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  • Remainder: e.g. adrenals, brain, upper L intestine, small intestine, kidneys, muscle, pancreas, spleen, thymus, and uterus
  • Not K-40 in body, cosmic rays, from rocks But YES for radon build up if ventilation can help YES for uranium mining, processing NORMs, etc.
  • Not K-40 in body, cosmic rays, from rocks But YES for radon build up if ventilation can help YES for uranium mining, processing NORMs, etc.
  • Not K-40 in body, cosmic rays, from rocks But YES for radon build up if ventilation can help YES for uranium mining, processing NORMs, etc.
  • Entrance Surface Dose proportional to 1/kv 2 Energy imparted proportional to 1/kv 2
  • Remainder: e.g. adrenals, brain, upper L intestine, small intestine, kidneys, muscle, pancreas, spleen, thymus, and uterus

Transcript

  • 1. Radiation Protection for Cardiologists John Saunderson Radiation Protection Adviser PRH ext 6690 Part 3 – Practical Protection for Patients & Staff
  • 2. Syllabus
    • Physics & hazards of ionising radiation to patients & staff
    • Statutory requirements for Medical Exposures
    • Equipment
    • Factors affecting patient & staff dose
    • Important aspects of cardioradiology
    • Above covers IRMER “Core of Knowledge” .
  • 3. Part 1 – Hazards of Ionising Radiation
  • 4. Deterministic Effects (“threshold effects”)
    • Large number of cells killed – physiological effect , e.g.
      • Erythema, epilation, cateracts, “radiation sickness”
    • No risk below threshold doses , e.g.
      • Transient erythema = 2 Gy
      • Opacities = 500 mGy
    • Bigger dose above threshold, more severe the effect , e.g.
      • 2 Gy transient erythema
      • 20 Gy secondary ulseration .
  • 5. Stochastic Effects (“chance effects”)
    • Where cells mutated in a such a way as to cause
      • Cancer, hereditary disease
    • Risk proportional to dose
    • e.g abdomen X-ray risk = risk of dying in a traffic accident in next year
    • Minimise risk by keeping doses a s l ow a s r easonably a chievable
    • A.L.A.R.A.
  • 6. Absorbed Dose (D)
    • Amount of energy absorbed per unit mass [D=d  /dm] – units, 1 Gray (Gy) = 1 J/kg
    • Typical Values of D
      • Radiotherapy dose = 40 Gy to tumour (over several weeks)
      • LD(50/30) = 4 Gy to whole body (single dose)
      • Typical 1 minute screening = 20 mGy skin dose
      • Chest PA = 160 uGy skin dose
      • Threshold for transient erythema = 2 Gy .
  • 7. Effective Dose (E)
    • Absorbed dose weighted for relative radio-sensitivity of different organs
    • Units are Sieverts (Sv)
    • Risk of inducing cancer or hereditary disease is proportional to Effective Dose
    • 1 in 20,000 risk of fatal cancer from 1 mSv
      • (= risk of dying in a road accident in next year)
    • e.g.
      • Pulmonary angiography = 5.4 mSv
      • Chest PA = 20 uSv
      • Annual background dose = 2.5 mSv .
  • 8. “ Small” risks so why worry?
    • Average effective dose for angiography = 6 mSv
    • Risk of fatal cancer from 6 mSv only 1 in 3,300
    • But, 321,174 angiography procedures in 2000
    • So
      • All exposures must be JUSTIFIED
      • Doses to patients, and staff, must be A s L ow A s R easonably A chievable ( ALARA principle ) .
  • 9. Part 2 – The Nature of Ionising Radiation
  • 10. Filament (heats up on prep.) Target kV + - X-ray s e - mA
  • 11. 80 kV p Diagnostic X-ray Beam
  • 12. At lower energies
    • PHOTOELECTRIC ABSORPTION dominates
    • Lots of contrast (density, size & Z 3 )
    • Less scatter, higher patient dose
    At higher energies
    • COMPTON SCATTERING dominates
    • Less contrast (density, & size)
    • More scatter, lower patient dose .
  • 13. Still to do . . .
    • Image formation, image intensifiers, flat plates, nuclear medicine imaging
    • Practical radiation protection
      • Staff
      • Patients
      • X-ray & nuclear medicine
      • Assessing doses
    • Regulations and Guidelines
    • Practical Session .
  • 14. Radiation Protection for Cardiologists John Saunderson Radiation Protection Adviser PRH ext 6690 Part 3 – Practical Protection for Patients & Staff
  • 15.
    • Justification
    • Optimisation
    • Limitation .
    International Commission on Radiological Protection Principles of Radiation Protection
  • 16. The Justification of a practice
    • “ No practice involving exposure to radiation should be adopted unless it produces sufficient benefit to the exposed individual or to society to offset the radiation detriment it caused .”
    • i.e. must be a net benefit .
  • 17. The Optimisation of Protection
    • “ In relation to any particular source within a practice, the magnitude of individual doses , the number of people exposed, and the likelihood of incurring exposures where these are not certain to be received should be kept as low as reasonably achievable , economic and social factors being taken into account . This procedure should be constrained by restrictions on the dose to individuals ( dose constraints ), or the risks to individuals in the case of potential exposures (risk constraints), so as to limit the inequity likely to result from the inherent economic and social judgements.”
    ALARA as low as reasonably achievable . ALARP as low as reasonably practicable
  • 18. Individual Dose and Risk Limits
    • “ The exposure of individuals resulting from the combination of all the relevant practices should be subject to dose limits, or to some control of risk in the case of potential exposure. These are aimed at ensuring that no individual is exposed to radiation risks that are judged to be unacceptable from these practices in any normal circumstances. Not all sources are susceptible of control by action at the source and it is necessary to specify the sources to be included as relevant before selecting a dose limit.”
    • Prevent deterministic effects
    • Limit risk of stochastic effects to acceptable level .
  • 19. ICRP’s Three Types of Exposure
    • Occupational
    • Medical
    • Public
  • 20. Occupational Exposure
    • 20 mSv a year effective dose
    • 150 mSv a year to lens of eye
    • 500 mSv a year to 1 cm 2 of skin, hands and feet
    • Fetus: from declaration of pregnancy
      • for external radiation, 2 mSv to surface of woman’s abdomen
      • for radionuclides, 1/20 Annual Limit of Intake .
  • 21. Medical Exposure
    • “ exposures incurred by individuals as part of their own medical diagnosis and treatment .”
    • “ and . . . individuals helping in the support and comfort of patients undergoing diagnosis and treatment (not occupationally) . . .”
    • No dose limits apply
    • Consider dose constraints
  • 22. Public Exposure
    • Limits apply to exposures from human activities
    • 1 mSv a year effective dose
      • in special circumstances, average over 5 years
    • 15 mSv a year to lens of eye
    • 50 mSv a year to 1 cm 2 of skin
    • (i.e. 1 /10 th of worker limit) .
  • 23. Optimisation - ALARA
  • 24. Practical Patient Protection
    • Field
    • Tube voltage
    • Beam filtration
    • Tube to patient distance
    • Fluoroscopy
    • CT
    • QA
  • 25. Field
    • Cover only area needed
    • Small fields give lower dose (and less scatter, therefore better image)
    • Avoid more radiosensitive areas - e.g. gonads, female breast
    • Position carefully - e.g. limbs
    • Use lead shields were appropriate - e.g. gonad shields
    • AP or PA? .
  • 26. Lead rubber
    • 0.35 mm
      • 60 kVp  0.5 % transmission
      • 120 kVp  10 % transmission
    • 0.25 mm
      • 60 kVp  1.5 % transmission
      • 120 kVp  16 % transmission .
  • 27. Tube Voltage (kV)
    • Higher kV = lower patient dose
    • e.g. changing from 100 to 110 kV leads to 12% reduction in skin dose
    • Higher kV = less contrast
    • e.g. changing from 100 to 110 kV reduces spine/soft tissue contrast from 1.48 to 1.34 (9% drop) .
  • 28. Filtration
    • More filtration = lower patient dose
    • e.g.  0.1 mm Cu   33% skin dose
    • More filtration = less contrast
    • e.g.  0.1 mm Cu   spine/soft tissue contrast at 80 kV from 2.76 to 2.46 (11% drop) .
  • 29.  
  • 30.  
  • 31. Transmission through 10 cm tissue
    • 80 keV  16 %
    • 60 keV  13 %
    • 50 keV  10 %
    • 40 keV  7 %
    • 30 keV  2 %
    • 20 keV  0.04 %
    • 15 keV  0.000008 %
    • 10 keV  10 -21 %
  • 32. Minimum Filtration
    • General tube  2.5 mm aluminium
    • Mammography  0.03 mm molybdenum or 0.5 mm Al
    • Dental (  70kVp)  1.5 mm Al
    • Dental (> 70kVp)  2.5 mm Al
  • 33. Tube to Patient Distance
  • 34. Tube to Patient Distance
    • Greater FSD = lower patient dose
    • e.g.  from 50 to 70 cm   49% skin dose
    • Greater FSD = less magnification
    • (so fewer distortions)
    • Tube to patient distance
      • never < 30cm,
      • preferably > 45cm
      • for chests > 60 cm .
  • 35. Time to erythema threshold dose (At 20 – 100 mGy/min, 70 cm FSD)
    • 70 cm from focus = 100 - 20 mins
    • 50 cm from focus = 50 - 10 mins
    • 30 cm from focus = 18 - 3 ½ mins
  • 36. Fluoroscopy
    • Only expose when looking at monitor
    • Keep patient close to image intensifier and far from tube (at least 30 cm from tube for mobile, 45 cm for static)
    • Use low dose setting, unless image unacceptable
    • Magnification increases dose rate to skin (although a smaller area irradiated)
    • Cone down where practicable
    • Special care if skin dose likely to exceed 1 Gy .
                                          
  • 37.  
  • 38.  
  • 39.  
  • 40. Dose Settings
    • Vary with manufacturer and model
    • Beware - can vary between different sets of same manufacturer and model!
    • Low dose
      • more filtration, higher kV, less pulses/second
    • High contrast
      • less filtration, low kV, more pulses/second .
  • 41. Automatic brightness control Brightness controlled mainly by adjustment of kVp Brightness controlled by simultaneous adjustment of kVp and mA The tube current is maximised at 3 mA Tube heating  kV x mA (99% energy goes to heat, typically ¼ kW over few mm 2 ) X-ray intensity  kV 2 x mA Penetrating power  with kV  Contrast  with kV 
  • 42.  
  • 43. Entrance Dose Rates for Standard Phantom
  • 44. Time to Reach 2 Gy for Standard Phantom
  • 45. Screening and Acquisition e.g. HRI CP1, 20 cm field size, 18.5 cm Perspex phantom
    • Screening
      • 77 kV, 2.2 mA
      • Skin dose rate = 19 mGy/min (Erythema threshold = 105 min)
    • Digital acquisition
      • 80 kV, 475 mA, 32 ms
      • Skin dose = 2.5 mGy/image (Erythema threshold = 800 images)
    • 1 min screening  7 spot images
  • 46. Dose Area Product
    • Stochastic risks approx. proportional to DAP
    • Skin dose is DAP / area irradiated
    • 1 Gy.cm 2  3 mGy skin dose (2 Gy  666 Gy.cm 2 )
    • 1 Gy.cm 2  0.2 mSv effective dose .
  • 47. Dose Area Product
    • Dose  1/distance 2
    • Area  1/distance 2
    • Therefore, dose x area indepenent of distance .
  • 48. DAP
    • Stochastic risks approx. proportional to DAP
    • Skin dose is DAP / area irradiated
    • 1 Gy.cm 2  3 mGy skin dose (2 Gy  666 Gy.cm 2 )
    • 1 Gy.cm 2  0.2 mSv effective dose .
  • 49. 20/11/96
  • 50.
    • High dose, so justification important, e.g.
      • Film abdomen = 1 mSv
      • CT abdomen = 10 mSv
    • ALARA by
      • Lowest mA practicable
      • Minimum number of slices necessary
      • Angulation of gantry can substantially reduce eye dose
    • Note, CT: 10 x 1mm slices may give higher dose than 1 x 10mm slice .
    CT
    • MX800Quad, HRI
    • CTDI/mAs vs Slice Thickness
        • 2 x 10 mm  191 uGy/mAs
        • 2 x 8 mm  197 uGy/mAs
        • 4 x 5 mm  190 uGy/mAs
        • 4 x 2.5 mm  208 uGy/mAs
        • 4 x 1 mm  253 uGy/mAs
        • 2 x 0.5 mm  445 uGy/mAs
    .
  • 51. Pregnancy
    • Diagnostic Medical Exposures: Advice on Exposure to Ionising Radiation during Pregnancy (NRPB/CoR/RCR)
    • out of print, but can be downloaded from www.nrpb.org/publications/misc_publications/advice_during_pregnancy.pdf
    • Deterministic effects – very unlikely
    • Stochastic effects – increase risk of childhood cancer .
  • 52. Examples of Risk of Childhood Cancer
    • “ Natural” risk: 1 in 1,300
    • Abdomen mean: 1.4 mGy  1 in 24,000
    • max.: 4.2 mGy  1 in 8,000
    • CT Abdomen mean: 8 mGy  1 in 4,000
    • max.: 49 mGy  1 in 700
    • Pelvis mean: 1.1 mGy  1 in 30,000
    • max.: 4.0 mGy  1 in 8,000
    • CT Pelvis mean: 8 mGy  1 in 4,000
    • max.: 79 mGy  1 in 400
  • 53. .
    • e.g.
    • abdominal CT (max. fetal dose = 49mGy)
    • pelvic CT (79mGy)
    • 131 I thyroid metastases (22mGy)
    • 75 Seleno-cholesterol (14mGy)
    • 67 Ga tumours and abscesses (12mGy) .
  • 54.
    • If fetus inadvertently exposed contact RPA for risk estimate
    • Risk from a diagnostic X-ray is small enough never to be grounds for
      • invasive fetal diagnostic procedures
      • for termination
  • 55. Infants and Children
    • Gonad shields should be used where relevant and practical
    • Restrict field to essential area
  • 56. From www.info.gov.hk/dh/diseases/CD/photoweb/RSVacutebronchiolitis-1.jpg
  • 57. Infants and Children
    • Gonad shields should be used where relevant and practical
    • Restrict field to essential area
    • Greater level of justification
  • 58. Probability of fatal cancer (Atom bomb “survivors”)
    • i.e. children risk  3 x adult risk
    Risk per million per mGy
  • 59. Also
    • Use AECs
    • Low attenuation table tops, etc. (e.g. c-fibre)
    • Quality assurance
    • DRLs
  • 60. Medical & biomedical research
    • Must be LREC approved
    • If no benefit to individual - DOSE CONSTRAINTS
    • If benefit to patient - INDIVIDUAL TARGET LEVELS of DOSE
    • Risks must be communicated to volunteer
    • Avoid pregnant women or children unless specific to study.
    • Only one study a year for healthy volunteers .
  • 61. Health screening
    • Medical Physics Expert must be consulted
    • Special attention to dose
    • Dose constraints
  • 62. e.g. is mammography screening of 40-49 year olds justified?
    • Currently 50-64’s screened
    • 300+ lives saved per year (UK)
    • Between 0 and 2 in 1000 will have life extended if 40-49 screened
    • For 50-64, 1 in 10 missed
    • For 40-49, 1 in 4 missed
    • 1 in 10,000 risk of inducing cancer (40-49)
    • other “risks”
  • 63. Radiation protection of staff
    • Controlled areas
    • Time, distance, shielding
    • lead aprons
  • 64.  
  • 65.  
  • 66.  
  • 67. Basic Principles
    • Time
    • Distance
    • Shielding
  • 68. Distance
    • Double distance = 1 / 4 dose
    • Triple distance = 1 / 9 th dose .
  • 69. Shielding
  • 70. Shielding
  • 71. Typical Transmission through Shielding (90 kV)
    • 0.25 mm lead rubber apron  8.5%
    • 0.35 mm lead rubber apron  5%
    • 2 x 0.25 mm apron  2.5%
    • 2 x 0.35 mm apron  1.0%
            • Double brick wall  0.003%
            • Plasterboard stud wall  32%
            • Solid wooden 1” door  81%
            • Code 3 lead (1.3 mm)  0.1% .
  • 72. Lead Apron Storage
    • Always return to hanger
    • Do not
      • fold
      • dump on floor and run trolleys over the top of them!!!
    • X-ray will check annually
    • But if visibly damaged, ask X-ray to check them .
  • 73. e.g. Coronary Angiogram
    • Primary beam = 100 mSv (4.9 min screening)
    • Scattered dose = 152 uSv @ 1 m (annual dose limit 39 patients)
      • Thru’ 0.25 mm Pb = 13 uSv (461 patients)
      • Thru’ 0.35 mm Pb x 2 = 1.5 uSv @ 1 m (4000 patients)
  • 74. Radiology Staff Protection
    • Only essential staff in radiation area
    • Protective clothing if not behind screen
    • Close doors
    • Minimum beam size (min. scatter)
    • Never point primary beam at screen
    • Use mechanical devices to support patients (unless …)
    • Record where staff hold, rotate staff .
  • 75. fin
  • 76. www.hullrad.org.uk
  • 77. Parameter Summary
    • Parameter Quality/Penetration Intensity
    • mA  - 
    • kV    (kV 2 )
    • Filtration   
    • Distance -  (1/r 2 )
  • 78. Tube Voltage (kV)
    • Higher kV = lower patient dose
    • e.g. changing from 100 to 110 kV leads to 12% reduction in skin dose
    • Higher kV = less contrast
    • e.g. changing from 100 to 110 kV reduces spine/soft tissue contrast from 1.48 to 1.34 (9% drop) .
  • 79. Filtration
    • More filtration = lower patient dose
    • e.g.  0.1 mm Cu   33% skin dose
    • More filtration = less contrast
    • e.g.  0.1 mm Cu   spine/soft tissue contrast at 80 kV from 2.76 to 2.46 (11% drop) .
  • 80. Tube to Patient Distance
    • Greater FSD = lower patient dose
    • e.g.  from 50 to 70 cm   49% skin dose
    • Greater FSD = less magnification
    • (so fewer distortions) .
  • 81. Medical and Dental Guidance Notes A good practice guide on all aspects of ionising radiation protection in the clinical environment
    • 240 pages, £20 (discount for bulk purchase!)
    • Buy from http://www.ipem.org.uk/publications/pubs-list2.htm#protection
    • View at http://www.ipem.org.uk/publications/ IRR99.html
    “ an essential reference book for all those working with ionising radiation in medical or dental practice, including medical and dental staff, radiographers, scientific and technical staff, and their employers .”
  • 82. Medical and Dental Guidance Notes
    • 1. General measures for radiation protection
    • 2. Radiation protection of persons undergoing medical exposures
    • 3 - 4. Diagnostic & interventional radiology
    • 5 - 6. Dental radiology
    • 7- 9. Radiotherapy
    • 10-18. Nuclear medicine and other uses of radioactive materials
    • (+ Appendices 1 - 21)
  • 83. Effective Dose (E)
    • Absorbed dose weighted for relative radio-sensitivity of different organs
    • Units are Sieverts (Sv)
    Tissue or organ w T Gonads 0.20 Red bone marrow 0.12 Colon 0.12 Lung 0.12 Stomach 0.12 Bladder 0.05 Breast 0.05 Liver 0.05 Oesphagus 0.05 Thyroid 0.05 Skin 0.01 Bone surfaces 0.01 Remainder 0.05 e.g. if gonads alone received 2 Gy to tissue, E = 0.20 x 2 = 0.4 Sv .
    • Risk of inducing cancer or hereditary disease is proportional to Effective Dose
    • 1 in 20,000 risk of fatal cancer from 1 mSv
      • (= risk of dying in a road accident in next year)