Image Gently, Pause and Pulse: Practice of ALARA in Pediatric Fluoroscopy

1
Image Gently, Pause and Pulse Practice of ALARA
inPediatric Fluoroscopy

• Sue C. Kaste, DO1, 2
• Marta Hernanz-Schulman, MD3
• Ishtiaq H. Bercha, M.Sc. 4
• 1 St. Jude Childrens Research Hospital
• 2 University of Tennessee Health Science Center
• 3 Monroe Carell Jr. Childrens Hospital at
  Vanderbilt
• 4 The Childrens Hospital, Aurora, Colorado.

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ALARA

• As Low As Reasonably Achievable
• General principle guiding radiation exposure
• Keep exposure to radiation dose as low as is
  possible for each procedure, while obtaining
  needed clinical information
• Image Optimization

3
Primary Learning Objective

• Review pediatric fluoroscopic procedures
• understand the source of radiation
• understand methods to reduce radiation
• effect on image quality

4
Other Learning Objectives

• Fluoroscopy radiation units.
• Scope of pediatric fluoroscopic procedures
• Methods available for dose reduction
• clinical settings to apply dose reduction

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Fluoroscopy Radiation Units
Basic Radiation Quantities

• Exposure Exposure Rate
• Air Kerma Air Kerma Rate

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Fluoroscopy Radiation Units
Radiation Measurement Quantities

• Incident Air Kerma Rate
• Entrance Surface Air Kerma Rate

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Fluoroscopy Radiation Units
Risk Related Quantities

• Absorbed dose
• Equivalent Dose
• Effective dose

8
Basic Radiation Quantities

• Exposure expresses intensity of x-ray energy
  per unit mass of air.
• Units Coulomb per kilogram (C/kg).
• Commonly used units are Roentgen or milli
  Roentgen, expressed as R or mR, respectively.
• 1 R 2.58 x 10-4 C/kg
• Exposure rate identifies x-ray intensity per unit
  time. Commonly used units are R/min or mR/min.

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Basic Radiation Quantities

• Air Kerma (K) sum of initial kinetic energies
  of all charged particles generated by uncharged
  particles such as x-ray photons released per unit
  mass of air.
• Unit Joule per kilogram, Commonly referred to
  as Gray/milli Gray (Gy or mGy).
• 1 Roentgen of exposure ? 8.7 mGy air kerma
• Air Kerma Rate quantifies air kerma per unit time
  and is written as, dK/dt, that is, incremental
  kerma per unit increment of time.

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Measurement Quantities

• Incident Air Kerma (Ka,i) is the air kerma from
  the incident beam along the central x-ray beam
  axis at the skin entrance plane.
• Only the primary beam is considered and the
  effect of back scattered radiation is excluded.
• Unit Joule per kilogram, Commonly referred to
  as Gray/milli Gray (Gy or mGy).
• Incident Air Kerma Rate quantifies air kerma per
  unit time. It is usually measured as mGy/min.

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Measurement Quantities

• Entrance Surface Air Kerma (Ka,e)
• It is the air kerma from the incident beam along
  the central x-ray beam axis at the point where
  radiation enters the patient and the effect of
  back scattered radiation is included.
• Given as Ka,e Ka,i x B
• B Back Scatter Factor.
• Unit Joule per kilogram, Commonly referred to
  as Gray milli Gray (Gy or mGy).
• Incident Air Kerma Rate quantifies air kerma per
  unit time.

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Risk Related Quantities

• Absorbed dose energy deposited per unit mass of
  a material, in our case, within tissue.
• Initially measured as rads
• Current unit based on Systeme Internationale (SI
  unit)
• SI Unit of Absorbed Dose Gray
• 1Gray (Gy) 100 rad
• 1rad 10 mGy

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Risk Related Quantities

• Dose Equivalent accounts for biological effect
  of type of radiation
• For example, difference in biological effect
  between
• ?, ? and ? radiation
• Radiation Weighting factor (wR) scaling factor
  used
• ?, Xray wR 1
• ? (wR) 20

• SI Unit is Sievert
• 1 Sievert (Sv) 100 rem
• 1 rem 10 mSv

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Risk Related Quantities

• Effective dose accounts for radio-sensitivity
  of specific organs
• Includes
• A tissue weighting factor (wT) for each sensitive
  organ
• Each tissue included in the clinical examination
  (HT)
• Effective dose ?wT x HT, (?) summed over all
  exposed organs.

• SI Unit is Sievert
• 1 Sievert (Sv) 100 rem
• 1 rem 10 mSv

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Background Radiation Exposure
Non-Medical Radiation Source Radiation Dose Estimate Equivalent Amount Background Radiation
Natural background radiation 3 mSv 3mSv/year
Airline passenger (cross-country) 0.04 mSv 4 days
estimate at sea level in US
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Medical Radiation Exposures
Medical Radiation Source Radiation Dose Estimate Equivalent Amount Background Radiation
Chest x-ray 0.1 mSv 10 days
Urinary tract fluoroscopy (VCUG)
Continuous Mode 0.45 0.59 mSv 2 months
Optimized fluoroscope 0.05 0.07 mSv 1 week
Ward et al Radiology 20082491002
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Practical Methods to Reduce Radiation Dose to
Fluoroscopy Staff Patients
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Staff Protection
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Reduce Radiation Dose Staff

• Staff dose is due to scattered radiation
• Scattered radiation is directly proportional to
• Patient Dose

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Staff Protection

• Well fitted lead apron (knees)
• Leaded glasses (with sides)
• Thyroid shield
• Lead gloves

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Staff protection Hands

• Keep hands out of the beam
• Collimate

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Staff protection Shields

• Lead shield on tower

• Do not turn your back to Xray beam if wearing
  front apron only

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In summary Have we.

• left our hands in the beam?
• sacrificed personal safety for expediency?
• turned our unshielded backs to the X-ray
  source?
• unnecessarily prolonged exposure?
• pushed away a protective barrier?

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Patient Protection
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Patient Protection

• Radiation dose is optimized when we use
• Least amount of radiation
• That delivers clinically adequate image quality

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Patient Positioning

• Proper patient positioning
• Make use of Inverse square law!
• Maximize distance between x-ray tube patient
• Minimize distance between patient Image
  Intensifier

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Control Fluoroscopic Exposures

• Choose pulsed fluoroscopy
• Choose as short a pulse width as possible
• Typically 5 10 msec pulse width

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Control Fluoroscopic Exposures

• Continuous fluoroscopy
• 30 pulses per second
• 33 msec pulse width

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Control Fluoroscopic Exposures

• Increase filtration to reduce patient radiation
  dose
• Balanced by need for shorter pulse widths to
  freeze motion

• Interposition of Aluminum and variable thickness
  of Copper
• Removes low energy radiation that does not reach
  the image intensifier
• scattered within the patient
• adds radiation dose
• does not contribute to image

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Control Fluoroscopic Exposures

• Remove anti-scatter grid whenever possible
• Removes scattered radiation
• Increased radiation dose
• Not necessary in small patients
• Avoid unnecessary magnification

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Control Fluoroscopic Exposures

• Collimate to area of interest
• No need to radiate tissue that is not clinically
  pertinent

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Control Fluoroscopic Exposures

• Use last image hold
• Whenever you need to inspect the anatomy, and do
  not need to observe motion or changes with time
• Use Fluoroscopy Store (FS)
• this method is ideal to convey and record
  motion, such as peristalsis, or show viscus
  distensibility, as in esophagram
• when you need information without excessive
  detail

Exposure
Fluoro-grab
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Control Number of Images

• Choose appropriate, patient-specific technique

• Limit acquisition to what is essential for
  diagnosis and documentation
• PAUSE Plan study ahead
• PAUSE- think frames / second
• PAUSE think magnification
• PAUSE think Last Image Hold
• PAUSE think Image Grab

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Control Fluoroscopic Use

• Use fluoroscopic examination when there is a
  clear medical benefit.
• Use alternative imaging methods whenever possible
• US
• MRI

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Special Pediatric Considerations

• Pediatric patient management more critical
• Increased radio-sensitivity, small size,
  longevity.
• Pediatric size
• Smaller patient leads to less scattered radiation
• There is an increased need for magnification

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Institutional Strategies to Optimize Radiation
Exposure Fluoroscopy
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To Start

• An in-house diagnostic medical physicist in
  pediatric hospitals is optimal.
• The physicist must have proper training and
  background in Medical Physics, such as CAMPEP
  accredited graduate and residency programs.
• Proper training is key

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To Start

• An Image Management committee, comprised of
  radiologists, technologists, administrators and
  medical physicists, under the direction of the
  department Chair, can be very helpful.
• Responsible for optimizing radiation procedures.
• Oversee the departmental QA/QC program.
• Meet criteria for accreditation, e.g. ACR

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To Start

• Oversee purchase of capital equipment and
  periodic hardware and software upgrades.
• Staff training on state of the art technologies.
• Technologists, radiologists
• Equipment, safety, physics, radiation biology
• Compliance with applicable state and federal
  regulations.

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Dosimetry Records

• Manage fluoroscopy parameters
• e.g., pulsed fluoroscopy, pulse rate, removable
  grid
• Record information related to patient radiation
  dose as displayed by the equipment
• Cumulative Dose Area Product.
• Cumulative Air kerma/Skin Dose.

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Summary

• PAUSE to properly plan and prepare for study
• Activate dose saving features of equipment
• No image exposures unless necessary
• Download image grab instead
• PULSE at lowest possible rate

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References

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