Dosimetry. II. Dosimetry of ionizing radiation Dosimetry of ionizing radiation

Dosimetry of ionizing radiation- a section of applied nuclear physics that examines the properties of ionizing radiation, physical quantities characterizing the radiation field and the interaction of radiation with matter (dosimetric quantities). In a narrower sense of the word D. and. And. - a set of methods for measuring these quantities. The most important feature of dosimetric quantities is their connection with radiation-induced effects that arise when objects are irradiated, living and inanimate nature. Radiation-induced effects in the general sense mean any changes in the irradiated object caused by exposure to ionizing radiation . The main dosimetric quantity is ionizing radiation dose and its modifications. Task D. and. And. - description of the dose field formed in a living organism in real conditions irradiation.

The need to develop D. and. And. arose shortly after the discovery by Roentgen (W.K. Röntgen) in 1895 of the radiation named after him (see. X-rays ). The intensive accumulation of data on the biological effects of X-ray radiation, on the one hand, opened up a real prospect for its use in medicine, and on the other, pointed to the danger of uncontrolled irradiation of a living organism. As a result, the question arose about dosimetric support for the practical use of ionizing radiation sources. At the beginning of the 20th century. The main sources of radiation were radium and X-ray machines, and D. and. And. was actually reduced to dosimetry of photon-ionizing radiation (X-ray and gamma radiation). Then, as it develops technical means nuclear physics, the creation and improvement of charged particle accelerators, and especially after the launch of the first nuclear reactor in 1942, the number of sources and associated types of ionizing radiation expanded significantly. In accordance with this, methods for dosimetry of fluxes of charged particles, neutrons, high-energy bremsstrahlung radiation, etc. appeared. The list of dosimetric quantities corresponding to the tasks of the diverse practical application of ionizing radiation of various natures began to grow.

The physical basis of D. and. And. is the transformation of radiation energy in the process of its interaction with atoms or their nuclei, electrons and molecules of the irradiated medium, as a result of which part of this energy is absorbed by the substance. Absorbed energy is the root cause of the processes leading to the observed radiation-induced effects, and therefore dosimetric quantities are related to the absorbed radiation energy.

The variety of exposure conditions and the multifactorial nature of its consequences do not allow one to make do with a single dosimetric value, adapting it to changes in these conditions and factors. A whole set of dosimetric quantities is required, from which, depending on the irradiation conditions and the task at hand, the most adequate measure of the radiation-induced effect is selected. An example of such a value is the dose equivalent indicator introduced by the International Commission on Radiological Units (ICRU) for radiation safety purposes (see. Ionizing radiation dose ) at the point of the radiation field - the maximum equivalent dose inside a tissue-equivalent ball with a diameter of 30 cm when the center of this ball coincides with a given point. The practical application of this indicator encounters certain difficulties, because the problem of the adequacy of dosimetry cannot yet be considered completely resolved.

With D. and. And. use both instrumental and calculation methods. All dosimetric instruments are designed on the principle of recording radiation-induced effects in a certain model object - an ionizing radiation detector. IN early period formation of D. and. and, photographic action of ionizing radiation, chemical transformations and heat generation were used. As methods for recording elementary particles developed, so did the methods of digital imaging. And. IN modern conditions a wide range of radiation-induced effects are used. To those already mentioned we can add ionization effects in gases and condensed media, changes in the electrical properties of semiconductors, destructive damage to solids,

luminescence, scintillation, etc.

A special place is occupied by biological dosimetry, which uses quantitative radiobiological effects as a measure of dosimetric value, for example, chromosomal aberrations, changes in the morphological composition of blood, and other indicators that are uniquely related to D. and. And. (cm. Radiation sickness , Radiosensitivity ).

Methods D. and. And. can be classified according to different criteria. Thus, depending on the type of the recorded effect, ionization, photographic, chemical, luminescent, calorimetric, scintillation methods, the damage trace method, etc. are distinguished. In this case, there is an unambiguous quantitative relationship between changes in physical or chemical properties radiation detector and absorbed energy. In clinical dosimetry, ionization methods are common, in which the detector is an ionization chamber, solid-state luminescent crystals, and semiconductors. The latter are attracted by the small size of the detector.

In the USSR, stationary, portable and individual dosimetric devices are produced. Stationary dosimeters are used in clinical practice, and wearable ones are most often used to assess the radiation situation for the purposes of radiation protection. They are self-powered and therefore can be used in any environment, incl. in the field. Personal dosimeters are designed to assess the dose received by persons working in contact with ionizing radiation. They can be directly showing ( rice. a, b ) or consist of ionization or thermoluminescent detectors worn by personnel (c), the readings of which, proportional to the radiation dose, are determined on a special reading device.

Clinical dosimetry- section D. and. i., engaged in measurements and calculations of quantities characterizing the physical and biophysical effects of irradiation of patients receiving radiation therapy . The main task of clinical dosimetry is to quantitatively describe the spatial and temporal distribution of absorbed radiation energy in the body of the irradiated patient,

as well as in the search, justification and selection of individually optimized conditions for its irradiation.

The basic concepts and quantities of clinical dosimetry are absorbed dose (see. Dose of ionizing radiation ), dose field, dosimetric phantom, target. The dose field is the spatial distribution of the absorbed dose (or its power) in the irradiated part of the patient’s body, a tissue-equivalent environment or a dosimetric phantom that models the patient’s body according to the physical effects of the interaction of radiation with matter, the shape and size of organs and tissues and their anatomical relationships. Information about the dose field is presented in tabular, matrix form, and also in the form of curves connecting points of equal values (absolute or relative) of the absorbed dose. Such curves are called isodoses, and their families are called isodose maps. The absorbed dose at any point in the dose field can be taken as a conventional unit (or 100%), in particular the maximum absorbed dose, which must correspond to the target to be irradiated (i.e., the area covering the clinically identified and expected zone of its distribution).

The formation of the dose field depends on the type and source of radiation, the method of irradiation (external, internal, static, moving, etc.), the patient’s physique, as well as the type of radiation therapeutic device. Therefore, the technical documentation of the device includes an atlas of dose fields and recommendations for its practical use. If necessary (for new options and complex irradiation plans), phantom measurements of dose fields are performed in medical institutions using clinical dosimeters with small-sized ionization chambers or other (semiconductor, thermoluminescent) detectors, dose field analyzers or isodosegraphs. Thermoluminescent detectors are also used to monitor absorbed doses in patients.

The radiation therapist, together with the physicist engineer, conducts dosimetric planning - selects the irradiation method, optimizes the patient’s irradiation conditions by calculating competing options for dose fields,

determines the irradiation technology on a specific device, and also monitors the implementation of the adopted plan and its dynamic adjustment in the process of radiation treatment. In connection with the development of methods and means of computer technology, the emergence of high-speed computers with large amounts of memory and means of automated input into the computer of initial graphic and text information about the patient, a gradual transition is taking place from manual to computer planning of radiation exposure. This opens up the possibility of solving the inverse problem of clinical dosimetry - determining the irradiation conditions based on the dose field specified by the doctor.

The USSR Ministry of Health system has a radiation metrological service that checks clinical dosimeters and dosimetric certification of radiation devices. In 1988, the USSR began the transition to metrological support for radiation therapy based on direct measurements of the absorbed dose in water, traceable to the state primary standard of the unit of its power. All this helps to increase the accuracy of planning and implementation of irradiation.

According to modern international requirements, to increase the effectiveness of radiation therapy in clinical dosimetry, it is necessary to strive to dose the patient’s radiation with an error of no more than 5%, based on the absorbed dose in the target, and measurements of absorbed doses should be carried out with an error of no more than 3%.

Bibliography: Ivanov V.I. Dosimetry course, M., 1988; Klepper L.Ya. Formation of dose fields by remote radiation sources, M., 1986, bibliogr.; Krongauz A.N., Lyapidevsky V.K. and Frolova A.V. Physical foundations of clinical dosimetry, M., 1969; Ratner T.G. and Fadeeva M.A. Technical and dosimetric support for remote gamma therapy, M., 1982, bibliogr.

Dosimetry of ionizing radiation

Goal of the work:

Familiarize yourself with the basic concepts and units of measurement in dosimetry and radiation safety.
Learn to measure gamma radiation dose rate.

Radioactive radiation is an integral part of the world in which we live: life itself on Earth arose against the background of these radiations. The radiation background is determined by radioactive isotopes of the series chemical elements in the Earth's rocks, soil, water and air, as well as cosmic radiation. The main sources of background radiation include the 40 K potassium isotope and radon gas. The element potassium is widespread in the earth's crust and is found in building materials and biological tissues. The radon isotope 222 Rn is one of the intermediate products of the decay of natural uranium; this gas is released from the soil and building materials and enters the air of residential premises. Throughout the biological history of the Earth, this background has always been present and has not changed significantly. Over the past half century, to the natural sources of background radiation, humans have added fallout after testing atomic weapons, radioactive waste from the nuclear industry, the results of the Chernobyl disaster, etc. With the development of nuclear science and technology and the exploration of outer space, on the one hand, there has arisen the danger of human exposure to radiation doses significantly higher than the natural background, but, on the other hand, the possibility of using nuclear technologies in science, industry, medicine, etc. has arisen.

To quantify the degree of exposure to nuclear radiation, special dose characteristics have been introduced.

Doses of ionizing radiation

Basic physical quantity, adopted in dosimetry for measuring ionizing radiation, is dose radiation. The concept of “dose” allows for two interpretations. In accordance with the first interpretation, the radiation dose is a quantitative characteristic of radiation, in accordance with the second interpretation, it is a quantitative characteristic of the result of the interaction of radiation with matter. The term “exposure dose” given below is more consistent with the first interpretation, and the term “absorbed dose” is more consistent with the second.

The radiation situation in an area is determined by the field of ionizing radiation present there, and primarily by the field of gamma radiation due to its high penetrating ability. Interacting with air, gamma radiation causes its ionization, and the level of ionization of air corresponds to the intensity of the radiation and can serve as a characteristic of the radiation field.

Exposure doseX is defined as the ratio of the total charge of all ions of the same sign created by gamma radiation in an elementary volume of air to the mass dm of air in this volume:

. (1)

The very determination of the exposure dose allows for a simple and convenient way of measuring it: for this it is enough to measure the charge of ions of the same sign formed in the irradiated air ionization chamber.

The SI unit of exposure dose should be coulomb per kilogram. However, historically, exposure dose is usually expressed in non-systemic units - roentgens.

X-ray- this is a unit of exposure dose of photon radiation, when passing through 0.001293 g of air (this is 1 cm 3 of air under normal conditions), as a result of all ionization processes in the air, ions are created that carry one electrostatic unit of the amount of electricity of each sign.

The fact that the exposure dose is determined only for air and only for photon radiation significantly limits the scope of its application. The transition to SI units involves eliminating the concept of exposure dose from use.

The effect of ionizing radiation on a substance depends both on the composition of the substance and on the energy transferred by the radiation to this substance. The result of exposure to radiation is characterized by the absorbed dose, determined as follows.

Absorbed dose ionizing radiation D is equal to the ratio of the average energy dE transferred by ionizing radiation to a substance in an elementary volume to the mass dm of the substance in this volume:

. (2)

In the SI system, absorbed dose is measured in joules divided by kilogram (J/kg), and has a special name - gray.

Gray is equal to the absorbed dose of ionizing radiation, at which a substance weighing 1 kg is transferred to the energy of ionizing radiation equal to 1 J.

The question of the correspondence between exposure and absorbed doses can only be raised if these doses are created by gamma radiation in the air. Even so, strictly speaking, there is no one-to-one correspondence between them. The same amount of energy absorbed by air can form a different number of ion pairs depending on the energy of gamma radiation. However, this difference is small and we can say that 1 roentgen on average corresponds to the energy absorbed in the air of 87.3 erg, i.e.

1Р ≈ 0.873·10 –2 Gy or 1 Gy ≈ 115 R.

Any dose is a time-integrated characteristic. The rate of dose accumulation is characterized by the concept powerdoses is the ratio of the dose increment dD over a certain period of time dt to this time interval:

. (3)

The exposure dose rate in the SI system should be expressed in units of amperes per kilogram [A/kg]. In practice, a non-systemic unit is used - roentgens per second and its derivatives: [R/hour], [mR/hour], [μR/hour].

Absorbed dose rate in SI is measured in units of gray per second [Gy/s]. Derived units are also used - [Gy/min], [µGy/hour], etc.

Impact of ionizing radiation on body tissues.

The absorbed dose of radiation received by the substance of any living organism due to the natural radiation background of the Earth is on the order of 10 –3 Gy/year. This dose is not believed to cause observable harmful biological effects. Moreover, life itself on Earth arose, evolved and exists under conditions of a certain radiation background.

However, too large doses of radiation are dangerous to living organisms and can even lead to death.

The mechanism of action of radiation at the molecular level can be described by the following sequence of events. Radiation particles penetrating biological tissues directly or indirectly cause the ionization of many atoms, stripping electrons from them. Charged particles (alpha or beta) directly ionize atoms with their electric field, electrically neutral particles (gamma or neutrons) cause ionization after interactions in which secondary charged particles are formed, the electric field of which causes ionization.

When an atom is ionized, an electron is removed from it, which can move freely in the substance. Both a free electron and an ionized atom, within a time of 10 - 8 seconds, participate in a complex chain of reactions, as a result of which new molecules are formed, including such extremely reactive ones as free radicals. Then, in a time of 10–6 seconds, the free radicals formed react both with each other and with other molecules and, through a chain of reactions that have not yet been fully studied, can cause chemical modification biologically important molecules necessary for normal cell functioning. Subsequent biochemical changes can occur within seconds or decades after irradiation and cause immediate cell death or changes in cells that can lead to cancer.

The more energy the radiation transfers to tissues, the greater the damage caused in a living organism by radiation. The transferred energy is completely determined by the absorbed dose of radiation. However, the absorbed dose does not completely determine the effects of radiation. The fact is that with the same absorbed dose, alpha radiation or neutrons are much more dangerous than beta or gamma radiation. The reason for this is the different spatial distribution of ionization. With the same total number of ions, their higher concentration (for example, in the tracks of alpha particles) also poses a greater danger to the cells of the body.

Taking this fact into account, to assess the consequences of radiation, the dose should be multiplied by a coefficient reflecting the ability of a given type of radiation to damage body tissue. The dose recalculated in this way is called equivalent dose, and the conversion factor is radiation quality factor.

Equivalent dose ionizing radiationН – product of the absorbed dose D by the average quality factor K of ionizing radiation in a given volume element of biological tissue of standard composition

(4)

Numerical values of quality factors for various radiations are given in Table 1.

Table 1.

Quality factors for various types radiation

Types of radiation	K
X-ray and γ-radiation	1
Electrons and muons	1
Neutrons with energy:
less than 10 KeV	5
from 10 KeV to 100 KeV	10
from 100 KeV to 2 MeV	20
from 2 MeV to 20 MeV	10
more than 20 MeV	5
Protons with energies greater than 2 MeV, except recoil protons	5
Alpha particles, fission fragments, heavy recoil nuclei	20

The unit of measurement for equivalent radiation dose is J/kg, which has a special name - sievert(Sv,Sv). Note that for X-ray, beta and gamma radiation, the numerical values of the absorbed and equivalent dose are the same.

The equivalent dose more adequately takes into account the possible damage to human health from exposure to ionizing radiation of arbitrary composition. However, it is necessary to take into account the fact that some parts of the body (organs, tissues) are more sensitive to the effects of radiation than others. For example, given the same equivalent dose of radiation, cancer is more likely to occur in the lungs than in the thyroid gland, and irradiation of the gonads is especially dangerous due to the risk of genetic damage. To take into account the unequal sensitivity of different organs to radiation, a special dose characteristic is introduced - the effective equivalent dose.

Effective equivalent dose is defined as the sum of the products of equivalent doses received by each organ by the corresponding radiation risk coefficients:

(5)

Where – equivalent dose in a given tissue or organ, – weighting factor for a given tissue or organ.

The list of organs and tissues for which the summation is made, as well as the values of the weighting coefficients, are given in Table 2.

Table 2.

Weighting factors for tissues and organs.

Organ, tissue	R
gonads	0,20
bone marrow (red)	0,12
colon	0,12
lungs	0,12
stomach	0,12
bladder	0,05
breast	0,05
liver	0,05
esophagus	0,05
thyroid	0,05
leather	0,01
bone surface cells	0,01
rest	0,05
Whole body	1,00

The effective equivalent dose reflects the total effect of radiation on the body and is used as a measure of the risk of long-term effects of radiation. It is also measured in sieverts.

A dose of 1 Gy received by water will only heat it by 0.00024  C. However, for a person, a dose of 1 Sv approximately corresponds to the threshold for the appearance of deterministic consequences after irradiation or, as they say, “radiation sickness”. At a dose of 6 Sv, mortality reaches 50%. At a dose of less than 1 Sv, no obvious effects of radiation are observed, but the likelihood of cancer or genetic disorders in the offspring increases. It is believed that the increase in the likelihood of adverse effects is proportional to the dose received.

Since 1 Sv is a very large dose, they usually use the thousandth or millionth dose of a sievert: mSv, μSv.

The exposure dose rate of background gamma radiation, typical for flat areas composed of sedimentary rocks, corresponds to 10 - 20 μR/hour (or 0.1 - 0.2 μSv/hour for the absorbed dose rate). This background is typical for the territory of Belarus. The annual dose is approximately 1 – 2 mSv, which is significantly lower than the threshold for “radiation sickness”.

Radiation safety

In the Republic of Belarus, the fundamentals of legal regulation in the field of ensuring radiation safety of the population are defined in the law on radiation safety of the population.

To ensure radiation safety, the principle of regulation is applied - not exceeding certain limits of exposure doses to citizens from all sources of ionizing radiation. At the same time, all types of activities using sources of ionizing radiation are prohibited, in which the benefit obtained does not exceed the risk of possible harm to humans and society. In addition, taking into account economic opportunities and social factors, the number of exposed persons is maintained at an achievably low level and their radiation doses are minimized.

Permissible limits of average annual effective radiation doses on the territory of the Republic of Belarus are established by law and amount to 0.001 sieverts per year for the entire population, 0.02 sieverts per year for personnel working with radiation sources.

The regulated values of the main limits of radiation doses do not include doses created by natural radiation and man-made background radiation, as well as doses received by citizens (patients) during medical exposure.

To determine the radiation doses received, it is necessary to measure not only the level of external exposure due to sources outside the human body. It is also necessary to determine the so-called internal exposure caused by radioactive substances contained in the inhaled air and consumed food. Internal exposure is not directly measured - control over internal exposure is carried out by measuring the content of radionuclides in the air and food and calculating the resulting radiation doses.

The main quantitative criterion for internal human exposure is annual income(the amount of radioactive substances that enter the body through the respiratory and digestive organs). Annual receipts are normalized by establishing permissible levels content of radionuclides in the air and in various food products, taking into account their average annual consumption.

For example, the permissible level of radionuclide 137 Cs in drinking water is 10 Bq/kg, and in milk – 100 Bq/kg.

When working with radioisotope sources of gamma radiation, the expected radiation dose rate can be calculated if the radionuclide of the source and its activity are known. The exposure dose rate of gamma radiation at a distance R from an isotropic point source with activity A is found by the formula

, (6)

Where the coefficient G (gamma constant) is determined by the emission spectrum of the radionuclide. The values of coefficients Г for various radionuclides can be found in reference literature. For radionuclides used in laboratory practice, the gamma constants G are as follows:

Cs-137 3.24 R cm 2 / hour mCi,

Co-60 12.85 R cm 2 / hour mCi,

Na-22 11.85 R cm 2 / hour mCi.

The indicated dimension Г requires substituting into formula (6) the activity in millicuries (1 mCi = 3.7·10 7 Bq), the distance R in centimeters, and the exposure dose rate will be obtained in roentgens per hour.

Formula (6) can be used if the dimensions of the source and observation area are much smaller than R, and there is no significant absorption of radiation on the way from the source to the observation area.

The presence of a substance that absorbs gamma radiation leads to a decrease in dose rate. To a first approximation, absorption can be described by the formula

D(x) = D 0 ·exp(– x). (7)

Here D 0 is the dose rate in the absence of absorption, D(x) is the dose rate taking into account absorption, x is the path of gamma radiation in the absorber,  – linear coefficient attenuation, depending on the absorber substance and the energy of gamma radiation.

Formula (7) is applicable only for monoenergetic gamma radiation and does not take into account the contribution of radiation scattered in the absorber.

If there is a plate of thickness d that absorbs gamma radiation, then the value x will coincide with d only in the case of normal passage of the gamma radiation beam through the plate.

Values of coefficients  for various substances and gamma radiation energies can be found in reference literature. For Cs-137 radiation with an energy of 662 keV, the linear attenuation coefficient in lead is 1.18 cm–1. Absorption of gamma radiation in air can usually be neglected over distances of several meters.

experimental part

Exercise 1.

Study the dosimeter operating manual DKG – AT2503A. Turn on the device, look at the image on the indicator. Go to menu submode. Go through all the menu messages and learn how to switch the device to the submodes of dose rate indication and accumulated dose indication. Reset the accumulated dose. Check the selection of alarm thresholds for dose and dose rate.

Subsequent dose rate measurements should be carried out with an error of 50% in accordance with brief instructions for working with the DKG-AT2503A dosimeter: the holding time before the first reading is taken is 4 minutes, the time before each subsequent reading is taken is 4 minutes, a total of three readings are taken and averaged.

Task 2.

Measure the dose rate of gamma radiation on the desktop. Monitor changes in the current readings of the device over time. Record the resulting dose rate value and measurement error.

Measure the dose rate in one of the following places (at the teacher’s choice): near the wall of the laboratory, on the windowsill, on the surface of a safe with radioactive sources, etc.

Compare the obtained values with each other and with the results of measurements on other tables.

Compare these data with the typical value of the natural background gamma radiation level.

Estimate the expected annual dose at the obtained dose rate on the desktop.

Task 3.

Obtain a radioactive source. Using the source number, determine its activity. Place the source on the desktop and place the dosimeter above the source on a special stand.

Measure the distance between the center of the source and the geometric center of the sensitive volume of the detector, which is marked with marks on the dosimeter body.

Measure the absorbed dose rate with the above placement of the source and dosimeter.

Compare the dose rate measurement results with the calculated value, taking into account the previously measured background radiation value.

Estimate the expected annual dose at the obtained dose rate at a selected distance from the source.

Compare the expected annual dose estimate with the acceptable dose limit.

In the dose indication mode of the dosimeter, view the value of the dose accumulated during the laboratory work.

Draw conclusions.

Task 4.

Measure the dose rate by placing a lead plate of known thickness (4 – 7 mm) between the source and the dosimeter in the same location.

Compare the obtained measurement results with calculations using formula (7).

Calculate the source activity under the same irradiation conditions, under which the annual dose limit is reached in one working day. (When working on the atomic project in the 40s of the last century in the USA, a daily dose limit of 0.1 roentgens was used. Now this is the annual dose limit for the population.)

Estimate how many times a dovetail-type lead block 5 cm thick attenuates gamma radiation from Cs-137.

Methods of dosimetry and radiometry, NRB

Dosimetry: quantitative assessment of the absorbed energy of ionizing radiation. The development of dosimetry was initially determined by the need to protect humans from ionizing radiation. Soon after the discovery of X-rays, biological effects that occurred when humans were irradiated were noticed. There is a need to quantify the degree of radiation hazard.

Radiation doses: Exposure dose = radiation dose (C/kg, extra-systemic P – x-ray) – quantitative characteristic ionizing ability of gamma radiation in air. Meaning: the amount of ionizing radiation energy falling on an object during irradiation. Absorbed dose = radiation dose (1Gy=1J/kg=100 rad, extra-systemic rad) – the amount of ionizing radiation energy transferred to the substance (D=de/dm). 1Gy=1J of energy of any kind is absorbed by 1kg of mass of substance

Dose load regulation in Russia (NRB-99) “Radiation Safety Standards/NRB-99/2009 SanPiN” from September 1, 2009 BASIC SANITARY RULES FOR ENSURING RADIATION SAFETY (OSPORB 99/2010)

RADIATION SAFETY STANDARDS NRB-99/2009 (introduced on September 1, 2009) Sanitary rules and regulations SanPiN I. Scope 1.1. Radiation safety standards NRB-99/2009 (hereinafter - the Norms) are applied to ensure human safety in all conditions of exposure to ionizing radiation of artificial or natural origin. The requirements and standards established by the Norms are mandatory for all legal entities and individuals, regardless of their subordination and form of ownership, as a result of whose activities human exposure is possible, as well as for the administrations of the subjects Russian Federation, local authorities authorities, citizens of the Russian Federation, foreign citizens and stateless persons living on the territory of the Russian Federation. These Standards establish the main dose limits, permissible levels of exposure to ionizing radiation to limit exposure of the population in accordance with the Federal Law of January 9, 1996 N 3-FZ " On Radiation Safety of the Population" The standards apply to the following sources of ionizing radiation: - man-made sources due to the normal operation of man-made radiation sources; - man-made sources as a result of a radiation accident; - natural sources; - medical sources.

Categories of persons: A – personnel permanently or temporarily working with sources of ionizing radiation; B – persons (population and personnel) who do not work directly with AI may be exposed to AI, for example, due to their living conditions or work conditions (cleaners, etc.); B – the entire rest of the population Dose limits have been established for all three groups (p. 110 Pivovarov, Mikhalev, 2004, table below)

Radiation safety standards adopted in Russia (NRB-99) Biological effect of identical absorbed doses different types radiation on the body is not the same (LET) Weighting factor: For x-ray, - and - radiation K=1; For -radiation K=20, the equivalent dose is equal to the product of the absorbed dose by the weighing factor. Effective dose (E, Sv - sievert) - a measure of the risk of long-term consequences of irradiation of the whole body and individual organs, is equal to the product of the equivalent dose in organs and tissues by the weighting factor (cm .table below)

Calculation of maximum permissible doses (MAD): concept of critical organs 1st group - whole body, gonads, red bone marrow; Group 2 – muscles, thyroid gland, adipose tissue, liver, kidneys, spleen, gastrointestinal tract, lungs, lens of the eye, etc. Group 3 – skin, bone tissue, hands, forearms, legs, feet and etc.

Weighting factors for organs and tissues (based on the rate of cellular turnover) Gonads0.20 Bone marrow (red)0.12 Large intestine (rectum, sigmoid and descending colons) 0.12 Lungs0.12 stomach0.12 Bladder0.05 Breast0. 05 Liver0.05 Esophagus0.05 Thyroid gland0.05 Skin0.01 Cells of bone surfaces0.01 Other organs (adrenal glands, brain, cecum, ascending and transverse colon, small intestine, kidneys, muscle tissue, pancreas, spleen, thymus gland, uterus) 0.05

Main dose limits according to NRB-09 personnel group A personnel group B (1/4 of group A) Population Effective dose on average for any consecutive 5 years, mSv/year 20 (50)5 (12.5)1 ( 5) Equivalent dose, mSv/year In the lens of the eye 15037.515 in the skin In the hands and feet

Dosimetry methods Physical: based on a change in the magnitude of any physical effect caused by the absorption of ionizing energy in a substance (ionization, glow, change in conductivity, etc.) Chemical: based on measuring changes in chemical systems under the influence of AI (valency of the element, angle of rotation of the plane of polarization of light, number of molecules of this type) Biological: based on registration of biological changes under the influence of AI at the molecular, subcellular, cellular, tissue level (mutations, chromosome rearrangements, survival, etc.) Biophysical: EPR dosimetry

1. Ionization method of dosimetry or Ionization chamber method In a chamber filled with gas (air), ions are formed, which, when placed in an electric field, collect on the electrodes and create electricity. (absorbed dose measurement) An ionization chamber is the simplest gas-filled detector. It is a system of two or three electrodes in a volume filled with gas (He+Ar, Ar+C2H2, Ne). The disadvantage of the ionization chamber is the very low currents. This disadvantage of the ionization chamber is overcome in gas-amplified ionization detectors. To register neutrons, a special modification of the ionization chamber is used - a fission chamber.

Fission chamber A fission chamber is a special modification of an ionization chamber designed to register neutrons. Fission chambers use a fission reaction. The inner surface of such an ionization chamber is covered with a thin layer of fissile material (235 U, 238 U, 239 Pu, 232 Th). Pulses from high-energy fission fragments cause greater ionization in the chamber gas and, accordingly, have a large amplitude. ionization chamber Diagram of a fission chamber. The dimensions of the fission chambers can be several times smaller than in the figure. However, the registration efficiency in a single-layer fission chamber even for thermal neutrons is small (fractions of a percent) and fission chambers are often made multilayer.

4. Scintillation method The light output of a number of substances (scintillators) depends linearly on the absorbed dose over a wide dose range. Such substances in combination with a photomultiplier are used as dosimeters. Advantages: -the ability to register almost any type of ionizing radiation; - Possibility of measuring the energy of particles or quanta - High efficiency of radiation detection Disadvantage: it is necessary to approximate the composition of the scintillator and absorber substance as much as possible, see Maksimov, Odzhagov Luminescent substances - scintillators: Inorganic and organic solids (zinc sulfide activated by silver; anthracene) Organic plastic (polystyrene with the addition of n-terphenyl) Liquid organic (solution of n-terphenyl in an aromatic compound); Gas (xenon)

Portable w/c counter Triathler(Hidex) with alpha/beta separation (battery powered possible) Certified MVI "Radium Institute" 3 H - SP (NRB-99) Sr-90 (for Cherenkov radiation and w/c radiochemistry)

10 6 Gy – for coloring crystals and glasses" title="5. Chemical methods of dosimetry Advantages: possibility of achieving high degree similarity of the dosimeter to the irradiated object in terms of chemical composition and in form. Range of application chemical methods: For doses > 10 6 Gy – for coloring crystals and glasses" class="link_thumb"> 20 5. Chemical methods of dosimetry Advantages: the ability to achieve a high degree of similarity of the dosimeter to the irradiated object in chemical composition and shape. Range of application of chemical methods: For doses > 10 6 Gy - for coloring crystals and glasses For doses from 10 4 to 10 5 Gy - for reactions in the liquid phase For doses 10 6 Gy - for coloring crystals and glasses "> 10 6 Gy - for staining of crystals and glasses For doses from 10 4 to 10 5 Gy - by reactions in the liquid phase For doses of 10 6 Gy - by coloring of crystals and glasses" title="5. Chemical methods of dosimetry Advantages: the ability to achieve a high degree of similarity dosimeter to the irradiated object by chemical composition and shape. Range of application of chemical methods: For doses > 10 6 Gy - for coloring crystals and glasses"> title="5. Chemical methods of dosimetry Advantages: the ability to achieve a high degree of similarity of the dosimeter to the irradiated object in chemical composition and shape. Range of application of chemical methods: For doses > 10 6 Gy – for coloring crystals and glasses">!}

5.1. Liquid (water) chemical detectors are based on reactions occurring between substances dissolved in water and the products of radiolysis of water. Ferrosulfate detector (Dosimeter Fricke, Tsyb, 2005, p. 82) Based on the property of divalent iron ions Fe 2+ to be oxidized in an acidic environment by OH* radicals to ferric Fe 3+ In a standard detector, at an absorption of 100 eV, 15.6 ferric ions are formed. The amount of Fe 3+ ions is determined by the color density of the reagent (potassium thiocyanate salt KCNS). The color intensity is proportional to the absorbed dose. The range of measured gamma radiation doses is rad. The detector is sensitive to organic impurities

Nitrate detector Based on the property of nitrate ions NO 3 - to be reduced by atomic hydrogen to nitrite ions NO 2 - Nitrites are detected by special indicators Cerium detector Quadrivalent cerium ions Ce 4+ are reduced by atomic hydrogen to trivalent Ce 3+

5.2. Chemical detectors based on chlorine-substituted hydrocarbons The increased sensitivity of detectors is explained by the emergence chain reactions in the detector material, due to which a large amount of final products detector based on chloroform (CHCl 3) – when chloroform is irradiated, hydrochloric acid (HCl) is formed. The yield of hydrochloric acid increases in the presence of oxygen. Hydrochloric acid can be detected using any acid-base indicator (for example, bromocresol purple). A detector based on carbon tetrachloride (CCl 4) is insensitive to CCl 4 radiation when introducing additives with mobile hydrogen atoms into it, which can significantly increase the yield of the product - hydrochloric acid. acids.

100 V/m Wide dose rate range > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Em" title="(!LANG :Individual dosimeters SYNODYS / MGPI EM resistance exceeds requirements >100 V/m Wide dose rate range > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Em" class="link_thumb"> 27 !} Personal dosimeters SYNODYS / MGPI EM resistance exceeds requirements >100 V/m Wide dose rate range > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Emax > 150 keV 100 V/m Wide dose rate range > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Em" > 100 V/m Wide dose rate range > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Emax > 150 keV" > 100 V/m Wide power range doses > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Em" title="Individual dosimeters SYNODYS / MGPI EM resistance exceeds requirements >100 V/m Wide dose rate range > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Em"> title="Personal dosimeters SYNODYS / MGPI EM resistance exceeds requirements >100 V/m Wide dose rate range > 10 Sv/h Wide energy range DMC 2000 S 50 keV to 6 MeV DMC 2000 X 20 keV to 6 MeV DMC 2000 XB 20 keV to 6 MeV + Beta Em"> !}

Individual gamma-neutron dosimeters DMC 2000 GN SYNODYS Electronic direct-reading dosimeter for gamma radiation and neutrons in a wide energy range. Neutron measurements: Dose: 10 µSv – 10 Sv Dose rate: 10 µSv/h – 10 Sv/h Energy: 0.025 eV – 15 MeV Gamma measurements: Dose: 1 µSv – 10 Sv Dose rate: 0.1 µSv/h – 10 Sv/h Energy: 50 keV – 6 MeV Polyethylene / Li6 / B10 converter/absorber (PTB license)

Personal dosimeter DIS, SYNODYS / RADOS Measurement range: Hp(10) 1 uSv to 0.5 Sv (40Sv) Hp(0.07) 10 uSv to 0.5 Sv (40Sv) Energy range: Hp(10) +30% from 15 keV to 9 MeV Hp(0.07) +30% from 6 keV to 9 MeV Beta particles: Hp(0.07) +10 … -50% from 240 keV to 2.2 MeV Weight and size: 41x44x9 mm; 20 g without holder

Methods of biological dosimetry (human) = retrospective dosimetry (identifying the effects of dose loads on the body during external and internal irradiation): Cytogenetic: recording the frequency of chromosomal rearrangements in peripheral blood or bone marrow cells; Molecular genetic: identification of the frequency of cells carrying somatic mutations at individual gene loci in peripheral blood using flow cytometry; Hematological: registration of the quantity and ratio of formed blood components during the acute radiation period, Immunobacteriological: measurement of the immune reactivity of the irradiated organism and the composition of the microflora of the integumentary tissues and intestines; Biochemical: changes in the biochemical properties of biological fluids (blood and urine) Biophysical: registration of changes in the biophysical properties of molecules (bioluminescence, electrochemiluminescence); ESR dosimetry of tooth enamel.

Methods based on chromosomal aberrations Unstable aberrations: karyological test - officially adopted by the IAEA in 1986 (proposed in the 1960s) Basis of the method - Dependence of the number of aberrations (mainly dicentrics and rings) in lymphocytes of peripheral blood and bone marrow on dose radiation Gives an idea of the average dose absorbed by the body; Lymphocytes are the most radiosensitive components of the blood. If there is a lack of lymphocytes in the peripheral blood, it is possible to use lymphocytes from the bone marrow. The dose range is from the natural background level to 1-2 Gy. The method became widespread after the development of a method for culturing human lymphocytes: Basics of the method: - 1 ml of blood contains 1-3 million small lymphocyte cells capable of dividing during cultivation. -In the peripheral blood, lymphocytes are in a naturally synchronized state (G0); -The level of spontaneous aberrations in clinically healthy people is not high (1-1.5%) -Long first mitotic cycle (2 days); -The number of aberrations during irradiation in vivo and in vitro are the same!! Limitations: the method gives adequate results within short period after acute irradiation due to the natural washing out of aberrant lymphocytes from the bloodstream (2-3 months) - the number of aberrant cells decreases by 2 times every 2-3 years. Retrospective assessment of doses in chronically exposed people and in long-term periods is DIFFICULT due to the effect of small doses (individual scatter of values is too large)

Stable aberrations (translocations) - a “new” method for assessing doses in the long-term period after irradiation Translocations are generated into the peripheral blood from irradiated bone marrow stem cells - persist for a long time; Experimentally (1970s) a correlation was established between physical doses and the yield of translocations in individuals who survived the atomic bombing in 1945. The method of fluorescent in situ hybridization of cells (FISH), promoted after 1986, is used - the method is based on selective staining of homologous pairs of chromosomes using molecular probes specific to certain DNA sequences. Advantages: currently the only method for retrospective assessment of doses in the long term! Problems: Choosing chromosomes for staining; Selection of types of translocations; Selecting the period after irradiation; Assessment of the spontaneous level of translocations - translocations in unirradiated individuals are more common than dicentrics. In the period from 10 to 65 years, the spontaneous level of translocations increases from 1.5 to 15 per 1000 cells; Selection of calibration dependencies; Expensive method. The chromosome that is labeled with green and red spots (upper left) is the one where the wrong rearrangement is present.

Micronucleus test Estimation of the number of micronuclei in a population of cells and their descendants. Advantages of the method: -Simplicity (compared to chromosome analysis) -Expressness -Can be used for asynchronous cell populations Disadvantages of the method: -the formation of micronuclei in blood cells occurs as a result of human exposure not only to ionizing radiation, but also to many other mutagens, that is, factors , capable of causing hereditary changes (mutations). These include ultraviolet radiation, numerous chemical compounds, including some medications, household chemical products, etc. Therefore, the number of micronuclei cannot be unambiguously associated only with the dose of ionizing radiation. It is advisable to use the micronucleus test method not for assessing doses, but only for identifying high-risk groups during mass surveys of the population.

Dosimetry based on molecular genetic methods Gene mutations occur in irradiated cells along with structural mutations (aberrations) The dependence of the frequency of induction of mutations in individual genes with increasing dose (mutations/Gy) is shown. Due to the low yield of mutations per unit dose, analysis of a large number of cells is required (), therefore peripheral blood cells are used; Flow cytometry methods; Currently, mutations in five genetic loci controlling hemoglobin, the major histocompatibility complex, T-cell receptor, glycophorin A, and hypoxanthine-guanine phosphoribosyltransferase are being studied. In general, the methods are in the development stage (see Tsyb et al., 2005, c)

Mutations at the T-cell receptor locus (TCR, ТкР) The frequency of TCR-mutant lymphocytes correlates with the dose in the first few years after irradiation, because mutations at the TCR locus occur in mature lymphocytes. The half-life of mutant cells is about two years. The possibility of using the method is limited to 2-4 years after irradiation. The theoretical sensitivity threshold of the method is 0.5 Gy. Experimental dose dependence has not yet been revealed. The frequency of TCR-mutant cells correlates with the frequency of unstable aberrations. It is also possible to determine the frequency of mutations at the hypoxanthine-guanine phosphoryltransferase (HGPRT) locus and a number of other loci. T-cell receptors (TCR, ТкР) surface protein complexes of T-lymphocytes responsible for recognizing processed antigens associated with molecules of the major histocompatibility complex (MHC) on the surface of antigen-presenting cells. protein T-lymphocytes of the major histocompatibility complex antigens of antigen-presenting cells TCR consists of two subunits , anchored in cell membrane and is associated with the multisubunit CD3.CD3 complex. The interaction of the TCR with the MHC and its associated antigen leads to the activation of T lymphocytes and is a key point in triggering the immune response.

Lifelong dosimetry - decades after irradiation In the long-term period after irradiation, the frequency of selectively neutral gene mutations occurring in long-lived stem-type cells is assessed: Flow cytometric analysis of the frequency of cells with mutations at the glycophorin A locus Dose dependence has been established; A high reproducibility of the parameters of the linear dose-effect relationship has been established; the field of radiation exposure (from 10 to 45 years) has been shown to correlate with the frequency of stable aberrations Common problems methods for assessing gene mutations: The number of cells with gene mutations increases under the influence of factors of a diverse nature, and not just AI - there is no specific marker of radiation exposure. Therefore, the frequency of mutations at the glycophorin A locus is considered as an integral indicator of genotoxic exposure throughout a person’s life. Glycophorins are a group of main transmembrane sialoglycoproteins (polypeptides) of erythrocytes. They consist of ~60% carbohydrate component, 40% protein component. erythrocytes The presence of glycophorins in the erythrocyte membrane was first shown in 1791 (Fairbanks et al). Four types of glycophorins (glycophorins A, D, C and D) make up 2% of all erythrocyte membrane proteins. In this case, glycophorin A predominates, present in an amount of 59·10 molecules per cell. The amounts of glycophorins B, C and D are 0.83·10, 0.51·10 and 0.2·10, respectively. Thanks to the availability large quantity sialic acid residues, glycophorins are responsible for approximately 60% of the negative charge on the surface of red blood cells. sialic acid These molecules play important role in the interaction of red blood cells with each other, with other blood cells and with the endothelium.endothelium

Population estimate cellular composition peripheral blood Study of the dynamics of the number of neutrophils and platelets Leuko-lymphocyte index - the conventional sum of leukocytes and lymphocytes of peripheral blood Methods mainly work in the field of high doses

EPR dosimetry Registration of EPR centers in the enamel of extracted teeth; the method is used to assess the individual radiation dose; Detection: spectroscopic registration of EPR signals from the enamel of teeth of irradiated individuals; The physical basis of the method: the accumulation of radiation-induced radicals (CO 2 -) in the chemical structure of hydroxyapatite, which is part of the biological tissue - tooth enamel. Hydroxyapatites (Ca 10 (PO 4) 6 (OH 2)) are the main form of calcium phosphate in bones and teeth.

History of the method - In 1968, during EPR spectroscopy of the femur and tooth enamel of mammals irradiated at doses of Gy, a strict linear dependence of the EPR signal value on the dose was discovered. –In tooth enamel, radiation-induced resonance centers give the most intense signals than in other tissues. Enamel is formed during childhood. –The signals are based on the formation of free radicals CO 2 -3 as a result of the capture of free electrons appearing in irradiated enamel by the CO complex. Advantages of the method: Long lifetime of EPR centers - they can persist in tooth enamel (10 7)10 9 years (with t=25 o C). Disadvantages of the method: resonant centers are formed under the influence of ultraviolet radiation; Labor-intensive collection of material (extracted teeth); In the presence of osteotropic radionuclides (90 Sr), additional EPR centers are formed.

Method for determining absorbed doses of external gamma radiation from electron paramagnetic resonance spectra of dental enamel (GOST R) SAFETY IN EMERGENCY SITUATIONS POPULATION CONTROL DOSIMETRIC METHOD FOR DETERMINING ABSORBED DOSES OF EXTERNAL GAMMA RADIATION USING SPECTRA OF ELECTRONIC PARAMAGNETIC RESONANCE OF DENTAL E MALI Final edition Official publication GOSTSTANDARD OF RUSSIA Moscow GOST R DEVELOPED by the Research Testing Center for Radiation Safety of Space Objects of the Federal Administration for Medical, Biological and Extreme Problems under the Ministry of Health and Medical Industry of Russia with the participation of the Institute of Biophysics of the Ministry of Health and Medical Industry of Russia, the All-Russian Research Institute of Physical, Technical and Radio Engineering Measurements of the State Standard of Russia, the All-Russian Research Institute of Mineral Raw Materials of Geolcom under the Council of Ministers of Russia, Limited Liability Partnership "Triton" INTRODUCED by the Technical Committee for Standardization TC 71 "Civil Defense, Prevention and Response to Emergency Situations" INTRODUCED Standards Publishing House, 1995

Dosimetry of ionizing radiation

a section of applied nuclear physics that examines the properties of ionizing radiation, physical quantities characterizing the radiation field and the interaction of radiation with matter (dosimetric quantities). In a narrower sense of the word D. and. And. - a set of methods for measuring these quantities. The most important feature of dosimetric quantities is their connection with radiation-induced effects that occur during irradiation of living and inanimate objects. Radiation-induced effects in a general sense mean any changes in the irradiated object caused by exposure to ionizing radiation (Ionizing radiation). The main dosimetric quantity is the Dose of ionizing radiation and its modifications. Task D. and. And. - description of the dose field formed in a living organism under real irradiation conditions.

The need to develop D. and. And. arose shortly after the discovery by Roentgen (W.K. Röntgen) in 1895 of the radiation named after him (see X-rays (X-rays)). The intensive accumulation of data on the biological effects of X-ray radiation, on the one hand, opened up a real prospect for its use in medicine, and on the other, pointed to the danger of uncontrolled irradiation of a living organism. As a result, the question arose about dosimetric support for the practical use of ionizing radiation sources. At the beginning of the 20th century. The main sources of radiation were X-ray machines and D. and. And. was actually reduced to dosimetry of photon-ionizing radiation (X-ray and gamma radiation). Then, with the development of technical means of nuclear physics, the creation and improvement of charged particle accelerators, and especially after the launch of the first nuclear reactor in 1942, the number of sources and associated types of ionizing radiation expanded significantly. In accordance with this, methods for dosimetry of fluxes of charged particles, neutrons, high-energy bremsstrahlung radiation, etc. appeared. The list of dosimetric quantities corresponding to the tasks of the diverse practical application of ionizing radiation of various natures began to grow.

The variety of irradiation conditions and its multifactorial consequences do not allow one to make do with a single dosimetric value, adapting it to changes in these conditions and factors. A whole dosimetric quantity is required, from which, depending on the irradiation conditions and the task at hand, the most adequate measure of the radiation-induced effect is selected. An example of such a value is the equivalent dose indicator introduced by the International Commission on Radiological Units (ICRU) for radiation safety purposes (see Dose of ionizing radiation) at a point in the radiation field - the maximum equivalent dose inside a tissue-equivalent ball with a diameter of 30 cm when the center of this ball coincides with a given point. The practical application of this indicator encounters certain difficulties, because the problem of the adequacy of dosimetry cannot yet be considered completely resolved.

With D. and. And. use both instrumental and computational methods. All dosimetric instruments are designed on the principle of recording radiation-induced effects in a certain model object - an ionizing radiation detector. In the early period of development of D. and. and, photographic effects of ionizing radiation, chemical transformations and heat were used. As methods for recording elementary particles developed, so did the methods of digital imaging. And. In modern conditions, a wide range of radiation-induced effects is used. To those already mentioned can be added ionization effects in gases and condensed media, changes in the electrical properties of semiconductors, destructive solids, luminescence, scintillation, etc.

A special place is occupied by the biological one, which uses quantitative radiobiological effects as a measure of dosimetric magnitude, for example, chromosomal aberrations, changes in the morphological composition of the blood, and other indicators that are uniquely related to D. and. And. (see Radiation sickness, Radiosensitivity).

Methods D. and. And. can be classified according to different criteria. Thus, depending on the type of the recorded effect, there are ionization, photographic, chemical, luminescent, calorimetric, scintillation methods, the damage trace method, etc. In this case, there is an unambiguous quantitative relationship between the change in the physical or chemical properties of the radiation detector and the absorbed energy. In clinical dosimetry, ionization methods are common, in which solid-state luminescent crystals and semiconductors serve as detectors. The latter are attracted by the small size of the detector.

In the USSR, stationary, portable and individual dosimetric devices are produced. Stationary dosimeters are used in clinical practice, and wearable ones are most often used to assess the radiation situation in order to radiation protection. They are autonomous and therefore can be used in any environment, incl. in the field. Personal dosimeters are designed to assess the dose received by persons working in contact with ionizing radiation. They can be directly showing ( rice. a, b ) or consist of ionization or thermoluminescent detectors (c) worn by personnel, which, proportional to the radiation dose, are determined on a special reading device.

Clinical dosimetry- section D. and. i., engaged in measurements and calculations of quantities characterizing the physical and biophysical effects of irradiation of patients receiving radiation therapy (Radiation therapy). The main task of clinical dosimetry is to quantitatively describe the spatial and temporal distribution of absorbed radiation energy in an irradiated patient, as well as to search, justify and select individually optimized conditions for his irradiation.

The basic concepts and quantities of clinical dosimetry are absorbed dose (see ionizing radiation (Ionizing radiation dose)), dosimetric phantom, . The dose field is the spatial distribution of the absorbed dose (or its power) in the irradiated part of the patient’s body, a tissue-equivalent environment or a dosimetric phantom that models the patient according to the physical effects of the interaction of radiation with matter, the shape and size of organs and tissues and their anatomical relationships. Information about the dose field is presented in tabular, matrix form, and also in the form of curves connecting points of equal values (absolute or relative) of the absorbed dose. Such curves are called isodoses, and their families are called isodose maps. The absorbed dose at any point in the dose field can be taken as a conventional unit (or 100%), in particular the maximum absorbed dose, which must correspond to the target to be irradiated (i.e., the area covering the clinically identified and expected zone of its distribution).

The radiation specialist, together with a physicist engineer, conducts dosimetric planning - selects the irradiation method, optimizes the patient's irradiation conditions by calculating competing options for dose fields, determines the irradiation technology on a specific device, and also monitors the implementation of the adopted plan and its dynamic adjustment during the radiation treatment process. In connection with the development of methods and means of computer technology, the emergence of high-speed computers with large amounts of memory and means of automated input into the computer of initial graphic and text information about the patient, a gradual transition is taking place from manual to computer planning of radiation exposure. This opens up the possibility of solving the inverse problem of clinical dosimetry - determining the irradiation conditions based on the dose field specified by the doctor.

1. Small medical encyclopedia. - M.: Medical encyclopedia. 1991-96 2. First health care. - M.: Great Russian Encyclopedia. 1994 3. encyclopedic Dictionary medical terms. - M.: Soviet Encyclopedia. - 1982-1984.

See what “Dosimetry of ionizing radiation” is in other dictionaries:

dosimetry of ionizing radiation- radiation dosimetry - [A.S. Goldberg. English-Russian energy dictionary. 2006] Topics energy in general Synonyms radiation dosimetry EN radiation dos ... Technical Translator's Guide

The main methods for recording ionizing radiation: ionization, ions formed by radiation are recorded, scintillation, light flashes arising in a special material are recorded, calorimetric registration... ... Wikipedia

- (from the Greek dosis share, portion, reception and metreo measure), measurement, research and theory. calculations of those characteristics of ionizing radiation (and their interaction with the environment), on which radiation depends. effects in irradiated objects of living and inanimate nature.... ... Physical encyclopedia

DOSIMETRY- a set of methods for determining (see) ionizing radiation, measuring levels radioactive contamination and the effects of radioactive radiation on the human body with the help of (see) ... Big Polytechnic Encyclopedia

- (from Dose and...metry) a field of applied nuclear physics in which physical quantities that characterize the effect of ionizing radiation on various objects are studied (see Radiation dose) ... Big Encyclopedic Dictionary

DOSIMETRY- ionizing radiation, a field of applied nuclear physics that studies physical quantities characterizing the effect of ionizing radiation on the environment, including biological objects (organisms, tissues), as well as methods and means for... ... Veterinary encyclopedic dictionary

DOSIMETRY, DOSIMETRY, and; and. [from Greek dosis dose and metreō measure] 1. A set of methods for determining the dose of radioactive radiation. 2. The field of applied physics in which physical quantities characterizing the action of ionizing ... ... are studied. encyclopedic Dictionary

An area of applied physics in which physical quantities are studied that characterize the effect of ionizing radiation (See Ionizing radiation) on objects of living and inanimate nature, in particular doses (See Dose) of radiation, as well as methods and... ... Great Soviet Encyclopedia

- (see ..metry) a set of methods for determining the dose of ionizing radiation, levels of radioactive contamination, the impact of radioactive radiation on the human body, etc.; dosimetric measurements are carried out by dosimeters. New dictionary… … Dictionary foreign words Russian language

dosimetry- I dosime/triya = dosimetry/i; (from the Greek dósis dose and metréō measure) 1) A set of methods for determining the dose of radioactive radiation. 2) The field of applied physics in which physical quantities characterizing the action of ionizing ... ... are studied. Dictionary of many expressions

G. A set of methods for determining the dose of ionizing radiation, the level of radioactive contamination, the effects of radioactive radiation on the human body, animal body, etc. Ephraim's explanatory dictionary. T. F. Efremova. 2000... Modern Dictionary Russian language Efremova

Dosimetry is a branch of applied nuclear physics that examines ionizing radiation, physical quantities characterizing the radiation field or the interaction of radiation with matter, as well as principles and methods for determining these quantities. Dosimetry deals with those physical quantities of ionizing radiation that determine its chemical, physical and biological effects. The most important property of dosimetric quantities is the established relationship between the measured physical quantity and the expected radiation effect.

HISTORY OF DEVELOPMENT OF DOSIMETRY

In the early years of scientists' work with X-rays and radioactive elements, no attempts were made to limit human exposure, despite understanding the dangers of ionizing radiation. Only almost 7 years after the discovery of X-ray radiation, the English scientist Rollins in 1902 proposed limiting the irradiation of workers to a dose that caused blackening of the photographic emulsions used at that time, which corresponded to an exposure dose of 10 R/day.

However, the first clear idea of a physically based concept of dose, quite close to the modern one, was developed by the Swiss physician and physicist Christen in the article “Measurement and Dosage of X-Rays.” Before physically based methods began to be used in dosimetry, biological dosimetry methods were used. Thus, the early lesions of the skin in people working with ionizing radiation, discovered and subsequently well studied, served as the basis for proposals from the world's leading radiologists to limit occupational exposure.

Subsequently, these issues began to be dealt with by specially created national committees for protection against ionizing radiation, which were created in 1921 in many countries. “During these years, such a unit of x-ray radiation as the x-ray was introduced. In 1925, the American radiologist Matcheller recommended a dose equal to 340 R (about 100 mR / day) as a tolerable (tolerable) dose per month. However, only in 1934, The International Commission on Protection against X-Rays and Radium, which was created in 1928 (now the International Commission on Radiological Protection (ICRP), first recommended that national governments adopt a tolerance dose of 200 mR/day. In 1936, this commission reduced the indicated dose is up to 100 mR/day.

Further accumulation of scientific data on the effects of ionizing radiation, in particular on the reduction in life expectancy of experimental animals, the term tolerant dose was replaced by a more cautious one - maximum permissible dose (MAD). Already in 1948, the ICRP recommended reducing the maximum exposure limit for professionals to 50 mR/day (6 Sv over 40 years of work), formulating the concept of the maximum exposure limit as “a dose that should not cause significant damage to the human body at any time during its life.”

In 1953, the International Commission on Radiation Units and Measurements (which was created in 1925) introduced a generally applicable dose quantity, the absorbed dose, instead of the x-ray, which began to be used as a unit of exposure dose. In 1958, based on new scientific data, the ICRP lowered the driving limit to 0.6 Sv for people under 30 years of age. IN former USSR, in 1987 the traffic limit was limited to 50 mSv/year.

In 1997, the Radiation Safety Standards of Ukraine (NRBU-97) for professionals (category A - professional workers who permanently or temporarily work with sources of ionizing radiation) adopted a maximum permissible limit of 20 mSv/year, for personnel (category B - persons not working directly with sources of ionizing radiation, but due to working or living conditions may be exposed to ionizing radiation) - 2 mSv/year, and for the population - 1 mSv/year.

FORMATION OF RADIATION DOSE IN THE BIOLOGICAL ENVIRONMENT

When forming a radiation dose in a biological environment, a distinction is made between directly ionizing particles and indirectly ionizing particles. Directly ionizing particles are charged particles: alpha particles(helium nuclei), beta particles(electrons, positrons), etc., and indirectly ionizing particles are uncharged particles: neutrons, gamma rays.

When irradiating biological individuals, a distinction is made between acute (manifested by the early effects of irradiation) and prolonged (long-term), single and multiple (fractionated) irradiation. Both acute and prolonged irradiation can be single or fractionated. In addition, chronic irradiation is possible, which can be considered as a type of fractionated irradiation, but produced over a long period of time at very low dose rates.

The dose generated by radiation in a substance can be assessed by measuring, for example, the temperature increase it causes. However, even at doses dangerous to human life, the released energy is not enough to heat the irradiated organism by thousandths of a degree. Therefore, when studying the effect of radiation on biological objects, doses are assessed using more sensitive dosimetry methods.

The dose distribution over time for radiation with different linear energy transfer (LET) can vary significantly and have different effects on the radiobiological effects of radiation. This is especially evident in the long-term consequences of the biological effects of radiation of different LETs, and therefore, serious attention is paid to determining the temporal distribution of dose in radiobiology.

Ionizing radiation, interacting with matter, transfers energy to it in small, finite portions. The transfer of energy is a random process. The energy transferred to the substance in each act of interaction is also random. Therefore, the energy absorbed in a certain volume of a substance when it is repeatedly irradiated under identical conditions with the same dose of ionizing radiation of the same type, strictly speaking, is somewhat different. It is necessary to remember about the fundamentally always present, but not always significant fluctuations (spreads) of the absorbed energy (and, accordingly, the absorbed dose).

In the case of small irradiated volumes, comparable in size to the volume of individual cells or subcellular structures, a situation is possible in which fluctuations in the absorbed dose are comparable and even exceed the dose value. Under such conditions, the comparison of the yield of radiation-induced effects with the absorbed dose becomes ambiguous and it becomes necessary to take these fluctuations into account. The fluctuations are more significant, the smaller the volume in which the absorbed dose is estimated, and the greater the LET value of the radiation forming this dose.

In the case of the formation of so-called “low doses” of radiation (in the microdosimetric understanding of this term, which does not always coincide with its biological understanding), the number of sensitive microvolumes penetrated by ionizing radiation tracks in the irradiated object is significantly less than their total number. In this case, the observed, on average, linear change in the degree of manifestation of one or another radiobiological effect from the radiation dose is simply associated with an increase in the number of sensitive microvolumes penetrated by radiation tracks, and not with the actual linear nature of the dose dependence of the output of this effect.

A similar situation most often occurs under normal conditions of professional exposure and when a person is exposed to radiation from the Earth’s background radiation, which, as is known, forms absorbed radiation doses at the level of hundreds of milligrays per year (mGy/year). This means that over the course of a year, more than one track very rarely passes through the sensitive volumes of individual cells of the human body, and no tracks pass through another part of them during the same time.

Quantitative radiobiology, on the contrary, most often studies the effect of radiation under conditions when each sensitive microvolume in an irradiated biological object is penetrated by a large number of tracks and an increase in the radiation dose corresponds to the condition of increasing the number of tracks through each of its sensitive microvolumes.

BASIC PHYSICAL QUANTITIES OF DOSIMETRY

The primary cause of radiation effects is the absorption of radiation energy by the irradiated object, and dose, as a measure of absorbed energy, is the main dosimetric quantity. Therefore, the main physical dosimetric quantity used to assess the effect of radiation on the environment is the absorbed dose of radiation.

Absorbed radiation dose (D)- this is a value determined by the radiation energy (J) of the absorbed unit of mass (kg) of the irradiated substance. The unit of dose in the SI system is the gray (Gy):

D = 1J/1kg=1 Gy.

Gray is a dose of ionizing radiation at which an energy of 1 J is transferred to a section of a substance weighing 1 kg. The extrasystemic unit is the “rad”. 1 rad = 0.01 Gy.

The absorbed dose characterizes not the radiation itself, but the degree of its impact on the environment. In principle, the same radiation flux in different environments and even in different parts of the same environment can generate different absorbed dose values. Therefore, when talking about the absorbed dose, it is necessary to indicate in what environment it was formed: in air, water or soft biological tissue.

To characterize the distribution of radiation dose over time, the absorbed dose rate, or radiation intensity, is used. This is understood as the amount of radiation energy absorbed per unit time by a unit mass of the irradiated substance (Gy/hour; Gy/year).

In the practical use of radiation, a person, excluding special cases of medical effects and radiation accidents, exposed to low doses of radiation. The working conditions of professionals today most often correspond to the situation when the sensitive targets of the cells of their body of single tracks of ionizing particles that form the radiation dose are significantly longer than the time during which the reparative (restorative) systems of cells work, eliminating the disturbances caused by the passing particle.

Under these conditions, the induced biological effects do not depend on factors such as dose rate, its distribution, conditions and rhythm of irradiation. The yield of effects is determined only by the total accumulated dose (regardless of the irradiation time), i.e. the effects of radiation will be the same when exposed to a given dose once, or when received over several days, months, or even a year. The degree of severity of the effect will be influenced only by the spatial distribution of ionization and excitation acts created in the tracks, i.e. linear energy transfer (LET) of ionizing radiation. Therefore, for such conditions, a special dose value has been introduced that takes into account both of these factors - the equivalent dose. This value can unambiguously relate the yield of radiation consequences of exposure to the radiation dose.

Equivalent dose (N) is defined as the product of the absorbed dose (D) of a given type of radiation by the average value of the weighing factor (quality factor) of ionizing radiation (WR) in a given element - the volume of biological tissue. The WR values for various types of radiation are presented in Table 1. This dose is a measure of the severity of the stochastic effects of radiation. It is applicable to assess the radiation hazard of chronic exposure to radiation of arbitrary composition (and acute exposure dose, less than 0.25 sievert) and is determined by the formula:

H = D W R

The unit of equivalent dose in the SI system is the sievert (Sv). The sievert is equal to the equivalent dose at which the product of the dose of ionizing radiation absorbed in biological tissue by the average value of the weighing factor for this radiation is equal to 1 J/kg. The non-systemic unit is the "rem" (the biological equivalent of an x-ray). 1 rem = 0.01 Sv.

From the definition it follows that for radiation with W R = 1, an equivalent dose of 1 Sv is realized with an absorbed dose of 1 Gy, i.e. for this case 1 Sv = 1 Gy. If W R is different from 1, then an equivalent dose of 1 Sv will be formed in biological tissue when the absorbed dose in it is equal to (1/W R) Gy. Summation of equivalent doses for evaluation is allowed general level exposure over a long period of time, if each single dose that occurred during fractionated acute exposure during this time did not exceed 0.25 Sv.

Table 1 - Values of radiation weighing factors (W R)

Type of radiation and energy range
Photons, all energies (including gamma and x-rays)
Electrons (positrons) and muons, all energies
Protons with energy > 2 MeV
Neutrons with energy< 10 кэВ
Neutrons with energies from 10 keV to 100 keV
Neutrons with energies from 100 keV to 2 MeV
Neutrons with energies from 2 MeV to 20 MeV
Neutrons with energy > 20 MeV
Alpha particles, fission fragments, heavy recoil nuclei

For mixed radiation, the equivalent dose is defined as the sum of the products of the absorbed doses of individual types of radiation and the corresponding values of the weighing factors of these radiations.

For a given equivalent radiation dose, the probability of stochastic consequences depends on the tissue or organ irradiated. Therefore, another coefficient has been introduced that takes into account the specifics of various tissues from the point of view of the probability of inducing stochastic effects of irradiation in them - the tissue weighing factor (W T). Currently accepted values of W T are presented in Table 2 and are used exclusively for calculating the effective dose. Tissue weighing factors are introduced based on the concept of non-threshold radiation action, and their values correspond to the yield of stochastic consequences for various organs and tissues, obtained on the basis of linear extrapolation of available data from the region of high radiation doses (since the real yield of stochastic consequences in the region of low doses is unknown).

Table 2 - Values of tissue weighing factors (W T)

Tissue or organ
Gonads (sex glands)	0.20
Red bone marrow	0.12
Colon	0.12
Lungs	0.12
Stomach	0.12
Bladder	0.05
Mammary gland	0.05
Liver	0.05
Esophagus	0.05
Thyroid	0.05
Leather	0.01
Bone surface	0.01
Other tissues and organs (adrenal glands, kidneys, brain, extrathoracic airways, muscles, uterus, spleen, small intestine, pancreas and thymus glands)	0.05
Whole body	1.00

Unlike stochastic effects, non-stochastic (deterministic) effects appear only when certain doses are received (Table 3).

Table 3 - Value of doses below which the occurrence of non-stochastic (deterministic) effects is excluded

Organ, tissue	Not stochastic (deterministic) effect	Dose, Gy
Whole body	Vomit
Bone marrow	Death
Leather	The physical meaning of the concept of effective dose is as follows: value effective dose (E) corresponds to a level of uniform irradiation of the whole organism at which the total yield of stochastic effects of irradiation will be the same as in the case of local irradiation of an organ (T) with an equivalent dose of magnitude (N): E = H W T The unit of effective dose in the SI system was also taken to be the sievert (Sv). With uniform irradiation, the effective dose is equal to the equivalent dose. For uneven exposure, the effective dose is equal to the product of the equivalent dose and the tissue weighting factor, or equal to the equivalent dose (for uniform exposure) that creates the same risk of adverse effects. It is impossible to measure the effective dose of radiation to the body. It is calculated as the sum of the products of equivalent doses (H) in individual organs and tissues by the corresponding values of the weighing factors (W T) indicated in Table 2. The effective dose is a measure of the yield of stochastic consequences of the biological effects of low doses of radiation on a given individual, i.e. it is a measure of individual danger caused by the effect of small doses of ionizing radiation on the body. For photon radiation, a specific value has been introduced in dosimetry - exposure dose. Numerically, it is equal to the absolute value of the total charge of ions of the same sign formed in a unit mass of air with the complete deceleration of electrons and positrons released by photons (X-ray radiation). That is, it is an air-equivalent dose unit, which is not intended for dosimetry in a substance. The unit of measurement of exposure dose in the SI system is coulomb/kg (C/kg), the non-systemic unit is roentgen (R).	Absorbed 1 Sv = 100 rem = 1 Gy