Image Gently, CT Imaging and Radiation Protection of Pediatric Patients Kalpana Kanal, Ph.D., DABR Associate Professor, Diagnostic Physics Director, Diagnostic

Image Gently, CT Imaging and Radiation Image Gently, CT Imaging and Radiation Protection of Pediatric PatientsProtection of Pediatric Patients

Kalpana Kanal, Ph.D., DABRKalpana Kanal, Ph.D., DABR

Associate Professor, Diagnostic PhysicsAssociate Professor, Diagnostic Physics

Director, Diagnostic Physics SectionDirector, Diagnostic Physics Section

Director, Resident Physics EducationDirector, Resident Physics Education

Dept. of RadiologyDept. of Radiology

UW MedicineUW Medicine

a copy of this lecture may be found at:a copy of this lecture may be found at:

http://courses.washington.edu/radxphys/r3.htmlhttp://courses.washington.edu/radxphys/r3.html

Challenges of Pediatric ImagingChallenges of Pediatric Imaging

Little body fat compared to adults Little body fat compared to adults Variations in normal growth and development Variations in normal growth and development Small physical size present challengesSmall physical size present challenges Lack of ability to breath hold, and potential need for sedation or Lack of ability to breath hold, and potential need for sedation or

other immobilization must be consideredother immobilization must be considered Radiation doses - important due to the increased vulnerability Radiation doses - important due to the increased vulnerability

(sensitivity) of tissues(sensitivity) of tissues Children have a longer lifetime in which to manifest stochastic Children have a longer lifetime in which to manifest stochastic

(i.e. cancer) risks(i.e. cancer) risks Children incur a higher dose when identical CT settings are usedChildren incur a higher dose when identical CT settings are used

© UW and Kalpana M. Kanal, PhD, DABR© UW and Kalpana M. Kanal, PhD, DABR 22

Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of Pediatric Patients

Alliance for Radiation SafetyAlliance for Radiation SafetyImage GentlyImage Gently

The Alliance for Radiation Safety in Pediatric Imaging, the The Alliance for Radiation Safety in Pediatric Imaging, the sponsors of the “Image Gently” campaign was formed in 2007 sponsors of the “Image Gently” campaign was formed in 2007

Fundamental principles of rad protection during ped imaging: Fundamental principles of rad protection during ped imaging: justification, utilization and optimizationjustification, utilization and optimization

www.imagegently.org


http://www.imagegently.org/

5. Image Gently Website5. Image Gently Websitewww.imagegently.org


http://www.imagegently.org/

5. CT Procedure Checklist5. CT Procedure Checklist

Are additional modifications to the protocol warranted, i.e. follow-Are additional modifications to the protocol warranted, i.e. follow-up examinations?up examinations?

If multiphase scanning is indicated, the highest exposure should be If multiphase scanning is indicated, the highest exposure should be for the phase that provides the most critical information. Consider for the phase that provides the most critical information. Consider lower doses for phases such as pre-contrast scanning if necessary lower doses for phases such as pre-contrast scanning if necessary or delayed images, such as with CT urographyor delayed images, such as with CT urography

Has appropriate use of sedation, and immobilization been Has appropriate use of sedation, and immobilization been implemented?implemented?


5. Image Gently Website5. Image Gently WebsiteCT Procedure ChecklistCT Procedure Checklist

Is CT the right test in this clinical situation? Is ultrasound or Is CT the right test in this clinical situation? Is ultrasound or MR imaging more appropriate?MR imaging more appropriate?

If CT is indicated, have appropriate adjustments based on If CT is indicated, have appropriate adjustments based on size, scan indication, and region scanned been made?size, scan indication, and region scanned been made?

Have general pediatric specific protocols been developed and Have general pediatric specific protocols been developed and uploaded to the scanner for common examinations?uploaded to the scanner for common examinations?



Has the environment been made as child friendly as possible?Has the environment been made as child friendly as possible?

Is shielding being used when appropriate? Is shielding being used when appropriate?

Have equipment and protocols been developed and reviewed Have equipment and protocols been developed and reviewed periodically with qualified medical imaging physicists?periodically with qualified medical imaging physicists?

Has the pitch (in helical scanning) been adjusted to lower Has the pitch (in helical scanning) been adjusted to lower dose? (Between 1 and 1.5)dose? (Between 1 and 1.5)



Has the appropriate scan field of view (bow tie filter) been Has the appropriate scan field of view (bow tie filter) been selected?selected?

Has patient positioning been optimized so that the patient is in Has patient positioning been optimized so that the patient is in the center of the gantry, the scan technique and length of the the center of the gantry, the scan technique and length of the projection scout views have been minimized and only those projection scout views have been minimized and only those phases necessary are being performed?phases necessary are being performed?

Have appropriate dose reduction technology such as tube Have appropriate dose reduction technology such as tube current modulation been activated? Understand these current modulation been activated? Understand these technologiestechnologies


2. Interventional Fluoroscopy: Step Lightly2. Interventional Fluoroscopy: Step Lightly

Treat kids with care: step lightly on the fluoroscopy pedal. Treat kids with care: step lightly on the fluoroscopy pedal. Stop and child size the technique. Consider ultrasound or Stop and child size the technique. Consider ultrasound or when applicable, MR guidance.” when applicable, MR guidance.”


3. General Fluoroscopy: Pause and Pulse3. General Fluoroscopy: Pause and Pulse

Stop and child-size the technique. Use lowest pulse rate Stop and child-size the technique. Use lowest pulse rate possible. Consider ultrasound or MRI when applicable.possible. Consider ultrasound or MRI when applicable.


4. Nuclear Medicine4. Nuclear Medicine

The pediatric nuclear medicine community has developed the The pediatric nuclear medicine community has developed the Pediatric Radiopharmaceutical Administered Doses: 2010 Pediatric Radiopharmaceutical Administered Doses: 2010 North American Consensus Guidelines to directly address the North American Consensus Guidelines to directly address the need to lower radiation dose and standardize the need to lower radiation dose and standardize the radiopharmaceutical dose for children throughout the United radiopharmaceutical dose for children throughout the United StatesStates


5. CR/DR Radiography5. CR/DR Radiography

This group has sponsored a vendor summit to promote This group has sponsored a vendor summit to promote standardization of exposure index and to promote awareness standardization of exposure index and to promote awareness of the need to optimize radiation exposure in routine of the need to optimize radiation exposure in routine radiographs in childrenradiographs in children

The group is working with digital radiography manufacturers The group is working with digital radiography manufacturers to develop educational materials to promote appropriate use to develop educational materials to promote appropriate use of their equipment in childrenof their equipment in children

Recently, a digital radiography safety checklist was created Recently, a digital radiography safety checklist was created for technologists to remind them of the critical steps needed for technologists to remind them of the critical steps needed when performing computed radiography or direct when performing computed radiography or direct radiography in childrenradiography in children


Image WiselyImage Wisely

The Image Wisely Campaign, the adult counterpart to the The Image Wisely Campaign, the adult counterpart to the Image Gently Campaign, is based on the success of the Image Gently Campaign, is based on the success of the Alliance for Radiation Safety in Pediatric Imaging. Alliance for Radiation Safety in Pediatric Imaging.

The constituent founding organizations are AAPM, ACR, ASRT, The constituent founding organizations are AAPM, ACR, ASRT, and the Radiological Society of North America (RSNA), with and the Radiological Society of North America (RSNA), with individuals from the Alliance providing consultation. individuals from the Alliance providing consultation.


CT Dose IndicesCT Dose IndicesCTDIvol and DLPCTDIvol and DLP



CT Dose IndicesCT Dose IndicesCTDIvolCTDIvol


CTDIvol = [2/3 * surface dose + 1/3 * central dose] / Pitch

The original application of CTDIvol was to provide a standardized method to estimate and compare the radiation output of different CT scanners.

CTDIvol was defined to be a dose index of CT scanners, not a patient dose index. Ref: RSNA/AAPM module: Imaging Gently: CT Imaging and Radiation Protection of

Pediatric Patients

DLPDLP


DLP does not represent a patient dose index, but rather the energy deposited in a standard phantom

The risk to the patient from ionizing radiation associated with a CT examination is affected by the amount of radiation energy deposited in the tissue and the volume of the patient’s irradiated tissues

Therefore, the longer the length of patient that is scanned (along the z axis), all other factors remaining equal, the higher the radiation risk to the patient

DLP = CTDIvol * Scan Length

DLPDLP



Patient Size ConsiderationsPatient Size ConsiderationsAffect on Attenuation of Patient SizeAffect on Attenuation of Patient Size


Mass (kg) PA (cm) # HVL LAT (cm) # HVLPreterm 2 6 1.5 6 1.5Newborn 3 9 2.2 10 2.51 yr 10 12 3 14 3.55 yr 19 16 4 22 5.512 yr 31 18 4.5 27 6.8Adult 68 22 5.5 33 8.3Adult 100+ 35 8.8 48 12


Patient Size ConsiderationsPatient Size Considerations



Why does patient dose decrease with Why does patient dose decrease with increasing patient size?increasing patient size?


Radiation output of the scanner in all three cases is identical

The entrance radiation dose to 32 cm phantom is 65% greater than the 10 cm phantom – closer to tube The exit dose of the beam after traveling through 32 cm of plastic is far less than the exit dose after traveling through only 10 cm of plastic

The superficial layers of tissue of the patient’s body shield and reduce the patient’s core tissue dose.


Affect of Patient Size on CTDIvol and DLPAffect of Patient Size on CTDIvol and DLP


The under or over estimate of the patient dose by the displayed CTDIvol as a function of patient size depending on if the 16 or 32 cm CTDI phantom is used

The displayed CTDIvol underestimates the patient dose and misleads the radiologic technologist or radiologist if they assume CTDIvol represents the patient dose.


Management of Image Quality and Radiation Dose for Management of Image Quality and Radiation Dose for Pediatric PatientsPediatric Patients

Consultation between qualified medical physicist, radiologist Consultation between qualified medical physicist, radiologist and technologist is essential in IQ and dose managementand technologist is essential in IQ and dose management



Recommended Adjustment of Tube Current FactorsRecommended Adjustment of Tube Current Factors


A method to establish reduced mAs scan protocols for children that is independent of the manufacturer, model, and age of the CT scanner may be found at www.imagegently.org.


Recommended Adjustment of Tube Current FactorsRecommended Adjustment of Tube Current Factors


When you fill in the baseline values, the table automatically calculates the mAs for the different ages.


Recommended Adjustment of Kilovoltage (kV)Recommended Adjustment of Kilovoltage (kV)


A lower kVp decreases patient dose and increases quantum mottle in the image while an increase in the kVp has the opposite effect, if mAs is unchanged.

The degree of change in radiation dose and quantum mottle caused by changes in high voltage is often reduced by changing the mAs in the opposite direction of the change in high voltage




To improve contrast or to perform CT angiography, 100 kVp is reasonable for medium sized pediatric patients.

Neonates to small pediatric patients may be imaged as low as 80 kVp

80 kVp images at the maximum tube current of the CT scanner will not produce an adequate number of x-rays to avoid artifacts and maintain reasonable quantum mottle in the image for larger pediatric patients




How does one practically adjust kVp for pediatric patients?

Lower kVp to improve contrast and adjust mAs to maintain radiation dose at original level

or reduce the radiation dose to maintain the contrast to noise ratio (CNR) in the original image. For example, 120 vs 80 kV

So now one can reduce mAs and patient dose until noise in the image increases up to 70% with no reduction in CNR compared to original image since the contrast in the image increased 70%


Size Specific Dose (SSDE) for Pediatric PatientsSize Specific Dose (SSDE) for Pediatric Patients

CTDIvol displayed on console of CT CTDIvol displayed on console of CT scanner underestimates dose to scanner underestimates dose to pediatric patientspediatric patients

Task Group 204 of AAPM prepared a Task Group 204 of AAPM prepared a report that provides scaling factors as a report that provides scaling factors as a function of patient size or age that can function of patient size or age that can be used to estimate the dose to patientbe used to estimate the dose to patient

CTDIvol displayed = 5.5, 32 cm phantom CTDIvol displayed = 5.5, 32 cm phantom used. Lateral Diam = 15 cmused. Lateral Diam = 15 cm

SSDE = CTDIvol * Correction FactorSSDE = CTDIvol * Correction Factor SSDE = 5.5 * 2.29 mGySSDE = 5.5 * 2.29 mGy SSDE = 13 mGySSDE = 13 mGy



Recommendations for Clinical ProtocolsRecommendations for Clinical Protocols


Use alternate modalities such as US and MRI if possible

If possible, eliminate multiphase scans

Adjust CT scan parameters for individual patient indications – only cover area of interest and adjust techniques according to patient size

Shielding? – controversialWe use shielding for our patients at both UWMC and HMC

Review QuestionReview Question

Challenges presented during pediatric CT imaging include all except which one of the following?

A.Children are more apt to move during the scan

B.Children often require lower doses than the smallest radiation levels that can be set on state-of-the-art CT scanners

C.Children are more sensitive to radiation than adults

D.Children present different disorders than adults



Which statement below is correct concerning CTDIvol, with all other parameters constant?

A.CTDIvol increases with a decrease in the tube current.

B.CTDIvol is unaffected by the composition and thickness of the bow-tie filter of the scanner.C.CTDIvol increases as the pitch of the CT scanner increases.

D.CTDIvol typically does not represent the absorbed radiation dose to the pediatric patient.



Which statement below is true concerning DLP?

A.DLP cannot be used to estimate changes to patient dose from changes to CT scan parameters. B.DLP decreases if CTDIvol during the examination increases.C.DLP represents the energy deposited in the patient during the CT scan acquisition. D.DLP is a less accurate estimation of patient dose than CTDIvol.



Which one of the following statements is true concerning radiation dose to pediatric patients during CT scanning?

A.Dose reduction protocols for pediatric patients should be developed and implemented by a team consisting of a radiologist and technologist. B.The dose reduction protocol on the Image Gently website can be used on multi detector or single detector CT scanners.C.The dose reduction protocol on the Image Gently website reduces absorbed pediatric radiation dose estimates to values less than those the facility would use on its adult patients.D.Pediatric dose reduction should be limited to adjustment of tube current (mA).



With respect to the kVp in CT protocols for scanning children

A.The primary reason relatively high kVp is reduced is the reduction of patient dose. B.If the kVp is reduced from 120 to 80 (66%), the mAs should be increased by 66%.C.If the mAs is increased correctly with reduction in kVp, the CNR can be held constant in the image.D.Pediatric CT protocols for infants and preschoolers are optimum if 120 kVp is typically used.



THANK YOU FOR YOUR ATTENTIONTHANK YOU FOR YOUR ATTENTION

Cruise Ship docked in Skagway, Alaska - Image provided by KanalCruise Ship docked in Skagway, Alaska - Image provided by Kanal

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Image Gently, CT Imaging and Radiation Protection of Pediatric Patients Kalpana Kanal, Ph.D., DABR Associate Professor, Diagnostic Physics Director, Diagnostic