Presentation on theme: "EXTERNAL AND INTERNAL CONTAMINATION DECONTAMINATION AND DECORPORATION"— Presentation transcript:
1EXTERNAL AND INTERNAL CONTAMINATION DECONTAMINATION AND DECORPORATION Module Medical XV. Contamination and decorporationEXTERNAL AND INTERNAL CONTAMINATION DECONTAMINATION AND DECORPORATIONPurposeTo give participants general information on the effects of external and internal exposure to radionuclidesTo recommend practical measures for assessment and treatment of contaminated peopleObjectivesTo enable the participants to:describe ways people become externally or internally contaminateddescribe techniques for decontaminationidentify samples useful for bioassay and explain the role of the health physicist in dose assessmentidentify pharmaceuticals and procedures for limiting uptake and facilitating removal of radionuclidesgive examples of treatment for removal of selected radionuclides from the bodydiscuss criteria for follow-up or hospitalization of internally contaminated patientsScopeThis module presents the routes of radioactive contamination; the consequences of contamination depending upon the physical and chemical nature of the contaminant and the route of intake; diagnostic techniques to measure contamination levels; decontamination and decorporation techniques.ActivityLecture, questions and discussionDuration2 hrsReferencesNATIONAL COUNCIL ON RADIATION PROTECTION, Management of persons accidentally contaminated with radionuclides. NCRP Report No. 65. Bethesda, MD 1993INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment and treatment of external and internal radionuclide contamination. IAEA-TECDOC-869. Vienna 1996INTERNATIONAL ATOMIC ENERGY AGENCY, Dosimetric and Medical Aspects of the Radiological Accident in Goiania in 1987, TECDOC-1009, IAEA, Vienna 1998Iljin L.A. ed. Radiation Medicine (in Russian), Volume 2, IzdAT, Moscow, 2001Module XV
2Introductıon Contamination risk Module Medical XV. Contamination and decorporationIntroductıon Contamination riskThe probability of external and internal radioactive contamination has increased with the use of radionuclides in research projects, medical applications, industrial processes and nuclear power plants. Of about 400 recorded radiation accidents, there were only a few with significant radioactive contamination of persons. Chernobyl in 1986 and Goiania in 1987 are the most important among them. Both these accidents resulted in a few dozen victims who required internal and external decontamination.Management strategies require knowledge of the physical and chemical characteristics of the radionuclides, their metabolism in humans, and the methods of accelerating their elimination from the body. Treatment should be a team effort that includes physicians, health physicists, analytical chemists, toxicologists, and dosimetry specialists.Module Medical XV.
3Contamination sources: reactor accidents Module Medical XV. Contamination and decorporationContamination sources: reactor accidentsExternal and internal can arise from a number of circumstances, such as:reactor accidents involving damage to the core leading to combined inhalation-peroral entry into the body of a mixture of fission products (primarily of volatile caesium and iodine isotopes).There were two reactor accidents which are known to have caused measurable contamination of the public with radionuclides: (1) the Windscale reactor accident in the UK in October and (2) the Chernobyl nuclear power plant accident in the Soviet Union in April 1986.Contamination of workers and members of the public with radionuclides may occur due to:accidental violation of the regulations or procedures governing work with radioactive substances, especially in form of powder or solution accidents involving leaking or damaged sealed sources (i.e. 192Ir, 137Cs, 60Co, 226Ra) errors in dosage of radionuclides used for diagnostic and therapeutic purposes accidents involving the fabrication and reprocessing of nuclear fuels and the transportation and disposal of radioactive waste Module Medical XV.
4Module Medical XV. Contamination and decorporation Goiania accidentThe Goiânia radiological accident resulted in the highest level of 137Cs internal contamination ever recorded (2-3 GBq). There were 249 contaminated persons, all members of the general public, 129 with internal contamination.In one case, doses from external and internal exposure were similar and the internal dose played a significant role in the victims' death.Area of contamination: m2249 contaminated (137Cs) persons,129 with internal contamination, 4 deathsModule Medical XV.
5External radionuclide contamination Module Medical XV. Contamination and decorporationExternal radionuclide contaminationExternal contamination: radioactive material, as dust, solid particles, aerosols or liquid, becomes attached to victim’s skin or clothesExternal contamination occurs when a radioactive material, in the form of dust, solid particles, aerosols or liquid, becomes physically attached to skin or clothes.Considerable contamination of clothing can occur during an accident or during the immediate cleanup.Wet clothing impregnated with radioactive substances brings the contaminant into more intimate skin contact, thereby increasing the skin dose, as was experienced in the Chernobyl accident.Beta emitting radionuclides are the most hazardous, and can cause serious burns of the skin and underlying tissue.Module Medical XV.
6External contamination measurement Module Medical XV. Contamination and decorporationExternal contamination measurementProper monitoring of patient can detect andmeasure alpha, beta or gamma emitters; radiation type depends on isotope in contaminantThere are a number of survey instruments available for beta-gamma detection and measurement. The great majority of instrument probes allow for discrimination between beta and gamma radiation and levels should be recorded both separately and as a total count.It is important to remember that some low energy beta emitters exist and special probes are required for their detection. Thus, the assistance of the experienced health or medical physicist is important.Alpha particles travel only a few centimetres in air and up to 40 micrometers in tissue and as such cannot penetrate the cornified epithelium. The low penetrating power of the alpha particles, therefore, dictates that alpha surveys must be accomplished with thin window probes, minimal absorbing material between the detector and source, and a limited physical distance between the probe and the surface monitored.Alpha MonitorModule Medical XV.
7Module Medical XV. Contamination and decorporation Radiological surveyAs soon as possible after an accident has occurred an initial external contamination survey (of skin, eyes, lips) should be made with instruments adequate for the particular situation. If there is any doubt regarding the radioactive materials involved, both a beta-gamma and alpha monitor should be used. The results of the radiological survey should be recorded on an anatomical chart and made a part of the patient's medical record.The probe can be held about one inch from the surface monitored and may be covered with a plastic or rubber glove to prevent contamination of the probe and subsequent false readings. If the probe cover becomes contaminated (evidenced by false increase in background) it should be changed. The results of all surveys should be recorded on anatomical charts (including clear personal data, date and time).Module Medical XV.
8Module Medical XV. Contamination and decorporation Radiological triageQuick `frisk’Triage following known or suspected radiation accidents includes both medical and radiological considerations. Medical triage should be based upon local procedures for medical management of persons involved in accidents with radioactive materials and on considerations dependent on the severity of injuries. Treatment in life threatening conditions has priority over considerations for exposure to or contamination with radioactive materials. Following medical stabilization of the patient’s condition, careful radiological assessment can be directed to determining the presence of both external and internal contamination.A slow, thorough survey of the entire body should permit radiological triage yielding two groups. One group consists of individuals with no detectable external contamination, and the other group with radioactive contamination of skin, hair or wounds. Survey should include techniques and instrumentation for detecting alpha, beta, and gamma radiations or any combination thereof. If large numbers of persons require radiological survey, such as occurred in the Goiânia (Brazil) 137Cs accident, a quick `frisk' may be initially used instead of a total body survey. The 'frisk' should include the hands, feet (and shoes), face and hairy top of the head. Quick frisks must always be followed by a more complete body survey. Individuals found to be externally contaminated should have their clothing removed, shower, dry, and then be resurveyed. Once decontaminated to the extent possible, clean clothing should be made available. Any wounds must be considered contaminated unless proven otherwise. Some of them may result in incorporation of radioactive material in the body.persons monitored in Goiania at olympic stadiumModule Medical XV.
9Module Medical XV. Contamination and decorporation DecontamınatıonSkin decontamination should be undertaken to decrease the risk of skin beta burns, to lower the risk of internal contamination of the patient, and to reduce the potential of contaminating caretakers and the environment.After the patient's clothing is removed, showering or washing the patient with detergent and lukewarm water is 95 per cent effective. Soap and detergents emulsify and dissolve contamination. Gentle brushing or the use of an abrasive soap or abrasive granules may be indicated. They physically dislodge some contamination held by skin protein, or remove a portion of the horny layer of the skin. Addition of a chelating agent helps by binding the contaminant in a complex as it is freed from the skin.Keep in mind that the stratum corneum of the epithelium is replaced every days. Thus, contamination that is not removed and is not absorbed by the body will be sloughed within one-two weeks.Module Medical XV.
10Decontamination techniques Module Medical XV. Contamination and decorporationDecontamination techniquesMany cases of skin decontamination will be performed by non-medical personnel at or near the accident scene. When initial cleansing methods are not effective, the patient should be referred to a physician. The physician's decision on decontamination procedures should be based on an understanding of the physical and biological principles involved. Success in achieving the objectives stated above requires thoughtful appraisal of the level of residual contamination, rate of decontamination, and condition of the skin - factors that change as the cleansing procedures proceed. The area of skin contaminated must be clearly determined using appropriate monitoring techniques. After monitoring, this should be covered to prevent spread of contamination. Contaminated skin on the head or near any body orifice is decontaminated followed by other areas. In the latter case, areas of highest contamination have first priority. Swipes or swabs of contaminated areas should be taken for analysis to determine amounts and identity of radionuclides, and decontamination effectiveness. Strict contamination control procedures should be used in handling these skin swipes/swabs.Module Medical XV.
11Decontamination procedures Module Medical XV. Contamination and decorporationDecontamination proceduresStart with gentle stream of warm waterUse mechanical action of flushing and/or friction of cloth, sponge or soft brushFor showering, begin with the head and proceed to the feetKeep materials out of eyes, nose, mouth and woundsUse waterproof draping to limit spreadCover uncontaminated area with plastic sheet and tape edgesBegin with the least aggressive techniques and the mildest agents and progress to more aggressive ones. Whatever the procedure, take care to limit mechanical and chemical or thermal irritation of the skin. Aggressive rubbing or shaving should be avoided since they tend to cause abrasion and erythema and can lead to internal contamination.Complete decontamination is not always possible because some radioactive material can remain fixed on the skin surface.Decontamination should be only as thorough as practical. The decontamination procedure stops when the radioactivity level cannot be reduced any more.Module Medical XV.
12Decontamination techniques Module Medical XV. Contamination and decorporationDecontamination techniquesUse single inward movements or circular motionThen rinse area with tepid water and gently dry using the same motionsAfter drying, remonitor skin to determine effectiveness of decontaminationDecontamination can be accomplished by moving from the outer edge of a contaminated area toward the centre. Single inward movements can be used or a circular motion with increasingly smaller circles. The process may be repeated 2 or more times using a clean, soft surgical brush, 4 x 4 gauze pads, sanitary napkins, etc., each time.Afterwards, the area should be rinsed with tepid water and gently dried using the same motions working inward. After drying, the skin should be remonitored to determine the effectiveness of decontamination. If two or three washing/drying procedures are used (especially if aggressive techniques are used) and if the contamination level is not decreased, stop the procedure and seek expert consultation.Likewise, if hypaeremia or irritation appears, stop the procedure and seek expert consultation. It should be recognized that the stronger agents are normally used after a certain amount of skin irritation has already occurred. It is a common mistake to underestimate the potential for skin irritation until too late. Particular care should be taken on the more sensitive and thin skin areas, and also areas of skin grafts or skin donor sites.Module Medical XV.
13Decontamination procedures: body orifices Module Medical XV. Contamination and decorporationDecontamination procedures: body orificesConsideration:Orifices need special attention because absorption of radioactive material more rapid than through skinProcedures:Oral cavity: brush teeth with toothpaste, , frequently rinse mouth with 3% citric acidPharyngeal region: gargle with 3% H2O2Swallowed radioactive materials: gastric lavageNose: rinse with tap water or physiological salineMouthNostrilsModule Medical XV.
14Decontamination procedures: body orifices Module Medical XV. Contamination and decorporationDecontamination procedures: body orificesProcedures:Eyes: rinse by directing stream of water or physiological saline from inner to outer canthus while avoiding contamination of nasolacrimal glandEars: - rinse externally with water- rinse auditory canal using ear syringeEyesEarsModule Medical XV.
15Useful therapeutic agents for skin decontamination-I Module Medical XV. Contamination and decorporationUseful therapeutic agents for skin decontamination-ICommon soap or detergent solution for skin and hair; low acidity (pH ~5) recommendedChelating agents:solution of EDTA 10% for skin or hair contamination with transuranium, rare earth and transition metalsDTPA 1% in aqueous acid solution (pH ~4) for washing skin after contamination with transuranics, lanthanides or metals (cobalt, iron, zinc, manganese)Soaps and detergents can emulsify and dissolve contamination and are frequently all that are needed for decontamination of skin. Abrasive soap or abrasive granules (i.e. cornmeal) dislodge some contamination physically held by skin protein or remove a portion of the horny layer. In any case, tepid water (never hot) should be used for decontamination.Chelating agents, sodium hypochlorite, and titanium dioxide (an abrasive) have been successfully used in previous contamination accidents. The abrasive agents must not be used on the face. While additional chemical techniques are seldom necessary, they can be used but only with care and expert advice.Module Medical XV.
16Useful therapeutic agents for skin decontamination-II Module Medical XV. Contamination and decorporationUseful therapeutic agents for skin decontamination-IIPotassium permanganate, 5% aqueous solution should be used carefullynot recommended for face, natural orifices and genital regionsuse when conventional washing ineffectivefollow with application of reducing agent, then rinse with waterHydroxylamine or sodium hyposulfite, 5% freshly prepared aqueous solutionsreducing agents - apply after KMn04 or Lugol, then wash with waterPotassium permanganate, an oxidizing agent, and subsequent application of sodium acid sulphite to neutralize the permanganate, will remove a portion of the horny layer. In cases where contamination is localized in thick, horny areas more aggressive methods can be used but again with expert advice. Fine sandpaper can be used to remove localized contamination.Dermabrasion should be used with great care and only after expert consultation. Sticky tapes have limited usefulness since they tend to remove the horny layer rapidly and can increase percutaneous absorptionModule Medical XV.
17Useful therapeutic agents for skin decontamination-III Module Medical XV. Contamination and decorporationUseful therapeutic agents for skin decontamination-IIIAntiphlogistic topical ointment:To be applied for fixed contamination, especially useful for contamination of fingersIsotonic saline solution for eyesIsotonic 1.4% bicarbonate solution for removing uranium from bodyLugol solutions for iodine contaminationAcetic acid solution (pH 4 to 5) or simply vinegar for decontamination of 32PAntiphlogistic topical ointment:To be applied for fixed contamination; must be kept hours under an occlusive dressing; creates an osmotic gradient which pumps the radionuclide from the skin towards the outside; especially useful for finger contamination.Isotonic saline solution for eyes.Isotonic 1.4% bicarbonate solution for removing uranium contamination.Lugol solutions (50 mg iodine and 100 mg potassium iodide per millilitre) for decontamination of radioactive iodine compounds from the skin. It has to be followed by application of sodium hyposulphite and then rinsed with water.Acetic acid solution (pH 4 to 5) or simply vinegar for contamination by 32P; wash and then rinse with water.Module Medical XV.
18Internal contamination Module Medical XV. Contamination and decorporationInternal contaminationOccurs when people ingest, inhale, or are injured by radioactive materialMetabolism of non-radioactive analogue determines radionuclide’s metabolic pathwayRadionuclides obey the same principles of toxicity as do non-radioactive toxins. Basically, toxins are absorbed into the body and then distributed throughout it or, for some chemicals, concentrated in critical organs. A toxicant may undergo metabolic changes in the liver or in target organs and become more active or less active metabolites. Ultimately, the toxicant is eliminated through the body's excretory mechanisms.Internalization consists of intake, distribution, and metabolism.Module Medical XV.
19Module Medical XV. Contamination and decorporation Extent of hazardFactors determining extent of contamination hazard:Amount of radionuclide(s)Energy and type of radiationBiological and radiological half-lifeCritical organChemical and physical properties of radionuclideThe extent of a contamination hazard is determined by a number of factors:Amount of radionuclideEnergy and type of radiationDuration of external/internal exposureEffect on critical organs:- Some internalized chemicals, including the radionuclide sodium-25, are evenly distributed throughout the human body.- Others have an affinity for critical organs, or target organs, where they concentrate. For example, the critical organ for lead is bone. Although lead is initially distributed in soft tissue organs, including the kidneys, liver, and red blood cells, it is redistributed to bone where it forms long lasting compounds and is slowly eliminated.- The critical organ for the iodine isotopes is the thyroid gland and, for the uranium isotope, the critical organs are kidneys, liver and bone.Chemical makeup of the radionuclide:Heavy metals like uranium are toxic for the kidneys and liver.Different radioactive isotopes and chemical compounds of uranium have different toxicity.Module Medical XV.
20Module Medical XV. Contamination and decorporation Intake routesIn order of decreasing frequency, contaminants enter the body by four principle routes:Inhalation:Particularly likely with explosion or fireParticle characteristics important (size, chemical composition, solubility in body fluids)Ingestion:Critical for general public after accidental environmentalreleaseWound contaminationAbsorptionThe usual routes for internal contamination are through inhalation, ingestion, and wounds but it may also occur by percutaneous absorption. Mechanical, chemical, or thermal injury to the skin during decontamination may also lead to internal contamination.Module Medical XV.
21Contamination sources in nuclear accidents Module Medical XV. Contamination and decorporationContamination sources in nuclear accidentsIn the immediate vicinity of a nuclear accident (the near field), exposure could begin immediately if the released plume is at a low level. Main route of exposure is inhalation.Further away from the site of the accident (the far field), the main route of exposure would be ingestion of contaminated food and drink, particularly milk. Exposure by these routes could last longer, cover a larger area, and affect a larger population than exposure in the near field.Module Medical XV.
22Module Medical XV. Contamination and decorporation InhalationThe inhalation pathway is the primary intake route for radioactive contamination. It is particularly likely when an explosion or fire occurs. Gaseous material or particulate matter may be inhaled and subsequently be absorbed or deposited throughout the respiratory tract.Module Medical XV.
23Module Medical XV. Contamination and decorporation InhalationFate of inhaled particles dependent on physicochemical characteristicsSoluble particles (3H, 32P, 137Cs) absorbed directly into circulatory systemInsoluble particles (Co, U, Ru, Pu,, Am) are cleared by lymphatic system or by mucociliary apparatus above alveolar level. Most secretions reaching pharynx swallowed, enter gastrointestinal systemAfter deposition, absorption will depend on the chemical solubility of the contaminant.Soluble particles will be absorbed either into the blood stream directly or pass through the lymphatic system with ultimate movement into the circulatory system. Examples of such radionuclides are 3H, 32P, 137Cs, radioiodines and some chemical forms of 90Sr.Insoluble particles are transferred from the site of deposition by phagocytosis (lymphatic circulation) and cell migration.The mucociliary apparatus will clear insoluble particles that are deposited within the respiratory tract above the alveolar level. Secretions containing the particles that reach the pharynx, are subsequently swallowed and enter the gastrointestinal system. Insoluble particles are usually metallic oxides or metals. Examples are the oxides of Co, U, Ru, Pu Am.Module Medical XV.
24Deposition and clearance from respiratory tract Module Medical XV. Contamination and decorporationDeposition and clearance from respiratory tractContaminant's particle size determines deposition in respiratory tractParticles <5 microns in diameter may reach alveolar areaParticles >10 microns too large to pass into alveoli, deposited in upper airwaysInsoluble particles, until cleared from the respiratory tract, will continue to irradiate surrounding tissue. Large particles deposited in the upper bronchi will be cleared from the respiratory tract within one hour. Clearance of insoluble particles from the alveolar spaces may take up to 1500 days. In the alveoli, fibrosis and scarring are more likely to occur due to the localized inflammatory response to foreign bodies.Module Medical XV.
25Module Medical XV. Contamination and decorporation IngestionAll swallowed radioactive material enters digestive tractprimarily from contaminated food and watersecondarily from respiratory tractAbsorption from the gastrointestinal tract depends onchemical make-up and solubility of contaminantIngestion of radionuclides is uncommon in industrial facilities or laboratories. However, it could be of importance for the general public.A striking example is the accidental ingestion of radiocaesium from a dismantled radiation therapy source by persons in Goiânia, Brazil.For large scale radiation accidents involving nuclear power reactors, the possibilities of ingesting milk or vegetables contaminated with radioiodine and meat, milk and vegetables contaminated with radiocaesium are of concern.All swallowed radioactive material, whether primarily from contaminated food and water, or secondarily from the respiratory tract, will enter the digestive tract, and will be handled like any other element. Absorption from the gastrointestinal tract depends on the chemical make-up of the contaminant and its solubility.Module Medical XV.
26Module Medical XV. Contamination and decorporation IngestionGI absorption <10% for most elementsElements of high absorption:radium (20%)strontium (30%)tritium (100%)iodine (100%)caesium (100%)Radioiodine and caesium are rapidly absorbed; plutonium, radium and strontium are not. The GI tract is considered the target organ for ingested insoluble radionuclides. The large intestine receives the greatest radiation exposure due to its slower transit time. The clearance time for the gastrointestinal tract is approximately 24 hours for individuals who maintain a high fibre diet. Individuals on a low fibre diet have a slower transit time, which may extend up to 5 days. Even in these individuals, insoluble alpha particle emitters will not cause significant injury because the exposure time within the critical organ is relatively short.Module Medical XV.
27Module Medical XV. Contamination and decorporation Wound contaminationAny wound considered contaminated until proven otherwiseAny wound must be considered contaminated until proven otherwise. All wounds must therefore be meticulously debrided and evaluated for the presence of radioactive contaminants when they occur in a radiological environment.Solubility, pH, tissue reactivity and particle size are factors that determine the speed of absorption from a wound. The higher the solubility, the faster the absorption rate. Insoluble particles of smaller size may be cleared by phagocytosis and enter the lymphatic system. If the contaminate is highly acidic, local tissue coagulation will occur decreasing the dispersion rate.For example, human wounds that contain depleted uranium may develop cystic lesions that decrease the uranium absorption rate. This has been demonstrated in Gulf War veterans wounded by depleted uranium shrapnel. Studies in these veterans and in animal models have demonstrated that uranium from these wounds is slowly distributed to the liver and kidneys.Open fracture demonstrates wound contamination with depleted uranium shrapnelModule Medical XV.
28Percutaneous absorption Module Medical XV. Contamination and decorporationPercutaneous absorptionGenerally, radionuclides do not cross intact skin, so uptake by this route does not occurMost important exceptions are: tritium, iodine, caesiumSkin wounds, including acid burns, abrasive scrabbing, create portal for particulate contamination to subcutaneous tissue, bypassing epithelial barrierSkin absorption occurs primarily through passive diffusion. The physical barrier of the epithelium is resistant to particulate matter.Very few radionuclides can penetrate the skin to any appreciable degree. Tritiated water is the primary exception to this since, like any other water, it can pass readily through the skin.All substances have a skin permeability rate dependent on their relative solubility in both lipids and water. Care must be taken during decontamination, as skin that has been mechanically damaged by repeated abrasive scrubbing will allow for greater absorption.Skin that has been exposed to certain chemicals, for example, dimethyl sulphoxide (DMSO), will also be more permeable. Skin wounds, including acid burns, create a portal for any particulate contamination to come into direct contact with the subcutaneous tissue, bypassing the epithelial barrier.Module Medical XV.
29Distribution and deposition Module Medical XV. Contamination and decorporationDistribution and depositionIodineUraniumOnce a radionuclide is absorbed, it crosses capillary membranes through passive and active diffusion mechanisms and is then distributed throughout the body.Radionuclides follow the same pharmacokinetics as do stable (non-radioactive) chemicals. For example, Sodium-25 (25Na) is evenly distributed throughout the body after resorption while iodine-131 (131I) has a strong affinity for the thyroid gland, the critical organ for iodine deposition. Uranium's primary sites for deposition are the liver and bones.The rate of distribution to each organ is related to the metabolism of the organ and the affinity of the radionuclide for naturally occurring chemicals within the organ. The liver, kidney, adipose tissue and bone have higher capacities for binding chemicals due to their high protein and lipid make-up.Module Medical XV.
30Module Medical XV. Contamination and decorporation MetabolismA radionuclide will be metabolized according to its chemical properties and will be excreted either in its original state, or as a metabolite. The biological half-life of a radionuclide is as important as its radiological half-life in determining the significance of the exposure. Most ingested heavy metal nuclides will pass through the gastrointestinal tract unchanged.Excretion is determined by the relative solubility of the compound and its delivery to the appropriate organ. Most elimination of absorbed nuclides will occur through the urinary tract. Other primary routes of excretion are through the liver and lungs. Minor routes of elimination include sweat, saliva or milk. In general, compounds that are water soluble are excreted through the urine, while lipid soluble compounds are secreted via the bile into the intestine. There is a lot of variability in elimination, depending on individual factors, including bowel motility, metabolism and diet.Diagram of intake, metabolism and excretion of radionuclides
31Module Medical XV. Contamination and decorporation Internal contamination measurement : direct methodsA number of methods are used to detect contamination and to estimate its extent.The methodology for assessing intake will depend on the systemic target organs or tissue, radionuclide emissions and excretion functions. For instance: the assessment of 3H, 32P, 90Sr which are pure beta emitters is possible from urine analysis. 131I (in the thyroid) or 137Cs (whole body) can be assessed in-vivo by measuring their gamma-ray emission.Direct contamination measurementDirect measurement methods include total body and partial body counters that also detect skin and wound contamination. The advantage of direct measurement is that it does not require the use of excretory rates for estimation of contamination. A major disadvantage is that measurements are influenced by external contamination and background radiation levels.Total and partial body counters measure beta and gamma radiation powerful enough to reach the body surface. Partial body counters are used for chest and thyroid measurements. Chest counters detect respiratory tract levels of contaminants such as plutonium and uranium. Alpha contamination measurement usually relies on detection of the gamma/beta radioactivity of daughter products or other contaminants.Whole body countersThyroid uptake systemModule Medical XV.
32Indirect contamination measurement Module Medical XV. Contamination and decorporationIndirect contamination measurementIndirect measurement of contamination includes nasal swipes to determine respiratory intake of radioactive aerosols, and also urine and faeces sampling to establish internal contaminationAlpha and beta emitters, the most hazardous internal contaminants, detected through bioassay samplingAccurate bioassays require carefully executed sampling over time and knowledge of type and time of contaminationSkin swipes and nasal swipes are used to estimate the extent and type of contamination . Nasal swipes are taken bilaterally, using moistened, cotton-tipped applicators to swab the nostrils. The swabs are then placed individually in test tubes or envelopes, which are labelled with the subject's name and the sample collection time and date. The swipes are sent to a facility with a laboratory counter where contamination can be measured.Detection of radioactive material in both nostrils indicates respiratory inhalation. Unilateral contamination usually indicates surface contamination only.Bioassay sampling of urine and faeces provide indirect measurement of intake of radioactive materials to the body. Radioactivity and concentration of the nuclide in urine and faeces depends on individual metabolic and clearance rates. Extrapolation curves to estimate internal contamination are based on average human metabolic and clearance rates.
33Module Medical XV. Contamination and decorporation Bioassay samplingBioassay sampling and excretion data are the principal methods of determining the presence of alpha and pure beta emitters, which are the most hazardous internal contaminants. Initial samples to be used to establish baseline levels of urine and faecal radioactivity should be obtained from a patient as soon as the medical condition allows.Measures should be taken to avoid accidental contamination of samples. For example, contaminated clothing from the victim should be removed and initial skin decontamination steps should be accomplished before sampling, and gloves should be worn by all personnel handling capture containers.Bioassay accuracy depends on baseline levels, multiple post-exposure samples, and knowledge of the precise time of contamination and of the type of contaminant.The activity in the urine represents the absorbed portion of the radionuclides.The activity in the faeces represents:ingested and unabsorbed materialthe unabsorbed portion of radionuclides physically cleared from the nasopharynx or the tracheobronchial systemradionuclides cleared from the body via bile and gastrointestinal secretion.
34Managment of internal contamination First Action Module Medical XV. Contamination and decorporationLife threatening conditions have priority over considerations of radioactive exposure or contamination. Attention to vital functions and control of haemorrhage take priorityContamination levels almost never serious hazard to personnel for time required to perform lifesaving measures and decontaminationWhen significant levels of radioactive materials are incorporated, pathological consequences may result and make emergency treatment particularly important.However, this must never take priority over treatment of life threatening conditions and of acute injuries. Following medical stabilization, careful radiological assessment can be performed to determine the presence of both external and internal contamination.It is important to note:Contaminated patients do not represent a direct hazard to health care providers.Lifesaving procedures should never be delayed regardless of the level of contamination.
35Treatment of internal contamination Module Medical XV. Contamination and decorporationTreatment procedures: the sooner started, the more effectiveIn practice, initial treatment decisions based on accident history rather than careful dose estimatesEarly recognition of internal contamination provides the greatest opportunity to remove the contaminant and reduces the potential for harm.Committed dose is the time integral of the dose rate, which decreases as radioactivity diminishes. If the therapeutic action is performed promptly, the benefit in reducing the dose may be significant. In practice, the critical initial treatment decisions have to be based on the accident history, rather than dose estimates. Additional treatment should then be based on more detailed estimates of the maximum credible accident, information from air and surface sampling, and early reports of in-vivo measurements and bioassay.The basic premise for treatment of persons with internal contamination is to reduce the absorbed radiation dose and hence the risk of possible future biological effects. The means available must be used to reduce absorption and internal deposition; and enhance excretion of absorbed contaminants. Both are most effective when begun at the earliest possible time after exposure.
36Basic principles of treatment Module Medical XV. Contamination and decorporationBasic principles of treatmentreduce absorption and internal depositionenhance excretion of absorbed contaminantsRespiratory contamination Little can be done to reduce lung absorption and deposition. Expectorants and mucolytics have not proven effective in increasing the transit rate of insoluble particles to the posterior pharynx. The deposition of insoluble particles may cause fibrosis and pulmonary scarring with resultant pulmonary restrictive disease.Lung lavage has been used in several patients. This is accomplished under general anaesthesia, with a double-cuffed, double-lumen endotracheal tube. One cuff is inflated within the trachea and the other cuff is inflated in one main stem bronchus to isolate the two lungs. One lung is filled with irrigating fluid and allowed to drain by gravity drainage. This is repeated two to three times for each lung. The greatest risk in this procedure is the general anaesthesia, not the fluid-filled lung. Lung lavage is used infrequently and the risk/benefit should be considered carefully.Gastrointestinal contamination The gastrointestinal system is more accessible and amenable for decontamination. Stomach lavage, if done early after ingestion of the contaminant, may be effective. Irrigating solution and gastric contents should be retained and sent for dosimetry analysis. Emetics can be used in conscious patients soon after ingestion. Syrup of Ipecac, followed by large amount of drinking water may induce vomiting. Apomorphine subcutaneously may also be used as an emetic. Magnesium sulphate forms insoluble sulphates with some radioactive materials, reducing absorption. Adsorbents like activated charcoal are used with some success to reduce chromium absorption. Aluminium containing antacids bind with strontium, decreasing the uptake of strontium. Alginates, made from brown sea algae (kelp) and used commonly as a bulking agent in ice cream products, decrease the uptake of strontium as well. The antacid Gaviscon contains 200 milligrams of alginate per tablet. Ten grams of alginate decreases the absorption of strontium by a factor of 10.Module Medical XV.
37Current methods of treatment of internal contamination Module Medical XV. Contamination and decorporationCurrent methods of treatment of internal contamination- Saturation of target organ e.g. potassium iodide for iodine isotopes- Complex formation at site of entry or in body fluids followed by rapid excretion, e.g. DTPA for Pu isotopes- Acceleration of metabolic cycle of radionuclide by isotope dilution, e.g. water for 3H- Precipitation of radionuclide in intestinal lumen followed by faecal excretion e.g. barium sulphate administration for 90Sr- Ion exchange in gastrointestinal tract, e.g. prussian blue for 137CsThe physician may encounter any number of radioactive contaminants following accidental release. Historically, however, only a relatively small number of radionuclides have commonly been encountered in potentially serious accidents. These include 3H, 60Co, 90Sr, 137Cs, 131I, 226Ra, 235U, 238U, 238Pu, 239Pu, and 241Am. Treatment for internal contamination requires a knowledge of the potential risk involved. Treatment is closely linked with metabolic information. The urgency and importance of the treatment depends on the efficiency of the therapeutic method and the amount of the contaminant.Current methods to remove radioactive contaminants involve: - saturation of the target organ e.g. potassium iodide for iodine isotopes - complex formation at the site of entry or in body fluids followed by rapid excretion, e.g. DTPA for Pu isotopes - acceleration of the metabolic cycle of the radionuclide by isotope dilution, e.g. water for 3H - precipitation of the radionuclide in the intestinal lumen followed by faecal excretion e.g. barium sulphate administration for 90Sr- ion exchange in the gastrointestinal tract, e.g. Prussian blue for 137Cs. For practical reasons, it is convenient to consider soluble and non-soluble materials separately. Indeed the metabolic behaviour and therapeutic actions are mainly governed by this duality.
38Diluting agents: water for tritium - 3H Module Medical XV. Contamination and decorporationDiluting agents: water for tritium - 3HSingle exposures are treated by forced fluid intake:Enhanced fluid intake e.g. water, tea, beer, milk has dual value of diluting tritium and increasing excretion (accelerated metabolism)Biological half-life of tritium daysForcing fluids to tolerance (3-4 L/day) reduces biological half-life to 1/3-1/2 of normal valueDiluting agentsTritium follows the pathway of water in the body, penetrates skin, lungs, and GIT, either as tritiated water (HTO) or in the gaseous form. Tritium contamination can be treated by forced fluid intake. Enhanced fluid intake e.g. water, tea, beer, milk has the dual value of diluting the tritium and increasing excretion (accelerated metabolism). This treatment reduces the biological half-life of tritium by a factor of two.Module Medical XV.
39Ion exchange: prussian blue for 137Cs Module Medical XV. Contamination and decorporationIon exchange: prussian blue for 137Cs137Cs - physical half-life Tp=30 years; biological half-life in adults average Tb=110 days, in children 1/3 of thisPrussian blue effective means to reduce body's uptake of caesium, thallium and rubidium from the GITDosage of prussian blue: one gram orally 3x daily for 3 weeks reduces Tb to about 1/3 normal valuePrussian blueCaesium-137 is easily absorbed by the body through ingestion, inhalation, and skin penetration. Its physical half-life is 30 years, and its biological half-life is 110 days. It emits beta and penetrating gamma radiation, and it is distributed uniformly throughout the body.Prussian blue is ferric ferrocyanide. This chemical is not absorbed by the gastrointestinal tract (GIT) and works through two modes of action. It decreases the absorption of many radionuclides from the GIT and removes some radionuclides from the capillary bed surrounding the intestine and prevents their reabsorption. Prussian blue is most effective when given early after ingestion and serially, for 2-3 weeks, thereafter.In Goiania (Brazil, 1987) following the release and human incorporation of caesium-137 from a medical radiation source, prussian blue was used to treat contaminated human victims. Prussian blue decreases the biological half-life of caesium-137 to 30 per cent.Module Medical XV.
40Chelation agents: DTPA for heavy metals and transuranic elements Module Medical XV. Contamination and decorporationChelation agents: DTPA for heavy metals and transuranic elementsCa-DTPA is 10 times more effective than Zn-DTPA for initial chelation of transuranics. Must be given as soon as possible after accidentAfter 24 hours, Ca-DTPA and Zn-DTPA equally effectiveRepeated dosing of Ca-DTPA can deplete body of zinc and manganeseChelation agentsChelators are mobilizing agents; they enhance the elimination of metals from critical organs. Chelators are organic compounds (ligands) that exchange less firmly bonded ions for metal ions. The stable complex, chelator and metal, is then excreted by the kidney. Hence, chelators are effective means for decorporation of radioactive heavy metals.Diethylenetriaminepentaacetic acid (DTPA), is generally more effective in removing many of the heavy metal, multivalent radionuclides. The chelates formed with many heavy metals are water soluble and excreted via the kidneys. The DTPA metal complexes are more stable and less likely to release the radionuclide before excretion. After intravenous administration, the agent is excreted rapidly with about 50% appearing in the first hour. Treating promptly with the highest recommended dose of the chelate produces the greatest enhancement of the radionuclide excretion. The effectiveness of treatment at later times following a radionuclide uptake is directly related to the solubility of the metal in vivo and its presence in the extracellular spaces.Actinides (plutonium, americium, curium, and californium), all have long biological half-lives. Inhalation is approximately 75% of industrial exposures. If the compound is soluble (nitrate, citrate, fluoride), it is ultimately translocated from the lungs to terminal disposition sites (bone and liver). Ca-DTPA and Zn-DTPA chelation therapy is the treatment of choice.Module Medical XV.
41Dosage of Ca-DTPA and Zn-DTPA Module Medical XV. Contamination and decorporationDosage of Ca-DTPA and Zn-DTPA1 g iv. or inhalation in a nebulizerInitially: 1 g Ca-DTPA, repeat 1 g Zn-DTPA daily up to five days if bioassay results indicate need for additional chelationPregnancy - First dose Zn-DTPA instead of Ca-DTPAAs with most chelators, it is more effective the earlier it is given. Both salts can be given intravenously or as a nasal inhalant. Dose recommendations are, for adults, 1 gram in 100 to 250 mL of normal saline infused intravenously slowly, over 3 to 4 minutes, and repeated on 5 successive days per week. Given as aerosol, 1 gram in a 4 mL vial is placed in a nebulizer, and the entire volume is inhaled over 3 to 4 minutes, repeated daily.With repeated dosing, Ca-DTPA can deplete the body of zinc and, to a lesser extent, manganese. Zinc-DTPA replacement therapy is recommended when repeated dosing is done due to loss of the body's zinc stores.Contraindications for Ca-DTPA: pregnancy, infancy, nephrosis and bone marrow depression. Teratogenicity and fetal death have occurred in mice.No serious toxicity in humans has been reported when used in recommended doses. When given repeatedly with short intervals for recovery, nausea, vomiting, diarrhoea, chills, fever, pruritus, and muscle cramps have been noted.Module Medical XV.
42Module Medical XV. Contamination and decorporation Additional chelating agentsDimercaprol (BAL) forms stable chelates, and may therefore be used for the treatment of internal contamination with mercury, lead, arsenic, gold, bismuth, chromium and nickelDeferoxamine (DFOA) effective for chelation of 59FePenicillamine (PCA) chelates with copper, iron, mercury, lead, gold. Superior to BAL and Ca-EDTA for removal of copper (Wilson’s disease)Chelation therapy has been used for lead, mercury, arsenic, and other heavy metals.Chelators are most effective prior to the binding of a toxicant in the critical organ but can be used with variable results after target organ acquisition.Before, during and after chelation therapy, pertinent measurements of radioactivity in the body should be made to determine the efficacy of treatment. By the fifth day, evaluate the bioassay data of urine and faeces samples and the total-body and chest count measurements. Continuation of therapy is determined by assessing chelation yield with remaining body burden..Module Medical XV.
43Treatment of uranium contamination Module Medical XV. Contamination and decorporationTreatment of uranium contaminationIn any route of internal contamination, treatment consists of slow intravenous transfusion of 250 mL of isotonic 1.4 % sodium bicarbonateLocal treatment: for skin contamination, wash with isotonic 1.4% solution of sodium bicarbonateInhalation is the usual route of occupational exposure.Average biological half-life is 15 days.85% of retained U resides in bones.In acidic urine, uranyl ion makes complex with renal tubuli surface proteins and causes acute tubular necrosis (ATN).Chemical toxicity for kidneys is the basis for occupational exposure limits.Alkalinization of urine reduces the chance of ATN.Module Medical XV.
44Module Medical XV. Contamination and decorporation SummaryAttend to life-threatening injuries firstEarlier skin decontamination decreases degree of beta burns, lowers risk of internal contamination, reduces chance of further contaminationGoal of internal contamination treatment: decrease uptake into circulatory system, decrease deposition in critical organs, increase excretory rate contaminantHealth physicists and medical specialists should advise on risks and benefits of decorporationQuiz1. What is the primary mode of intake of a radiocontaminant?a) dermal absorption b) wound absorption c) inhalation d) via GIT2. Prussian blue is effective in reducing the body burden from:a) plutonium b) uranium c) caesium d) plutonium and uranium3. Body burden from intaken radionuclides can the most completely be estimated by:a) whole body counting (WBC) and contamination surveyb) WBC and measurments of radionuclides in urine, faeces and thyroid glandc) WBC, metabolite and thermoluminescence measurementsd) WBC, metabolite measurement in urine and fecal metabolite measurement4. Which of the following reflects an incorrect substance/target organ relationship?uranium/bone b) iodine/thyroid c) lead/bone d) caesium/gut5. Select the false statement.a) Potassium iodide (KI) increases the rate of thyroid hormone productionb) KI should be given as soon as possible following exposure to I-131c) Although rare, side effects, including rhinitis, conjuctivitis, and skin rashes, may occur due to the use of KId) Effectiveness of KI is time dependent following exposure to I-131Module Medical XV.