Basic Radiation Protection for the Safe Use of Radiation and Nuclear Technologies

Abstract

Any use of both ionizing radiation and nuclear technologies requires ensuring appropriate safety and security of persons as well as the adequate protection of the environment. This is why the applications and handling of sources of ionizing radiation should be in line with the relevant national and international standards containing appropriate safety and security requirements and recommendations. In order to understand and follow these standards, it is necessary to assess the related radiation risks, which should be quantified by using specific dosimetry and radiation protection quantities and units. The chapter introduces and discusses these quantities and units aimed at the evaluation of the biological harms attributed to both stochastic and deterministic effects. The correct use and interpretation of radiation quantities are important to follow relevant regulations and to communicate radiation risks to workers and the public. The chapter takes into account the latest situation in the field, relying on the recent position of relevant international expert bodies.

1. Introduction

Radiation can be divided into two groups, namely ionizing radiation and nonionizing radiation. While ionizing radiation of sufficient energy is able to ionize the atoms of the matter with which it interacts, nonionizing radiation has not this ability. In general, ionizing radiation—particles or electromagnetic waves—carries enough energy to knock electrons from atoms or molecules, thereby ionizing them. The result is a positive ion and a free electron, which may be later attached to a neutral atom, thus forming a negative ion.

An illustration of nonionizing and ionizing radiation wavelengths (from the left with increasing values to the right) is shown in Figure 1 (based on [1]).

Figure 1.

Nonionizing and ionizing photon radiation.

In principle, ionizing radiation can be directly ionizing radiation (charged particles) and indirectly ionizing radiation represented by photons (gamma, X-ray, annihilation photons) and neutrons. The interaction of this radiation can also result in positive and negative ions and free electrons, which were created by secondary charged particles released by the interaction of indirectly ionizing radiation with matter. It means that indirectly ionizing radiation is ionizing the matter through the charged particles released by such interactions as photoeffect, Compton effect, and pair production. Neutrons themselves cannot directly ionize atoms. They do it through charged particles released as a result of their interaction with matter.

This chapter will deal only with ionizing radiation (further only as radiation). As to its interaction with matter, the following processes should be considered:

• Interaction of charged particles such as electrons, protons, alpha particles, and heavy ions;

• Interaction of electromagnetic radiation causing the removal of one of the orbital electrons accompanying by the bremsstrahlung (braking radiation) and production of characteristic radiation;

• Neutron interaction includes a variety of processes characterized by elastic and inelastic scattering and other nuclear reactions, which may lead to the initiation of both charged and uncharged particles.

Radiation is emitted by sources, which may be in the principle of two categories: radioactive sources and radiation generators. Radioactive sources (radionuclides) produce radiation that produces, as a result of the decay of unstable nuclei, radiation continuously, and the process cannot be stopped. Radiation generators (X-ray tubes and charged particle accelerators) produce radiation only when appropriate conditions are created. This requires a power supply from outside. When the supply is disconnected or switched off, the production of radiation will be stopped.

These features of two different radiation sources have a significant implication for radiation protection. On one side, we have sources that continuously emit radiation whether we use them, transport or store them, and we have to keep them under control all the time. As to radiation generators, the care for radiation protection is much simpler since when they are not in operation practically, no protection measures should be in place.

For safety reasons, it is important to use standard warning signs in places where radioactive sources, radioactive or nuclear waste, and radiation generators are present (Figure 2).

Figure 2.

Radiation warning signs, a) a universal sign, b) a new symbol of radiation presence (based on [2, 3]).

The term radiation protection is used universally with the meaning of radiation safety or radiation security. Strictly speaking, one may apply these terms in a more specific manner: radiation safety is related to ensuring people and the environment against harmful effects of radiation emitted by the source, while radiation (nuclear) security is associated with providing sufficient protection of the source of radiation against a person who may not be aware of the source or who may use it to commit a malevolent or terrorist attack.

2. Biological effects of radiation exposure

It is well-known fact that radiation can be harmful to the human body. Biological and medical knowledge about the effects of ionizing radiation has been gained since the beginning of the last century and is currently extensive but not yet complete. They include observations of clinical, experimental, and above all, group investigations, which are necessary to demonstrate an increased frequency of those diseases that are clinically indistinguishable from spontaneous diseases (e.g., cancer).

The health effects caused by radiation exposure fall into two groups: stochastic effects and deterministic effects (tissue reactions).

The stochastic effects of radiation are those effects that we do not know with certainty that they will manifest after exposure; they are manifested only with a certain probability. This includes an increased risk of cancer and hereditary diseases. On the other hand, deterministic effects appear only above a certain level of exposure (dose), which is relatively high. In both cases, the effects may affect a person exposed (somatic effects) or his offspring (genetic effects), as shown in Figure 3.

Figure 3.

An overview of the biological effects of radiation on the person and their offspring.

The stochastic effects are caused by the mutations (changes in the genetic information of the cell) and are characterized by a threshold-free, linear dose-response relationship. The dose dependence of these effects is statistical in nature, and therefore, the designation stochastic effects (probable, accidental) have been introduced for them. The size of the radiation dose does not change the severity of the individual’s manifestation, but in the population, it changes the frequency of the additional appearance of malignant neoplasms and hereditary damage. Thus, with the dose, the likelihood of injury increases for the individual.

The exposure above certain threshold results in deterministic effects where the severity of the body reaction is roughly proportional to the exposure (Figure 4). Exposure to radiation under this level causes no impact.

Figure 4.

Comparison between stochastic and deterministic effects.

3. Quantification of stochastic and deterministic effects

The interaction of radiation with matter leads to the deposition of some or full of its energy in the absorption medium, the temperature of which may increase. Since the deposition energy is very low, this is not the main cause of consequent effects in the living tissues where the type of particles, the density of the energy lost per unit of the tracking sensitivity of different tissues exposed, and other factors play a more significant role. This is why the response of the body cannot be expressed by pure physical quantities, and other factors related to the tissue reactions to formed radicals are of primary importance.

The risk created by radiation to the human body cannot be expressed by means of only physical quantities and some specific quantities—we may call them biophysical rather than physical quantities. The biophysical quantities are based on the physical quantities weighted by specific factors taking into account the biological harm of various types of radiation as well as the sensitivity of particular organs and tissues to the exposure.

3.1 Physical quantities and units

One of the first attempts to quantify radiation exposure to a person was based on ionizing abilities of radiation (at that time, only X-ray photos were assumed) where a unit roentgen was introduced as a measure of the ability of photons to ionize the air. Later on, the roentgen (R) became a unit of a quantity exposure, introduced by the equation

$$X=\frac{\mathit{dQ}}{\mathit{dm}}$$E1

where dQ is the total charge of the ions of one sign generated by the electrons (negatrons and positrons) produced by photons in the mass of air dm.

The SI unit of this quantity is C kg⁻¹, the relation with the old unit—roentgen (R)—is 1 R = 2.58 × 10⁻⁴ C.kg⁻¹ (exactly). Because of the definitions, the quantity of exposure could be applied in practice only to photons of energy up to about 300 keV [4].

Later on, when radiation protection had to address the results of interactions of other types of radiations, including beta, alpha, neutrons, and others, a universal quantity of (absorbed) dose was introduced. This is a universal physical quantity reflecting the deposition of radiation in any substance. The dose was introduced as follows:

$$D=\frac{d{E}_i}{\mathit{dm}}$$E2

where dE_i is the mean energy imparted to the matter of mass dm. The unit of the dose and the dose rate are Gy (gray) and Gy.h⁻¹ (gray per hour). Commonly, units mGy, μGy, and mGy h⁻¹ or μGy.h⁻¹ are frequently used. Before, for the old unit, the rad unit was in use, where 1 Gy = 100 rad [5].

The dose is considered to be a universal quantity in dosimetry, and it is a basis for most quantities used in radiation protection. It can be used for any type of radiation and for any medium or absorber.

The last physical quantity to be mentioned here is the kerma (K), which is the acronym for Kinetic Energy Released per unit Mass. This quantity can only be used for photons and neutrons in any media. It is still widely used especially in computational dosimetry. The kerma is defined by the equation

$$K=\frac{d{E}_{\mathit{tr}}}{\mathit{dm}}$$E3

where dE_tr is the sum of the initial kinetic energies of all the charged particles liberated by uncharged particles in a mass dm of material. The medium should always be specified.

The special name for the unit of kerma is gray (Gy); the unit for the kerma and dose is thus the same. In addition, here, one can specify this quantity related to the unit of time as the kerma rate, defined as the kerma per second. The main unit for this quantity is analogical to the dose rate, i.e., Gy.s⁻¹.

The illustration of the dose and kerma is shown in Figure 5, documenting their relationship. It is obvious that the kerma reflects the energy of secondary particles released by indirectly ionizing radiation at the point of interest, while the dose represents the energy absorbed by these particles. This absorption takes place at a certain distance from the origin of their production.

Figure 5.

The relationship between the kerma and the dose depends on the depth.

Figure 5 shows the attenuation of photons in their penetration through the absorber where at the surface, the kerma has a maximum value and then shows a continuous decrease, while the dose is first increasing its value and after reaching the maximum; it decreases with the same rate as the kerma (equilibrium). This behavior is due to the fact that at a certain depth, the particles from the layer above contribute to the dose where the kerma is lower because of the attenuation.

3.2 The need for assessment of biological risk

Although up to the middle of the last century, practically only the physical quantities of radiation were used for assessing the harm caused by radiation exposure to persons, it was felt that for this purpose, another set of quantities had to be introduced. Such quantities were supposed to reflect biological effects regardless of the type of radiation and irradiation geometry. This was why several weighting factors were adopted to convert pure physical quantities into quantities, which would be better related to the biological response of the exposed human body to the most common types of radiation under typical exposure conditions. The values of applicable weighting factors were derived from the investigation of some radiation accidents and incidents, and especially from extensive epidemiological studies, including those carried out on the survivors of the atomic bombing in Hiroshima and Nagasaki. Of course, these data have never been considered final since more studies led to more relevant and reliable results of the weighting factors. This was why even throughout the last few decades, there had been certain biological quantities, which serve for the radiation risk assessment used for the control of radiation exposure in order to implement the basic requirements and philosophy of radiation protection known as justification, limitation, and optimization.

As mentioned above, for the assessment of the health risk related to exposure to radiation, other types of quantities should be used. These quantities are based on specific dosimetry quantities weighted by appropriate factors in order to reflect stochastic or deterministic biological effects.

Stochastic (probabilistic) effects are random phenomena and manifest as mutations of cells and not their death. It has been found that there is no threshold dose for these effects. This concept is known as linear no threshold model. In most cases, any cell mutations caused by ionizing radiation will be eliminated by the body’s defense; however, when this does not occur, the mutations can induce cancers (Figure 6).

Figure 6.

Radiation-induced carcinogenesis occurs following interaction with ionizing radiation that leads to cell mutation (based on [6]).

At higher doses, the deterministic effects (tissue reactions) take place. These are known as the biological effects, which are manifested after the dose exceeds the so-called threshold level. It is not the same for all organs; the susceptibility of cells to radiation damage is described by the term radiosensitivity.

The individual categories of radiation-induced biological effects are summarized in Figure 7.

Figure 7.

An overview of biological consequences of radiation effects.

3.3 Quantities reflecting stochastic effects

Such quantities could be used only for relatively small doses where only probabilistic effects are expected.

The most frequently used quantities for this purpose include dose equivalent, equivalent dose, effective dose, committed effective dose, and specific operational quantities (introduced for external exposure only) approximating main radiation protection quantities.

One of the earlier quantities in radiation protection introduced for this purpose was the dose equivalent (H) defined at the point of interest in tissue as

$$H=D·Q_F$$E4

where D is the absorbed dose, and Q_F is the mean value of the quality factor for the specific radiation at this point. The unit of the dose equivalent is sievert (Sv), which corresponds to J.kg⁻¹ (multiplied by Q_F). The coefficient Q_F is one of those weighting factors mentioned above.

Since the dose equivalent is a point quantity, it itself has limited practical applications with the exception of its use in the definitions of so-called operational quantities (to be discussed later). More useful are the following main radiation protection quantities, namely the equivalent dose and the effective dose.

The first of these quantities (H_T) is defined by the summation of the average of doses (D_T,R) in a tissue or organ T caused by radiations of type R multiplied by the relevant radiation weighting factors (w_R). This quantity is quantified by the unit Sv (sievert and is defined by the expression

$$H_T=\sum _R{w}_R·D_{T,R}$$E5

While the equivalent dose represents the health effects in individual tissues or organs, the effective dose (E) is a measure of radiation exposure to the whole body, which may be exposed to radiation inhomogeneously, and various sensitivities should be taken into account. This is done by so-called tissue weighting factors (w_T) recommended by ICRP [7, 8].

The effective dose (E) is the main quantity in radiation protection for the assessment of biological effects at low doses. It has been defined only for stochastic effects. The definition of the effective dose can be written in the form

$$E=\sum _T{w}_T\sum _R{w}_R·D_{T,R}$$E6

here w_T is the tissue weighting factor, w_R is the radiation weighting factor and D_T,R. The unit of this quantity is sievert (Sv); more often, however, units such as mSv or μSv are used. The factor w_R is related to the Linear Energy Transfer (LET), which reflects the average amount of energy transferred per unit of distance traveled). The values of LET are usually expressed in units of keV/μm. The values of w_R for some radiations are as follows: low-LET radiation (photons, electrons, muons), 1; protons and charged pions, 2; and alpha particles, fission fragments, and heavy ions, 20. For neutrons, this factor depends on the energy [7, 8].

The LET values for some radiation are given in Table 1. The definition of LET is related to charged particles in any medium. As indirectly ionizing radiation, as gammas or X-rays, this quantity is associated with the secondary charged particle released by the interaction of indirectly ionizing radiation.

Type of radiation	LET (keV/μm)
Co-60 gamma photons	0.3
X-ray radiation, 250 kVp	2.0
Protons, 10 MeV	4.7
Protons, 150 MeV	0.5
Recoil protons from fission neutrons	45.0
Neutrons, 14 MeV	12.0
Alpha particles, 2.5 MeV	166.0

Table 1.

The LET values of various types of radiations (based on [7]).

There is some relation between the LET and the Relative Biological Effectiveness (RBE). They both are important terms in radiation biology and reflect the relative damage that will occur under different circumstances. As LET increases, more energetic electrons are deposited closely together and thus, damage to DNA is more likely.

Since the LET is strictly speaking defined only for charged particles, its values for uncharged particles (photons and neutrons) are related to the secondary charged particles formed by this indirectly ionizing radiation.

The weighting factor w_T for calculating the effective dose represents a relative measure of the risk of stochastic effects that might result from exposure of a specific tissue T. It takes into account the variable radiosensitivities of organs and tissues in the body affected by radiation. The w_T values for main tissues are shown in Table 2.

Type of tissues	wT
Remainder tissues, red bone marrow, breast, colon, lung, stomach	0.12
Gonads	0.08
Bladder, esophagus, liver, thyroid	0.04
Bone surface, brain, salivary glands, skin	0.01
All tissues	1.00

Table 2.

The w_T values of various types of radiations (based on [8]).

The remainder tissues include some 13 tissues that are significantly exposed. They comprise the following tissues: adrenals, extrathoracic region, gall bladder, heart, kidneys, lymph nodes, muscle, oral mucosa, pancreas, prostate, small intestine, spleen, thymus, uterus/cervix.

Both the abovementioned quantities can be related to the unit of time as the equivalent dose rate and effective dose rate where the same units, Sv.s⁻¹ are used. More practical are widely used units such as mSv.h⁻¹ or, in the case of the effective dose, even mSv.y⁻¹.

Both the equivalent dose and effective dose can be used to assess stochastic effects due to the external radiation as well as internal radiation emitted by radionuclides, which entered the body and exposed its tissues and organs from inside. The overall risk attributed to the component related to the internal radioactive contamination can be assessed by the quantities committed equivalent dose – H_T(τ) and committed effective dose.

The committed equivalent dose represents the sum of the equivalent doses received in a particular tissue or organ of a person due to the intake of radionuclides during the period of τ, which is 50 years for adults or 70 years for children. This refers explicitly to the dose in a specific tissue or organ, in a similar way to the external equivalent dose. This quantity reflects the contribution of the internal exposure to the total equivalent dose. The committed equivalent dose H_T(τ) in a tissue or organ T is defined by

$$H_T\left(\mathrm{\tau }\right)={\int }_{t_O}^{t_0+\mathrm{\tau }}{H}_T\left(t\right)\mathit{dt}$$E7

The committed effective dose – E(τ), is the sum of the products of the equivalent dose a tissue or organ, T, received from the intake of radioactive materials by inhalation and ingestion, and the appropriate tissue weighting factors, w_T, as shown in the following formula:

$$E\left(\mathrm{\tau }\right)=\sum _T{w}_T{H}_T\left(\mathrm{\tau }\right)$$E8

The integration time τ follows the intake at time t₀. Since the radiation weighting factor is considered to be a dimensionless factor, the unit of both the equivalent dose and committed equivalent dose is Sv (provided the dose is in Gy).

The quantity E(τ) is used rather rarely: only in the case of working with unsealed radioactive sources or an accident, which resulted in the release of substantial radioactive material contaminating the surrounding area. This may affect persons present especially by the inhalation of contaminated air.

Since the main radiation protection quantities mentioned above cannot be directly measured or monitored, specially defined quantities for assessing the risk due to external exposure have been introduced to assess this risk by means of measurable quantities. Such a set of so-called operational quantities have been introduced by the International Commission for Radiological Units and Measurements (ICRU) [9]. These quantities can provide an estimate or upper limit for the value of the protection quantities related to the external exposure or potential exposure of persons. They are characterized as follows:

• The ambient dose equivalent H*(d) represents the dose equivalent at a certain point in the radiation field that would be induced by an expanded and aligned field at a depth of d in a 30 cm standard tissue-equivalent ICRU sphere at a radius opposite to the direction of the field.

• The directional dose equivalent H´(d,Ω) at a given location corresponds to the dose equivalent H that would be induced in the extended field in the ICRU sphere at depth d on the radio in the defined direction of the radiation field represented by the angle Ω.

• The personal dose equivalent H_p(d) was introduced for personal monitoring and is actually the dose equivalent in ICRU tissue at the relevant depth d below a specific point on the surface of the human body.

An overview of operational quantities is presented in Table 3. The basic unit of all operational quantities is Sv.

Task	Operational quantities
	Area monitoring	Individual monitoring
Control of effective dose	Ambient dose equivalent, H^*(10)	Personal dose equivalent, Hp(10)
Control of doses to the skin, the hands and feet, and the lense of eye	Directional dose equivalent, H′(0.07,Ω)	Personal dose equivalent, Hp(0.07)

Table 3.

Operational quantities proposed for dose monitoring of external exposure.

Figure 8 illustrates the position and the role of operational quantities in relation to physical quantities and radiation protection quantities. It should be noted that while operational quantities can apply only for the assessment of the exposure due to external radiation, radiation quantities represent general quantities for the quantification of the exposure resulting from both external radiation and internal exposure caused by the intake of radioactive material.

Figure 8.

Relationship between quantities used in radiation protection.

From physical quantities (exposure, kerma, dose), one can move to operational quantities using the quality factor Q(L) and to protection quantities through radiation weighting factor (w_R) and tissue weighting factor (w_T). The relation between operational and protection quantities is obtained based on measurement and calculation.

3.4 Quantifies for assessment of deterministic harm

While the quantities and units for the assessment of stochastic effects are well elaborated and defined, this is not the case with regard to deterministic effects. Quantities aimed at the estimation of stochastic effects include both the potential harm in selected individual organs (equivalent dose) and the health impact of the irradiation of the whole body, where contributions from the exposure of individual organs are taken into account (effective dose). The stochastic effects are of primary interest at low exposure, where there are no visible signs of the reaction of tissues or organs exposed. At sufficiently higher doses where the damage caused by radiation is apparent, more interest should be paid to deterministic effects.

Deterministic effects (nonstochastic effects, tissue reactions) are characterized by a threshold dose that must be exceeded for effect to occur. The severity of deterministic effects increases with dose, which could result in such harms as cataracts, erythema, and sterility. The main role of radiation protection consists of keeping radiation exposure not only below the established dose limits to avoid the deterministic effects but ensure that the doses and radioactive contamination are as low as possible to achieve under the circumstances taking into account all possible specific conditions, including economic factors.

While for the assessment of stochastic effects, several quantities were defined, there has not been developed a similar approach to quantify deterministic effects [10, 11]. At present, a concept based on the RBE (Relative Biological Effectiveness) is being introduced. The relevant quantity, RBE-weighted dose (or, in short, RBE dose), is applied for this purpose [7, 12].

The RBE represents the relative absorbed dose of reference radiation (usually 250 kVp X-rays or cobalt-60 gamma rays) required to produce the same magnitude of the similar effect as the absorbed dose of the radiation in question (RBE >1 indicates that the radiation is more effective than the reference radiation). This factor is influenced by both the biological effects (cell killing, cell survival with mutations) and the LET of the radiation.

It looks like under present circumstances, the best way to call the main quantity for the assessment of the risk associated with the deterministic effects in terms of the RBE dose defined as

$$\mathrm{RBE}\text{dose}=\mathrm{RBE}\times \mathrm{D}$$E9

with the unit Gy-Eq (gray equivalent). Therefore, a dose in Gy-Eq is the absorbed dose in Gy multiplied by a recommended RBE, which takes into account that ionizing radiation of different types and energies affects living organisms differently. The values of the RBE for some typical radiation are given in Table 4.

Type and energy of the radiation	RBE
Low-level radiations (e.g., photons, electrons)	1.0
Protons (>2 MeV)	1.5
Heavy ions (e.g., helium, carbon, neon, argon)	2.5
Neutrons <5 MeV	6.0
5 MeV	5.0
> 5 MeV	3.5

Table 4.

The RBE values for individual types of radiation (based on [8]).

In this context, the RBE is analogous to the weighting factor w_R used to define the equivalent dose, except that in this case, the RBE is a measured quantity for a specific deterministic endpoint. In this regard, there is no equivalent to the effective dose in the case of high exposure of many tissues or organs in the body. Although the term RBE dose would be an appropriate choice for the quantity expressing the harm following high exposure, it is still not widely used.

There are still some inconsistencies in using units for effective dose (Sv) and RBE-dose (Gy-Eq). In some cases, the unit Sv is also wrongly used for the assessment of deterministic effects.

3.5 Contributions from external and internal exposure

In general, radiation protection mechanisms have to provide adequate protection of persons against both external and internal exposure. The total exposure can be presented as a sum of the contribution from radiation incident on the surface of the body as well as radiation emitted by radionuclides, which enter the body through inhalation or ingestion and exposes the tissues from inside.

In order to control external radiation sources, some specific protective measures have to be in place. The radiation situation, including its impact on persons, is evaluated by appropriate quantities and other parameters characterizing the potential of the source, intensity of radiation field, and finally, the exposure of the affected person using appropriate quantities and units. The source is usually described by activity (number of radioactive decays per second) or emission (number of particles or photons emitted by the source in 1 second). The situation is illustrated in Figure 9.

Figure 9.

Relations between various radiation protection quantities used to assess stochastic and deterministic effects following the external exposure (based on [12]).

In an analogous way, we may also characterize the circumstances in the case of personal exposure (Figure 10).

Figure 10.

Quantities characterizing personal exposure from the intake of radioactive material or from skin contamination (based on [12]).

4. Application of radiation in medicine and some other fields

The principal objectives of radiation protection are to ensure adequate safety of persons against the harmful effects of radiation. This includes radiation workers, patients as well as members of the public. In addition, the satisfactory protection of the environment, especially from its radioactive contamination, should also be taken into account. Special attention should be paid to the security of strong radioactive sources since they may be misused for terrorist and other malevolent actions.

There is no debt that exposure to radiation may cause severe hazards to workers, members of the general public, as well as to patients if the application of radiation sources is not under strict control during all their cycles, including production, transport, storage, and decommissioning. It is worth emphasizing the main role of safety and security in radiation protection. As has already been indicated above, radiation safety includes any operation aimed at the protection of persons against radiation emitted by the sources, while the radiation (nuclear) security role consists of protecting and securing radiation sources and nuclear installations against any attempt to handle or approach them by unauthorized persons including terrorists who may deliberately misuse radiation sources for malevolent actions.

Radiation and nuclear applications proved to be extremely beneficial and effective in many branches of technologies, especially in medicine, industry, and science. In a number of cases, these methods are the only feasible way to solve a problem or task. This applies to various medical fields where especially in diagnostic radiology. It would be impossible to carry out many examinations without a radiation generator or special radioactive materials (radiopharmaceuticals).

There are three main uses of radiation in medicine:

• Diagnostic radiology – based on photons produced by X-ray machines to obtain information from inside the patient’s body. This includes conventional radiography (including fluoroscopy), computed tomography (CT), and some other modality specific to the examination purpose).

• Nuclear medicine – a small amount of radiopharmaceuticals is used to detect or treat disease. The type of radiopharmaceuticals is chosen or specially developed to be taken up predominantly by one organ or one type of cell in the body.

• Radiotherapy – utilizes high radiation doses to treat malignant and benign diseases by means of external radiation produced by X-ray tubes and specifically designed charged particle accelerators. This modality is applied to treat about half of all newly diagnosed cancer cases.

• Sterilization – relies on radiation, mainly gamma, X-ray, or electron, to deactivate harmful microorganisms (for example, bacteria, viruses, fungi, etc.).

Ensuring appropriate radiation protection of workers, patients, and other persons potentially affected by medical applications (e.g., members of the household of patients treated by radiopharmaceuticals) is one of the most important tasks. This is becoming more and more important at present, and it will be even more imperative in the future. The number and variety of methods used in medicine involving radiation are going continuously up. Moreover, some new diagnostic methods, especially CT modalities, are characterized by relatively high doses, which results in an increased radiation burden on the population. The situation can be illustrated by a comparison of exposure of members of the public receiving about 30–40 years ago and in some recent years (Figure 11). Although the data are from the USA, the situation is becoming similar in many industrialized countries, where medical exposure is responsible for more than 50% of the total annual effective dose.

Figure 11.

Average annual effective dose/person received in 1980 (left panel) and 2006 (right panel) in the United States (based on [13]).

Medical applications of radiation sources and radionuclides are contributing to the total exposure of the population up to 50% of the total exposure, and this is why ensuring appropriate control of dose in this field is most important. We cannot neglect, however, other areas where these technologies are used. This includes especially industrial applications where exposures are relatively low and practically always below set limits, but in the case of accidents or any other emergency, the consequences may be fatal. One has to learn lessons from such nuclear accidents as happened in Chornobyl in 1986 and Fukushima in 2011. The relevant comparison chart is shown in Figure 12 (based on [14]).

Figure 12.

Difference between Chornobyl and Fukushima nuclear power plant accidents.

An overview of a variety of applications of various methods and principles of radiation and nuclear technologies in the industry is presented in Figure 13 (based on [15]).

Figure 13.

Applications of radiotracer and radionuclide techniques in the industry.

5. System and legislative framework for radiation protection

The present system of radiation protection used across Europe and worldwide relies on the basic recommendations of the International Commission for Radiation Protection (ICRP). The basic conceptual framework of these fundamental materials has been constantly updated and modified, taking into account the recent development in the field.

The latest general recommendations of the ICRP were published in 2007 as ICRP Publication 103. At present, the ICRP is about to be reviewed and revised its last recommendations [16].

The structure and relations among the most important international committees, commissions, associations, agencies, and other related organizations are outlined in Figure 14. In addition to the ICRP, the most influential expert bodies among them are especially UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation). Other abbreviations used in Figure 14 have the following meanings: BEIR – Biologic Effects of Ionizing Radiation, IRPA – International Radiation Protection Association, ISR – International Society of Radiology, PAHO – Pan American Health Organization, NEA – Nuclear Energy Agency, WHO – World Health Organization, FAO – Food and Agriculture Organization, BSS – Basic Safety Standards, ISO – International Organization for Standardization, IEC International Electrotechnical Commission.

Figure 14.

The most important international expert and scientific bodies engaged in developing radiation protection recommendations and standards.

The ICRP developed three main principles of radiation protection based on justification, optimization, and dose limitation.

The principle of justification requires that every activity related to the use of radiation sources be fully justified by a benefit that outweighs the possible risks arising from its use.

When carrying out activities leading to the exposure, it is necessary to set and maintain such a level of radiation protection that the risks arising from the use of radiation are as low as can reasonably be achieved with regard to economic and social aspects. This is the main concept of optimization in radiation protection.

The dose limitation principle of radiation protection requires that the dose to persons should not exceed the limits introduced by the national and international standards.

Under normal or planned circumstances, the doses are not supposed to exceed the limits recommended by the ICRP (Table 5). The majority of countries transposed these limits for occupational and public exposure into their respective national regulations. The exposure of patients and rescue workers is controlled by specific reference doses.

Quantity	Organ	Dose limit for exposure
		Occupational	Public
Effective dose, E	Whole body	20 mSv/y averaged over five consecutive years, and 50 mSv in any single year	1 mSv/y
Equivalent dose, HT	Lens of the eye	20 mSv/y, averaged over defined periods of 5 years, with no single year exceeding 50 mSv	15 mSv/y
Equivalent dose, HT	Skin	500 mSv/y (average dose over 1 cm^2 of the most highly irradiated area of the skin)	50 mSv/y
Equivalent dose, HT	Extremities (hands and feet)	500 mSv/y	—

Table 5.

Dose limits on occupational and public exposure (based on [17, 18]).

6. Conclusion

Sources of ionizing radiation as well as other nuclear-related technologies have been used extensively in medicine (from cancer treatment to sterilization of medical equipment), industrial applications (nuclear power plants, production of radiopharmaceuticals, industrial radiography, radioisotope thermoelectric generators, oil well logging, industrial gauges, etc.), research, chemistry, agriculture, and in many other areas. These applications have been here for decades for the benefit of society. In their use, however, reliable safety and security measures should be introduced and followed so that any potential harm to people or the environment is kept to the minimum acceptable by the society. Here, a significant role is played by radiation protection, which should ensure the implementation of the strict regulations and safety standards aimed at the adequate protection of workers, patients as well as members of the general public against potentially harmful health effects of radiation exposure. Similar rules have been introduced to limit radioactive contamination of the environment.

Besides radiological protection of the persons in routine situations, the use of radiation sources involves several important tasks associated with the prevention and mitigation of radiological or nuclear accidents. Special attention has also to be devoted to the risk associated with possible terrorist attacks and the danger from orphan sources (lost, stolen, abandoned), which are no longer under the regulatory control.

One of the ways how to solve the present problems in radiation protection concept and philosophy could include the change regarding radiation protection quantities and units. It is believed that the limitation of the number of quantities currently in use would be undoubtedly helpful. One possible approach may rely on splitting the radiation protection quantities into two categories: the first group would include a limited number of measurable quantities that can be used in regulatory control of personal exposure, while the second category may include the continuation in using the present complicated system; this will serve for research and theoretical aspects.

Acknowledgments

The chapter has been partially supported by the project VI20192022162 carried out at the Department of Crisis Management of the PA CR in Prague.