Image Guided Radiation Therapy (IGRT)

Overview of IGRT practice and commercially available solutions for image guidance in Radiation Therapy.

1. Image Guided Radiation Therapy (IGRT)
Teekendra Singh Faujdar
Sr. Radiation Therapist
Medanta The Medicity, Gurgaon

2. Introduction
•Radiotherapyhasalwaysrequiredinputsfromimagingfortreatment
planningaswellasexecution,whenthetreatmenttargetisnot
locatedonthesurfaceandinspectionandvisualconfirmationarenot
feasible.
•Traditionalradiotherapypracticesincorporateuseofanatomic
surfacelandmarksaswellasradiologiccorrelationwithtwo-
dimensionalimagingintheformofportfilmsorfluoroscopicimaging.

3. Treatment planification in radiotherapy
Patient
simulation:
CT, RM…
Treatment
Differencesin target position
Planningtreatment
-Determinationof interest
volumes:
GTV, CTV, PTV, OR
-Conformation-beams

4. Treatment planification in radiotherapy
POSITION IN THE CT SCAN POSITION IN THE TREATMENT
In thetreatmenttheprostate
position changeswithrespectto
thereferenceposition.
Determines thereference
position of theprostate
throughoutthetreatment.

5. Why may the target be elsewhere?
•Mispositioning(interfraction)
•Organ motion (intrafraction)
•Shape change (interfraction)
Mayresultin absorbed dosein thevolumes
of interestand organsat riskthatdo not
correspondto thetheoreticaldoseplanned.
Sourcesof
uncertainties

6. Image Guided Radiotherapy
•Howcanweknowthepositionofthetarget?
•WhatisIGRT
•Image-basedRT(useofimagingtodefinethetargetandnormaltissuesfor
treatmentplanning)-suchascontrastenhancedcomputedtomography(CECT)scans,magnetic
resonanceimaging(MRI),positronemissiontomography(PET)scans,andangiographyobtainthree-
dimensional(3D)structuralandbiologicinformation
•Image-guidedRT(useofimagingtomonitorandmodifytreatment)-suchas
planar,volumetric,video,orultrasound-basedimagingmethods,inwhichobtainingperiodicinformation
ontargetpositionandmovement(withinthesamesessionorbetweenconsecutivesessions)by
comparingitwithreferenceimaging,andgivefeedbacktocorrectthepatientsetupandoptimizetarget
localization.
IGRT

7. BroadDefinition–6D’sofIGRT
•Detection anddiagnosis
•Determining biologicalattributes
•Delineationoftargetandorgansatrisk
•Dose distributiondesign
•Dose deliveryassurance
•Deciphering treatment responsethrough imaging

8. Errors and Margins in Radiotherapy:
•Anerrorinradiotherapydeliveryisdefinedasanydeviationfromintendedor
plannedtreatment.
MechanicalUncertainties-relatedtotreatmentunitparameterssuchascouchandgantrymotion
GeometricalUncertainties-relatedtopositionandmotionoftarget
DosimatricUncertainties–relatedtoQualityAssurance
•IGRTdealswiththegeometricuncertainties,whichmaybeeitherintrafractional
orinterfractional.
•M.vanHerk,“Errorsandmarginsinradiotherapy,”SeminarsinRadiationOncology,vol.14,no.1,pp.52–64,2004.
•C.Rasch,R.Steenbakkers,andM.vanHerk,“Targetdefinitioninprostate,head,andneck,”SeminarsinRadiationOncology,vol.15,no.3,pp.136–145,2005.

9. Errors and Margins in Radiotherapy:
•Both inter-and intra-fractional uncertainties may be a result of a combination of systematic
and random errors.
Asystematicerror,isessentiallyatreatmentpreparationerrorandisintroducedintothechainduringtheprocess
ofpositioning,simulation,ortargetdelineation.Thiserror,ifuncorrected,wouldaffectalltreatmentfractions
uniformly.
Arandomerror,isatreatmentexecutionerror,isunpredictable,andvarieswitheachfraction.
SystematicerrorsshifttheentiredosedistributionawayfromtheCTV,whilerandomerrorsblurthisdistribution
aroundtheCTV.
MarginsareaddedtotheCTVtotaketheseerrorsintoaccount.
•ThesemarginsaregeometricexpansionsaroundtheCTVandmaybenon-uniforminalldimensionsdependingon
theexpectederrors.Thesemarginsensurethatdosimetricplanninggoalsaremetdespitethevariationsduring
andbetweenfractions.
•ICRU62definestheexpansionofPTVaroundtheCTVasacompositeoftwofactors—internaltargetmotion
(internalmargin)andsetupvariations(setupmargin).Dependingonobservedsystematicandrandomerrorsina
givensetupforaparticulartreatmentsite,avarietyofrecipesforcalculatingPTVmarginsexistinliterature.
•J. C. Stroomand B. J. M. Heijmen, “Geometrical uncertainties, radiotherapy planning margins, and the ICRU-62 report,” Radiotherapy and Oncology, vol. 64, no. 1, pp. 75–83, 2002.
•M. van Herk, P. Remeijer, C. Rasch, and J. V. Lebesque, “The probability of correct target dosage: dose-population histograms for deriving treatment margins in radiotherapy,” International
Journal of Radiation Oncology, Biology, Physics, vol. 47, no. 4, pp. 1121–1135, 2000.
•J. C. Stroom, H. C. J. de Boer, H. Huizenga, and A. G. Visser, “Inclusion of geometrical uncertainties in radiotherapy treatment planning by means of coverage probability,” International Journal
of Radiation Oncology Biology Physics, vol. 43, no. 4, pp. 905–919, 1999.

10. IGRT Technology Solutions
•Depending on the imaging methods used, the IGRT systems may broadly be divided into two groups:
•J. M. Balterand Y. Cao, “Advanced technologies in image guided radiation therapy,” Seminars in Radiation Oncology, vol. 17, no. 4, pp. 293–297, 2007
•J. de los Santos, R. Popple, N. Agazaryanet al., “Imageguidedradiation therapy (IGRT) technologies for radiation therapy localization and delivery,”
IJROBP, vol. 87, no. 1, pp. 33–45, 2013.
Non-Radiation Based Systems Radiation Based Systems
•Ultrasound based systems
•Camera-based systems
•Electromagnetic tracking,
•MRI based systems
•Electronic Portal Imaging Devices (EPID)
•Cone Beam CT (CBCT) –KV or MV
•Fan Beam KV CT (CT-on-Rails)
•Fan Beam MV CT (TomoTherapy)
•Exac-Trac X-Ray 6-D Stereotactic IGRT System
•Hybrid Systems for Real Time 4D Tracking
2D KV Stereoscopic Imaging (Cyber-Knife)
Real Time Tumor-Tracking (RTRT) System.
VERO system

11. Non-Radiation Based IGRT Systems

12. Ultrasound Based Systems:
•Vendors:
•BAT
•SonArray
•Crarity
•I-Beam
•Thesesystemsacquire3Dimagesthathelpalign
targetstocorrectforinter-fractionalerrors.
•Geometricaccuracyis3–5mmandthegreatest
advantageislackofanyionizingradiation.
•Sitesofcommonapplicationincludeprostate,
lung,andbreastradiotherapy.
•M. Fuss, B. J. Salter, S. X. Cavanaugh et al., “Daily ultrasound-based image-guided targeting for radiotherapy of upper abdominal malignancies,”
International Journal of Radiation Oncology Biology Physicsvol. 59, no. 4, pp. 1245–1256, 2004.

13. Camera-Based (Infrared) or Optical Tracking Systems
•Vendor-VisionRT(AlignRT)
•Thesesystemsidentifythepatientreferencesetuppoint
positionsincomparisontotheirlocationintheplanning
CTcoordinatesystem,whichaidsincomputingthe
treatmentcouchtranslationtoalignthetreatment
isocenterwithplanisocenter.
•Opticaltrackingmayalsobeusedforintra-fraction
positionmonitoringforeithergating(treatmentdelivery
onlyatacertainpositionoftarget)orrepositioningfor
correction.

14. Camera-Based (Infrared) or Optical Tracking Systems
•Vendor-VisionRT(AlignRT)
•AlignRTsystem, image the patient directly and track the
skin surface to give real time feedback for necessary
corrections.
•These systems have found application in treatment of
prostate and breast cancer and for respiratory gating
using external surrogates.
•Geometric accuracy is 1-2 mm, but application is limited
only to situations where external surface may act as a
reliable surrogate for internal position or motion.
•C. Bert, K. G. Metheany, K. P. Doppke, A. G. Taghian, S. N. Powell, and G. T.Y.Chen, “Clinical experience with a 3Dsurface patient setup system for
alignment of partial-breast irradiation patients,” International Journal of Radiation Oncology, Biology, Physics, vol. 64, no. 4, pp. 1265–1274, 2006.

15. Electromagnetic Tracking Systems
•Vendor -CALYPSO
Five elements of the calypso system:
•Beacon Electromagnetic transponder
•4D Console
•4D Electromagnetic Array
•4D Tracking Station
•Optical System

16. Electromagnetic Tracking Systems
•Vendor-CALYPSO
•Thissystemmakeuseofelectromagnetic
transponders(beacons)embeddedwithinthe
tumor,andmotionofthesebeaconsmaybe
trackedinrealtimeusingadetectorarray
system.
•Beaconsneedtobeplacedthroughaminimally
invasiveprocedure,theirpresencemayintroduce
artifactsinMRimages,andtherearelimitations
tothepatientsize.
•Calypsohasageometricaccuracyof<2mm.
•D.W.Litzenberg, T. R.Willoughby, J.M. Balter et al., “Positional stability of electromagnetic transponders used for prostate localization and continuous, real-time tracking,”
International Journal of Radiation Oncology Biology Physics, vol. 68, no. 4, pp. 1199–1206, 2007.
•T. R.Willoughby, P. A. Kupelian, J. Pouliotet al., “Target localization and real-time tracking using theCalypso4D localization system in patients with localized prostate
cancer,” International Journal of Radiation Oncology Biology Physics, vol. 65, no. 2, pp. 528–534, 2006.

17. MRI Guided IGRT
•Vendors:
•ViewRay
•Philips
•Elekta
Purpose
Treat the patient while simultaneously imaging with a ‘conventional’
1.5T diagnostic MRI
How:
•Mount the Linac on a rotatable gantry around the MRI Magnet
•The radiation isocenteris at the centreof the MRI imaging volume
•Modify the Linac to make it compatible with the MR environment
•Modify the MRI system
•Minimize material in the beam path
•Minimize magnetic field at the Linac

18. •Thesesystemshelprealtimeassessmentofinternal
softtissueanatomyandmotionusingcontinualsoft
tissueimagingandallowforintrafractionalcorrections.
•Geometricaccuracyofthesystemis1-2mm.However,
MRIhascertaindrawbackssuchasmotionartifacts,
distortionwithnon-uniformmagneticfields,and
cannotbeperformedforpatientswithpacemakersor
metallicimplants.
•AlltheselimitationsofdiagnosticMRIapplytothisIGRT
systemaswell.Awideapplicationpotentialexistsin
treatmentofprostate,liver,andbrain,aswellasfor
brachytherapy.
MRI Guided IGRT
•J. Dempsey, B. Dionne, J. Fitzsimmons, A. Haghigat, and J. Li, “A real-time MRI guided external beam
radiotherapy delivery system,” Medical Physics, vol. 33, article 2254, 2006.
•B. G. Fallone, B. Murray, S. Ratheeet al., “First MR images obtained during megavoltage photon irradiation
from a prototype integrated linac-MR system,” Medical Physics, vol. 36, no. 6, pp. 2084–2088, 2009.

19. •These include static as well as real time tracking, using either kilovoltage(KV),
megavoltage (MV), or hybrid methods.
Radiation Based IGRT Systems

20. Electronic Portal Imaging Devices (EPID)
•Vendors
•ELEKTA
•VARIAN
•SIEMENS
•EPIDwasdevelopedasareplacementoffilmdosimetry
fortreatmentfieldverificationandisbasedonindirect
detectionactivematrixflatpanelimagers(AMFPIs).
•Theyareofferedasstandardequipmentbynearlyall
linearaccelerator(LINAC)vendorsasbothfield
verificationandqualityassurance(QA)tools.
•Imageacquisitionis2D,withageometricaccuracyof2
mm.
Varian Trilogy
MV portalvision
Elekta Synergy™(MV) Portal View
SiemensK-View™

21. Electronic Portal Imaging Devices (EPID)
•Bonylandmarksonplanarimagesareusedas
surrogatesfordefiningpositionalvariationsrespective
tothedigitalreconstructedradiographs(DRRs)
developedfromtheplanningCTdataset.
•DifferentsystemsmayuseeitherKVorMVX-raysfor
imaging,withtheimagecontrastbeingsuperiorwith
KVimageswhilethereislesserdistortionfrommetallic
implants(dental,hipprostheses)inMVimages.
•EPIDsystemsareunabletodetectorquantify
rotations.
•Averagedoseperimageis1–3mGyforKVsystems
whileitisashighas30–70mGyforMVsystems
DRR-AP Live-AP
DRR-Lat Live-Lat
•C.W. Hurkmans, P. Remeijer, J. V. Lebesque, and B. J.Mijnheer, “Set-up verification using portal imaging;
review of current clinical practice,” Radiotherapy and Oncology, vol. 58, no. 2, pp. 105–120, 2001.
•C. Walter, J. Boda-Heggemann, H. Wertz et al., “Phantom and in-vivo measurements of dose exposure by
image-guided radiotherapy (IGRT): MV portal images vs. kV portal images vs. cone-beam CT,” Radiotherapy
and oncology, vol. 85, no. 3, pp. 418–423, 2007.

22. Cone Beam CT (CBCT)-KV or MV
•Vendors
•ELEKTA(XVI)
•VARIAN(OBI)
•SIEMENS(KView-MV)
•ThesesystemsconsistofretractableX-raytubeandamorphoussilicon
detectorsmountedeitherorthogonalto(ElektaXVI,VarianOBI)or
alongthetreatmentbeamaxis(SiemensArtiste).
•Thesehavecapabilityof2D,fluoroscopicandCBCTimaging.
•Geometricaccuracyis1mmorlesserwithpossibilityof2Dand3D
matchingwithDRRsorX-rayvolumetricimagesgeneratedfrom
planningCTdatasets.
•Scanningisdonethroughacontinuouspartialorcompletegantry
rotationaroundthecouch,acquiringthe“average”positionoforgans
withrespiratorymotion.
Varian TrilogyOBI®
ElektaSynergy™
VolumeView
SiemensArtiste™
KVision
•D.A.Jaffray,“Kilovoltagevolumetricimaginginthetreatmentroom,”FrontiersofRadiationTherapyand
Oncology,vol.40,pp.116–131,2007.
•C.A.McBain,A.M.Henry,J.Sykesetal.,“X-rayvolumetricimaginginimage-guidedradiotherapy:the
newstandardinontreatmentimaging,”InternationalJournalofRadiationOncology,Biology,Physics,vol.
64,no.2,pp.625–634,2006.

23. Cone Beam CT (CBCT)-KV or MV
•Bothinterfractionsetupchangesandanatomical
changesrelatedtoweightchangesororganfilling
(bladder,rectum)maybemonitoredwiththese
systems.
•Repeatscansattheendoftreatmentmaygivean
estimateofintrafractionalchanges.
•Fortumorsdiscernibleseparatelyfromsurrounding
normaltissue,treatmentresponsemayalsobe
monitoredandthesescansmaybeusedfordose
recalculationortreatmentplanadaptationafter
necessaryimageprocessing.
•KVCTgivesbettercontrastresolutioncomparedto
MVCT,butmaybelimitedbyartifactsfrom
prosthesesandscatterfrombulkypatientanatomy.
•Averagedoseperimageis30–50mGy.
Before Correction
After Correction
•O.Morin,A.Gillis,J.Chenetal.,“Megavoltagecone-beamCT:systemdescriptionandclinicalapplications,”MedicalDosimetry,vol.31,no.1,pp.51–
61,2006
•J.Pouliot,A.Bani-Hashemi,M.Svatosetal.,“Low-dosemegavoltagecone-beamCTforradiationtherapy,”InternationalJournalofRadiationOncologyBiology
Physics,vol.61,no.2,pp.552–560,2005.

24. Fan Beam KVCT (CT on Rail)
Vendor:
•Varian / Siemens Linacs with CT Scanner
inside the treatment room (GE/Siemens)
Varian Linac with in room GE CT ScannerSiemens ARTISTE with in room Siemens CT Scanner

25. Fan Beam KVCT (CT on Rail)
•Thissystemhasanin-roomCTscannerandgantrythatmovesacrossthe
treatmentcouch/patient,whichcanberotatedtowardseitherthescanneror
thegantryforimagingandtreatment,respectively.
•3Dimagesaretakenwiththepatientimmobilizedonthecouch,thedifference
fromadiagnosticCTbeingalargerboresize(>80cmdiameter)to
accommodatebulkyimmobilizationdevices,andamulti-slicedetector.
•AccuracyandapplicationsaresimilartoCBCTwithaveragedoseof10–50mGy
perimage
•R.deCrevoisier,D.Kuban,andD.Lefkopoulos,“Image-guidedradiotherapybyin-roomCT-linearaccelerator
combination,”Cancer/Radiotherapie,vol.10,no.5,pp.245–251,2006.

26. Fan Beam MV CT
•Accuray -Tomotherapy
•Thissystemincludesanon-boardimagingsystem
toobtainMVCTimagesofthepatientintreatment
position.
•ThesameLINACisusedtogenerateboththe
treatment(6MV)andimagingbeam(3.5MV).
•Axenondetectorlocatedonthegantryopposite
theLINACcollectsexitdataforgenerationofMV
CTimages.
•Patientdosefromimagingvarieswithpitchsetting
andistypically10–30mGyperscan
•K.J.Ruchala,G.H.Olivera,E.A.Schloesser,andT.R.Mackie,“MegavoltageCT
onatomotherapysystem,”PhysicsinMedicineandBiology,vol.44,no.10,pp.
2597–2621,1999.

27. Hybrid Systems for Real Time 4D Tracking

28. 2D KV Stereoscopic Imaging (Cyberknife)
Accuray-Cyberknife VSI
TheAccurayCyberkniferobotic
radiosurgerysystemconsistsofa
compactLINACmountedonan
industrialroboticmanipulatorarmwhich
directstheradiationbeamstothe
desiredtargetbasedoninputsfromtwo
orthogonalX-rayimagingsystems
mountedontheroomceilingwithflat
panelfloordetectorsoneithersideof
couch,integratedtoprovideimage
guidanceforthetreatmentprocess.

29. •Imagesareacquiredthroughoutthetreatmentdurationatperiodicintervalsranging
from5to90seconds,andthecouchandroboticheadmovementsareguidedthrough
anautomaticprocess.
•Several tracking methods may be used depending upon the treatment site:
•6D Skull
•X-Sight Spine
•X-Sight Lung
•Fiducial Synchrony Tracking
•In-Tempo Tracking
•The system also has a couch that has 6 degrees of freedom to correct for positional
variations.
•Treatment may be limited by patient position and size, and posterior treatment beams
cannot be used.
•A semi-invasive procedure may be required if Fiducial markers are needed for tracking.
•This system can be employed for both cranial (frameless) and extra-cranial radiosurgery
or SRT.
2D KV Stereoscopic Imaging (Cyberknife)
•J. R. Adler Jr., S. D. Chang, M. J. Murphy, J. Doty, P. Geis, and S. L.Hancock, “The Cyberknife: a frameless robotic system for radiosurgery,” Stereotactic
and Functional Neurosurgery, vol. 69, no. 1–4, pp. 124–128, 1997.
•C. Antypasand E. Pantelis, “Performance evaluation of a CyberKnifeG4 image-guided robotic stereotactic radiosurgery system,” Physics in Medicine and
Biology, vol. 53, no. 17, pp. 4697–4718, 2008.

30. Real Time Tumor-Tracking (RTRT) System
•Thissystemisdesignedforrealtimetrackingof
tumorsbyimagingimplantedfiducialsandusing
thisinformationforgating.
•ItconsistsoffourX-raycamerasystemsmounted
onthefloor,aceiling-mountedimageintensifier,
andahigh-voltageX-raygenerator.
•TheLINACisgatedtoirradiatethetumoronly
whenthemarkeriswithinagiventolerancefrom
itsplannedcoordinatesrelativetotheisocenter.
•H.Shirato,S.Shimizu,K.Kitamuraetal.,“Four-dimensionaltreatmentplanningandfluoroscopicreal-timetumortrackingradiotherapyformoving
tumor,”InternationalJournalofRadiationOncology,Biology,Physics,vol.48,no.2,pp.435–442,2000.
•H.Shirato,S.Shimizu,T.Kuniedaetal.,“Physicalaspectsofareal-timetumor-trackingsystemforgatedradiotherapy,”
InternationalJournalofRadiationOncologyBiologyPhysics,vol.48,no.4,pp.1187–1195,2000.

31. VERO System
•ThissystemhastwoX-raytubesandcorresponding
flatpaneldetectorsandusesacombinationofinitial
couchmotionandapairofradiographsforpatient
alignment.
•Thecouchiscapableof3Dalignmentforinitial
coarsesetupandthentheon-boardimaging
subsystemhelpsfine-tuning.
•Apairofradiographsisacquiredandregisteredwith
priorDRRsusingbonylandmarkstoevaluatethe
translationalandrotationalshifts.
•Thesystemcanalsocompensatefororganmotion Vero 4DRT System
•Y.Kamino,K.Takayama,M.Kokuboetal.,“Developmentofafour-dimensionalimage-guidedradiotherapysystemwithagimbaledX-rayhead,”
InternationalJournalofRadiationOncology,Biology,Physics,vol.66,no.1,pp.271–278,2006.

32. ExacTracX-Ray 6-D Stereotactic IGRT System
•ItusesacombinationofopticalpositioningandKVradiographicimaging
foronlinepositioningcorrections.
•Therearetwomainsubsystems:aninfrared-basedsystemforinitial
patientsetupandprecisecontrolofcouchmovementusingarobotic
couchandaradiographicKVX-rayimagingsystemforposition
verificationandreadjustmentbasedoninternalanatomyorimplanted
markers.
•Infraredsystemmayalsobeusedforrespiratorymonitoringand
signalingtoLINACforbeamtrackingandgating.
•NovalisTxcombinesthissystemwithanadditionalon-boardimaging
system(MV,KVXrays,andKVCBCT)onamulti-photon/electronbeam
LINAC.
•Z.Chang,Z.Wang,Q.J.Wuetal.,“DosimetriccharacteristicsofNovalisTx
systemwithhighdefinitionmultileafcollimator,”MedicalPhysics,vol.35,no.
10,pp.4460–4463,2008.
•[38]J.-Y.Jin,F.-F.Yin,S.E.Tenn,P.M.Medin,andT.D.Solberg,“Useofthe
BrainLABExacTracX-Ray6DSysteminImage-GuidedRadiotherapy,”
MedicalDosimetry,vol.33,no.2,pp.124–134,2008.

33. As well as the imaging dose to the patient

34. Imaging Protocol on the basis of Treatment Technique:
•DailyXVI:ForSBRT(StereotacticBodyRadiationTherapy),VMAT(Volumetric
ModulatedArcTherapy)andIGRT(ImageGuidedRadiationTherapy)cases.
•Pre,MidandPostXVI:ForSRS/SRT(StereotacticRadiationTherapy)andSBRTcases.
•ForSBRT(>8Gy/#):PreandposttreatmentXVIonday1andthendailyXVI.
•WeeklyXVI:For3DCRT&IMRTcases(First3daysdailythenweeklyXVI).
•RandomXVI:Anytimeincasesofdoubtinpatientsetuporincaseofmissing
referencemarks.
•Note:Onthebasisofclinicalrequirementsorsiteofthepatient,DailyXVIor
AlternativedayXVIcanbeacquiredwiththepriorapprovalfromdutyconsultant.

35. Traffic Light Protocol:

36. Summary:
•IGRTseekstoaddressgeometricuncertaintiesindoseplacementfortarget
andnormaltissues.
•UseoftheIGRTprocesshasimprovedourawarenessandunderstandingof
dailyinter-andintra-fractionalsetupvariationsandmotion.
•IthasbecomearoutinepartofcurrentRTpracticeworldwide.
•SafeapplicationofIGRTtechnologyrequiresadditionaltrainingandcareful
integrationintotheclinicalprocess.
•IGRTrevealschangesinanatomyduringRTthatchallengeconventional
practices
•Theexperienceandappropriatetrainingsoftheteamislikelymore
importantthantheactualdevice/treatmenttechniqueused.

37. Thank You..!!
No matter how good is the beam, if the target is not where we thought”.