SRS Uncertainty: Linacand CyberKni ?· SRS Uncertainty: Linacand CyberKnifeUncertainties ... Depuydt,…

Download SRS Uncertainty: Linacand CyberKni ?· SRS Uncertainty: Linacand CyberKnifeUncertainties ... Depuydt,…

Post on 11-Jun-2018

212 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • 6/19/2014

    1

    SRSUncertainty:Linac andCyberKnife Uncertainties

    SonjaDieterich,PhD

    Linac/CyberKnifeTechnologicalUncertainties

  • 6/19/2014

    2

    LinacMechanical/RadiationIsocenters

    Depuydt,Tom,etal."Computeraidedanalysisofstarshotfilmsforhighaccuracyradiationtherapytreatmentunits."Physicsinmedicineandbiology 57.10(2012):2997.

    TG142MechanicalToleranceLimitsforSRS/SBRT

    Procedure SRS/SBRTTolerance

    Radiation/Mechanical Isocenter 1mmfrombaseline

    CollimatorRotationIsocenter 1mmfrombaseline

    Gantry RotationIsocenter 1mmfrombaseline

    CouchRotationIsocenter 1mmfrombaseline

    LaserLocalization 1mm

    CollimatorSizeIndicator 1mm

    CouchPosition 1mm/0.5

    TableTopSag 1mm

    Independenterrorsareaddedinquadrature:2mm!

  • 6/19/2014

    3

    CKMechanicalIsocenter

    CKMechanicalIsocenter:RobotPointing

    LinacCAXlaserlightintensityonisocrystal

    Robotrunsautomatedgridpatternforhighestlightintensityoncrystal

    Calibrationfollowedbyverification

    Acceptance

  • 6/19/2014

    4

    Linac/ImagingIsocenterMatch

    Sharpe,MichaelB.,etal."ThestabilityofmechanicalcalibrationforakVconebeamcomputedtomographysystemintegratedwithlinearaccelerator)."Medicalphysics 33.1(2005):136144.

    CKImaging/RobotIsocenterMatch

    Isocrystal definesspatialoriginofroomcoordinatesystem

    Imageofisocrystal onimagercentertolerance

  • 6/19/2014

    5

    LinacMechanical/Radiation:WinstonLutz

    Lutz,Wendell,KenR.Winston,andNasserMaleki."Asystemforstereotacticradiosurgerywithalinearaccelerator."InternationalJournalofRadiationOncology*Biology*Physics 14.2(1988):373381.

    FramelessSRS:TheE2E(modifiedWinstonLutz)

  • 6/19/2014

    6

    DetailsofE2Etest Isocentricplan

    HomogeneousPhantom

    Measureshiftofdelivered70%isodoselinevs.plan

    Tolerance

  • 6/19/2014

    7

    CKE2E:ThemanParameter E2Eforallrobotpathsforeach

    trackingalgorithm(cranial,spine,) DeterminesystematicshiftofE2E Resultisappliedasglobal correction Repeatuntil(nominally)

  • 6/19/2014

    8

    WhatisthetoleranceoftheCyberKnifeIsocrystal toImagerCenter?

    Feedback:Theimageoftheisocrystal shouldbewithin1mmoftheisocenter.

    SlideLocation:Mechanical:Imaging/RobotIsocenterMatch(#11)

    Reference:1)AAPMTG1352)CKPhysicsUserGuide

    UncertaintiesCommontoAllSRSDeliverySystems

  • 6/19/2014

    9

    ImagingAlgorithmUncertainty

    1. TargetLocalizationError:errorextractingtargetposition

    2. Targetregistrationerror:meandistancebetweenimagedataandrealpatientafterregistration

    3. TargetPositioningerror:Mismatchbetweenintendedpositionandactualposition

    MethodologyofMeasuringisthesameforallalgorithms

    TargetLocalizationError

  • 6/19/2014

    10

    TargetRegistrationError Testingagainstagoldstandard

    E.g.trackwithfiducials,theneditthemoutandtrackonskeletalfeatures

    Fu,D.,etal."3Dtargetlocalizationusing2DlocaldisplacementsofskeletalstructuresinorthogonalXrayimagesforimageguidedspinalradiosurgery."Int JCARS 1.Suppl1(2006):198200.

    TargetPositioningError

    Dependsonhowyouadjustforpatientposition

    Withcouch: couchmotionaccuracy Measureusingrealisticpatientweight!

    Withdeliverysystem(CK,VERO,Linac): Robotpointingaccuracy Gimbalrotationaccuracy MLCshiftaccuracy

  • 6/19/2014

    11

    WhatistheTargetRegistrationError?

    20%

    20%

    20%

    20%

    20% 1. Errorextractingtargetposition2. Meandistancebetweenimagedataandre

    patientafterregistration3. Mismatchbetweenintendedandactual

    position4. Errorcausedbychoosingincorrectfusion

    algorithm5. Uncertaintyincouchmovement

    10

    WhatistheTargetRegistrationError?

    Feedback:Meandistancebetweenimagedataandrealpatientafterregistration

    SlideLocation:ImagingAlgorithmUncertainty

    Reference:UncertaintiesinExternalBeamRadiotherapy,Chapter14ImageGuidancetoReduceSetuperror

  • 6/19/2014

    12

    Dosimetry:DoseCalculationAlgorithm

    CommonMCuncertaintysetting:2%atmaximumdose

    WhyIncludeDoseCalculation?

    Dosecalculationuncertainty=spatiallyshiftingisodoselines!

  • 6/19/2014

    13

    Dosimetry:CommissioningBeamData

    Allmeasureddatacomeswitherrorbars

    TG106statesinteruserandequipmentrepeatabilityshouldbe

  • 6/19/2014

    14

    QualitativeAccuracyComparisonofSRS/SBRT

    Linac GK CK

    Mechanical Simplerthanlinac Similartolinac

    CommissioningData Simplerthanlinac Similartolinac

    PatientPositioning Similar: frame Similar: IGRT

    Targetlocalization Similar: frame Similar: IGRT

    Dosecalculation Similar similar

    Biologicalmodel Same

    TargetDefinition Same

    3Dimaging(inbeamimaging)

    TBD (CBCT?) Depends on2D3D imagingfrequency

    MajorContributorstoUncertaintyType Uncertainty Linac CK Type

    Mechanical MechanicalIsocenter Starshots Robotpointing B

    Collimator MLC starshot,picketfence,etc

    Film/Largechamber A/B

    ImagingIsocenter Phantom Isocrystal onimager B

    Imaging algorithm ? Anthropomorphicphantom

    B?

    Dosimetry Beamdata Watertanksetup,kQ, detector/beamnoise,dataprocessing,detetcor correctionfactors

    A

    Dosecalculationalgorithm

    Algorithmuncertainty MCuncertainty A

    Planning(Geneserlecture)

    Contouring Similarforbothmachines B

    Treatment Residualpatientmotion

    Similarforbothmachines A/B

  • 6/19/2014

    15

    QuantitativeAccuracyComparison:ItsComplicated

    WhileLinacSRSaccuracycontributingfactorsaregenerallysimilartoCK

    theycombinedifferently. Why?

    DeltamanconceptonCKtodetermine&adjustsystematicmechanical/imagingerrors

    WinstonLutzvs.E2Econcept Intrafractionimaging&positioncorrection:

    clinicalonCK, underdevelopmentonlinac

    MyDream:measureuncertaintywithsametestprocedureonallthreeSRS/SBRTmodalities

    HigherAccuracyMeansLessRoomforUncertainty

    a) Isocentric,1coneb) Isocentric,1cone

    coverage96.8%4%

    c) DynamicConf.Arcd) DynamicConf.Arc

    coverage78%4.4%

  • 6/19/2014

    16

    Whatimpacthashighertechnicaltargetingaccuracyontherequiredtargetcontouringaccuracy?

    20%

    20%

    20%

    20%

    20% 1. Thetwoarenotrelated2. TheCTVmargincanbereduced3. Afusedimagesetshouldbeused4. Acontouringatlasmustbeused5. Itleaveslessroomforcontouring

    uncertainty

    10

    Whatimpacthashighertechnicaltargetingaccuracyontherequiredtargetcontouringaccuracy?

    Feedback:TheCTVmargindependsontheextentofthemicroscopicdisease.Ahighertechnicalaccuracymeansthereismoreconformalitytothetumorcontour.Therefore,thetightcoverageleaveslessroomforcontouringuncertainties.Usingacontouringatlasmayhelpinaccuratelycontouringorgansatrisk.

    SlideLocation:HigherAccuracymeanslessroomforuncertainty(#41)

    Reference:Buis,DennisR.,etal."StereotacticradiosurgeryforbrainAVMs:roleofinterobserver variationintargetdefinitionondigitalsubtractionangiography."InternationalJournalofRadiationOncology*Biology*Physics62.1(2005):246252.

  • 6/19/2014

    17

    Conclusion1. DedicatedRadiosurgerymachinescandeliverydose

    veryaccuratelytohomogeneousphantoms

    2. TreatmentPlanningsystemsaregettingmuchmoreaccurate InvivostudiesofdosecalculationaccuracyoranthropomorphicphantomDQAsparseinSRS/SBRT

    DQAmethodshavetechnicallimitsmeasuringtoaccuracybetterthan3%/1mm

    3. UncertaintiesinRadiationBiology,imagingdisease,imageregistration&contouringarenowlargecomparedtomechanical&dosimetryuncertainty

Recommended

View more >