Occupational and technical correlations of interventional radiology

REVIEW ARTICLE

Occupational and technical correlations of interventional radiology

Edvaldo de Souza^I; José Paravidino de Macedo Soares^II

^IMSc., Vascular Surgery, Universidade Federal de São Paulo (UNIFESP), São Paulo, SP, Brazil. Specialist, Angiology and Vascular Surgery, SBACV and Associação Médica Brasileira (AMB), São Paulo, SP, Brazil. Member, SBACV-SP. Member, Associação Nacional de Medicina do Trabalho (ANAMT).

^IIMSc. Professor and head, Specialization in Labor Medicine, Universidade Federal Fluminense (UFF), Niterói, RJ, Brazil.

ABSTRACT

Diagnostic radiology is a field of physical medicine that uses X rays to obtain functional and anatomical information on the human body. The techniques associated to this area use X ray tubes as radiation sources, films to record information, and monitoring systems using television and computers for the digitalization of images. Fluoroscopic equipment is considered as artificial springs of ionizing radiation and is used in diagnostic exams and procedures of vascular illnesses. The objective of this study was to critically analyze the protection methods regarding the radiation emitted by fluoroscopy used by professionals dealing with interventional radiology in a hospital environment. An evaluation of protection methods adopted by professionals directly involved in procedures of interventional radiology was performed based on extensive literature review of textbooks and medical journals indexed on MEDLINE in Portuguese, English, French, and Spanish from 1966 to 2005. It is in accordance with the radiological protection security norms and regulations guided by Edict 453/98 of the Brazilian Department of Health and the National Commission of Nuclear Energy NN-3.01 of the Brazilian Department of Science and Technology.

Keywords: Radiation, ionizing, interventional radiology, fluoroscopy, radiation protection, X rays.

RESUMO

A radiologia diagnóstica é a área da física médica relacionada ao uso de raios X para a obtenção de informações anatômicas e funcionais do corpo humano. As técnicas associadas a essa área utilizam tubos de raios X como fontes de radiação, filmes para o registro das informações, sistemas de monitoração por televisão e equipamentos que digitalizam as imagens utilizando computadores. Os equipamentos de fluoroscopia são considerados fontes artificiais de radiação ionizante e são utilizados para a realização de exames e procedimentos nas doenças vasculares. O objetivo deste estudo foi analisar criticamente os métodos de proteção em relação à radiação emitida pela fluoroscopia utilizados pelos profissionais que lidam com a radiologia intervencionista no ambiente hospitalar. Foi realizada uma análise crítica das atitudes de proteção tomadas pelos profissionais engajados nos procedimentos da radiologia intervencionista a partir da revisão bibliográfica realizada em livros-textos e em revistas periódicas indexadas no MEDLINE, nas línguas portuguesa, inglesa, francesa e espanhola, no período de 1966 a 2005, conforme os princípios e as normas de segurança de proteção radiológica norteadas pela Portaria 453/98 do Ministério da Saúde e a norma da Comissão Nacional de Energia Nuclear NN-3.01 do Ministério da Ciência e Tecnologia.

Palavras-chave: Radiação ionizante, radiologia intervencionista, fluoroscopia, proteção radiológica, raios X.

Introduction

Interventional radiology can be defined as the medical area that uses ionizing radiation, such as X ray and fluoroscopy, to obtain information for diagnostic and therapeutic procedures. It has been increasingly used, since half of the population performs one radiological examination a year.^1-6 Due to the benefits provided by use of fluoroscopy devices in varied types of procedures related to vascular diseases, whose main characteristic is to allow real-time visualization, guiding diagnostic and/or therapeutic maneuvers. Its frequent use is able to produce harmful effects on the health of involved professionals, as they are considered artificial sources of ionizing radiation.^2,5 Therefore, professionals should be the least exposed to the radiation emitted by devices.^4-12

It is known that lack of individual protection clothing and absence of a periodic control are some of the examples that show the lack of attention given to ionizing radiation in Brazil,¹³ which confirms the need of specific qualification programs for professionals involved in these activities not only to ensure personal safety, but also a good technical quality of the examination.^8,12,14,15 The system of radiological protection should try to maintain occupational exposure below the recommended level, avoiding stochastic effects, as biological effects produced by radiation are cumulative. To do so, use of adequate personal protection equipment (PPE) is essential.⁶

An evaluation of protection methods adopted by professionals directly involved in procedures of interventional radiology was performed based on extensive literature review of textbooks and medical journals indexed on MEDLINE in Portuguese, English, French, and Spanish from 1966 to 2005. It is in accordance with the radiological protection security norms and regulations guided by Edict 453/98 of the Brazilian Department of Health and the National Commission of Nuclear Energy NN-3.01 of the Brazilian Department of Science and Technology.

Radioprotection system

Radiological protection aims at properly protecting professionals without unnecessarily limiting the beneficial practices that use ionizing radiation. The radioprotection system is based on basic principles that aim to ensure that the equivalent dose received by an individual is as low as readily achievable, ALARA principle); that no use of radiation is unjustified in relation to its benefits; and that the equivalent dose does not exceed annual limits for professionals. Thus, in an occupational monitoring program, the items of greater concern with exposed individuals are working hours, formation of employees, periodic training, personal dosimetry, and routine medical examinations.^2,3,5,16,17 There should also be annual training and permanent continued education on radiological protection by all professionals involved in these activities, as the responsibilities of complying with the regulation apply to everyone.^17,18 According to regulations of the Brazilian National Standards Organization (ABNT), every professional working with radiodiagnosis should always use a dosimeter when in the risk area, in addition to sending it for data reading every month to monitor accumulated individual radiation, providing information on exposure to ionizing radiation.^3,15,19 Nowadays, most stores provide individual monitors or dosimeters for professionals; on the other hand, in some cases professionals are unaware of the importance of using individual monitors and recommended dose limits per month. Evidence of this is the common practice of storing dosimeters collectively, and not individually, in the standard monitor by the end of a working shift. In addition, dosimeters are not used as recommended.^13.15

According to Soares² and the norm CNEN-NN-3.01,²⁰ the main quantities recommended for use in radiological protection as defined by the International Commission on Radiological Protection (ICRP) to limit professionals' exposure to ionizing radiation are: a) absorbed dose in an organ, which serves to quantify the energy absorbed in an organ or tissue. This dosimetric quantity is expressed by D = dε/d_m, in which dε is the mean energy absorbed by the radiation in an elementary volume of mass with mass d_m. The unit of absorbed dose in the international system (IS) is the joule per kilogram (J/kg), called Gray (Gy); b) equivalent dose, which not only quantifies the energy absorbed in an organ or tissue, but also provides information on the biological damage caused by each type of radiation (in this case, X ray). Equal quantities of absorbed dose in an organ or tissue, due to different types of radiation, will cause different biological effects. The IS unit is J/kg, called Sievert (Sv); c) effective dose, defined as the sum of equivalent doses by a weighting factor (W_T) for tissues or organs, used to consider the type of radiation that absorbs energy in the human body and also to consider the amount of contribution of each radiated organ to the detriment of health. Values of effective dose are associated with the radiosensitivity of the radiated organ or tissue. The IS unit is J/kg, also called Sv, and varies according to the weight of most organs or tissues (Table 1). Regulation 453/98 of the Brazilian Department of Health (MS), which is equivalent to ICRP 60 (publication no. 60, 1990), defines that mean annual effective dose should not exceed 20 miliSievert (mSv) in any consecutive period of 5 years; 50 mSv in any year; or 500 mSv for hands and feet and 150 mSv for the lens of the eye (Table 2).^15,20 In case the professional works in other services, those in charge of each service should ensure that the sum of occupational exposures does not exceed the limits set in Resolution 453/98 of MS.¹⁵ Taking into consideration the ALARA principle, it is necessary to know the equivalent doses of hemodynamic unit teams. For a good positioning of team members in examination rooms, optimizing the radiological protection system and minimizing radiation doses justify implantation of a standardization in units that have fluoroscopy devices operated by such teams. This resulted in the development and implantation of a safety system to control sources of radiation and radiological protection of exposed professionals at Universidade Federal do Rio Grande do Sul (UFRGS) since 2001.^12,15,16 Shields are used to prevent radiation, avoiding unnecessary exposure of individuals involved with equipment that emit ionizing radiation. Their efficiency is determined by the capacity of X ray penetration, as well by nature and thickness of the shield.^2,10,21 Professionals in the examination room should be positioned so that any part of their body, including limbs, is reached by the primary beam without protection by 0.5 mm lead equivalent. They should also protect themselves from the radiation scattered by protective clothing or barriers with attenuation of at least 0.25 mm lead equivalent.^15,17 The objectives of radioprotection are prevention and reduction of radiation somatic effects and reduction in genetic deterioration of the populations. Accumulated dose throughout the years gradually causes more gene changes, although intermittent doses received during the period are small. Exposure to ionizing radiation always causes damages to cells. There is no safe radiation dose. Some of the somatic damages caused by exposure can be reversible, but genetic damages are cumulative and irreversible. For this reason, radiological exposure by professionals and the population should be as low as possible.²

Table 1 - Click to enlarge

Table 2 - Click to enlarge

Oliveira,⁵ relative to recording radiation dose, reports that ICRP defined the "recording level" as the value from which the numeric register of the measured value should be performed. Values below the recording level are of little importance for radiological protection and are considered as zero. In Brazil, according to the norm CNEN-NN-3.01 and Resolution 453/98 of MS, recording level should be equal or higher than 0.20 mSv.^15,20

Oliveira⁵ classifies the professional as under "investigation level" when his monthly dose of radiation obtained from the monitor is between 1.2 and 4.0 mSv. In these cases local investigations are performed to verify the situation, and a justification of procedures during the reference month is requested to the professional.

According to Oliveira,⁵ classification of "monthly excess" indicates that radiation doses reached the limit of 4.0 mSv and, therefore, this should be communicated to competent authorities. The institution may be inspected by an inspection agency, and the worker, depending on exposure severity, may be prevented from performing any activity using ionizing radiation.

The term "unknown dose" means that, for some reason, the monthly dose of radiation was not evaluated and, therefore, a mean value should be attributed to the period in which the dose was not recorded, which is obtained from mean values measured in a given year.⁵

Professionals should follow a standard of radiological protection that have the following fundamental principles: a) justification – any activity involving radiation or exposure should be justified in relation to available alternatives and also produce a significant benefit for society. The benefit should be such as to compensate a radiological procedure or examination; b) optimization – always use the lowest possible dose of radiation; c) dose limitation – individual doses of professionals and individuals should not exceed the primary limits of annual doses established by CNEN norms, which reflect norms by international agencies of radiological protection; d) prevention – every effort should be made to establish rigid measures for accident prevention.^2,6

Resolution 518/2003 issued by the Brazilian Department of Work and Employment, published in the Official Gazette on April 7, 2003, adopts as dangerous activities, among others, activities of X ray device operation that are included in the list of risk activities and areas presented in regulatory norm (NR) 16. Such Resolution stresses that any worker's exposure to ionizing radiation is potentially harmful to their health, taken into consideration that even new technologies introduced in radiology devices and in individual protection equipment (IPE) do not allow elimination of this risk. Such activities are also considered as dangerous activities and operations by CNEN. Dangerous work relative to worker's exposure to ionizing radiation assures a 30% extra pay for job hazards, according to paragraph 1, article 193, Labor Laws Consolidation (CLT).^22-24

Type of radiation dose monitors

There are several types of radiation dose monitors or dosimeters, such as the photographic monitor (film), thermoluminescent (TLD), which is the most widely used in radiology services, and the electronic dosimeter. Extremity dosimeters (bracelet, ring) are usually indicated for professionals dealing with fluoroscopy equipment.^6,25 However, each type of monitor has advantages and disadvantages that should be "weighed" in relation to varied factors of each radiology service.^4,26

The TLD dosimeter is a device comprised of crystals with thermoluminescent properties – emits light when heated – used to measure ionizing radiation doses, such as those generated by X ray devices or radioactive sources, whose intensity is proportional to the incident radiation dose. TLD monitors should be placed above the lead apron at the chest level, and the service of radiological protection should inform the company in charge of individual monitoring, which has to calculate effective dose.^6,27

Individual dosimeters should be used during the entire work shift. When it is not being used, it should be kept along with other dosimeters of other professionals in the institution and the standard dosimeter. The standard dosimeter is used as a reference in the reading system, that is, the doses indicated in the monthly dose report are calculated by measuring the dose of each user's dosimeter and subtracting the value of the accumulated dose in the standard dosimeter.^27,28

In addition to individual monitors, areas under radiological protection control should have area monitors for regular control of environment radiation. Areas considered radiation-free are those in which the radiation does not exceed 1 mSv/month. Restricted areas have controlled access, since they have radiation levels higher than 1 mSv/month, and are subdivided into a) supervised area, for radiation levels between 1 and 3 mSv/month; b) controlled area, for radiation levels higher than 3 mSv/month.⁶

Resolution 453/98 of MS, for purposes of psychical barrier planning and verification of radiation level adequacy in radiometric measurements, specifies the following levels of equivalent dose: 5 mSv/year for controlled areas and 0.5 mSv/year for radiation-free areas.¹⁵

Individual protection equipment

According to the NR 6, IPE is every device that a worker must wear to protect him from likely risks of threatening his safety and health. They should have an Approval Certificate (AC) issued by the MTE, which is in charge of inspecting the quality of IPE.^29,30

IPE include the following: a) 0.5 mm lead equivalent aprons; b) 0.5 mm lead equivalent lead thyroid shield; c) 0.25 mm lead equivalent finger gloves; d) 0.5 mm lead equivalent glasses with side and front shield.

Professionals that are not close to the primary beam should be protected from scattered radiation with protective equipment having attenuation not lower than 0.25 mm lead equivalent.¹⁵

Secondary or scattered radiation is the main source of radiation in professionals. Lead aprons measuring 0.5 mm in thickness can absorb up to 98% of secondary radiation; 0.25 mm aprons absorb up to 96%, protecting gonads and about 80% of the active bone marrow. Thyroid protectors may reduce gland exposure in up to 10 times.³¹

Lead surgical gloves, which can be bought in the market, have an attenuation factor against radiation ranging between 5 and 20%, depending on the model. However, even wearing protective gloves, the physician should avoid hand exposure in the radiation field or under the image intensifier, since such procedure is rarely a medical necessity. Because it reduces tactile sensitivity, can prolong the procedure and also cause more radiation in the hand, as such gloves do not provide efficacious protection, their use is not frequent.³¹

In addition to the equipment listed above, every fluoroscopy equipment should have lead curtain or drape, inferior and lateral, as well as mobile lead blinds or shields, thickness not lower than 0.5 mm lead equivalent to protect the operator against the radiation scattered by the patient. Studies on cardiac catheterization procedure reported an efficient reduction in physicians' doses by 50% when the side lead shield is well located between the physician and the patient during an examination. Mobile screens, when well used, reduce exposure of workers operating the hemodynamic device in up to 85% of radiation; when the screens are used, the gross position of a two-step distance from the examination table may reduce secondary radiation by half.^{6,14,15,17,18,31}

Lead clothing should never be folded and, when not being used, they should be maintained at a horizontal position or on an appropriate support, since folding can fracture the lead lining and violate the radioprotection system.^6,15

Balter³¹ warns that protection flaws in lead clothing can rarely be detected visually, and that they should be submitted to fluoroscopy annually to verify their integrity.

Protection equipment should be available for free and in good conditions of use in radiodiagnostic services, and health professionals should be able to properly wear and store such equipment.^17,29,30

According to Balter,³¹ not wearing lead IPE during vascular catheterization procedures increases exposure dose by a factor of 10 or more.

Physical principles of X ray production

X rays are photons originating in the atom electrosphere. Because they are electromagnetic radiations, they have no charge or mass (different from alpha and beta nuclear radiations, which are charged and have their own mass numbers) and are composed of pure energy, such as visible light.^1,2

Production of radiation occurs in the X-ray tube, when a high-voltage electric current is applied. By heating a metallic filament called cathode, it causes an accelerated displacement of electrons, which will collide against a metal shield called anode after passing through the vacuum present in X-ray tubes. The energy of electrons and, consequently, of the X-ray beam generated in the anode is directly related to the tension (kilovolt, kV) imposed between the cathode, the anode and the electric current (milliampere, mA) applied to the device.^2,32

X rays have very important physical characteristics, such as: a) they blacken photographic film; b) they produce secondary or scattered radiation when passing through a body; c) they travel in a straight line and in all directions; d) their ability of passing through a body is directly proportional to the tension (kV) given to the tube; e) they obey the inverse-square law (1/r²); f) they can cause genetic mutations by interacting with reproductive cells.⁶

The X-ray beam, when incident on a patient's body, has part of its radiation absorbed, a part that goes through it and reaches the image intensifier, and another part that produces secondary or scattered radiation, which scatters to the sides and even behind. Levels of scattered radiation depend on the patient's thickness or weight, kilovoltage and milliamperage, collimator opening, tube-intensifier distance, and angiographic projection. Projections in which the X-ray tube is on the same side as the operator cause the highest levels of secondary radiation.²

Biological effects of radiation

Risks of improper use of ionizing radiation are known to the public. Based on these principles, the CNEN regulated its use in the norm CNEN-NN-3.01. Due to lack of personnel training, most radiology units do not have proper safety standards to perform procedures. Because of these situations, professionals involved in radiological procedures and the population that consumes such services are mostly affected. Due to inadequacy of techniques, accessories, consumption material and individual protection equipment, they are all are exposed or submitted to high doses of ionizing radiation when radiological procedures or exams are performed.^6,20,33

The mechanisms by which ionizing radiation acts on the living cell are several and partly unknown. In the interaction process between radiation and matter, there may be ionization and excitation of atoms and molecules, causing changes in molecule structure. The most important lesion occurs in the deoxyribonucleic acid (DNA). Acute effects are possibly due to water ionization, which is decomposed and forms free radicals, which influence cellular metabolism, generating oxidized substances and hydrogen oxide. Such oxidation affects enzymatic protein groups, especially the sulfhydryl group. A simple electronic excitation is able to break 20 hydrogen bonds. Even in small radiation doses quantitative effects may be higher and with multiple breaks of protein chains. In addition, there may be complete cell disintegration, although there is a possibility of its self-restitution.^1,6,33,34

Radiation-induced effects may be classified according to dose value, form of organism response, and time of manifestation and severity in the organism. The main consequence of the radiation/matter interaction is atomic-molecular excitation, and their biological effects are classified as: a) stochastic effects that cause a random change in the DNA of a single cell, which continues to reproduce itself, and are proportional to the received radiation dose, with inexistence of a safe dose limit (for example, cancer and leukemia); b) deterministic effects, which are somatic changes due to cell death and usually occur days or weeks after radiation of the affected organ or tissue and only if the organism has absorbed a minimal radiation dose, which is specific for each organ (for example, leucopenia, nausea, anemia, sterility, radiodermatitis, and cataract).^{1,2,6,7,11,20,32,34} The most frequent deterministic effects are chronic radiodermatitis, changes in white and red cell counts, vasculitis, and changes in the reproductive system. Leukemia, for being the main disease due to chronic exposure to radiation, requires periodic blood tests as one of occupational medical controls.^1,2,34

Ionizing radiations may produce gene and chromosomal mutations and the relationship between dose and effect is linear for these changes. There does not seem to be a limit below which a radiation dose has ineffective action. If a mutation occurs in a gamete, it can be logically transmitted one single time. In case it occurs in a spermatogonium (even of a child), it may be present in such cells throughout the entire individual's life continuously passing to gametes. Therefore, radiations may be harmful as mutagenic agents not only when they affect adults in reproductive period, but also when administered to children.^1,20,33-35

Even when exposure levels to X rays are low, it is important to stress that chronic exposure may lead to malignant disease and also to cataract. For the different types of malignant disease that radiation may cause, risks follow different time patterns; leukemia seems to have a constant relative risk in time, especially if the professional is continuously exposed to fluoroscopy. For solid tumors, such as lung, breast, thyroid, stomach and colon cancer, relative risk is reduced after about 10-20 years of exposure. Leukemia is the most common type of neoplasm secondary to radiological exposure, followed by gastrointestinal, breast, lung and thyroid tumors.³⁵

The human body has enough plasticity to revert such effects and often repair cells that have not suffered irreversible lesions to inhibit their proliferation, but damaged germinative cells may be irreversibly damaged, and changes can be transmitted to the fetus.^1,6

Azevedo⁶ warns that the effects of prenatal radiological exposure depend on gestation period, and there may be flaws in embryo fixation, with abortions and malformation of organs, increased likelihood of cancer in the newborn, and reduced intelligence quotient (IQ).

Labor law, by means of NR 7 and 9, ensures prevention and protection of workers employed by health institutions against the effects caused by exposure to ionizing radiation, making the Program of Medical Control of Occupational Health (PCMSO) mandatory, in association with the Environmental Risk Prevention Program (PPRA). The PCMSO has to include a mandatory occupational and periodic medical examination for professionals exposed to radiation, as well as minimal laboratory tests, such as complete blood count and platelet count every 6 months.^30,36

Conclusion

Even with all the benefits in medical area, radiodiagnostic techniques may imply health risk, since obtaining images to have a diagnosis or performing a treatment involves use of X rays and, therefore, may cause harm to the health of physicians and health team working in the hemodynamic laboratory.

Due to the inherent risks in radiation use, it had to be regulated. Thus, MS, CNEN and MTE established resolutions and norms that follow the guidelines published by ICRP, determining the implantation of a high-quality radiologic department, with an efficient basic program to ensure quality control in radiation services, images and doses in both professionals and patients.

Therefore, it is extremely important to develop and implement a radiological protection and safety system to be applied in radiodiagnosis. Such system should comprehend control of radiation sources and staff manipulating these sources using a regular training program of professionals.

Hence, it is important that medical teams working in hemodynamic services have proper conditions to perform their functions, minimally exposed and with a radioprotection service that follows international guidelines.

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Correspondence

Publication Dates

• Publication in this collection
  20 Feb 2009
• Date of issue
  Dec 2008

History

• Received
  19 Aug 2007
• Accepted
  26 Aug 2008