Radiological Protection
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Radiological Protection

Radiological ProtectionClinica Universitaria de RadiologiaDirector Prof Doutor Filipe Caseiro AlvesS. I. Gonçalves, PhD1

OutlineA. Why Radiological Protection?B. Dosimetric definitionsC. Biological EffectsD. Dose constraints in radiation exposureA. Radiological protection and shieldingB. Summary2


Why Radiological Protection?• Radiation is all around us…Natural Radiation: Cosmic rays, radiation within ourbody, in food we eat, water we drink, house we livein, lawn, building material etc.Human Body: K-40, Ra-226, Ra-228e.g. a man with 70 kg wt.4028,000 photons emitted/min(T1/2 of K-40 = 1.3 billion yrs)140 gm of K140 x 0.012%=0.0168 gm of K-0.1 Ci of K-44

Why Radiological Protection?• Radiation is all around us…Earth: Top 1m of 0.1 acre (405 m 2 ) garden=1200 kg of K of which K-40 =1.28 Kg= +3.6 Kg of Th + 1 Kg UrGy/yrNew Delhi 700Bangalore 825Bombay 424Kerala 4000(in narrow coastal strip)5

Why Radiological Protection?6

Why Radiological Protection?• Radiation from natural sourcesNormally 1-3 mSv/yearIn areas of high background, 3-13 mSv/year7

Why Radiological Protection?• The question is:Do we need radiological protection?8

Why Radiological Protection?Cup of coffeeΔT=60º-37º=23º1 sip = 3 mlE = 3×23=69 calLethal Dose = 4 GyE = 4 x 70 = 280 Joules= 280/418= 67 calories= 1 sip9

Radiological protection isneeded…12

Dosimetric definitionsX- RaysProduced by electrons surrounding the atomicnucleus(as opposed to Gamma rays generated in thenucleus)“Soft” X-rays – λ between 10 and 0.10 nm (E isbetween 0.12 to 12 keV);“Hard” X-rays - λ between 0.10 and 0.01 nm (Eis between 12 and 120 keV)14

Dosimetric definitionsX- RaysUsed in diagnostic and interventionalradiology“Hard” X-rays - λ between 0.10 and 0.01 nm (Eis between 12 and 120 keV)15

Dosimetric definitions• Exposure and exposure rate• Absorbed dose and KERMA• Mean absorbed dose in a tissue• Equivalent dose H• Effective dose• Other related measures16

Dosimetric definitions• Exposure: XThe exposure is the absolute value of the total charge ofthe ions of one sign produced in air when all theelectrons liberated by photons per unit mass of air arecompletely stopped in air.Q - electric chargem- massX = dQ/dm17

Dosimetric definitions19

Dosimetric definitions• KERMAThe KERMA (kinetic energy released in a material)K = dE trans /dmwhere dE trans is the sum of the initial kineticenergies of all charged ionizing particles liberatedby uncharged ionizing particles in a material of massdmThe SI unit of kerma is the joule per kilogram (J/kg),termed Gray (Gy).In diagnostic radiology, Kerma and D are equal.20

Dosimetric definitions• Absorbed dose, DThe absorbed dose D, is the energy absorbed per unitmass.This quantity is defined for all ionizing radiation (notonly for electromagnetic radiation, as in the case of the“exposure”), and for any material.D = dE/dm. The SI unit of D is the Gray [Gy].1 Gy = J/kg.The former unit was the “rad”. 1 Gy = 100 rad.21

Dosimetric definitions• Relation between D and XIt is possible to calculate the absorbed dose ina material if the exposure is knownD [Gy]. = f . X [C kg -1 ]f = conversion coefficient depending onmediumThe absorbed energy in a quantity of airexposed to 1 [C kg -1 ] of X Rays is 0.869 [Gy]f(air) = 0.86922

Dosimetric definitions• Examples of factor ff values ([Gy] / Ckg -1 ])Photon energy Water Bone Muscle10 keV 0.91 3.5 0.93100 keV 0.95 1.5 0.9523

Dosimetric definitions• Mean absorbed dose in atissueThe mean absorbed dose in a tissue or organDT is the energy deposited in the organdivided by the mass of that organ.24

Dosimetric definitions• Ratio of absorbed dose intissue to that in airValues of absorbed dose to tissue will vary by a fewpercent depending on the exact composition of themedium that is taken to represent soft tissue.The following value is commonly used (for 80 kV and 2.5mm depth):Dose in soft tissue = 1.06 Dose in air25

Dosimetric definitions• Equivalent dose: HH = wR×DwR is the radiation weighting factor.To avoid confusion with the absorbed dose, theSI unit of equivalent dose is called the sievert(Sv). The old unit was the “rem”1 Sv = 100 rem26

Dosimetric definitions• Radiation weigthing factor:wRFor most of the radiation used in medicine (X Rays, , e-) wR is = 1, so the absorbed dose and the equivalentdose are numerically equal.The exceptions are:alpha particles (wR = 20)neutrons (wR = 5 – 20)27

Dosimetric definitions• Effective dose: EE = T wT.HTE: effective dosewT: weighting factor for organ or tissue THT: equivalent dose in organ or tissue T28

Dosimetric definitions• Entrance Surface Dose: ESD• Absorbed dose is a property of the absorbing medium as wellas the radiation field, and the exact composition of themedium should be clearly stated.• Usually ESD refers to soft tissue (muscle) or water• Absorbed dose in muscle is related to absorbed dose in airby the ratio of the mass energy coefficients29

Dosimetric definitions• Entrance Surface Dose: ESD• On the other hand, the ESD measured on the surface of thepatient or phantom includes a contribution from photonsscattered back from deeper tissues, which is not present forfree air measurements• For this reason, correction factor (backscatter factor) mustbe introduced• If measurements are made at other distances than the truefocus-to-skin distance, doses must be corrected by theinverse square law30

Dosimetric definitions• Dose-Area product (I): DAP• The dose-area product (DAP) quantity is defined as the dosein air in a plane, integrated over the area of interest• The DAP (cGy·cm2) is constant with distance since the crosssection of the beam is a quadratic function which cancelsthe inverse quadratic dependence on dose• This is true neglecting absorption and scattering of radiationin air and even for X Ray housing near the couch table31

Dosimetric definitions• Inverse square law: 1/d 2D (10×d) = 1/100 × D (d)32

Dosimetric definitions• Dose-Area product (II): DAP• It is always necessary to calibrate and to check thetransmission chamber for the X Ray installation in use• In some European countries, it is compulsory that newequipment is equipped with an integrated ionizationtransmission chamber or with automatic calculation methods• It is convenient, in this case, also to check the read-out assome systems overestimate the real DAP value33


Biological effects• Subject matter: radiobiology• The mechanisms of different types of biologicaleffects following exposure to ionizing radiation35

Biological effects• Classification of radiation health effectsTYPEOFEFFECTSCELL DEATHDETERMINISTICSomaticClinically attributablein the exposedindividualCELL TRANSFORMATIONSTOCHASTICsomatic & hereditaryepidemiologicallyattributable in largepopulationsBOTHANTENATALsomatic andhereditary expressedin the foetus, in the liveborn or descendants36

Biological effects• Deterministic• e.g. Lens opacities, skininjuries,• infertility, epilation, etc• Stochastic• Cancer, genetic effects.37

Biological effects• Deterministic (Threshold/non-stochastic)• Existence of a dose threshold value (below this dose,the effect is not observable)• Severity of the effect increases with dose• A large number of cells are involved38

Biological effectsThreshold doses for deterministic effects• Cataracts of the lens of the eye 2-10 Gy• Permanent sterility• males 3.5-6 Gy• females 2.5-6 Gy• Temporary sterilitySeverity ofeffect• males 0.15 Gy• females 0.6 Gythresholddose39

Biological effects• Stochastic• No threshold• Probability of the effect increases with dose• Generally occurs with a single cell• e.g. Cancer, genetic effects40

Biological effects (stochastic)Probability of cell death5000Acute dose(in mSv)43

Dose-effect response curve1-10 GyAcute irradiationsyndromeChronic irradiationsyndromeBONEMARROWGASTROINTESTINAL10 - 50 Gy> 50 GyCNS(central nervoussystem)Steps:1. Prodromic(onset ofdisease)2. Latency3. ManifestationLethal dose 50 / 30Dose•Partial-bodyirradiation•Mechanism:Neurovegetativedisorder•Similar to a sickfeeling•Quite frequent infractionatedradiotherapy

Lethal dose 50 / 30• “Dose which would cause death to 50% ofthe population in 30 days”.• Its value is about 2-3 Gy for humans forwhole body irradiation.

Effects of antenatal exposure• As post-conception time increases the risk for radiation effectsdecreases.• It is not easy to establish a cause-effect relation because thereare a lot of teratogenic agents, effects are unspecific and notunique to radiation.• There are 3 kinds of effects: lethality, congenital anomalies andlarge delay effects (cancer and hereditary effects).

Effects of antenatal exposure%LethalityCongenital anomaliesPre-implantation Organogenesis FoetusTimeICRP directivesD

Effects of antenatal exposure• Lethal effects can be induced by relatively small doses (such as0.1 Gy) before or immediately after implantation of the embryointo the uterine wall. They may also be induced after higherdoses during all the stages during intra-uterine development.Mental retardation:ICRP establishes that mental retardation can be induced byradiation (Intelligence Quotient score < 100).It occurs during the pregnancy period period: 8-25 week.Risks of antenatal exposure related to mental retardation are:8-15 weekSevere mentalretardation with a riskfactor of 0.4/Sv15-25 weekSevere mentalretardation with a riskfactor of 0.1/Sv48

Delayed effects of radiation• Classification:• SOMATIC: they affect the health of the irradiatedperson. They are mainly different kinds of cancer(leukemia is the most common, with a delay period of2-5 years, but also colon, lung, stomach cancer…)• GENETIC: they affect the health of the offspring of theirradiated person. They are mutations that causemalformation of any kind (such as mongolism)49


Dose constraints in radiationexposure• Persons are medically exposed as part of their diagnostic ortreatment.• According to ICRP, two basic principles of radiationprotection are to be complied with: justification andoptimization• Dose limits are not applicable, but a Guidance is given ondose levels• Investigation of exposures is strongly recommended

Dose constraints in radiation exposureGuidelines• Different categories of radiation exposure• Justification• Optimization• Guidance (or reference) levels - practical aspects• Guidance levels and effective doses

Dose constraints in radiation exposureThree types of exposureMedical Exposure1. Exposure of persons as part of their diagnostic or treatment2. Exposures (other than occupational) incurred knowingly andwillingly by individuals such as family and close friends helpingeither in hospital or at home in the support and comfort ofpatients3. Exposures incurred by volunteers as part of a program ofbiomedical researchOccupational Exposure(exposure incurred at work, and practically as a result ofwork)Public Exposure(including all other exposures)

Dose constraints in radiation exposureGuidelines for medical exposure• Justification• Optimization• The use of doses limits is NOTAPPLICABLE• Dose constraints andguidance (or reference)levels ARERECOMMENDED54

Dose constraints in radiation exposureThe justification of a practice involving radiationexposure• The decision to adopt or continue a practice involvingradiation involves a review of benefits and disadvantages ofthe possible optionsE.g. Choosing between the use of X-Rays or ultrasound• Radiation detriment will be only a small part of the totaldetriment• Assessment needed for the justification of a practice madeon the basis of experience, professional judgement, andcommon sense55

Dose constraints in radiation exposureThree levels of justification• First (General) level: The use of radiation in medicine isaccepted as doing more good than harm• Second (Specific) level: Specific procedure with a specificobjective: e.g. Chest radiographs for patients showingrelevant symptoms(National Regulatory Authorities)• Third level: the application of the procedure to an individualpatientSimple Procedure, generic justificationComplex procedure (CT, IR), individual medical justification56

Dose constraints in radiation exposureOptimization (I)• Optimization is usually applied at two levels:• The design and construction of equipment andinstallations• Day to day radiological practice (procedures)• Reducing the patient dose may reduce the quantity as wellas the quality of the information provided by the examinationor may require important extra resources• The optimization means that doses should be “as low asreasonably achievable, economic and social factors beingtaken into account” compatible with achieving the requiredobjective57

Dose constraints in radiation exposureOptimization (II)• There is a considerable scope for dose reductions indiagnostic radiology (ICRP 60)• Simple, low-cost measures are available for reducing doseswithout loss of diagnostic information (ICRP 60, 34)• The optimization of protection in diagnostic radiology doesnot necessarily mean the reduction of doses to the patient• Anti-scatter grids improve the contrast and resolution of theimage but increase the dose in a factor of 2-458

Dose constraints in radiation exposureGuidance levels for medical exposure• Guidance levels are intended:I. to be a reasonable indication of doses for averagesized patientsII. to be established by relevant professional bodies inconsultation with the Regulatory AuthorityIII. to provide guidance on what is achievable with currentgood practice rather than on what should beconsidered optimum performanceIV. to be applied with flexibility to allow higher exposures ifthese are indicated by sound clinical judgementV. to be revised as technology and techniques improve59

Dose constraints in radiation exposureDose constraints• For medical research purposes• For individuals helping in care, support or comfort ofpatients, and visitors• 5 mSv during the period of the examination or treatment• 1 mSv for children visiting• Maximum activity in patients discharged from hospitals• Iodine 131-1100 MBq60

Dose constraints in radiation exposureDose constraints• For patients• Values of measured quantities above which some specifiedaction or decision should be taken• The ICRP recommends the use of DIAGNOSTICREFERENCE LEVELS (DRL) for patients (Report 73, 1996)• The DRL will be intended for use as a convenient test foridentifying situations where the levels of patient dose areunusually high.61

Dose constraints in radiation exposurePractical issues (I)• DRL’s are not dose limits• DRL’s could be assimilated to investigation levels• DRL’s are not applicable to individual patients. Comparisonwith DRL shall be only made using mean values of a sampleof patients• Quantities used as guidance (or reference) levels should beeasily measured62

Dose constraints in radiation exposurePractical issues (II)• DRL’s should be understood by radiologists andradiographers• DRL’s should always be used in parallel to image qualityevaluation (enough information for diagnosis shall beobtained)• DRL’s can mean several quantities (such as DAP) andparameters (such as fluoro time and number of images)• The main objective of DRL is their use in a dynamic andcontinuous process of optimization63

Dose constraints in radiation exposureReference levels for diagnostic radiographyExaminationEntrance surface dose perradiograph (mGy)Lumbar spine AP 10Lumbar spine LAT 30Lumbar spine LSJ 40Pelvis AP 10Chest LAT 1.5Thoracic spine LAT 20Dental AP 5Skull AP 564

Dose constraints in radiation exposureReference levels for CTExaminationMultiple scan average dose(mGy) (a)Head 50Lumbar spine 35Abdomen 25(a) Derived from measurements on the axis of rotation in waterequivalent phantoms, 15 cm in length and 16 cm (head) and 30 cm(lumbar spine and abdomen) in diameter.65

Dose constraints in radiation exposureReference levels for FluoroscopyExaminationEntrance surface dose(mGy/min) (a)Normal 25High Level (b) 100Normal 25(a) In air with backscatter(b) For fluoroscopes that have an optional 'high level’ operationalmode, such as those frequently used in interventional radiology66

Dose constraints in radiation exposureDiagnosticprocedureTypicaleffectivedose (mSv)Equiv. no. ofchest x-raysApprox. equiv.period of naturalbackgroundradiationHip 0.3 15 7 weeksPelvis 0.7 35 4 monthsAbdomen 1.0 50 6 monthsBarium meal 3 150 16 monthsCT head 2.3 115 1 yearCT chest 8 400 3.6 yearsCT Abdomenor pelvis10 500 4.5 years67


Radiological Protection andShieldingImportant topics‣ Personal protective equipment‣ Individual monitoring and exposure assessment‣ Investigation and follow up‣ Health surveillance‣ Records69

Radiological Protection and ShieldingPersonal protective equipment• Gowns, aprons and thyroid protectors madeof a material (such as vinyl) which containslead• Aprons should be equivalent to at least 0.25mm Pb if the X Ray equipment operates upto 100 kV and 0.35 mm Pb if it operatesabove 100 kV• Aprons may be of the style which is open, orcontains less lead, at the back, due to theextra weight of lead required - this assumes,however, that the wearer is always facingthe radiation source• Gauntlets are heavy gloves. They havelimited value because they are difficult touse and should therefore only be usedwhere appropriate70

Radiological Protection and ShieldingPersonal protective equipmentSCREENANDGOGGLESCURTAIN71

Radiological Protection and ShieldingPersonal protective equipment• Additional protective devices should be available in fluoroscopyand interventional radiology rooms which include:• Ceiling suspended protective screens.• Protective lead curtains mounted on the patient table.• Protective lead curtains for the operator if the X Ray tubeis placed in an over couch geometry and if the radiologistmust stand near the patient72

Radiological Protection and ShieldingIndividual monitoring and exposureassessment (I)Individual dose monitoring shall be undertaken for workers whoare normally exposed to radiation in controlled areas:• radiologists, medical physicists, radiographers and nurses• Other frequent users of X Ray systems such as endoscopists,anaesthetists, cardiologists, surgeons etc., as well asancillary workers who frequently work in controlled areas,shall also be monitored.73

Radiological Protection and ShieldingIndividual monitoring and exposureassessment (II)• Individual external doses should be determined by usingindividual monitoring devices:• Thermoluminescent• Film badges• Electronic dosimeters• Worn at breast level, between the shoulders and the waist• The monitoring period should be one month, and shall notexceed three months.• The exchange of dosimeters and report receipt should notexceed three months.74

Radiological Protection and ShieldingPersonal dosimetrySeveralpersonaldosimeters arerecommendedFrom: Avoidance of radiation injuries from interventional procedures. ICRP draft 200075

Radiological Protection and ShieldingDifferent types of dosimetersýýýFilm (A)termoluminescencedosimeters (TLD) (B)”electronic” dosimeters (C)ABBC

Radiological Protection and ShieldingIndividual monitoring and exposureassessment (III)• Evaluation of dose is an important aspect ofradiation protection• It is important that workers return dosimeters ontime for processing• Delays in the evaluation of a dosimeter can resultin the loss of the stored information• Licensees should make every effort to recover any missingdosimeters77

Radiological Protection and ShieldingIndividual monitoring when using lead apron (I)• The dosimeter should be worn under the apron for estimatingthe effective dose• The other body areas not protected by the apron will receivehigher dose• One dosimeter worn under the apron will yield a reasonableestimate of effective dose for most instances• In case of high workload (interventional radiology) an additionaldosimeter outside the apron should be considered by the RPO78

Radiological Protection and ShieldingIndividual monitoring when using lead apron (II)• When expected doses are high, two dosimeters are required:• 1 under the apron at waist level• 1 over the apron at collar level• The effective dose E is given by:• E = 0.5 Hw + 0.025 Hn• where:• Hw : dose at waist level under the apron• Hn : dose recorded by a dosimeter worn at neck level overthe apron• Note: The thyroid shielding allows 50% reduction of the E• The dosimeter worn over the apron at collar level gives also anestimation of thyroid and eye lens doses79

Radiological Protection and ShieldingInvestigation levels• A suitable quantity for use as investigation level is themonthly individual effective dose.• The dose measured outside the lead apron (at collar orshoulder level) and the dose to the hands can also be usedas a quantity for an investigation level for staff ininterventional radiology.• Monthly values higher than say 0.5 mSv (for the dosimeterworn under the lead apron) should be investigated.• Values higher than say 5 mSv per month in the over aprondosimeter or in the hand or finger dosimeters should also beinvestigated with a view to optimization.80

Radiological Protection and ShieldingHealth Surveillance• Under normal working conditions, the doses incurred in aradiology department are lower than the dose limits.• No specific radiation-related medical examinations are normallyrequired for persons who are occupationally exposed to ionizingradiation, as there are no diagnostic tests which yieldinformation relevant to exposures that are close to or belowdose limits.• However in the case of accidental exposure to high doses (ofthe order of magnitude of 0.2-0.5 Sv or higher), specificradiation-related medical investigation are necessaryAverage reference occupational dose level: 20 mSv over 5 yrs81

Summary• Radiological Protection is essential in the working routineof a radiology department;• Working staff should be aware of this importance andcomply with the protection procedures indicated by theguidelines;• This includes using personal dosimeter properly andreturning it on time for reading;• But also be aware that patient dose should be acompromise between diagnostic value of exam andamount of radiation delivered;• Report any problem regarding equipment. 82


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