质子治疗笔形束扫描技术

ParticleTherapyBeamDeliveryGoals&ChallengesJayFlanzFeb.2017Asimplegoalisto“spread”abeamAcceleratorbeamisnarrow(longitudinallyandtransversely)(a“Pencilbeam”)Thedistributionofthatbeam~Braggian&GaussianThesedistributionsdoNOTmatchthetargetshape.ItisnecessarytospreadittoconformtothetargetProjectionis~GaussianDistribution•DeliverthePrescribedDose.(RightDose)•DeliverDosetotheTarget.(RightPlace)•DeliverthePrescribedDoseDistribution.•UsephysicalprinciplestocreateaPrescribedDistribution?Longitudinal–DepthDirectionBraggShapeTransverse–PerpendiculartotheDepthDirectionGaussianShapePositionAngleFlanz_Chiba20173CurrentParticleTherapy“Goals”ImageGuidedTherapy(IGRT)•Needformoreaccuratealignment•Possibilitytouseproton‘properties’forImagingMoreConformal(Techniques+Beamparameters)AchieveultimatePBSpossiblebeamparametersOrganMotionBeamtiming;BeamTracking;Flexible-PlansAdaptiveTherapyImage;Re-Plan(Deformableregistration);TreatNopatientspecificEquipmentCouldbealargescalecomputationalproblem?UsetheEndofRange;AccuracyCanoneuseDET?SimplerPlans;BUTRBEeffects(Radiobiology)Ions/LET/RBEDesignerDeliveryHypofractionation•NeedconformalityandfirsttimetargetingLowerCost(vs.Alltheabove)IncreasedThroughput•Lesspatienthardware(Fieldtofieldtime)•FasterInstrumentation(allowhigherdoserate)3?ClinicalRealityPhysicalPotentialSecoMGH3Flanz_Chiba2017BeamDelivery(ScatteringandScanning)ABCDEDosimetricRegionsofInterestDepthDirectionTransverseDirectionABCDEDosimetricRegionsofInterestDepthDirectionTransverseDirection(Scattering)EFlanz_Chiba2017ScanScanScatteringcoversentirevolume‘instantly’.Butparametersdegraderthroughinteractionwithmaterial.Scanningtakestime(asofnow)butsimpler(?)deliveryandmoreconformalityispossibleWHATISSCANNING?WhatisParticleBeamScanning(PBS)?TheideaistoSPREADthebeamwithadosedistributionthatconformstotheprescription.Beamscanningcanbedefinedastheactofmovingachargedparticlebeam(‘relativetothetarget’)ofparticularpropertiesandperhapschangingoneormoreofthepropertiesofthatbeamforthepurposeofspreadingthedosedepositedbyabeamthroughoutthetargetvolume.Position(x,y)Speed(vx,vy)Energy(E)Time(t)Intensity(I)Size()Dose(D)Flanz_Chiba2017Scanning:spreadoutthebeam(4d)Controlbeampositiontransverselyanddepth.Atpresent,theEnergy(Range)Changetimeislonger(e.g.5secto0.1sec(PSI))vs.millisecondstransversely.Scatteringtechniquescoverthe3Dvolumeeitherinstantly(Ridgefilter)oratmostoverabouta0.1secondtimeinterval.Normally,Scanningstartsatonepositionandirradiates‘sequentially’takingtimetoreachthelast3Dposition.(Allthingsbeingequal(intime)onecoulddoitdiff)5secx25Layers=125sec(2min)0.1secx25Layers=2.5secondsOrganmotion??TrajectoryOptimizationdependsonmanyfactors(e.g.direction/speed…).DepthBeamBeamTransverseTwoextremeexamples~RespirationCycleTransverseConformity,Width,TransverseFall-offLongitudinalConformity,WidthDistalFall-offFlanz_Chiba2017Scanning:Timing&TransverseDoseDistributionDoseDrivenScanning:Doseataspotdetermineswhattodonext(nottime).SpotScanning:Irradiateone“spot”atatime.Stopthebeamwhilemovingtothenextspot.Doseataspotdetermineswhentomove.(LCD/LEDTV)RasterScanning:Irradiateone“spot”atatime(mostly).Movethebeamtothenextspotwhilethebeamison.Flanz_Chiba2017SpotRasterManySpots=Anything?ContinuousTransverseConformityWidth,TransverseFall-offContinuous(TimeDriven):DosedistributionsensitivetoDoseRateDoseDriven“Spot”ScanningCurrentDosePositionIttakesTIMEtomeasureandstopthebeamifsomethingiswrong.DoseRateLIMITTimeTimeDoseRateDoseRateDetectedDosedistributionNOTsensitivetoDoseRateWhytheseoptions?Outofnecessity,notdesire?WhyDoseDrivenSpotScanning?Isthereanyadvantageoverothermethods?Ifonecannotcontrolthebeamcurrentaccuratelyenough.(Accelerator)Ifonecannotmeasurethebeamchargedeliveredfastenough,whileitismoving.(Instrumentation)Otherwise:Continuous?Whatisthebehavioroftheacceleratoranddesignthescanningsystemaroundthat.vs.Whatistheidealscanningmethodologyanddesigntheacceleratortoachievethat.Flanz_Chiba201700.20.40.60.811.200.511.522.533.544.5DeliveryTechnology–anExampleIonizationChamberFeedbackHallProbeFeedbackBeamCurrentFeedbackBeamCurrentCommandProtonbeam*IsocenterXandYSteeringCommandXandYfeedbackScanningcontroller,PTCProtonsource,IBAScanningmagnetpowersupply,IonizationChamberScanningmagnetsIonizationChambersElectrometers,PTCFlanz_Chiba2017NamesforScanning(Clinical/Delivery)SFUD:SingleFieldUniformDoseDeliveradosedistributionwithascanningbeam.Attheendofonefieldthedosetothetargetshouldbeuniform.(NotethatthissaysNOTHINGaboutthedistributionofanygivensubsetofthatdose.)SFUDREQUIRESDoseModulationDepthDoseDirectionTransverseDirectionFlanz_Chiba2017NamesforScanning(Clinical/Delivery)SFUD:SingleFieldUniformDoseMFO:IMPTMultiFieldOptimizedScannedbeamdeliveryDeliveradosedistributionwithascanningbeam.AttheendofonefieldthedosetothetargetmayNOTbeuniform.Multiplefieldswillcreateauniformorprescribeddistribution.Ithasa-priori,absolutelyNOTHINGtodowithIntensityModulationThesenameslabeltheTPmethod!NotethatthereisNOdifferencebetweenSFUDandIMPT/MFUDinth