproduces itself in channels of a functioning |worker| atomic reactor).

Radiosensitivity| depends on age (at children|kids| it is considerably higher, than at adults and elderly persons|personalities,individuals|), genetic constitution, state|figure,camp,mill| of health (patients are usually more radiosensitive than healthy persons), nourishment|nourishment| (the valuable and balanced nourishment |nourishment| promotes|raises| radioresistance), hormonal status (the hormonal status violation promotes|raises| radiosensitivity|), sex|reason,sex| (females are more radioresistant, than males|husbands,spouse|), the amount|quantity| of oxygen in the atmosphere during irradiating biological objects (the oxygen effect is the increase|rise| of radiosensitivity| at the growth|height| or decline|lowering| of the oxygen partial| pressure in the atmosphere), teADLrature (cooling of the body below the norm is accompanied by the increase|rise| of radioresistance).

In 1906 І. Bergonie and L. Tribondo noted that|notes| radiosensitivity| of tissues is directly proportional to the proliferative| activity and inversely proportional to the degree of differentiation of the cells|cells| constituing it|it|. That is why the |that is why|еру haemopoetic| tissue, the lymphoid| tissue, the sexual glands, the lens of the eye and others, are the |appears| most sensitive|sensitive|.It concerns the muscular tissue first of all.

Depending on radiosensitivity,| 3 groups of critical organs or tissues are established:

Group I - the whole body, gonades| and the red marrow, the lymphoid| tissue.

Group II - thyroid, the fatty tissue, the liver, the kidney|kidneys|, the spleen, GIT, the lungs, muscles, lens of the eye and the organs which do not belong|behaves| to groups|by| I and III.

Group III - the skin, the bone tissue, hands, forearms, shins and feet.

The mechanism of tumours|swelling| cells radiation damage|cells|

Radiotherapy is based on the biological effect|act| of ionizing radiations (see|q.v.| section|division| 1). As a result of the radio influence there is the oppression of cellular division in a tumour|swelling|.The doses like 0,1 Gy| cause the |calls| disappearance of normal mitotical| figures. With the increase of the dose still more cells|cells| lose the ability to |to| reproduction|duplication|. The number of abnormal|abnormal| mitoses| of the tumour cells grows |swelling|, and the|but| cells|cells| which continue to reproduce themselves after some divisions, perish as a result of the harmful influence of chromosomal aberation| and genes mutations related|tied| to the damage of DNA|. There appear endophlebitis| and proliferative endarteritis|| in the blood vessels of the tumour|swelling|. The obliteration| of tiny|small| vessels violates|excites| the tumour feeding|nourishment||swelling|, which strengthens|aggravates| dystrophic changes|changing| in it|it|, and contributes to the tumour perish |swelling| with substituting it by the connecting tissue. Specialists in radiotherapy aspire to the most complete destruction of tumours|swelling| elements at the least damage of the surrounding healthy tissues. It becomes|stands| possible because in the integral|whole| organism at the same absorbed dose the damage of the tumour|swelling| tissue usually sets in quicker and is expressed to a greater degree as a result of|because of,owing to| a low differentiation of tumours|swelling| cells|cells| and their higher radiosensitivity| (the appearance of the physiological reeffect to radiation exposure) in comparison with surrounding normal cells,|cells| the nervous system activity and the presence of the antiblastic| defence|protection| of healthy tissues factors.

The difference in normal and tumours|swelling| cells|cells| radiosensitivity |is named|calls| the therapeutic interval|space| of radiosensitivity|. The greater this interval is|space|, the easier|lighter| is to obtain the tumour destruction|swelling| at saving|safety| the viability of the surrounding tissues.

The |space radiotherapeutic interval can be extended by changing|changing| the radiation exposure rhythm: the set|planned| total dose of radiation exposure is divided into separate portions (fractions). The tumour|swelling| is expose to the rays repeatedly|multiple|, by small (2-3 Gy|), middle (5-6 Gy|) or large|great,big| (8-12 Gy|) fractions. The other way of increasing the radiotherapeutic interval|space| is the dose protraction.| In these cases each fractioned radiation exposure is prolonged|extend| by decreasing the power of the dose |capacity|. Radiomodifiers— radiosensibilizators| and radioprotectors – are also used.

The expansion of the radiotherapeutic interval is promoted by: radiosensibilizators| (increase thetumours |raises| radiosensitivity| |swelling|); the satiation of the tumour|swelling| by oxygen (radiation exposure in the conditions of oxygenotherapy|); synchronization of cells division cycles; hyperthermia| and magnetotherapy|. Some|certain| chemical means strengthen|aggravate| a radio effect — fluorouracil|, methatrexat|, heparin | ( strengthen the primary damage of DNA|); weaken the postradiation| renewal of the tumour cells|cells| - |swelling| antibiotics of the acthinomycine group | — actinomycin-d|, aurentine| and others|; worsens the tumours|swelling| trophic conditions - gexamine and others.

Radioprotectors - reduce the sensitiveness of normal tissues to|by| radiation exposure. These are pharmacological preparations (serotonine, cystamine|, cysteine| and other|) hypothermia and hypoxia| (inhalation of the mixture of nitrogen with oxygen containing up|content| to 12% of oxygen, putting a tourniquet on an extremity|ending,limb|).

With the purpose of strengthening the radio defect of cells|cells| the so-called radiosensibilizators| are used. Here belong the chemical remedies which strengthen|aggravate| the primary radiation defect by the increase|rise| of satiation by oxygen of tumours|swelling| cells|cells| (heparin|), that strengthens|aggravates| the primary damage of DNA|. |behaves| They also strengthen the radio effect – (fluorouracil|, methatrecsat), loosen the postradiation| renewal of tumour cells|cells||swelling| (the antibiotics of the acthinomycine group |- acthinomycine-d |, aurentine| and others)|, worsen | theconditios of the tumour trophic| |swelling|( mexamine| and others).|aggravat

In 1938 Peterson| on the basis of the study of tumours radiosensitivity| |swelling|, developed the classification of radiosensitivity|, which in our days is acknowledged by many scientists:

1) radiosensitive tumours|swelling| - seminoma|, thymoma|, lymphosarcoma|, Ewings tumour|, basalioma and others;

2) moderately radiosensitive - epidermoidal carcinoma;

3) moderately radioresistant - adenocarcinoma;|

4) radioresistant tumours|swelling| - neurofibrosarcoma|, fibrosarcomas, teratomas, skin|skins| melanomas, chondrosarcomas| and others.

The radiosensitivity| of tumours|swelling| depends on their histological structure|building|, the degree of differentiation of cellular elements, the correlation of stroma and parenchyma (tumours|swelling| rich in stroma are | less sensitive|sensitive| to|by| radiation as a result of|because of,owing to| poor oxygenation), blood supply|, localization, the size|value| of a tumour|swelling| (tiny are |small| more sensitive|sensitively| than large ones|great,big|), the speed and character|nature| of the growth:|height| endophytic carcinomas are ||swelling| more sensible|sensitive| than exophytic| ones|shapes|.

The success of the radiotherapy of malignant tumours|swelling| depends on the method of radiation exposure and the dose. There is an optimal dose within |lines|60 to 120 Gy| depending on the histological structure,|building| localization of a tumour|swelling| and other factors.

Very high doses can affect healthy tissues around|about| a tumour|swelling|, violates the vascularisation| which causes|calls| the anoxia| of tumour|swelling| tissues and increase their radioresistance|. Consequently|so,thus|, very high doses can be harmful, and|but| small ones are simply|just| not effective. That is why|that is why| the choice of the optimal effective dose dependes on the morphological structure |nature| of a tumour|swelling|,the stage of disease, the state|figure,camp,mill| of the surrounding normal tissues, the common condition of a patient and other of the factors listed above.

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