Presentation Transcript

1. Radiation Protection & Associated Regulations

   Module 9
2. Fundamental Knowledge Background radiation Sources Magnitude Radiation limits Public Radiation workers Roles of & differences between: Advisory bodies Accrediting organizations Regulatory organizations Principles of time, distance & shielding ALARA Methods used to monitor occupational exposure Equipment used to monitor areas Patient & fetal doses Shielding design Radiological emergencies
3. Sources of Radiation Exposure Background Radiation Non-Medical Sources Medical Sources
4. % Contribution to Annual Effective Dose TOTAL 6.2 mSv/yr 100% BACKGROUND 3.1 mSv/yr 50% MEDICAL 3.0 mSv/yr 48%
5. Background Radiation Cosmic Cosmic rays Primary extraterrestrial radiation striking earth’s atmosphere Cosmogenic Radionuclides Secondary radiations produced by interaction of primary cosmic rays & atmosphere Terrestrial Primordial radionuclides Radioactive material present on earth since its’ formation Internal Ingestion of food/water containing primordial radionuclides Radon Inhalation of alpha-emitting Rn-222 Decay product from primordial radionuclide
6. Cosmic Rays Primary cosmic rays Extremely penetrating high-energy particles ~10 GeV 80% protons Almost all collide w/ atmosphere Collisions produces showers of: Secondary particulate radiations electrons & muons & E-M radiation Average per capital effective dose 0.33 mSv/yr 11% of natural background Indoor effective dose ~20% lower Altitude effects 0.3 (sea level) – 0.82 mSv/yr(mountains) Dose ~ doubles every 1500 m in altitude ↑ ↓ atmosphere to attenuate cosmic radiation Latitude effects Exposure @ poles > equator Charged particles interacting w/ earth’s magnetic field lines forced to travel down to poles
7. Cosmic Ray Shower
8. Cosmogenic Radionuclides Some secondary cosmic ray particles collide w/ stable atmospheric molecules Produces radionuclides Majority of dose from Carbon-14 714N [n,p] 614C Avg effective dose small ~0.01 mSv/yr < 1% of natural background
9. Terrestrial Primordial radionuclides Physical half lives comparable to age of earth ~4.5 billion years Nuclides w/ t1/2 < 108yrs→ decayed to negligible levels Nuclides w/ t1/2 > 1010yrs→ negligible contribution due to slow rate of decay U-238, Th-232, & their decay products including Rn-222 K-40 Results in population dose from: External exposure 0.21 mSv/yr Range: 0.1 – 0.4 mSv /yr Depending on local concentrations 7% of natural background Incorporation into body 0.15 mSv/yr 5% of natural background Inhalation 2.1 mSv/yr 68% of natural background
10. U-238 Decay Chain “When I was young I used to feel so alive, so dangerous! In fact, would you believe I started life as U-238? Then 1 day I accidentally ejected an αparticle…now look at me, a spent old atom of Pb-206. Seems that all my life since then has been nothing but decay, decay, decay…”
11. Th-232 Decay Chain Kerala Sea Beach, India Levels up to 70 mGy/yr external exposure (300x avg terrestrial exposure in US!)
12. Internal Potassium-40 most significant K-39 (stable) 93.26% abundance K-40 (radioactive-t1/2 = 1.26x109 yrs) 0.01% K-41 (stable) 6.73% In body: Total amount = 140 g Daily intake 3.3 g Skeletal muscles have highest concentration Average annual effective dose 0.15 mSv/yr 5% of natural background Th-232 & U-238 & decay products Also found in food/water Average annual effective dose 0.13 mSv
13. Radon-222 Part of U-238 decay chain From decay of Radium-226 Rn-222 decays by α (t1/2 = 3.8 d) to Po-218 Followed by additional α, β decays Prevalent in soils containing uranium-rich deposits Concentrated w/in structures Weatherproofing Building materials Well water Avg indoor concentration in US ~46 Bq/m3 Can exceed 2,750 Bq/m3 Poorly ventilated structures w/ high soil concentrations of U-238 EPA recommends taking steps to ↓ concentrations if >147 Bq/m3 Avg outdoor concentrations indoor Avg annual effective dose 2.1 mSv/yr 68% of natural background Dose primarily to bronchial epithelium Smokers esp. @ risk Attributable lung cancers appear to be greater for smokers than those attributable from either one individually
14. US Radon Zones EPA Map of Radon Zones
15. Radon Testing / Mitigation Home tests easy to find & inexpensive to purchase Short Term Test kits 3-5 days Charcoal Test Activated charcoal collects radon atoms from air that can be counted in a laboratory later Less accurate than long term tests Long Term Test kits 3 months Alpha Track Test Special pieces of plastic that are marked when hit by αparticles that can be counted in a laboratory later Radon water test kits Continuous monitoring tester Can be ↓ by: preventing entry or removing it General solution: Active ventilation in basement/below slab of home
16. Non-Medical Sources Nuclear Power Emissions Tobacco Technologically-Enhanced Naturally-Occurring Radioactive Material (TENORM) Fallout Fiesta ware: Red color achieved by adding uranium oxide to glaze - by weight, up to 14 % of glaze might be uranium (estimated that a single plate contains 4.5 grams of uranium) Uranium gives interesting yellow & green colors & fluorescence effects when included in glass
17. Atmospheric testing of nuclear weapons 450 detonations (1945 – 1980) Radioisotopes C-14 H-3 Cs-134 Cs-137 Sr-90 Pu trans-Pu elements Avg per capita annual effective dose est. < 10 µSv Most have decayed/become less available for biologic uptake
18. Consumer products & activities Tobaccoproducts 210Pb & 210Po (α emitters) measured in tobacco leaves/smoke 1 pack/day smoker ↑ annual effective dose by ~ 0.36 mSv ~35% of effective dose of all consumer products/activities Building materials Brick, concrete, granite concentration of primordial radionuclides Avg per capita annual effective dose ~ 0.035 mSv Air travel e.g. 5-h transcontinental flight ~ 0.025 mSv Avg per capita annual effective dose ~ 0.034 mSv Smoke detectors, gas lantern mantles, dental prostheses, optical lenses, etc. < 12% contribution
19. Occupational % contributions to mean effective dose rate of galactic radiation components Related to: Altitude @ equator @ high latitude Mining Agriculture Aircraft crew Avg annual effective dose ~ 3.1 mSv + > avg for many diagnostic radiology personnel Nuclear workers Power plant Military Research Medical workers
20. Medical Sources: Occupational & Patient Doses Projection Radiography Mammography Fluoroscopy Interventional Radiology & Diagnostic Angiography CT Sealed Source Radioactive Material Unsealed Radioactive Material Therapeutic External Radiation Non-Ionizing
21. Medical Exposures to medical personnel In 2009, for monitored medical personnel: Avg annual effective dose 0.75 mSv Low (inclusion of supervisors, radiologists who do few fluoro exams) Radiologist (non-interventional) Avg effective doses 0.1 - 0.2 mSv/yr common Techs in large facilities performing mostly CT/radiographic exams Avg effective doses 0.5 – 1 mSv/yr common Staff involved w/ fluoro-guided interventional procedures Much ↑, depending on: roles, # performed, type, case difficulty & use of protection Annual does range: 5 – 15 mSv typical Measured w/ dosimeter worn outside Pb aprons @ collar Effective dose actually << (by factor of 3+) Nuclear Medicine Routine procedures ~ <1 µSv/procedure Avg annual effective doses 2 – 3 mSv PET ~ 1 – 5 µSv/procedure Avg annual effective doses 10 – 15 mSv
22. Medical Exposures* to Patients *(Excluding radiation therapy) Single greatest controllable source of radiation exposure Avg per capita annual effective dose est. 3 mSv in 2006 97% of total artificial radiation sources 50% from all sources Up from est. of 0.53 mSv in 1980’s 566% increase Largest factors are ↑ in CT, NM procedures Esp. CT abdomen, pelvis & Tl-201 myocardial perfusion studies 22% 75%
23. Avg Annual Effective Doses from Medical Procedures 2006 1980
24. Factors Affecting Patient Dose Radiography Fluoroscopy and Interventional Radiology Computed Tomography (CT) Mammography Nuclear Medicine Regulatory Dose Limits and “Trigger” Levels Institutional Local State Federal JCAHO Reviewable and Non-Reviewable Events Person or Agency to Receive Report
25. Radiation Doses in Medical Imaging 2 main methods to limit radiation doses: Avoid unnecessary exams Ensure dose no larger than necessary Goal is to produce images of adequate diagnostic quality Not unnecessarily high quality
26. Radiography Factors Tube voltage Beam filtration Field area Organ shielding Geometry Image receptors
27. Tube Voltage Lower energy x-rays do not penetrate patient Do not reach receptor/create image Attenuated (absorbed) by patient Adding to dose w/out diagnostic benefit As voltage ↑, effective beam energy ↑ Beam becomes “harder” & penetration ↑ Since mAs is ↓ @ same time (to keep signal @ receptor =) Incident exposure to patient ↓ Concomitant ↓ in contrast as beam energy ↑
28. Beam Filtration Filtering polychromatic x-ray beam also ↑ effective energy Selectively removes lower energy x-rays Little to no contribution to image Absorbed by patient Dose ↓ Amount of filtration limited by: ↓ in tube output Can only ↑ output to compensate until tube loading becomes an issue Harder beam, ↓ contrast Spectrum: 1 From anode 2 W/ inherent filtration 3 Added filter
29. Field Area Restrict beam to VOI by using collimation Limits extraneous tissue exposed Entrance dose in primary beam same But ↓ volume of tissue in primary beam ↓ energy imparted to patient Amount of scattered radiation ↓ ↓ dose to adjacent tissue Image contrast ↑ SNR ↑
30. Organ Shielding If possible, shield radiosensitive organs e.g. gonadal shielding Equivalent thickness ≥ 0.5 mm Pb if in primary beam Lens of the eye Breast tissue in girls/young women Placement must: Not interfere w/ exam Be placed between x-ray source & patient Not interfere w/ AEC sensor If exposure unavoidable: Try to place radiosensitive organ on side of patient away from tube
31. Geometry ↑ Distance from x-ray source to patient ↓ dose AKA Source-to-Object Distance (SOD) As distance ↑: ↓beam divergence limits volume being irradiated, thus ↓ dose ↓ entrance dose due to inverse square law Exposure from tube leakage also ↓ Federal regs specify min. patient-to-focal spot distance = 20 cm ≥ 30 cm strongly recommended to prevent excessive exposure
32. Image Receptors Film-Screen Film speed determines # x-ray quanta (thus dose) necessary to achieve appropriate film darkening e.g. 400 speed req’s ¼ exposure as 100 speed film to produce same OD Specialized film processing can also affect system speed ↑ speed, ↑ quantum mottle (noise) Thicker intensifying screen ↓ patient exposure Thicker screen, ↓ spatial resolution Built-in safety feature for over-exposure: too dark film Digital (CR or DR) Post-acquisition processing can compensate for over- or under-exposure Excessive under-exposure  ↑ quantum mottle, ↓ CNR Excessive over-exposure  needless patient exposure But still acceptable image! Critical to routinely monitor exposures
33. Fluoroscopy Factors Only 18% cumulative effective dose in medical imaging But gives some of largest tissue doses to individual patients Modest techniques , but often many minutes “on” time
34. Reducing Fluoroscopy Doses USE LESS FLUORO TIME Keep focal spot-to-skin distance as large as possible ↑ filtration ↓ frame rates ↑ kV, ↓ mAs techniques Collimation Use lowest magnification mode possible Ensure patient's arms out of FOV w/ lateral projections Tube under table to spare lenses & breast tissue Operating physicians should be trained/credentialed Understand technology Dose implications of different operational modes Normal vs. “turbo” Biological effects of x-rays Techniques used to min. dose to patient/personnel Familiar w/ regs Dose rate limited to 10 R/min (87.3 mGy/min) normal mode 20 R/min turbo (175 mGy/min)
35. Fluoroscopic Skin Injuries Long fluoro-guided interventional procedures: Percutaneous transluminal coronary angioplasty RF cardiac catheter ablation Vascular embolization Transjugularinterhepaticportosystemic shunt placement Other percutaneous endovascular reconstruction Doses can exceed 10 Gy! Injuries may not be apparent until weeks/months after Recommendations: Screen patients Prior large radiation exposures to same body part Some drugs Some hereditary diseases affecting DNA repair Other diseases: connective tissue disorders, diabetes, hyperthyroidism Note cumulative Air Kerma, Kerma Area Product in report Can also place dosimeters on patient’s skin Have guidelines in place Dose exceeds max. recommended, plan to follow up w/ patient Examine techniques
36. CT Factors From 1980 to 2006 avg annual effective dose from medical imaging ↑ by 5x ½ from CT
37. Moderating CT Doses Operator-selectable parameters kV, mA Time per rotation Table pitch Beam filter Not using adult protocols on children Automatic tube current modulation Iterative image reconstruction Setting notification/alerts if dose expected to exceed preset value Protocol AAPM, 2011
38. CT Protocol Optimization Slice thickness Overlapping thicker slices rather than thin slices Thin slices noisier so mA may need to be ↑ Thin slices less partial volume averaging ↑Tissue contrast Allowing for ↓ mA Tissue w/ high inherent contrast can be acquired w/ ↓ dose Obese patients Generally req↑ dose But adipose tissue better delineates soft tissue acceptable contrast more easily achieved ↓ kV can ↑ visibility of contrast material Angiography Brain perfusion Scan only z-axis length needed
39. Avoid radiation directly to eyes Contrast phases Review necessity of multiple contrast phases Only scan contrast phases necessary e.g. follow-up may not need precontrast images Vary tube current according to phase mA for noncontrast phases Protocols Compare w/ optimized protocols for same model of CT Protocols of similar body parts have similar doses Create low-dose protocol versions for use when indicated e.g. follow-up exams Use iterative reconstruction if available Automatic tube current modulation Use for most procedures If not used, make sure technique adjusted for body habitus Make sure max. mA setting is reasonable Beyond which ↑ kV
40. Mammography Factors
41. Factors Speed of film-screen receptor Film optical density SNR level in digital detectors Amount of x-ray absorption Breast thickness Breast composition kVp Antiscatter grid Digital acquisition w/ higher effective beam energy MQSA limits avg glandular dose to 3 mGy/image 4.2 cm compressed breast 50% glandular; 50% adipose tissue Avg Glandular Dose (mGy)
42. Nuclear Medicine Factors
43. Nuclear Medicine Factors Assure correct pharmaceutical & correct dose are administered Women, when appropriate: Mothers instructed to discontinue breastfeeding Pregnancy test Each syringe/vial properly labeled Name of pharmaceutical Name of patient Therapy Written directive Patient may need to be hospitalized
44. Persons at Risk Occupational Non-Occupational Staff Members of the Public Fetus Patient Adult Child Pregnancy Identified Pregnancy Status Unknown
45. Imaging Pregnant/Potentially Pregnant Patients Risks vary w/ dose & gestational age Each dept. must have policies & procedures Determine pregnancy status prior to exam All women of childbearing age (12 – 50) All exams: Tech asks & documents If no, LMP Exams where dose to fetus/embryo may exceed 100 mSv e.g. Prolonged fluoro, multiphase CT of abdomen/pelvis Pregnancy test obtained w/in 72 hrs Unless medically urgent or documented hysterectomy Possible exceptions include those where fetal dose very low e.g. mammograms, diagnostic x-rays of head, arms, hands, lower legs, feet If known or suspected to be pregnant, now what?
46. Imaging Pregnant/Potentially Pregnant Patients Options: Delay exam until after pregnancy Alternative exams w/out ionizing radiation Ways to modify exam to ↓ radiation to embryo/fetus Radiation dose & potential risks estimated Imaging physician must obtain informed consent from patient If pregnancy discovered after exam: Fetal age, dose, & potential risks estimated Patient counseled by physician If fetal dose < 100 mSv, no intervention ever recommended If fetal dose > 100 mSv, guided by fetal age & circumstances In general, all x-ray exams where fetus not close to examined area, fetal dose << 100 mSv Even x-ray exams of abdomen/pelvis, including single phase CT, fetal dose < 100 mSv
47. Dose limits Occupational Dose Limits Effective Dose Specific Organ Pregnant Workers Members of the Public General Caregivers Limit to Minors
48. Occupational Dose LimitsNRC Regulations & ICRP Recommendations
49. Public Dose LimitsNRC Regulations & ICRP Recommendations
50. Radiation Detectors Personnel Dosimeters Area Monitors
51. Personnel Dosimeters Film Thermoluminescent Dosimeters (TLDs) Optically-Stimulated Luminescent (OSL) Dosimeters Electronic Personnel Dosimeters Applications: Appropriate Use and Wearing Limitations and Challenges in Use
52. Film Badges Radioactivity will darken ("fog") photographic film Effect used to measure how much radiation has struck film Employees likely to be exposed wear film badges Sent to a lab to be developed, just like photographs Allows us to measure dose that each worker has received usually each month Film sensitivity highly dependent on incident photon energy
53. TLD Solid state detector LiF Simulates absorption of x-rays by soft tissue Zeff = 8.3; (Zeff soft tissue = 7.7) Shielded by metal foil or Al disk Allows differentiation between whole body &skin dose Energy absorbed by incident radiation creates +/- charge pairs Form of negative e- & positive “holes” Crystalline structure stores energy absorbed in (higher energy level) e- “traps” Readout e- releases stored energy in form of visible light when heated Light released α incident radiation Air KERMA Energy independent measurement Response does not depend on incident radiation energies Largely replaced film badges Far superior energy response Can be used for personnel/patient dosimetry
54. Thermoluminescence Econduction band 2) 3) Trap level Photons: TL Signal 4) Egap Incident x-ray Recombination center 1) Evalence band Free carrier creation by irradiation Trapping e-’s on trap level Release of trapped carriers by heating Recombination of e-’s w/ holes on a recombination center: emission of light, TL signal
55. OSLD Measures exposure due to x-ray, β, & γradiation Radiation passes through thin layer of Al2O3 +different filters After use RSO returns them to vendor for processing Al2O3stimulated w/ blue laser → luminesces Luminescence αamount of radiation exposure to dosimeter Report of exposure results generated
56. Electronic Personal dosimeter Pocket dosimeters measure radiation exposure & can be read immediately Can be set to audibly alarm if exposure exceeds preset value Often used when high doses expected e.g. cardiac cath procedures Analog – Pocket ion chamber Digital – Pocket GM tube or Semiconductor diodes
57. Summary
58. Appropriate Use / Wearing Typically worn on the part of torso expected to receive largest exposure or is most sensitive to damage Waist/shirt pocket Fluoroscopy Placed @ collar level outside Pb apron Measure dose to lens/thyroid 2nd can be worn @ waist under apron Pregnant workers 2nd worn @ waist If apron worn, under apron
59. Limitations NOT WORN Left in radiation field when not being worn Contamination w/ radioactive material Lost or damaged Positioned so that body is between it & radiation source Attenuation cause underestimation of exposure
60. Area Monitors Dosimeters Ion Chambers Geiger-Mueller (GM) Scintillators
61. Ionization Chamber Simplest of all gas-filled radiation detectors Gas-filled enclosure between 2 conducting electrodes When gas ionized by radiation, ion-pairs (IP) created + ions & dissociated e-s move to electrodes of opposite polarity Creating measureable ionization current Applied voltage allows device to work continuously: Mops up e-s which prevents device from becoming saturated Prevents recombination of IPs Provides output αradiation dose
62. G-M Counter Tube filled w/ Ar gas ~+400 Volts applied to thin wire in middle Particle enters tube, pulls an e- from Ar atom e-attracted to central wire: as it rushes towards wire, knocks other e-s from Aratoms, causing an "avalanche" 1 single incoming particle will cause many e-s to arrive @ wire, creating a pulse which can be amplified & counted Very sensitive detector Dead time For a short time after discharge, tube insensitive to radiation @ sufficiently high count rates, causes loss of counts Limits count rates to between 104 – 105 cps Above this, need ion chamber
63. Variation of IP charge w/ applied voltage Constant Incident Radiation Ion Chamber Region Geiger Region Proportional Counting Region Onset of continuous discharge Charge Collected (Log Scale) Not used Not used Limited proportionality-not used Voltage Applied (Linear Scale)
64. Scintillation Detectors Charged particle strikes scintillator Atoms excited & photons emitted Photons hit photomultiplier tube's (PMT) photocathode, Emits e-s by photoelectric effect e-s accelerated & focused by electrical potential e- strike 1st dynode Single e- releases several secondary e-s which, in turn, accelerate & strike 2nd dynode More e- released @ each subsequent dynode i.e. current amplifying effect @ each dynode stage Each stage @ higher potential than previous to provide accelerating field Resultant output signal @ anode in form of measurable pulse for each photon detected @ photocathode Pulse carries info about energy of original incident radiation on scintillator Both intensity &energy of radiation measured
65. Principles of Radiation Protection Time Distance Shielding Contamination Control As Low As Reasonably Achievable (ALARA) Procedure Appropriateness “Still, let’s do an x-ray just to be sure.”
66. Time – Distance – Shielding
67. Time ↓Time spent near radiation source Not all sources produce constant exposure rates Radiography-high exposure rate during short intervals Typical chest ~20 mR in < 1/20 s = 1,440 R/h Min. exposure by not activating when staff near Nuclear medicine-lower exposure rates over extended periods Minimize time by having thorough understanding of task & having appropriate equipment
68. Distance ↑ Distance from radiation source Exposure rate from point source ↓ as Consider isotropic point source @ center of a sphere Surface area of sphere = 4r2 Surface area over which radiation is distributed ↑ as r2 Not valid for non point sources Source whose dimensions not small compared to distance e.g. 1 meter from patient injected w/ radioisotope Dose rate ↓ less rapidly w/ distance Scattered radiation from patient, shield, table Rule of thumb: 1 m from patient 90º to incident beam radiation intensity ~0.1% of intensity striking patient NCRP recommends ≥ 2 m from tube & patient (mobile exams)
69. ALARA: As Low As Reasonably Achievable Dose limits to workers/public are upper limits Not reasonable doses Not safety thresholds Licensees req’d to: Practice good health physics Implement radiation safety programs NRC regs apply ALARA only to: Workers Members of public Many organizations recommend applying ALARA to imaging patients Culture of Safety “Open Door” Policy
70. Traits of Safety Culture Leaders demonstrate commitment to safety in their decisions/ behaviors All individuals take personal responsibility for safety Issues potentially impacting safety promptly identified, evaluated, & corrected commensurate w/ their significance Work activities planned & conducted so that safety is maintained Opportunities to learn ways to ensure safety are sought out & implemented Work environment is maintained in which people feel free to raise safety concerns Communications maintain a focus of safety Trust & respect permeate organization Workers avoid complacency & continually challenge, in spirit of cooperation, conditions & activities in order to identify discrepancies that might result in error
71. Shielding Facility Workers Caregivers Patients Members of the Public Appropriate Materials
72. Shielding Design Philosophy Occupancy Workload Controlled vs. Uncontrolled Areas Examples of Shielding Design Diagnostic X-Ray Room PET Facility Hot Lab and Nuclear Medicine Facility
73. Structural Shielding Goal: ↓Exposures to staff, public, patients Variables: Type Thickness Location Design depends on: Photon energy Diagnostic/Interventional ≤ 140 keV Nuclear Medicine typically ≤ 365 keV PET = 511 keV Intensity & geometry of radiation sources Exposure rate goals @ various locations Desirable qualities: High Z ↑ Photoelectric absorption ↓ Mass req’d High density Permits thinner shield Low $
74. Shielding Materials Most common material is Pb Pb sheets Specified in lbs/ft2 " up to “ thick Leaded glass/acrylic Other options: Gypsum wallboard (sheetrock) Concrete block Continuity/integrity very important Joints Must be 10 - 15 mm overlap between adjoining sheets of Pb Penetrations in walls & floor Window frames Doors & frames Lead Sheet Rock/Plywood Lead Seam filler & Screw Shielding
75. Defined Areas Controlled Access limited for purposes of radiation protection e.g. procedure rooms, control booths Occupational exposure under supervision of person responsible for radiation protection Workers in these areas typically monitored Uncontrolled Most other areas
76. Exposure Limits NCRP Report No. 147 (2004) Structural Shielding Design for Medical X-ray Imaging Facilities Quantity used: Air Kerma (mGy) Controlled Areas 5mGy / yr 0.1 mGy / wk Uncontrolled Areas 1 mGy / yr 0.02 mG / wk
77. Assumptions Neglect patient attenuation of beam Typically attenuates beam 10 – 100x Assume perpendicular incidence of beam w/ barrier Perpendicular incidence has greatest transmission Ignore other attenuating materials in beam’s path Assume large x-ray beam size for scattered radiation levels Assume high occupancy factors for uncontrolled areas Using these assumptions in shielding design keeps worker’s effective doses << occupational limits
78. Exposure Sources Primary Radiation AKA useful beam Depends on: Tube output Avg # exams performed/wk Fraction time tube directed towards barrier Distance Presence/absence of built-in primary barrier in equipment Secondary / Stray Radiation Scattered Radiation From interaction of primary radiation w/ patient αField size ~ 0.1% incident exposure @ 1 m from patient Leakage Radiation Radiation other than useful beam emanating from tube housing FDA regs: 100 mR/h (0.87 mGy/h) @ 1 m from housing Tube operated @ max. allowable continuous mA (3-5 mA)
79. Exposure to Individuals in Adjacent Areas Amount of radiation produced by source Distance between patient & radiation source Amount of time individual spends in adjacent area Amount of shielding between source & individual Distance between source & individual
80. Primary Barrier: intercepts primary beamSecondary Barrier: Intercept Secondary Radiation
81. Shielding Terminology Occupancy Factor, T Average fraction of time max. exposed individual present while x-ray beam on Workload, W Time integral of x-ray tube current over 1 week period mA∙min/wk NCRP Report 147 describes normalized workloads/patient (Wnorm) Includes multiple exposures depending on type of exam & clinical goal Total workload/wk = Wnormx N (N = avg # patients/wk) Use Factor, U Fraction of primary beam workload directed toward given primary barrier Depends on type of radiographic room & orientation of equipment
82. Typical Workloads
83. Occupancy Factors T=1Administrative offices & receptionist areas; laboratories, pharmacies & other areas fully occupied by an individual; attended waiting rooms; children's indoor play areas; adjacent X-ray rooms; image viewing areas; nurses' stations; X-ray control rooms; living quarters T=1/2Rooms used for patient examinations & treatments T=1/5Corridors; patient rooms; staff lounges; staff rest rooms T=1/8Corridor doors T=1/20Public toilets; unattended vending areas; storage rooms; outdoor areas w/ seating; unattended waiting rooms; patient holding areas T=1/40Outdoor areas w/ only transient pedestrian/vehicular traffic; unattended parking lots; vehicular drop off areas (unattended); attics; stairways; unattended elevators; janitor's closets
84. Use Factors
85. Example Room Considerations X-ray Clinic X-ray Clinic Waiting Area Radiation worker P=5mGy/yr T=1 Receptionist P=1mGy/yr T=1 Visitor P=1mGy/yr T=1/20 Lawyer’s Office next door Members of the Public P=5mGy/yr T=1
86. N: avg # patients/wk P: Desired mGy/wk T: Occupancy factor d: distance from source Example Data from NCRP 147
87. Pb Shielding Req’s: X-ray Vs. PET *Avg primary for rad room) Note: Drywall 5/8" thick w/ 1/16" thick Pb= 6.05 lbs/ft2
88. Conclusions “ Pb standard barrier for: Radiographic Fluoroscopy Interventional Suites If cassette/grid/table attenuation assumed: Standard density concrete floors suffice Mammography Standard construction gypsum wallboard Wooden solid core doors
89. CT Shielding All walls considered secondary barriers Detector array is primary barrier
90. Conclusions Detector ring primary barrier “ Pb sufficient for secondary wall barrier Ceilings/floors may need attention
91. Personnel Protection Staff protected by structural shielding except when req’d to be in room during imaging Fluoroscopic procedures Some of the following patient populations: Pediatric Critically ill Uncooperative Staff protection Staff positioning w.r.t. patient Protective clothing Pb aprons Pb thyroid shields Leaded glasses/goggles Pb gloves Sn, Ba aprons Radiation barriers Ceiling-, table-mounted Mobile
92. Radiation Protection Pb “pig” Syringe carrier
93. Contamination Control Uncontained material located where it is not wanted Protective clothing & handling precautions Similar to “universal precautions” Disposable plastic gloves Lab coats Closed toe shoes Work surfaces covered w/ plastic-backed absorbent paper Unlike other hazards, easy to detect small quantities Effectiveness of contamination control monitored by: GM meter surveys Wipe Tests Areas considered contaminated if ≥ 2x background
94. Advisory Bodies International Commission on Radiological Protection (ICRP) National Council on Radiation Protection & Measurements (NCRP) Conference of Radiation Control Program Directors (CRCPD) International Atomic Energy Agency (IAEA) Joint Commission on Accreditation of Healthcare Organizations (JC) American College of Radiology (ACR) National Electrical Manufacturers Association (NEMA) (Medical Imaging & Technology Alliance or MITA)
95. Regulatory vs. Advisory Regulatory agencies Carry force of law Agencies can: Inspect facilities & records Levy fines Suspend activities Revoke radiation use authorization Advisory Bodies Periodically review scientific literature & issue recommendations Do not carry force of law Usually the basis of regs Basis of “best practice” standards voluntarily adopted
96. IAEA Independent intergovernmental science & technology-based UN organization Assists its Member States in planning for & using nuclear science & technology for various peaceful purposes e.g. electricity generation, facilitates transfer of technology & knowledge to developing Member States Develops nuclear safety standards promotes protection of human health & environment against ionizing radiation Verifies, through inspection,that States comply w/ their commitmentsto use nuclear material & facilities only for peaceful purposes under Non-Proliferation Treaty & other non-proliferation agreements
97. ACR 36,000 members include: radiologists radiation oncologists medical physicists interventional radiologists nuclear medicine physicians allied health professionals Mission: Maximizing value of radiology, radiation oncology, interventional radiology, nuclear medicine & medical physics by: advancing science of radiology improving quality of patient care positively influencing socio-economics of the practice of radiology providing continuing education for radiology & allied health professions conducting research for the future of radiology
98. ACR Safety Mission Elements Reports & statements Practice guidelines Technical standards Appropriateness criteria Pediatric radiation safety Patient information Occupational safety
99. TJC (Formerly JCAHO) Independent, not-for-profit organization Accredits & certifies19,000+ health care organizations & programs in US State gov’t conditions Medicaid reimbursement on accreditation Sentinel Event Unexpected occurrence involving death or serious physical or psychological injury, or risk thereof ≠ Medical error necessarily TJC defined prolonged fluoro w/ cumulative dose>15 Gy to single field as sentinel event Sentinel Event Alerts Issues SEAs identifying serious unanticipated incidents that could/did harm patients in healthcare setting
100. TJC Suggestions Use imaging techniques other than CT (e.g.US, MR) & collaboration between radiologist & referring physician Use ALARA principle & pediatric, adult guidelines from Society for Pediatric Radiology ACR RSNA Use proper protocols & review all protocols annually /biannually Expand RSO role to include patient safety & education of all physicians/techs who prescribe/use diagnostic radiation Use of diagnostic medical physicist in: Designing/altering CT protocols Quality/safety monitoring of all equipment that can emit high amounts of cumulative radiation Testing imaging equipment initially, biannually thereafter Designing programs for QC, testing, preventive maintenance Investing in dose optimization/reduction technologies
101. CRCPD Primary membership: Radiation professionals in state & local government that regulate use of radiation sources Mission: Promote consistency in addressing & resolving radiation protection issues Encourage high standards of quality in radiation protection programs Provide leadership in radiation safety & education Primary goal: Assure radiation exposure to individuals is kept to lowest practical level, while not restricting its beneficial uses
102. ICRP Since 1928, ICRP has developed, maintained, & elaborated International System of Radiological Protection used world-wide as the common basis for radiological protection standards legislation guidelines programs practice 100+ reports published on all aspects of radiological protection. International System of Radiological Protection has been developed by ICRP based on: (i) Current understanding of science of radiation exposures & effects (ii) Value judgments Takes into account societal expectations, ethics, & experience gained in application of system
103. NCRP Nonprofit corp. chartered by congress to: Collect Analyze Develop Disseminate Info & recommendations about radiation: Protection Measurements Quantities Units Also stimulate cooperation & effective utilization of resources w/ other organizations
104. NEMA & MITA NEMA Leading standards-development organization for medical imaging & radiation therapy equipment Voluntary guidelines that establish commonly accepted methods of design, production, testing & communication for imaging & cancer treatment products MITA division of NEMA Leadership for medical imaging & radiation therapy industries on legislative & regulatory issues @ state, federal & international levels Advocates for fair legislative & regulatory proposals that encourage innovation, investment in R&D
105. Regulatory Agencies U.S. Nuclear Regulatory Commission & Agreement States 10 CFR Parts 19, 20, 30, 32, 35, 110 Guidance Documents (NUREG 1556, Vols. 9 & 11) Regulatory Guides States: for Machine-Produced Sources Suggested State Regulations U.S. Food & Drug Administration Center for Devices & Radiological Health (CDRH) Center for Drug Evaluation & Research (CDER) U.S. Office of Human Research Protections U.S. Department of Transportation U.S. Department of Labor (OSHA) International Electrotechnical Commission (IEC)
106. NRC Atomic Energy Act (1954) established Atomic Energy Commission (AEC) NRC  regulatory arm Regulates Special nuclear material Plutonium Uranium Source material Thorium, Uranium & their ores By-product material used in: Commercial nuclear power Research Medicine Other commercial activities Material made radioactive by particle accelerator* *Added by Federal Energy Policy Act (2005)
107. Agreement States Most states administer own radiation control program Additionally these states regulates all sources of ionizing radiation Diagnostic x-ray machines Interventional x-ray machines Linear accelerators
108. NRC Regulations Title 10 of the Code of Federal Regulations (CFR) Part 20 “Standards for Protection against Radiation” Definitions used in regs & req’s for radiation surveys Personnel monitoring Radiation warning signs/symbols Shipment, receipt, control, storage, disposal radioactive materials Max. permissible doses to workers/public Environmental release limits Documentation & notification reqs after significant event Part 35 “Medical Use of By-Product Material” Req’s for medical use Training req’s Precautions Req’s for reporting events involving specific errors in administration
109. Licensing License req’d from NRC or state regulatory agency to possess & use radioactive material in medicine License lists: Radioactive material that may be used Amounts of material that may be possessed Uses of material allowed Physicians permitted to use & supervise the use of materials Procedures & record-keeping req’s for material: Receipt Transportation Use Disposal i.e. “Cradle-to-Grave” control Each institution must designate Radiation Safety Officer Responsible for day-to-day oversight Named in license
110. FDA Under US Department of Health & Human Services (HHS) Regulates development & manufacturing of Radiopharmaceuticals Medical x-ray equipment Design & performance req’s Does not directly regulate end users Except mammography Publishes guidance documents Req’s reporting serious injuries/deaths a medical device has caused or contributed to
111. Center for Devices & Radiological Health (CDRH) Subset of FDA Mission: Assure that patients & providers have timely & continued access to safe, effective, & high-quality medical devices & safe radiation-emitting products Provide consumers, patients, caregivers, & providers w/ understandable & accessible science-based information about products they oversee Facilitate medical device innovation by advancing regulatory science, providing industry w/ predictable, consistent, transparent, & efficient regulatory pathways, & assuring consumer confidence in devices marketed in U.S
112. Center for Drug Evaluation & Research(CDER) Subset of FDA Mission: Assures all prescription & over-the-counter drugs safe & effective Evaluates all new drugs before they are sold Serves as a consumer watchdog for 10,000+ drugs on market to be sure they continue to meet highest standards Routinely monitors TV, radio, & print drug ads to ensure they are truthful & balanced Plays critical role in providing health professionals & consumers information to use drugs appropriately & safely
113. Office for Human Research Protections (OHRP) Under US Department of HHS Mission: Provides leadership in protection of rights, welfare, & wellbeing of subjects involved in research conducted or supported by HHS Helps ensure this by: Providing clarification & guidance Developing educational programs & materials Maintaining regulatory oversight Providing advice on ethical & regulatory issues in biomedical & social-behavioral research
114. Occupational Safety and Health Administration (OSHA) Part of US Department of Labor Mission: Assure safe & healthful working conditions for working men & women by Setting & enforcing standards Providing training, outreach, education & assistance
115. DOT Regulates transportation of radioactive materials The DOT issues an orange alert
116. International Electrotechnical Commission (IEC) International standards & conformity assessment for all electrical, electronic & related technologies Provides a platform to companies, industries & governments for meeting, discussing & developing the International Standards they require
117. Radiation Safety with Radioactive Materials Surveys Area Wipe Test Spills Ordering, Receiving, & Unpacking Radioactive Materials Contamination Control Radioactive Waste Management Qualifications for Using Radioactive Materials Diagnostic (10 CFR 35.200 & 35.100, or Equivalent Agreement State Regulations) Therapeutic (10 CFR 35.300 & 35.1000, or Equivalent Agreement State Regulations) Medical Events Reportable Non-reportable Person or Agency to Receive Report Special Considerations Pregnant Patients Breast-Feeding Patients Caregivers Patient Release
118. Qualifications for Using Radioactive Materials Diagnostic 10 CFR 35.200 & 35.100, or Equivalent Agreement State Regulations Therapeutic 10 CFR 35.300 & 35.1000, or Equivalent Agreement State Regulations
119. TJC - Sentinel Event Event resulted in unanticipated death or major permanent loss of function, not related to natural course of patient’s illness or underlying condition, or Event is one of following (even if outcome was not death or major permanent loss of function): Suicide of any individual receiving care, treatment or services in a staffed around-the-clock care setting, or within 72 hours of discharge Unanticipated death of a full-term infant Abduction of any individual receiving care, treatment or services Discharge of an infant to the wrong family Rape Hemolytic transfusion reaction involving administration of blood or blood products having major blood group incompatibilities Surgical and nonsurgical invasive procedure on the wrong patient, wrong site or wrong procedure Unintended retention of a foreign object in an individual after surgery or other procedure Severe neonatal hyperbilirubinemia (bilirubin >30 milligrams/deciliter) Prolonged fluoroscopy w/ cumulative dose: >1500 rads to a single field, or Any delivery of radiotherapy to wrong body region, or 25% above planned radiotherapy dose
120. Non-Reportable Events Any close call (“near miss”) Full or expected return of limb or bodily function to the same level as prior to the adverse event by discharge or within two weeks of the initial loss of said function Any sentinel event that has not affected an individual served Medication errors that do not result in death or major permanent loss of function Suicide other than in an around-the-clock care setting or following elopement from such a setting A death or loss of function following a discharge against clinical advice (AMA) Unsuccessful suicide attempts unless resulting in major permanent loss of function
121. Response to Sentinel Event Accredited HCOs should have a policy on: What constitutes a reportable event Reporting methodology Remediation Steps Conduct a timely, thorough, & credible root cause analysis Develop action plan designed to implement improvements to ↓ risk Implement the improvements Monitor the effectiveness of those improvements
122. Estimating Effective Fetal Dose (Procedure-Specific Doses) Radiography Mammography Fluoroscopy Computed Tomography (CT) Nuclear Medicine
123. Factors Affecting Fetal Dose Beam Factors Output intensity X-ray equipment Air kerma or exposure Fluoro equipment Air kerma rate or entrance exposure HVL Beam penetrability Conditions of exam X-ray Location No. of views Radiographic exposure factors Fluoro Beam-on time No. spot films Exposure factors Patient Fetal age Patient’s Size/thickness Depth of fetus Orientation of patient wrt tube
124. Estimating Fetal Dose Direct Exposure Inside FOV Results in highest exposure Maternal entrance exposure calculated using Measured values of exposure/Air kerma Specific technique factors Entrance exposure used to calculate dose @ depth of fetus Published depth-dose/tissue-air ratio tables Indirect Exposure Outside FOV Primarily from scatter from FOV Maternal entrance exposure calculated as before Published scatter factors applied Account for location relative to exam FOV
125. Est. Doses to Uterus from Diagnostic Procedures Report 54 NCRP Mammo, Skull, C-Spine, Extremity, Chest exams ~ 0 exposure
126. “Now that’s scary!” Radiological Emergencies Incidents Nuclear Power Military Equipment Transportation Accidents Research Lab & Radiopharmacy Accidents Purposeful Exposures Nuclear Detonation Radiological Dispersion Device (RDD) Environmental Contamination Radiological Exposure Device (RED) Treatment of Radiological Casualties Notification & Patient Arrival Triage: Evaluation, Dispensation & Initial Treatment External Exposure & Internal Contamination Radiological Assessment Medical Management Oak Ridge Radiation Emergency Assistance Center
127. Acute Radiation Syndrome (ARS)
128. Approx. Thresholds for ARS *At higher doses the time to onset of signs/symptoms may be compressed
129. Acute Doses: Approx. Skin Injury Thresholds *At higher doses the time to onset of signs/symptoms may be compressed
130. ARS: estimation of Dose Crude estimation: Time to Emesis (TE) TE < 2 hrs, effective whole-body dose likely > 3 Gy TE < 1 hr, whole body dose most probably >4-6 Gy Conversely, if patient has not vomited w/in 8-10 hrspost-event, whole-body dose likely < 1 Gy More accurately estimations w/ observing kinetics of circulating WBC Obtain initial baseline CBC w/ differential, if possible, & repeat q 6 h Lymphocyte depletion follows dose-dependent, 1st-order kinetics after high-level γ & criticality incidents, while the neutrophil/lymphocyte ratio (N/L) ↑over the 1st few days post-exposure Both are sensitive indicators of radiation dose
131. ARS Medical Management Focused mainly on support & recovery of hematologic system 2 major aimsare efforts to prevent: Neutropenia Sepsis as heralded by fever Hospital management issues: Antibiotic, antiviral, & antifungal agents Early cytokine therapy Early wound closure GI decontamination Minimization of invasive procedures Barrier isolation Reverse isolation for patients w/ whole body doses > 2-3 Gy Strict environmental control, including isolation, strict hand washing, surgical scrubs & masks for staff, & possibly laminar flow Avoid antacids & H2 blockers to maintain gastric acidity, sucralfate to avoid stress ulcers Oral feeding is preferable to IV, if possible (only cooked foods, no root crops) Meticulous oral & nail hygiene Povidone-iodine or chlorhexidine for skin & hair
132. External Radioactive Contamination Irradiation vs. Contamination Person is irradiated when they are “exposed” to ionizing radiation When people have radioactive materials on/in them they are contaminated Decontamination Remove contaminated clothing Wash area w/ soap & water W/out spreading contamination to other: Areas of body People W/out inhaling contaminants W/out abrading skin Progress assessed using portable radiation survey meter Decontamination continues until: Remains approach background No more progress can be made
133. Internal Radiation Contamination Major routes of intake: Inhalation Ingestion Absorption through open wound contamination Transdermal absorption Externally contaminated casualties w/ no respiratory protection Esp. if significant contamination found on face, in/around nostrils or mouth, or in/around open wounds Medical management Specific & isotope-dependent Identifying isotope crucial Radioactive decay /biological elimination rid body of materials Combining both rates gives effective half-life Always shorter than either radiological or biological half-life Metabolism &elimination kinetics of non-radioactive analog determine metabolic pathway of radionuclide
134. Radioactive Iodine Readily taken up by thyroid &retained w/ long biological half-life Children particularly susceptible to potential for thyroid cancer following exposure to radioactive iodine Medical management Administer large amounts of nonradioactive I to block thyroid uptake of radioactive I Oral potassium iodide (KI) should be given w/in 4 hours of exposure Or ASAP
135. KI Recommended Doses
136. Common Isotopes Involved in Exposures “University 5” 14C, 32P, 125I, 131I, 252Cf Isotopic labeling in biochemistry laboratories, & in medicine Tritium also common (3H) “Industrial 3” 192Ir, 137Cs, 60Co 192Ir widely used in industrial radiography to photograph large objects such as oil pipes, airplane wings, etc. 137Cs & 60Co used in industry because of their penetrating γrays & considered to be prime agents for terrorism events “Military 5” 3H, 235U, 238U, 239Pu, 241Am Primarily used in the weapons complex, both in DOE system & military Fission/Activation Products Encountered in response to: Nuclear detonation IND/weapon Reactor accident Waste transportation incident Some are volatile &, depending on activity, can pose significant risk to populace
137. Radiation Incident w/ Trauma or Illness Life Threatening Problem? YES NO Stabilize Externally Contaminated? NO YES Admit to regular ED. Medical/Surgical Tx. Medical Event History. ID Contaminant. Admit to Controlled Area Possible External Irradiation of Internally Contaminated? NO Remove Clothing Follow usual Tx procedures Medical Event History. ID/Contain Contaminant. Minimize Possible Intakes. Assess & Treat Medical Problem Survey & Document YES Collect Samples for Radiological Analysis Baseline CBC w/ Diff. Serum Amylase, Urinalysis, Baseline Rad Urine, Start 24-hr urine collection. Minimize Uptake or Facilitate Excretion of contaminant. YES NO Stable? Stabilize Persistent Vomiting, Erythema, Fever? YES NO Identify Decontamination Priority Transfer or Discharge Repeat CBC & Diff. every 4-6 hrs 1) Wounds 2) Body Orifices 3) Intact Skin Observe for Vomiting w/in 24 hrs Collect Samples NO Significant Absolute Lymphocyte ↓ or Other Medical Problem? NO Decontaminate YES Contamination ↓ to Acceptable Level? Resurvey YES Discharge Other Contaminated Areas? YES Follow-up: Medical Eval./Rx Collect excretions Dose Assessment Whole Body Count Medical & Radiological Follow-up? CytogeneticsBiodosimetry NO Still Externally Contaminated? YES Confirmation Survey of Entire Body NO
138. Clinical Application Safety considerations for patients & staff, including pregnant staff, in mobile radiography (“portables”). Use knowledge of radiation effects in planning for & reacting to an emergency that includes exposure of personnel to radiation. Contributions of medical sources to collective effective dose. Responsibilities & qualifications of authorized user (all categories) & RSO. Training & experience req’sfor using sealed & unsealed sources of radioactive material. Use of personnel radiation protection equipment. Appropriate equipment for wipe tests & contamination surveys. Information to public concerning radon. Clinical examples that demonstrate ALARA principles. Discriminate between workers in an area who are occupationally exposed & those who are treated as members of general public.
139. Clinical Problem-Solving Discuss factors that determine dose to a pregnant person seated next to a patient injected w/ a radionuclide for a diagnostic or therapeutic procedure. Describe steps used in applying appropriateness criteria. Describe what must be done before administering a radioactive material in a patient. Describe what is required to have a person listed on a facility’s Nuclear Materials license as an Authorized User.
140. End Module