05-4d ct lung planning
TRANSCRIPT
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4D CT For Lung Planning4D CT For Lung Planning
25 June 2009
Dr Ho Gwo FuangClinical Oncologist
University of Malaya Medical Centre
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LungLung tumourtumouris a MOVING targetis a MOVING target
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Problems of Treating a MovingProblems of Treating a Moving
TargetTarget
Interfraction movement
Intrafraction movement
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Target Miss or Organ Hit
Miss Target Hit organ
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Respiratory MotionRespiratory Motion
Traditionally, treatment volume is defined on static CTimage
Static CT imaging does not precisely define tumour inmotion due to respiration.
Target may move in and out of treatment field
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ICRU 52 and 60ICRU 52 and 60
CTV
PTV2 cm
2 cm
1 cm1 cm
GTV is expanded to CTV(microscopic spread) and PTV (set-
up and other errors)
To account for respiratory
movement, margins are added to
the clinical target volume
Treated volume
Increases the normal tissue dose
and limits the target dose
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UnUn--gated Treatmentgated Treatment
PTV increases to include the target in motion
for treatment planning and dose delivery Large volume of normal tissue is exposed un-necessarily for high radiation dose
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Target MovementTarget Movement -- 3D Solution3D Solution
Expand the PTV to cover the maximum ranges of
target motions along all three directions
Problems: Difficult to generate isodose distributions conforming to
the moving target such as lung tumor with 3DCRT
Unable to minimize the doses to the surrounding normal
tissues
Therefore limiting total dose and dose fraction sizes
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ChallengeChallenge
Goal How do you accurately deliver appropriate
dose distributions conforming to a moving
lung target and meantime effectively
minimize doses to surrounding normal
lung tissues?
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Solutions for organ or target motionSolutions for organ or target motion
managementmanagement
1) Breath-hold technique Radiation is delivered with breath-hold
2) Tracking technique Radiation is delivered by tracking the motion of thetarget. Dynamic Tracking
Real time Tracking
3) Gating technique
Gated radiation delivery is based on the selected phaseof breathing cycle
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Solutions for organ or target motionSolutions for organ or target motion
managementmanagement
1) Breath-hold technique Radiation is delivered with breath-hold
2) Tracking technique Radiation is delivered by tracking the motion of thetarget. Dynamic Tracking
Real time Tracking
3) Gating technique
Gated radiation delivery is based on the selected phaseof breathing cycle
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Active Breathing CoordinatorActive Breathing Coordinator
Valve-controlled cessation of
inhalation and exhalation duringpredetermined comfortable level ofmoderately deep inspiration
A
B
C
D
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ABC TreatmentABC Treatment
ABC Immobilise the tumour motion results inreduced margins
Lower doses to normal tissue
Prescribed dose can be higher
Free breathing Breath-hold
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Additional benefit of inspirationAdditional benefit of inspiration
techniques with ABCtechniques with ABC
Healthy tissue density lung tissue is less dense at deep
inspiration, therefore less healthy tissue
in path of irradiation
Expiration / normal inspiration Deep Inspiration
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ABC ApparatusABC Apparatus
Digitalspirometer
Balloon
valve
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Visual display of breathingVisual display of breathing
motionmotion
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Breath Holding & its ChallengesBreath Holding & its Challenges
Initial patient set up
Detecting patient movement during
treatment
Patient training
Patient compliance
Repeatability of breath holding
Margins added to compensate for all theabove
Requires a breath-hold that is:
reproducible
consistent
Accurate
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Solutions for organ or target motionSolutions for organ or target motion
managementmanagement
1) Breath-hold technique Radiation is delivered with breath-hold
2)Tracking technique Radiation is delivered by tracking the motion of the
target. Dynamic Tracking
Real time Tracking
3) Gating technique
Gated radiation delivery is based on the selected phaseof breathing cycle
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TrackingTracking
Dynamic tracking
e.g. Cyberknife, RTRT system
Real time tracking
e.g. Calypso System
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ConceptConcept
External position sensor
Internal fiducial
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Internal movement
Location of the tumour known using fiducial tracking
External movement
Tracking Marker system monitors external movements
Correspondence model
Relationship between internal and external movements Continuously follow the internal movement via externalmovement
Model update continuously throughout the treatment
ConceptConcept
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CyerknifeCyerknife
Diagnostic
X-Ray Sources
ImageDetector
TreatmentCouch
LinearAccelerator
Robotic Arm
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Prediction AlgorithmPrediction Algorithm 200ms delay allows robot to smooth jerky offset
calculations
Based on pattern searching
1) Look at the record of model results just before
2) Compare this pattern with the record of model results over a
longer period of elapsed time
3) Find the position at which they match. Sample the model
position 200ms later this is the prediction
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KUKA RobotKUKA Robot
Made by KUKAof Germany
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Solutions for organ or target motionSolutions for organ or target motion
managementmanagement
1) Breath-hold technique Radiation is delivered with breath-hold
2) Tracking technique Radiation is delivered by tracking the motion of the
target. Dynamic Tracking
Real time Tracking
3) Gating technique
Gated radiation delivery is based on the selected phaseof breathing cycle
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Beam Off
Beam OffBeam On
Beam On
Treatment Field
1.1. 2.2.
3.3. 4.4.
Gating -
Treatment beam is turned on and off as tumor enters and exits
a static treatment field
GatingGating
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GatingGating
Respiration-gated radiotherapy offers asignificant potential for improvement in the
irradiation of tumour sites affected by
respiratory motion such as lung, breast andliver tumours.
An increased conformality of irradiationfields leading to decreased complications
rates of organs at risk
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Respiratory motion solutionsRespiratory motion solutions Breath-hold techniques (e.g. ABC)
Uncomfortable for patients, limited applicability (MSKCC: 7/13patients)
Increases treatment time (MSKCC: 17 to 33 minutes for conventionalRT)
Respiratory gating Residual motion within
gating window
Increases treatment time Baseline shift
4D Radiotherapy
Hardware/Softwarecomplexity
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0 5 10 15 20
Time (s)
Displacement(cm)
Exhale gate
Inhale Gate
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4D Radiotherapy4D Radiotherapy
The explicit inclusion of the temporal changesin anatomy during the imaging, planning and
delivery of radiotherapy
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4D Solution for Organ Motion4D Solution for Organ Motion
4D CT provides insight into organ motionduring respiration, with volumetric anatomic
data set
Treatment planning explicitly accounts for
the internal target motion
This can be implemented at various levels ofcomplexity
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Utilization of 4D CT in RadiotherapyUtilization of 4D CT in Radiotherapy
Treatment Planning
Image Acquisition & Registration Acquisition of a sequence of CT
image sets over consecutive phases of abreathing cycle
Designing treatment plans on CT
image sets obtained for each phase
of the breathing cycle
Continuous delivery of the 4D
treatment plans throughout the breathingcycle
Treatment Delivery
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CT Motion ArtifactsCT Motion Artifacts
CT data acquisition is serial
Data at adjacent couch positions are acquired serially
Collection of projection data one slice afteranother in combination with motion of the
scanned object leads to significant interplay
Depending on the relative motion of the advancing
scan plane and the tumour, different artifacts can be
imaged
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3D CT - Distorted images, incorrect anatomicalDistorted images, incorrect anatomical
positions, volumes or shapespositions, volumes or shapes
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Gated CT
Keall et alAust Phys Eng Sci Med 2002
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Standard helical CT scan acquiredunder light breathing
One respiratory phase of a 4D CTscan
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4D
Images
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4D CT Scan4D CT Scan
Assumptions Organ motions such as lungs are related to the motionsof an external marker
Concepts If patients can breathe periodically and regularly, the
CT image acquisition is fast enough to generate many
images at all phases in a series of respiratory cycles
When the scan is done, all the images of the selectedphase are retrospectively organized to form 4D video
images
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4D CT: Data Acquisition (1)4D CT: Data Acquisition (1)
4D CT technique images multiple respiratory
states within one data acquisition
Temporally oversampling data acquisition at each
couch position CT tube rotates continuously for the duration of the
respiratory cycle and acquire projection data thorugh all
respiratory states (typically 10-20)
Typically 5-10 revolutions during the respiratory cycle
is achieved
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4D CT: Data Acquisition (2)4D CT: Data Acquisition (2)
A 4D CT scan consisting of a series of 3D CT
image sets acquired at different respiratory phases
Typically 10-20 images per slice are reconstructed,
representing 10-20 respiratory phase states This results in a total number of images between
1000 and 2000 per 4D CT study
The acquisition time decreases linearly with
number of rings of detectors
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External Sorting SignalExternal Sorting Signal
After 4D CT data acquisition and image
reconstruction
in order to sort these images into specific temporallycoherent volumes, additional information is required
One such sorting signal is the rise and fall of theabdominal surface, as a surrogate for respiratory
motion
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4D CT imaging4D CT imaging
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Retrospectively Reconstructed CT SlicesRetrospectively Reconstructed CT Slices After data acquisition, a software (e.g. GE
Advantage4D software) is used to retrospectivelysort the images into multiple temporally coherentvolumes
The software loads the 4D CT images as well asthe respiratory trace (recorded by the RPM system)
Based on the data acquisition time stamps in theimage Dicom headers and the correlation signal inthe RPM trace, a specific respiratory phase can be
assigned to each image
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Respiration Waveform from
RPM Respiratory Gating System
X-ray on
Exhalation
Inhalation
First couch position Second couch position Third couch position
Image acquired
signal to RPM
system
Retrospective 4D-CT imaging
TinsuTinsu PanPan
Respiratory Bin
R i 4D I A i i i
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0:00
00.0 cm
Retrospective 4D Image Acquisition
4 x 2.5 mm Multi Slice
(10 mm total coverage)
X-ray Tube
Table location
Acq. Time
R i 4D I A i i i
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0:01
00.0 cm
Retrospective 4D Image Acquisition
4 x 2.5 mm Multi Slice
(10 mm total coverage)
X-ray Tube
Table location
Acq. Time
R i 4D I A i i i
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0:02
00.0 cm
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R t ti 4D I A i iti
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0:03
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R t ti 4D I A i iti
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R t ti 4D I A i iti
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Retrospecti e 4D Image Acq isition
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0:03
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4 x 2.5 mm Multi Slice
(10 mm total coverage)
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0:04
02.0 cm
4 x 2.5 mm Multi Slice
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02.0 cm
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4D CT scan Acquired
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Identify the motion
Decide the treatment window with min.displacement and max. beam-on time
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Contour CTV and critical structures on one or
several phases of CT images in the window
Determine the max. displacement of CTV of allphases in the window
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Treatment planning with IGTV/ ICTV
Beam placements and calculations for treatment plan Plan review, approval, and validation
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4D CT planning4D CT planning
The explicit inclusion of temporal effects in
radiotherapy treatment planning is referred to as
4D treatment planning
Intrafrational motion can be included in treatment
planning at different levels
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4D CT planning4D CT planning Simplest solution:
To generate a composite target volume thatencompass the CTV throughout organ motion
during the respiratory cycle
Advanced:
Multiple dose calculations & deformable
registration
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Targets DelineationTargets Delineation
With the 4D CT dataset, we can design the
internal gross target volume (IGTV), that is the
volume containing the GTV throughout its motion
during respiration
One method of combining the data from the
multiple CT datasets is to create a maximalintensity projection, which can be used as an aid in
contouring the IGTV
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MIP and Average CTMIP and Average CT
The MIP (or MIV) is a 3D CT dataset created by
assigning each voxel the value of the highest value
voxel at that location across the breathing phases
The average CT is a 3D CT dataset created by
performing a voxel-by-voxel numerical averaging
over all the breathing phases
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4D CT simulation demosntrated tumour motion during breathing cycle. (A) End of Inspiration, (B) End
of Expiration, (C)Average CT, (D) MIP. In this patient, MIV image was used to design IGTV
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Targets DelineationTargets Delineation
Another approach is to contour the GTV with the
end of inspiration and expiration breath-holding
and then combine these two volumes to form the
IGTV this approach can be used with regularspiral CT without 4D
All CT databases are transferred to the treatment-planning system for reference.
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4D CT inhale /exhale fusion4D CT inhale /exhale fusion
coronalcoronal saggitalsaggital
Maria Hawkins, RMH
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Treatment PlanningTreatment Planning
All 10 respiratory-phase datasets, the MIP, and the
average CT along with extended range free-
breathing CT acquired during the same imaging
session are transferred to the treatment planningsystem
The information is crucial for target delineatingusing the internal taget volume (ITV) approach to
take tumour motion into consideration
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4D4D vsvs 3D Target Volumes3D Target Volumes
4D target volumes differ from those derived
from conventional helical scanning
Differences: the shapes of volumes of
interest and their centroids change more
accurate from 4D CT
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3D BEV 4D BEV
BEVsBEVs
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MLC leaf motionMLC leaf motion
3D 4DKeall et alPMB 2001 46:1-10
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Image RegistrationImage Registration Another approach is to use a deformable
registration technique in which the tumour volumeoutlined on the expiratory phase of the 4D imagesis registered on other phases of the images to
create a union of target contours, enclosing allpossible positions of the target
Mathematically, this is to find the transformation matrix, that maps
an arbitrary point from the fixed image to the corresponding pointon the floating image (or vice versa)
e.g. using a freeware tool vtkCISG (Hartkens et al 2002)
The resulting IGTV contour is then evaluatedacross all phases
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Treatment Planning with ImageTreatment Planning with Image
RegistrationRegistration
A treatment plan was created on the end-exhale
CT image set and then automatically created on
each of the 3D CT image sets corresponding with
subsequent respiration phases, based on the beam
arrangement and dose prescription in the end-
exhale plan.
Dose calculation using e.g. Monte Carlo, issimultaneously performed on each of the 3D
image sets
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Treatment PlanningTreatment Planning
The dose distribution from each respiratory phase
CT image set was mapped back to the end-exhale
CT image set for analysis
4D dataset therefore provides the ability to study theimpact of respiratory motion on dose distribution
The use of deformable image registration to merge all
the statistically noisy dose distributions back onto one
CT image set effectively yields a 4D Monte Carlo
calculation with a statistical uncertainty equivalent to a
3D calculation
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4D Imaging and Treatment Planning; Eike Rietzel and George T.Y. Chen
3D ( lid) 4D (d h d) DVH3D ( lid) 4D (d h d) DVH
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3D (solid) vs 4D (dashed) DVHs3D (solid) vs 4D (dashed) DVHs
4D Planning Flow Chart
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Acquire 4D CT
Define anatomy
Create/adjust treatment plan
Evaluate dose distribution
1
4
3
2
Proceed to treatment6
Plan acceptable?No
Yes
Deformableregistration
Automatedplanning
Defor
mable
registra
tion
5
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Treatment deliveryTreatment delivery
Treatment delivered to the planned volume
Treatment can be delivered with a gated beam
control
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Beam ONBeam ONBeam OFFBeam OFF
Respiratory Gated Radiation Therapy
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4D Solutions4D Solutions
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4D Solutions4D SolutionsUnUn--gated Acquisitiongated AcquisitionGated TreatmentGated Treatment
4D (x,y,z,t) CT (GE Adv4D)
allows to acquire all images in free breathing.
divides the respiratory cycle in various phases.
Gated window (Varian RPM) is set for minimum tumour
position uncertainty and maximum beam-on time interval
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4D radiotherapy delivery4D radiotherapy delivery
Linac Controller MLC Workstation
MLC Controller4DC
Tracking Signal
Treatment
parameters
Linac Controller MLC Workstation
MLC Controller4DC
Tracking Signal
Treatment
parameters
GE Avd4D CT Scanner withGE Avd4D CT Scanner with
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GE Avd4D CT Scanner with
VarianVarians RPM Respiratory Gating Systems RPM Respiratory Gating System
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Gated IMRT for LungGated IMRT for Lung
Gating for Liver IrradiationGating for Liver Irradiation
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Maria Hawkins, Royal Marsden Hospital
Gating for Liver IrradiationGating for Liver Irradiation
Liver motion, 1-5 cm, increases volume of normal
tissue irradiated
Respiratory gating reduces volume of liverirradiated
GTVPTV
Volume to
be irradiated
Free breathing Breath hold RT
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What is The Next Exciting NewDimension in IGRT ?
4D PET/CT4D PET/CT
f /C h l i
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Impact of PET/CT on Therapy PlanningImpact of PET/CT on Therapy Planning
PET/CT helps to find unsuspected involvementin the mediastinum
Can PET/CT help to re-define the treatment volume of a
primary tumour ???
Images courtesy of Community Cancer Center, FL
CT PET PET/CT Fusion
Gated PETGated PET
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time
7
3
4 5
6
8
3
45
6
7
Bin 8
8
2
Trigger
1
Bin 1
2
1
Trigger
Prospective fixed forward time binning (DLS&DST)
Ability to reject cycles that dont match
Single 15 cm FOV Gated PET
Helical CT attenuation correction
Gated PETGated PETC i
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Images courtesy of Holy Name Hospital
PET MIP
4D PET MIP
Primary tumor
?
CT PET Fusion
Trans.
Coronal
4D PET Coronal
GatedGated acqacq. statistics. statistics Single FOVSingle FOV
Helical CTACHelical CTAC
10 minute scan duration10 minute scan duration
8 respiratory gated bins8 respiratory gated bins
ImpactImpact
Max Intensity project (MIP)Max Intensity project (MIP)
Increased quantitativeIncreased quantitative
accuracyaccuracy
Motion assessmentMotion assessment
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4D Radiotherapy: Caveats4D Radiotherapy: Caveats Other variables exist:
Cardiac motion
Interfractional motion set up errors, variations inphysiologic state (e.g. stomach size)
The data acquired in 4D CT is synthesized frommultiple breaths during an acquisition time of afew minutes
Reproducitiliby of this pattern during each treatmentfraction is implicitly assumed when analyzing theseresulting 4D dose distributions
Possible variations may be monitored by examining therespiratory trace on a daily basis
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4D Radiotherapy: Looking Ahead4D Radiotherapy: Looking Ahead Techniques to deliver 4D treatment is still being developed
and refined to take full advantage of the knowledgeprovided by 4D CT
Image guided therapy in the treatment room could wellinclude 4D cone beam CT, if appropriate
The aim is to mitigate the dose-perturbing effects of motion,and possibly lead to safe decrease of geometric margins andincreased therapeutic gain
Incorporation of functional imaging informations
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Respiratory motion causes problems during the
imaging, planning and treatment stages ofradiotherapy
Several methods have been proposed to address
respiratory motion:1) Target positioning
2) Robotic tracking
3) Real-time monitoring
4) 4D planning & gating
4D radiotherapy has some advantages over existingmethods
There are still many unanswered questions
ConclusionsConclusions
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AcknowlegementAcknowlegement I am indebted to Professor Andrew Wu, PhD, of
Department of Radiologic Sciences,Thomas JeffersonUniversity, Philadelphia, Pennsylvania, Varian, Elekta and
Siemens for lending me slides & videos for this talk.
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Thank You !Thank You !