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Justin McWilliams, MD
Assistant Professor
Interventional Radiology
   You need a lateral view. Is it better to rotate the image intensifier
    toward you or away from you?
   Why is fluoro time a poor indicator of radiation exposure ?
   How many Grays of radiation puts the patient at risk for skin
    injury?
   A 5-second DSA run uses how much more radiation than 5
    seconds of fluoro?
   A typical embolization procedure exposes the patient to how
    many CXRs worth of radiation?
     What is the increased cancer risk of such a procedure?
     What is the cancer risk to the operator if he does 1 embo procedure
      per working day for 30 years?
   Radiation exposure

   Radiation effects

   Minimizing radiation to the patient

   Minimizing radiation to you
Radiation
   X-rays are produced by
    accelerating electrons
    through high voltage (50-
    150 kVp) applied to a
    tungsten target in an X-ray
    tube

   Amount of X-rays produced
    are determined by tube
    current (mA) and the tube
    voltage (kVp)
   Dose is not administered uniformly throughout the
    patient’s body
     Radiation field is moved, angled, collimated

   Both fluoro and DSA are used
   Four metrics are used to estimate patient radiation
    dose
       Fluoro time
       Peak skin dose (not yet measured by equipment)
       Reference dose (air kerma)
       Dose-area product (DAP)
   Also called “cumulative dose”
   The Air Kerma for the entire
    procedure, measured in Gy at a fixed
    reference point near the isocenter of the
    tube
   Does not account that the radiation field
    is moved to different areas of the patient
    during the procedure
   Conservative, generally overstates risk
   Measurement is likely accurate to within
    +/- 50%
   Measure of total X-ray
    energy absorbed by the
    patient

   Basically the air kerma
    (dose) multiplied by the
    area of body exposed
    (area)
   Fluoro time is only a very rough indicator of
    radiation dose, affected by:
       Patient size
       Beam location
       Beam angle
       Normal vs. high dose rate
       Distance of tube from the patient

   These can all add up to 10-fold difference in dose
    for the same fluoro time!
DOSE-AREA PRODUCT (DAP)                       CUMULATIVE AIR KERMA
   Product of the air kerma and the             Air kerma = Kinetic Energy
    exposed area (in cm2)                         Released per unit Mass of Air;
                                                  basically, how much radiation dose
   Good measure of stochastic risk               is being delivered at a specific
    (cancer risk) because it estimates            point (about where the patient’s
    total radiation energy delivered to           skin is)
    a patient
                                                 Also known as reference dose or
   Poor estimator of skin dose and               cumulative dose
    deterministic effects
       large dose over small area or small      Easy to measure, expressed in Gy
        dose over large area?
                                                 Absorbed dose in tissue will be
   Unit of measurement (Gy-cm2)                  about equal to the air kerma at
    does not translate into standard              that point
    units of dose (hard to use)
                                                 Notification threshold = 3 Gy
Radiation
   Patients and staff are exposed to radiation, but
    only a portion is absorbed into the body
   Absorbed dose is measured in Gray or rads
     1 Gray = 100 rads

   Approximate radiation doses:
       Fluoro = 2-10 rads/min
       CXR = 0.02 rads
       CT abdomen = about 2-10 rads
       Natural background radiation = 0.3 rads/year
   Different forms of radiation (X-rays, alpha
    particles, etc) produce different biologic
    effects for same absorbed dose

   Dose equivalent (rem or Sievert) is used to
    measure biologic “harmfulness” of a radiation
    dose

   For diagnostic X-rays, 1 rem = 1 rad and 1 Gy =
    1 Sv
   Effective dose is the dose equivalent to the
    whole body caused by irradiating just a
    localized area
     This is calculated by multiplying the dose to each
        irradiated organ by a weighting factor based on
        the radiosensitivity of that organ

   Example effective doses:
       CXR = ~0.1 mSv
       PTA = 10-20 msV
       Biliary drainage = 40 mSv
       Transcatheter embolization or TIPS = 50-100 mSv

   Additional cancer risk = ~5%/Sv
   So, a long embolization procedure in a 30 year
    old increases risk of developing a fatal cancer
    by about 0.5%
   Fluoro machines operate in automatic
    brightness control

   When brightness of picture is inadequate, the
    ABC automatically increases mA or kVp (or both)
    to increase X-ray penetration
     Large patients = more dose than small patients (up to
      4-10x higher!)
     Abdominal fluoro = more dose than chest fluoro
     Oblique fluoro = more dose than AP fluoro
   Direct exposure rate refers to entrance skin
    exposure where the X-ray beam enters the
    patient
     2-10 rads/min for fluoro
     ~50 rads/min for DSA
     30 mins of fluoro = 60-300 rads = 0.6-3 Gy
   Indirect exposure rate refers to exposure to the
    staff from scattered radiation from the patient

   ~1/1000 of the skin entrance exposure rate at a
    distance of 1 meter
     Large patients increase scatter radiation
     Larger field (not collimated) increases scatter
     Scatter much higher on the X-ray tube side of the
      patient
      ▪ For lateral view, stand next to II, not next to tube!
Radiation
   Radiation effects with a threshold dose;
    effect is not observed unless threshold is
    exceeded
Radiation
Radiation
   Early erythema – 3 Gy – 1-2 days –
    sunburn
   Epilation – 3-7 Gy – 3 weeks – hair loss
   Main erythema – 10 Gy - onset 1-4
    weeks – burning, itching
     If >14 Gy, progresses to dry
      desquamation 1 week later
     If >18 Gy, progresses to moist
      desquamation (blistering, sloughing) 1
      week later

   Ulceration – 24 Gy – 2-12 months
   No threshold

   Any dose increases the chance of the
    effect, with higher doses increasing the
    chances

   Radiation-induced cancer
   Approximate additional risk of fatal cancer
    for an adult for an examination:
       Extremity X-ray: <1/1,000,000
       CXR: 1/100,000 to 1/1,000,000
       Chest CT: 1/10,000 to 1/1,000
       Multiphase abdominal CT: 1/1,000 to 1/500

   These risks are additive to the ~25%
    background risk of dying of cancer
Radiation
   Very small (<10 kg) or very large
    (>135 kg) patients
   Age (3x risk for newborns, 1x risk at
    age 25, 0.2x risk for patients in 60s)
   Pregnant patients
   Prior radiation exposure within last
    2 months
   Diabetes, autoimmune
    diseases, connective tissue
    diseases increase risk of skin
    effects
   Ultrasound instead of fluoro when possible (biliary, arterial
    access)
   Patient should be as far from tube, and as close to II, as
    possible (good to be tall!)
   Don’t step on the pedal
   Pulse fluoro mode (7.5 or 15 frames/sec instead of 30/sec)
   View and save images with “last image hold”
   Exclude bone from the image
   Collimate to smallest field of view possible
     Avoid exposure to eyes, thyroid and gonads

   Position and collimate without fluoro
     5-8% of radiation exposure is delivered during preparation for
      imaging, positioning the table and adjusting collimators

   Avoid magnification
     ABC uses more radiation to brighten and sharpen the image in mag
      view

   Avoid high-dose or detail modes
   Use higher kVp (but can reduce contrast)
   Minimize overlap of fields and repeated acquisitions
Radiation
Radiation
Radiation
   Less time on the pedal

   Use last image hold

   Pulsed fluoro

   Low dose fluoro
   Inverse square law
     Double distance from patient = ¼ the radiation
      dose from scatter radiation
     Nonessential personnel should be outside a 6-foot
      radius from the X-ray source
     Step out of room for DSA runs
   Lead apron (0.5 mm Pb equivalent) blocks
    about 95% of scatter radiation

   Thyroid shield, leaded glasses are essential
     Most radiosensitive organs


   Lead drapes and clear leaded glass barriers
Radiation
   Record dose in the medical record

   If dose exceeded deterministic thresholds
     Discuss possible effects and management with
      patient
     Have patient or family member notify IR if
      deterministic effects occur
     Institute a clinical follow-up plan for the patient
   Necessary when large radiation dose was
    used

   Telephone call at 2 weeks or so
     Redness? Blistering? Hair loss?
     Location of radiation field


   May need follow up for >1 year
Radiation
   You need a lateral view. Is it better to rotate
    the image intensifier toward you or away
    from you?
   You need a lateral view. Is it better to rotate
    the image intensifier toward you or away
    from you?

   Toward you! Keep the beam away from
    you, because most of the scatter occurs at
    the point the beam enters the patient
   Why is fluoro time a poor indicator of
    radiation exposure ?
   Why is fluoro time a poor indicator of radiation
    exposure?

 Does not include DSA runs
 Dose varies greatly for the same fluoro time
     Thin or obese patient
     AP or oblique views
     Magnification
     Distance from X-ray source
   How many Grays of radiation puts the patient
    at risk for skin injury?
   How many Grays of radiation puts the patient
    at risk for skin injury?

   3 Grays!
   A 5-second DSA run uses how much more
    radiation than 5 seconds of fluoro?
   A 5-second DSA run uses how much more
    radiation than 5 seconds of fluoro?

   About 10x more radiation for DSA!
   A typical embolization procedure exposes the
    patient to how many CXRs worth of
    radiation?
     What is the increased cancer risk of such a
      procedure?
     What is the cancer risk to the operator if he does 1
      embo procedure per working day for 30 years?
   A typical embolization procedure exposes the
    patient to how many CXRs worth of radiation?
    About 1000!
     What is the increased cancer risk of such a procedure?
      About 0.5% for a 30 year old!
     What is the cancer risk to the operator if he does 1
      embo procedure per working day for 25 years?
        100 mSv (patient equivalent dose) x 1/250 (scatter fraction at 18 inches) x 1/20 (fraction of radiation that
                          gets through the lead) x 5000 (# of procedures) = 100 mSv


       A career in IR is probably equivalent to having an embolization
       procedure done on yourself (0.5% additional cancer risk)
   Mitchell E and Furey P. Prevention of radiation injury from
    medical imaging. J Vasc Surg 2011; 53:22S-27S.
   Miller D, et al. Clinical radiation management for
    fluoroscopically guided interventional procedures.
    Radiology 2010;257:321-332.
   Cousins C and Sharp C. Medical interventional procedures
    – reducing the radiation risks. Clin Radiol 2004;59:468-473.
   Wagner L. Angiography radiation dose – limiting dose to
    the patient while maintaining effective image quality.
    http://www.uth.tmc.edu/radiology/RSNA/2008/RSNA_wa
    gner_2008.pdf

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Radiation

  • 1. Justin McWilliams, MD Assistant Professor Interventional Radiology
  • 2. You need a lateral view. Is it better to rotate the image intensifier toward you or away from you?  Why is fluoro time a poor indicator of radiation exposure ?  How many Grays of radiation puts the patient at risk for skin injury?  A 5-second DSA run uses how much more radiation than 5 seconds of fluoro?  A typical embolization procedure exposes the patient to how many CXRs worth of radiation?  What is the increased cancer risk of such a procedure?  What is the cancer risk to the operator if he does 1 embo procedure per working day for 30 years?
  • 3. Radiation exposure  Radiation effects  Minimizing radiation to the patient  Minimizing radiation to you
  • 5. X-rays are produced by accelerating electrons through high voltage (50- 150 kVp) applied to a tungsten target in an X-ray tube  Amount of X-rays produced are determined by tube current (mA) and the tube voltage (kVp)
  • 6. Dose is not administered uniformly throughout the patient’s body  Radiation field is moved, angled, collimated  Both fluoro and DSA are used  Four metrics are used to estimate patient radiation dose  Fluoro time  Peak skin dose (not yet measured by equipment)  Reference dose (air kerma)  Dose-area product (DAP)
  • 7. Also called “cumulative dose”  The Air Kerma for the entire procedure, measured in Gy at a fixed reference point near the isocenter of the tube  Does not account that the radiation field is moved to different areas of the patient during the procedure  Conservative, generally overstates risk  Measurement is likely accurate to within +/- 50%
  • 8. Measure of total X-ray energy absorbed by the patient  Basically the air kerma (dose) multiplied by the area of body exposed (area)
  • 9. Fluoro time is only a very rough indicator of radiation dose, affected by:  Patient size  Beam location  Beam angle  Normal vs. high dose rate  Distance of tube from the patient  These can all add up to 10-fold difference in dose for the same fluoro time!
  • 10. DOSE-AREA PRODUCT (DAP) CUMULATIVE AIR KERMA  Product of the air kerma and the  Air kerma = Kinetic Energy exposed area (in cm2) Released per unit Mass of Air; basically, how much radiation dose  Good measure of stochastic risk is being delivered at a specific (cancer risk) because it estimates point (about where the patient’s total radiation energy delivered to skin is) a patient  Also known as reference dose or  Poor estimator of skin dose and cumulative dose deterministic effects  large dose over small area or small  Easy to measure, expressed in Gy dose over large area?  Absorbed dose in tissue will be  Unit of measurement (Gy-cm2) about equal to the air kerma at does not translate into standard that point units of dose (hard to use)  Notification threshold = 3 Gy
  • 12. Patients and staff are exposed to radiation, but only a portion is absorbed into the body  Absorbed dose is measured in Gray or rads  1 Gray = 100 rads  Approximate radiation doses:  Fluoro = 2-10 rads/min  CXR = 0.02 rads  CT abdomen = about 2-10 rads  Natural background radiation = 0.3 rads/year
  • 13. Different forms of radiation (X-rays, alpha particles, etc) produce different biologic effects for same absorbed dose  Dose equivalent (rem or Sievert) is used to measure biologic “harmfulness” of a radiation dose  For diagnostic X-rays, 1 rem = 1 rad and 1 Gy = 1 Sv
  • 14. Effective dose is the dose equivalent to the whole body caused by irradiating just a localized area  This is calculated by multiplying the dose to each irradiated organ by a weighting factor based on the radiosensitivity of that organ  Example effective doses:  CXR = ~0.1 mSv  PTA = 10-20 msV  Biliary drainage = 40 mSv  Transcatheter embolization or TIPS = 50-100 mSv  Additional cancer risk = ~5%/Sv  So, a long embolization procedure in a 30 year old increases risk of developing a fatal cancer by about 0.5%
  • 15. Fluoro machines operate in automatic brightness control  When brightness of picture is inadequate, the ABC automatically increases mA or kVp (or both) to increase X-ray penetration  Large patients = more dose than small patients (up to 4-10x higher!)  Abdominal fluoro = more dose than chest fluoro  Oblique fluoro = more dose than AP fluoro
  • 16. Direct exposure rate refers to entrance skin exposure where the X-ray beam enters the patient  2-10 rads/min for fluoro  ~50 rads/min for DSA  30 mins of fluoro = 60-300 rads = 0.6-3 Gy
  • 17. Indirect exposure rate refers to exposure to the staff from scattered radiation from the patient  ~1/1000 of the skin entrance exposure rate at a distance of 1 meter  Large patients increase scatter radiation  Larger field (not collimated) increases scatter  Scatter much higher on the X-ray tube side of the patient ▪ For lateral view, stand next to II, not next to tube!
  • 19. Radiation effects with a threshold dose; effect is not observed unless threshold is exceeded
  • 22. Early erythema – 3 Gy – 1-2 days – sunburn  Epilation – 3-7 Gy – 3 weeks – hair loss  Main erythema – 10 Gy - onset 1-4 weeks – burning, itching  If >14 Gy, progresses to dry desquamation 1 week later  If >18 Gy, progresses to moist desquamation (blistering, sloughing) 1 week later  Ulceration – 24 Gy – 2-12 months
  • 23. No threshold  Any dose increases the chance of the effect, with higher doses increasing the chances  Radiation-induced cancer
  • 24. Approximate additional risk of fatal cancer for an adult for an examination:  Extremity X-ray: <1/1,000,000  CXR: 1/100,000 to 1/1,000,000  Chest CT: 1/10,000 to 1/1,000  Multiphase abdominal CT: 1/1,000 to 1/500  These risks are additive to the ~25% background risk of dying of cancer
  • 26. Very small (<10 kg) or very large (>135 kg) patients  Age (3x risk for newborns, 1x risk at age 25, 0.2x risk for patients in 60s)  Pregnant patients  Prior radiation exposure within last 2 months  Diabetes, autoimmune diseases, connective tissue diseases increase risk of skin effects
  • 27. Ultrasound instead of fluoro when possible (biliary, arterial access)  Patient should be as far from tube, and as close to II, as possible (good to be tall!)  Don’t step on the pedal  Pulse fluoro mode (7.5 or 15 frames/sec instead of 30/sec)  View and save images with “last image hold”  Exclude bone from the image
  • 28. Collimate to smallest field of view possible  Avoid exposure to eyes, thyroid and gonads  Position and collimate without fluoro  5-8% of radiation exposure is delivered during preparation for imaging, positioning the table and adjusting collimators  Avoid magnification  ABC uses more radiation to brighten and sharpen the image in mag view  Avoid high-dose or detail modes  Use higher kVp (but can reduce contrast)  Minimize overlap of fields and repeated acquisitions
  • 32. Less time on the pedal  Use last image hold  Pulsed fluoro  Low dose fluoro
  • 33. Inverse square law  Double distance from patient = ¼ the radiation dose from scatter radiation  Nonessential personnel should be outside a 6-foot radius from the X-ray source  Step out of room for DSA runs
  • 34. Lead apron (0.5 mm Pb equivalent) blocks about 95% of scatter radiation  Thyroid shield, leaded glasses are essential  Most radiosensitive organs  Lead drapes and clear leaded glass barriers
  • 36. Record dose in the medical record  If dose exceeded deterministic thresholds  Discuss possible effects and management with patient  Have patient or family member notify IR if deterministic effects occur  Institute a clinical follow-up plan for the patient
  • 37. Necessary when large radiation dose was used  Telephone call at 2 weeks or so  Redness? Blistering? Hair loss?  Location of radiation field  May need follow up for >1 year
  • 39. You need a lateral view. Is it better to rotate the image intensifier toward you or away from you?
  • 40. You need a lateral view. Is it better to rotate the image intensifier toward you or away from you?  Toward you! Keep the beam away from you, because most of the scatter occurs at the point the beam enters the patient
  • 41. Why is fluoro time a poor indicator of radiation exposure ?
  • 42. Why is fluoro time a poor indicator of radiation exposure?  Does not include DSA runs  Dose varies greatly for the same fluoro time  Thin or obese patient  AP or oblique views  Magnification  Distance from X-ray source
  • 43. How many Grays of radiation puts the patient at risk for skin injury?
  • 44. How many Grays of radiation puts the patient at risk for skin injury?  3 Grays!
  • 45. A 5-second DSA run uses how much more radiation than 5 seconds of fluoro?
  • 46. A 5-second DSA run uses how much more radiation than 5 seconds of fluoro?  About 10x more radiation for DSA!
  • 47. A typical embolization procedure exposes the patient to how many CXRs worth of radiation?  What is the increased cancer risk of such a procedure?  What is the cancer risk to the operator if he does 1 embo procedure per working day for 30 years?
  • 48. A typical embolization procedure exposes the patient to how many CXRs worth of radiation? About 1000!  What is the increased cancer risk of such a procedure? About 0.5% for a 30 year old!  What is the cancer risk to the operator if he does 1 embo procedure per working day for 25 years? 100 mSv (patient equivalent dose) x 1/250 (scatter fraction at 18 inches) x 1/20 (fraction of radiation that gets through the lead) x 5000 (# of procedures) = 100 mSv A career in IR is probably equivalent to having an embolization procedure done on yourself (0.5% additional cancer risk)
  • 49. Mitchell E and Furey P. Prevention of radiation injury from medical imaging. J Vasc Surg 2011; 53:22S-27S.  Miller D, et al. Clinical radiation management for fluoroscopically guided interventional procedures. Radiology 2010;257:321-332.  Cousins C and Sharp C. Medical interventional procedures – reducing the radiation risks. Clin Radiol 2004;59:468-473.  Wagner L. Angiography radiation dose – limiting dose to the patient while maintaining effective image quality. http://www.uth.tmc.edu/radiology/RSNA/2008/RSNA_wa gner_2008.pdf