Transcript Learning objectives

Image Gently, Pause and Pulse:
Practice of ALARA in
Pediatric Fluoroscopy
Sue C. Kaste, DO1, 2
Marta Hernanz-Schulman, MD3
Ishtiaq H. Bercha, M.Sc. 4
St. Jude Children’s Research Hospital
2 University of Tennessee Health Science Center
3 Monroe Carell Jr. Children’s Hospital at Vanderbilt
4 The Children’s Hospital, Aurora, Colorado.
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ALARA
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“As Low As Reasonably Achievable”
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General principle guiding radiation exposure
Keep exposure to radiation dose as low as is
possible for each procedure, while obtaining needed
clinical information
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= Image Optimization
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Primary Learning Objective
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Review pediatric fluoroscopic procedures
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understand the source of radiation
understand methods to reduce radiation
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effect on image quality
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Other Learning Objectives
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Fluoroscopy radiation units.
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Scope of pediatric fluoroscopic procedures
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Methods available for dose reduction
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clinical settings to apply dose reduction
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Fluoroscopy Radiation Units
Basic Radiation Quantities :
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Exposure & Exposure Rate
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Air Kerma & Air Kerma Rate
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Fluoroscopy Radiation Units
Radiation Measurement Quantities:
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Incident Air Kerma & Rate
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Entrance Surface Air Kerma & Rate
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Fluoroscopy Radiation Units
Risk Related Quantities:
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Absorbed dose
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Equivalent Dose
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Effective dose
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Basic Radiation Quantities
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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
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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
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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.
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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
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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
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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)
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SI Unit of Absorbed Dose = Gray
1Gray (Gy) = 100 rad
1rad = 10 mGy
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Risk Related Quantities
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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
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SI Unit is Sievert
 1 Sievert (Sv) = 100 rem
 1 rem = 10 mSv
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Risk Related Quantities
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Effective dose – accounts for radio-sensitivity of
specific organs
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Includes
 A tissue weighting factor (wT) for each sensitive organ
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Each tissue included in the clinical examination (HT)
Effective dose = wT x HT, () summed over all
exposed organs.
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SI Unit is Sievert
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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
Airline passenger (cross- 0.04 mSv
country)
3mSv/year*
4 days
* = estimate at sea level in US
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Medical Radiation Exposures
Medical Radiation Source
Radiation Dose
Estimate
Chest x-ray
0.1 mSv
Equivalent Amount
Background
Radiation
10 days
Urinary tract fluoroscopy
(VCUG)
Continuous Mode*
0.45 – 0.59 mSv
2 months
0.05 – 0.07 mSv
1 week
Optimized fluoroscope*
* Ward et al Radiology 2008;249:1002
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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
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Staff dose is due to scattered radiation
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Scattered radiation is directly proportional to
Patient Dose
Patient Dose
Staff Dose
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Staff Protection
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Well fitted lead apron (knees)
Leaded glasses (with sides)
Thyroid shield
Lead gloves
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Staff protection: Hands
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Keep hands out of the beam
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Collimate
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Staff protection: Shields
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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….
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… 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
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Radiation dose is optimized when we use
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Least amount of radiation
 That delivers clinically adequate image
quality
Patient Positioning
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Proper patient positioning
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Make use of Inverse square law!
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Maximize distance between x-ray tube & patient
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Minimize distance between patient & Image
Intensifier
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Control Fluoroscopic Exposures
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Choose pulsed fluoroscopy
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Choose as short a pulse width as possible
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Typically 5 – 10 msec pulse width
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Control Fluoroscopic Exposures
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Continuous fluoroscopy
30 pulses per second
33 msec pulse width
Grid-controlled fluoroscopy
 e.g. 15 pulses / sec
 10 msec pulse width
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Control Fluoroscopic Exposures
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Increase filtration to reduce patient radiation dose
 Balanced by need for shorter pulse widths to
freeze motion
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Interposition of Aluminum and variable
thickness of Copper
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Removes low energy radiation that does not
reach the image intensifier
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scattered within the patient
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adds radiation dose
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does not contribute to image
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Control Fluoroscopic Exposures
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Remove anti-scatter grid whenever possible
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Removes scattered radiation
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Increased radiation dose
Not necessary in small patients
Avoid unnecessary magnification
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Control Fluoroscopic Exposures
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Collimate to area of interest
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No need to radiate tissue that
is not clinically pertinent
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Control Fluoroscopic Exposures
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Use “last image hold”
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Whenever you need to inspect the anatomy, and do not need to
observe motion or changes with time
Use Fluoroscopy Store (FS)
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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
Fluoro-grab
Exposure
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Control Number of Images
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Choose appropriate, patient-specific technique
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Limit acquisition to what is essential
for diagnosis and documentation
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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
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Use fluoroscopic examination when there
is a clear medical benefit.
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Use alternative imaging methods whenever
possible
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US
MRI
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Special Pediatric Considerations
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Pediatric patient management more critical
 Increased radio-sensitivity, small size, longevity.
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Pediatric size
 Smaller patient leads to less scattered radiation
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There is an increased need for magnification
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Institutional Strategies to
Optimize Radiation
Exposure Fluoroscopy
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To Start:
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An in-house diagnostic medical physicist in
pediatric hospitals is optimal.
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The physicist must have proper training and
background in Medical Physics, such as CAMPEP
accredited graduate and residency programs.
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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.
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Responsible for optimizing radiation procedures.
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Oversee the departmental QA/QC program.
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Meet criteria for accreditation, e.g. ACR
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To Start:
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Oversee purchase of capital equipment and periodic
hardware and software upgrades.
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Staff training on state of the art technologies.
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Technologists, radiologists
Equipment, safety, physics, radiation biology
Compliance with applicable state and federal
regulations.
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Dosimetry Records
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Manage fluoroscopy parameters
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e.g., pulsed fluoroscopy, pulse rate, removable
grid
Record information related to patient
radiation dose as displayed by the
equipment:
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Cumulative Dose Area Product.
Cumulative Air kerma/Skin Dose.
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Summary
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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
-Gelfand, D.W., D.J. Ott, and Y.M. Chen, Decreasing numbers of gastrointestinal studies: report of data from 69 radiologic practices.
AJR Am J Roentgenol, 1987. 148(6): p. 1133-6.
-Margulis, A.R., The present status and the future of gastrointestinal radiology. Abdom Imaging, 1994. 19(4): p. 291-2.
-Page, M. and H. Jeffery, The role of gastro-oesophageal reflux in the aetiology of SIDS. Early Hum Dev, 2000. 59(2): p. 127-49.
-Strauss KJ, Kaste SC. The ALARA (as low as reasonably achievable) concept in pediatric interventional and fluoroscopic imaging:
striving to keep radiation doses as low as possible during fluoroscopy of pediatric patients—a white paper executive summary.
Radiology 2006 240(3):621-622.
-Ward VL, Strauss KJ, Barnewolt CE, Zurakowski D, Venkatakrishnan V, Fahey FH, Lebowitz RL, Taylor GA. Pediatric radiation
exposure reduction and effective dose reduction during voiding cystourethrography. Radiology 2008 249:1002-1009.
-Hall, E. and J. Amato, Radiobiology for the Radiologist. 2005: Williams & Wilkins.
-Lederman, H.M., et al., Dose reduction fluoroscopy in pediatrics. Pediatr Radiol, 2002. 32(12): p. 844-8.
-Ward, V., et al., Radiation exposure reduction during voiding cystourethrography in a pediatric porcine model of vesicoureteral reflux.
Radiology, 2005. 235.
-Boland, G.W.L., et al., Dose Reduction in Gastrointestinal and Genitourinary Fluoroscopy: Use of Grid-Controlled Pulsed Fluoroscopy.
Am. J. Roentgenol., 2000. 175(5): p. 1453-1457.
-Brown, P.H., et al., A multihospital survey of radiation exposure and image quality in pediatric fluoroscopy. Pediatr Radiol, 2000. 30(4):
p. 236-42.
-Strauss KJ. Pediatric interventional radiography equipment: safety considerations. Pediatr Radiol (2006) 36 (Suppl 2):126-135.
-Hernanz-Schulman M, Emmons M, Price R. Radiation dose reduction and image quality considerations in pediatric patients.
Radiology RSNA syllabus, November, 2006
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