ClincalUseof4DCT Low

8/4/2019 ClincalUseof4DCT Low

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Clinical Use of 4DCTClinical Use of 4DCT

Daniel Low, Ph.D.Daniel Low, Ph.D.

Director, Division of Medical PhysicsDirector, Division of Medical Physics

Radiation OncologyRadiation OncologyWashington UniversityWashington University


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ColleaguesColleagues Wei LuWei Lu

Parag ParikhParag Parikh James HubenschmidtJames Hubenschmidt

Jeffrey BradleyJeffrey Bradley

Sasa MuticSasa Mutic Joe ReppJoe Repp

Sasa WahabSasa Wahab

Issam El NaqaIssam El Naqa

Gary ChristensenGary Christensen


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Washington University School of MedicineDepartment of Radiation Oncology


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OutlineOutline

Why is 4D CT necessary?Why is 4D CT necessary?

What is 4D CT?What is 4D CT?

How do we characterize breathing?How do we characterize breathing?

What do we do with 4D CT information?What do we do with 4D CT information?


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OutlineOutline






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Why is 4D CT Necessary?Why is 4D CT Necessary?

BreathingBreathing QuasiQuasi--voluntary functionvoluntary function

Breath hold possibleBreath hold possible

Modification of breathing pattern possibleModification of breathing pattern possible MotionMotion

Image artifactsImage artifacts

DoseDose--delivery artifactsdelivery artifacts Increases irradiated volume/treatmentIncreases irradiated volume/treatment

complexitycomplexity


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Image Artifact ReductionImage Artifact Reduction

Rietzel med phys 32 874


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Treatment EffectsTreatment Effects

Breathing motion increases the apparentBreathing motion increases the apparent

size of the tumorsize of the tumor Increases portal sizesIncreases portal sizes

Increases normal organ irradiationIncreases normal organ irradiation


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Motion BlurringMotion Blurring

McCarter and Beckham, PMB 2001 = 10 mm

Required Margin


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Effects of Motion on IMRTEffects of Motion on IMRT

Blurring of IMRT dose distributionsBlurring of IMRT dose distributions

Interplay effectsInterplay effects

Dose deformation (interface effects)Dose deformation (interface effects)

How big are these effects?How big are these effects?


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Interplay EffectsInterplay Effects

Simulate dynamic IMRT field and moving tumor

Yu et al, PMB 1998


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Examples of Dose ErrorExamples of Dose Error

1 cm wide slit beam, 3 cm amplitude, 4 s breathing period


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Interplay: FractionatedInterplay: Fractionated

Fractionated therapy tends to blur doseFractionated therapy tends to blur dose

errorserrors

Beam motion tends to be orthogonal toBeam motion tends to be orthogonal to

patient motionpatient motion


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Bortfeld et al, PMB 2002

Multiple simulations with

realistic IMRT dose distributions

Analyzed multiple points todetermine dose error due tomotion

Results: Dose error depended

on whether point was in/nearsteep dose gradient region, butdose was local average


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OutlineOutline



How do we characterize breathingHow do we characterize breathing



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What is 4D CT?What is 4D CT? Process for obtaining image datasetsProcess for obtaining image datasets

Images used to determine tumor/normalImages used to determine tumor/normalorgan motionorgan motion

Motion information used as inputs forMotion information used as inputs for

treatment planning, delivery, verificationtreatment planning, delivery, verification Ultimate goal is NOT 4D CT image datasetUltimate goal is NOT 4D CT image dataset

It is a model for breathing motion that can beIt is a model for breathing motion that can be

used for planning, delivery, verificationused for planning, delivery, verification However, we are not there yetHowever, we are not there yet


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Some Issues to AddressSome Issues to Address

Breathing is not perfectly periodicBreathing is not perfectly periodic

No electronicNo electronic monitorablemonitorable surrogatesurrogate

(metric) such as with cardiac gating(metric) such as with cardiac gating

CT images are acquired throughoutCT images are acquired throughoutbreathing cyclebreathing cycle

Not in the same physical locationNot in the same physical location

How do we register imagesHow do we register imagesacquired at different times?acquired at different times?


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MetricMetric Chest HeightChest Height Chest Height (Varian RPM)Chest Height (Varian RPM)

Infrared reflective marker placed onInfrared reflective marker placed on

abdomenabdomen

Vedam et al Med Phys 30, 505 (2003)


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MetricMetric -- SpirometrySpirometry TurbineTurbine--shaped fan encased in tubeshaped fan encased in tube

Rotation rate determines flow rateRotation rate determines flow rate

Software removes nonlinearitiesSoftware removes nonlinearitiesand integrates flowand integrates flow


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4D CT Process4D CT Process Image acquisitionImage acquisition

CinCin or helical modesor helical modes Simultaneous monitoring of patient breathingSimultaneous monitoring of patient breathing

CinCin acquires CT images without moving theacquires CT images without moving the

couchcouch Images are typically selected from a sequence ofImages are typically selected from a sequence of

acquired images according to breathing phaseacquired images according to breathing phase

Helical modeHelical mode Easiest for commercial applications: uses cardiacEasiest for commercial applications: uses cardiac

gating softwaregating software


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Acquisition Process

SpirometryTidal VolumeAcquisition

Spirometer

BronchialBranch

12-Slice mode

PhilipsBrilliance16-slice

CT Scanner

Motion ModelParameter

Determination

Volume-GatedImages

SynchronizationSignal

CT Data

Philips Bellows

Spirometry Drift Correction

DICOMTransfer


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timevolume

98 ml90 ml

94 ml

3D CT

At 100 ml


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GatingGating Have process thatHave process that

Acquires CT imagesAcquires CT images Sorts CT images using metric dataSorts CT images using metric data

HoweverHowever

What criteria are used to determine theWhat criteria are used to determine thepatients breathing phase associated withpatients breathing phase associated with

each image?each image?

Inhalation

Exhalation


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Breathing Cycle DefinitionBreathing Cycle Definition AmplitudeAmplitude

Breathing phase defined by depth ofBreathing phase defined by depth ofbreathingbreathing

Phase AnglePhase Angle

Breathing cycle described as purely periodicBreathing cycle described as purely periodic

processprocess

InhalationInhalationexhalationexhalationdefined by angles fromdefined by angles from

00--360 degrees360 degrees

Vedam et al, PMB 2003


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Phase vs. AmplitudePhase vs. AmplitudeAmplitude

Phase

Time (s)

TidalVolu

me(ml)

TidalVolume

(ml) Select mid-inspiration

Mid-inspiration definedby percentile tidalvolumes

Mid-inspiration defined

by time betweenexhalation and inhalationpeaks


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Amplitude sortingAmplitude sorting Phase sortingPhase sorting


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AmplitudeAmplitude vsvs PhasePhase

A

P


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What 4D CT Can DoWhat 4D CT Can Do


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Clinical ImagesClinical Images Difficulties with amplitudeDifficulties with amplitude--basedbased

retrospective gating is that images are notretrospective gating is that images are notnecessarily acquired at the samenecessarily acquired at the same

breathing phase for each couch positionbreathing phase for each couch position

Interpolation may be a method forInterpolation may be a method for

interpolating to a common breathing phaseinterpolating to a common breathing phase

Requires a deformable map of motionRequires a deformable map of motion


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InterpolationInterpolation

using optical flow deformation:using optical flow deformation:Removal of Residual ArtifactsRemoval of Residual Artifacts

Erhardt et al, SPIE 2006


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Quality AssuranceQuality Assurance Accuracy of 4D processAccuracy of 4D process

Phantoms developed to QA processPhantoms developed to QA process

Some operate in 1D, periodicSome operate in 1D, periodic

Breathing is nonBreathing is non--periodicperiodic Breathing motion is 3DBreathing motion is 3D


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QA of 4DQA of 4D

Motorized

Stages

Independent

3DDigitizer


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Example: CalypsoExample: Calypso


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QA of 4DQA of 4D


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What Next?What Next? We have a method for describingWe have a method for describing

breathing cyclebreathing cycle We can create 3D image datasets atWe can create 3D image datasets at

specific breathing phasesspecific breathing phases

What do we do with this info?What do we do with this info? A) Create 3D CT at specific phasesA) Create 3D CT at specific phases

Contour these phases and use the dataContour these phases and use the data

B) Use CT data to fit a motion modelB) Use CT data to fit a motion model

Model will be used to drive treatment planningModel will be used to drive treatment planning


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OutlineOutline Why is 4D CT necessary?Why is 4D CT necessary?





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Tumor Trajectories:Tumor Trajectories:

What our Model Has To BeWhat our Model Has To BeAble To DoAble To Do

Seppenwooldeet al.

Int. J. Radiation Oncology Biol. Phys.,Vol. 53, No. 4, pp. 822834, 2002


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Breathing Motion ModelingBreathing Motion ModelingSeppen

woolde,RedJ53,822-834

2002


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Breathing Motion ModelingBreathing Motion Modeling

Seppenwoolde, Red J 53, 822-834 2002

Mathematical ModelMathematical Model


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Mathematical ModelMathematical ModelLinear Approximation

Breathing cycle is defined by Tidal Volume and Airflow

Nonlinear motion comes from airflow f = dv/dt and shape of

airflow curve

5D B thi M ti M d li


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5D Breathing Motion Modeling


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Points in Same Patient

0.62 mm 0.70 mm 0.66 mm

0.72 mm

0.66 mm

0.46 mm


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BreathingBreathing How do we define the breathing cycle?How do we define the breathing cycle?

What is an inhalation and exhalation?What is an inhalation and exhalation? How do the acquired images correspond to theHow do the acquired images correspond to the

actual tumor positions during treatment?actual tumor positions during treatment?

ITV creation requires accurate understanding ofITV creation requires accurate understanding ofbreathing cyclebreathing cycle

How do we define a gating threshold?How do we define a gating threshold?

Planning processPlanning process Efficiency versusEfficiency versus conformalityconformality


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Breathing PatternsBreathing Patterns


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Breathing PatternsBreathing Patterns

Good Gating Window


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v5

v85v90

v95

v98

RegularRegularBreatherBreather

vx = Volume atwhich patienthad v or less

volume x% ofthe time


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v5

v85 v90

v95

v98

IrregularIrregularBreatherBreather


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VV9898 (93%(93% of timeof time)) vsvs VV8585 (80%(80% of timeof time))

Ratio 1.38 0.19

Images that cover 80% of breathing cycle show only 72% of the

motion at 93% of the breathing cycle!

Available 3D Image DatasetsAmount of Motion We Want to Know


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OutlineOutline Why is 4D CT necessary?Why is 4D CT necessary?

What is 4D CT?What is 4D CT? How do we characterize breathing?How do we characterize breathing?



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Treatment PlanningTreatment Planning Images provide Geometry (functional) data forImages provide Geometry (functional) data for

treatment planningtreatment planning

Treatment planning provides prediction ofTreatment planning provides prediction oftreatment coursetreatment course Spatial uncertainties = marginsSpatial uncertainties = margins

ExtrapolationExtrapolation

Breathing motionBreathing motion ITVITV

GatingGating TrackingTracking

ITVITV


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ITVITV


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GatingGating Spatial windowSpatial window

Determined by planning process viaDetermined by planning process viadosimetric considerationsdosimetric considerations

4D CT and breathing motion model4D CT and breathing motion model

Couples spatial window to fraction of timeCouples spatial window to fraction of timespent in that windowspent in that window

Determines duty cycleDetermines duty cycle

Planning system provides cost/benefitPlanning system provides cost/benefitanalysis ofanalysis of conformalityconformality versus deliveryversus deliveryefficiencyefficiency

Breathing Trajectories

Spatial Window


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Breathing Trajectories

During 4D CT

Craniocaudal

An

teroposterio

r

Probability Distribution

Breathing Trace

Probability Determines

Duty Cycle (efficiency)


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TrackingTracking Tracking system require very accurateTracking system require very accurate

understanding of tumor positionunderstanding of tumor position When you track the tumor, youWhen you track the tumor, you untrackuntrack

everything elseeverything else

Critical structures define dose limits, notCritical structures define dose limits, not

tumorstumors

Planning system will need to providePlanning system will need to providepredictions of normal organ dosespredictions of normal organ doses


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Tumor Tracking Methods (1/2)Tumor Tracking Methods (1/2) Imaging + SurrogateImaging + Surrogate

OBI ConeOBI Cone--beam CTbeam CT SoftSoft--tissue contrast of conetissue contrast of cone--beam CT used tobeam CT used to

identify tumor in 3Didentify tumor in 3D

Surrogate maps motion and that map used toSurrogate maps motion and that map used todetermine position throughout treatmentdetermine position throughout treatment

(monitor surrogate)(monitor surrogate)


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Tumor Tracking Methods (2/2)Tumor Tracking Methods (2/2) ImplantsImplants

Implants + SurrogateImplants + Surrogate Fluoroscopic imagingFluoroscopic imaging

systemssystems

Implants aloneImplants alone

Calypso MedicalCalypso Medical

These systems willThese systems will

require significantrequire significant

developmental effortsdevelopmental efforts


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ConclusionsConclusions More quantitation is required!More quantitation is required!

AmplitudeAmplitude--based gating = ability tobased gating = ability toextrapolate from existing image dataextrapolate from existing image data

4D CT should be used as data to feed a4D CT should be used as data to feed a

mathematical/physical model of humanmathematical/physical model of human

breathingbreathing

The model feeds the treatment planningThe model feeds the treatment planningprocessprocess

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ClincalUseof4DCT Low