05-4d ct lung planning

8/4/2019 05-4d Ct Lung Planning

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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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2) Tracking technique Radiation is delivered by tracking the motion of thetarget. Dynamic Tracking

Real time Tracking

3) Gating technique



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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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2)Tracking technique Radiation is delivered by tracking the motion of the

target. Dynamic Tracking

Real time Tracking

3) Gating technique



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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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2) Tracking technique Radiation is delivered by tracking the motion of the

target. Dynamic Tracking

Real time Tracking

3) Gating technique



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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

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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 !

05-4d ct lung planning

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