image gently, pause and pulse: practice of alara in pediatric fluoroscopy sue c. kaste, do 1, 2...

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

1 St. Jude Children’s Research Hospital2 University of Tennessee Health Science Center

3 Monroe Carell Jr. Children’s Hospital at Vanderbilt4 The Children’s 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

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

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Fluoroscopy Radiation Units

Exposure & Exposure Rate

Air Kerma & Air Kerma Rate

Basic Radiation Quantities :

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Incident Air Kerma & Rate

Entrance Surface Air Kerma & Rate

Radiation Measurement Quantities:

6


Absorbed dose

Equivalent Dose

Effective dose

Risk Related 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.

8

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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Basic Radiation 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.

10

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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Measurement 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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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 BackgroundRadiation

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 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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Staff dose is due to scattered radiation

Scattered radiation is directly proportional to

Patient Dose

Reduce Radiation Dose: Staff

Patient Dose Staff 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

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

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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Radiation dose is optimized when we use

Least amount of radiationThat delivers clinically adequate image

quality

Patient Protection

Proper patient positioning

Make use of Inverse square law!

Maximize distance between x-ray tube & patient

Minimize distance between patient & Image

Intensifier

Patient Positioning

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Choose pulsed fluoroscopy

Choose as short a pulse width as possible

Typically 5 – 10 msec pulse width

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 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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Remove anti-scatter grid whenever possible

Removes scattered radiation Increased radiation dose

Not necessary in small patients

Avoid unnecessary magnification

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Collimate to area of interest

No need to radiate tissue that is not clinically pertinent


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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 Exposure32

Control Number of Images

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

Choose appropriate, patient-specific technique

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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-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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image gently, pause and pulse: practice of alara in pediatric fluoroscopy sue c. kaste, do 1, 2...

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