Download Radiation Dose Reduction in Pediatric CT

RadiationDoseReductionin
PediatricCT
ArastooVossough,MD,PhD
AssociateProfessorofRadiology
Disclosures:
No relevant conflicts of Interest
Objectives
• To be aware of advances in CT applications and dose
reduction in pediatrics.
• To become familiar with resources available to help
implementing radiation dose reduction.
• To become familiar with the various modifications that can
be done to reduce neuroradiological CT examination
radiation doses in pediatrics (on both older and newer
generation scanners).
Source: WHO
ThresholdvsnoThreshold
CTDose:
CTDIvol xZ-axislength=DLP(doselengthproduct)
ReducingCTRadiationExposure
• Don’tscanifunnecessary
• TraumaHeadCTrules,panscan,ICUpatients,multiperfusion
• Scanonlyspecificareasneeded
(e.g.,entirevspartofspine,face,neck)
(DLP=CTDIxlengthofscan)
• Don’tdomultiphasestudiesifunnecessary
• Considerothermodalities
• Paradigmshift:fromhighestimagequalityto
what’sgoodenoughfortheclinicalquestion
ALARAPrinciple
(i.e.,GoodEnough)
“Considerationforradiationprotection
shouldincludethefactthatimaging
professionalsmustthinkaboutacceptable
imagequalityasopposedtooptimal
quality.”
Frush,D.,Radiationsafety,PediatricRadiology(2009)39(Suppl 3):S385-S390
ReducingCTDose
NeuroCTScenarios
•
•
•
•
CT,s/ptrauma
CT,checkventriclesize
CT,r/ostroke
CT,craniofacialdeformities
Do they all need
the same dose ?
• HeadCTA,afterclippedaneurysm
• HeadCTA,r/ostroke
• NeckCTA,pencilinjurytoposteriorthroat
What’sDifferentinPediatrics
• Scanneroutputvs.patientdose
– ConversionfactorfrommGy tomSv isdifferentinPeds
• PitfallsofvolumeCTDIandDLP
– CTDIisreferencedtophantom(32cm
vs16cm)
– Canunderestimatedosetoverysmall
patients
– Differentmanufacturers’ordifferent
protocols’modellingmayvary
– Size-specificdoseestimates(SSDE)vs
CTDI(Siebert,JAetal,JACR2014)
Turner et al, RSNA 2009
ACRAccreditationforCT
CTDIvol:VolumetricCTDoseIndex
• ADULT:
– CTDIvol :80mGy
• CHILDREN:
– Diagnosticreferencelevel:CTDIvol :35mGy (1yo)
– Pass/faillimit:CTDIvol :40mGy
• (foraroutine1-year-oldheadexam- maybedifferent
(higherorlower)foranindividualpatientwithunique
indications).
imagegently.org
TechnicalfactorsinReducingCT
RadiationDose
• Tailordosetopatientsize
– Age/sizebasedcategories,automatedtubecurrentmodulation,
automatedtubevoltagemodulation
• Useofradiationshields
• UseoflowerkVp of80or100or120ifpossible
• MinimizingZaxisscanlength
• Optimizepitchperclinicalindication
• Optimizecollimationperclinicalindication
• Accuratepatientcenteringinthegantry
• Iterativereconstructiontechniquesinsteadof
backprojection ifavailable
• Optimizethedoseperformanceofdetector,collimator,
andbeam-shapingfilter
ReducingCTRadiationDose
1. Tailortechnicalfactorstoindicationand
patient– evenonoldscanners
1. Automaticexposurecontrol
1. Iterativereconstruction
GantryTilt
OptimizemAs
• Tubecurrent(mA) =rateofx-rayproduction
• Decreaseoftubecurrentandexposuretime(mAs)
decreasesdosebutincreasesnoise/quantum
mottle
• Canbequitelowforairwayorlungparenchyma
• Canbelowerforchildren
OptimizemAs
CTDIvol =5.3
Imagegently.org
Optimizepitch
• Pitch=distanceCTtableadvancesin1
rotation/widthofx-rayfanbeaminz
direction– definitioninhighMDCT
• Increasedpitchdecreasesdose&likelihood
ofmotionartifactbutincreasesquantum
mottle
• Variablebasedonclinicalindication
• NeedstobelowfortemporalboneCT
studies
X-raybeamonlessthanafull
rotation
AutomaticTubeCurrentControl
• Tubecurrentchangesduringcourseofscan
baseonpresets
– Setupperlimit
• Differentmanufacturers:
– Translationofsamedoselevelsisnoteasy
– Samedoselevelsmaynotproduceidentical
imagequality
AutomaticTubeCurrentControl
3 y/o
15 y/o
CTScouts(Scanograms)
• Centerthepatientinthegantry
– Helpstheautomateddoesreductionmeasures
workmoreaccurately
– Reducesdose
• APvs.APandlateral
• Doseofscout
IterativeReconstruction
• Useaniterativereconstructioninsteadof
filteredbackprojection
• ASIR,SAFIRE,iDose4,AIDR
• Newergeneration(modelbased):ADMIRE,
Veo,IMR
• Allowsacceptablequalityscansatmuch
lowerdoses
IterativeReconstruction
None
Mild
CTDIvol =7
Strong
ReducingCTADose
K-edge of iodine
Can go lower on kVp
CTDIvol = 5
DualEnergyCTA
80kVp
140kVp
DualEnergyCTA
• Doseneutral?
•
DIR
of the American College of Radiology
Report > 100 pages
ReducingCTRadiationDoseinPediatrics
• ALARA– goodenoughscans
• Technicalmodificationsregardlessof
generationofscanner
• Needssomedegreeofpersonalizationper
eachindicationand/orpatient
• Needsradiologisttimeinprotocolling