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

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

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ALARA

 “

A

s

L

ow

A

s

R

easonably

A

chievable”  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

2

Primary Learning Objective

 Review pediatric fluoroscopic procedures   understand the source of radiation understand methods to reduce radiation  effect on image quality 3

Other Learning Objectives

 Fluoroscopy radiation units.

 Scope of pediatric fluoroscopic procedures  Methods available for dose reduction  clinical settings to apply dose reduction 4

Fluoroscopy Radiation Units

Basic Radiation Quantities :  Exposure & Exposure Rate  Air Kerma & Air Kerma Rate 5

Fluoroscopy Radiation Units

Radiation Measurement Quantities

:

 Incident Air Kerma & Rate  Entrance Surface Air Kerma & Rate 6

Fluoroscopy Radiation Units

Risk Related Quantities

:

 Absorbed dose  Equivalent Dose  Effective dose 7

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 (K a,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 (K a,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 K a,e = K a,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. 11

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 12

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 (w R ) – scaling factor used   , Xray w R = 1   (w R ) = 20  SI Unit is Sievert  1 Sievert (Sv) = 100 rem  1 rem = 10 mSv 13

Risk Related Quantities

 Effective dose – specific organs accounts for radio-sensitivity of   Includes  A tissue weighting factor (w T ) for each sensitive organ  Each tissue included in the clinical examination (H T ) Effective dose =  w T x H T , (  ) summed over all exposed organs.

 SI Unit is Sievert  1 Sievert (Sv) = 100 rem  1 rem = 10 mSv 14

Background Radiation Exposure

Non-Medical Radiation Source Radiation Dose Estimate Equivalent Amount Background Radiation

3mSv/year* Natural background radiation 3 mSv Airline passenger (cross country) 0.04 mSv 4 days * = estimate at sea level in US 15

Medical Radiation Exposures

Medical Radiation Source Radiation Dose Estimate

Chest x-ray 0.1 mSv Urinary tract fluoroscopy (VCUG) Continuous Mode* 0.45 – 0.59 mSv Optimized fluoroscope* 0.05 – 0.07 mSv

Equivalent Amount Background Radiation

10 days 2 months 1 week * Ward et al Radiology 2008;249:1002 16

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

Patient Dose Staff Dose

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Staff Protection

 Well fitted lead apron ( knees )  Leaded glasses ( with sides )  Thyroid shield  Lead gloves 20

Staff protection: Hands

 Keep hands out of the beam  Collimate 21

Staff protection: Shields

 Lead shield on tower  Do not turn your back to Xray beam if wearing front apron only 22

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

Patient Positioning

 Proper patient positioning  Make use of Inverse square law!

 Maximize distance between x-ray tube & patient  Minimize distance between patient & Image Intensifier 26

Control Fluoroscopic Exposures

 Choose pulsed fluoroscopy  Choose as short a pulse width as possible  Typically 5 – 10 msec pulse width 27

Control Fluoroscopic Exposures

   Continuous fluoroscopy 30 pulses per second 33 msec pulse width  Grid-controlled fluoroscopy   e.g. 15 pulses / sec 10 msec pulse width 28

Control Fluoroscopic Exposures

 Increase filtration to reduce patient radiation dose  Balanced by need for shorter pulse widths to freeze motion  Interposition of A luminum and variable thickness of C opper  Removes low energy radiation that does not reach the image intensifier    scattered within the patient adds radiation dose does not contribute to image 29

Control Fluoroscopic Exposures

 Remove anti-scatter grid whenever possible   Removes scattered radiation  Increased radiation dose Not necessary in small patients  Avoid unnecessary magnification 30

Control Fluoroscopic Exposures

 Collimate to area of interest  No need to radiate tissue that is not clinically pertinent 31

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 Fluoro-grab Exposure 32

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 33

Control Fluoroscopic Use

 Use fluoroscopic examination when there is a clear medical benefit.

 Use alternative imaging methods whenever possible  US  MRI 34

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 35

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 37

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 38

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 

A

ctivate dose saving features of equipment 

N

o image exposures unless necessary 

D

ownload image grab instead 

PULSE

at lowest possible rate 41

References

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Decreasing numbers of gastrointestinal studies: report of data from 69 radiologic practices.

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Early Hum Dev, 2000.

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-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.

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(12): p. 844-8.

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Radiation exposure reduction during voiding cystourethrography in a pediatric porcine model of vesicoureteral reflux.

Radiology, 2005.

235

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-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 42