Treatment Planning - AAPM
Transcript of Treatment Planning - AAPM
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�� Acquisition of imagingdataAcquisitionof imaging data
�� Delineationof regionsof interestDelineationof regionsof interest
�� Selectionof beamdirectionsSelection of beamdirections
�� DosecalculationDosecalculation
�� Optimizationof theplanOptimizationof theplan
TreatmentPlanning
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Proton Planni ng SystemHU versus rel . stopping power
Photon Planning SystemHU versus electron density
Hounsfield Units (HU)
HU
0 500 1000 1500 2000 2500 3000
?
TreatmentPlanning (Protonsvs.Photons)
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Protonbeams (fields)haveanendof range(i.e. pointing to critical structuresis anoption)
TreatmentPlanning(Protonsvs.Photons)
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TreatmentPlanning (Protonsvs.Photons)
Dose versus time
20508095100
Isodoselevels
Planned to the PTV
© Martijn Engelsman, MGH
The PTV conceptis not applicable in proton therapy
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Treatment Planning
• Passivescatteredproton beams• Scannedproton beams• Intensity modulatedproton beams• Comparativetreatmentplans
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High-DensityStructu re
BodySurface
CriticalStructure
TargetVolume
Beam
Aperture
Doublescatteringsystem
© HanneKooy, MGH
Doseshaping for passive scatteredprotons
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SOBP ModulationSOBP Modulation
Apert ure
High- DensityStru cture
BodySurface
Crit icalStructure
TargetVolume
Beam
© HanneKooy, MGH
Prescription:• Range• Modulation• Compensator• Aperture
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+ =
Aperture andRangeCompensator
To be‘designed’ by theplanningsystem !
© HanneKooy, MGH
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Dosimetry andQA for SOBP protonfields
Beam rang e: 17.19 cmModulat ion width: 6.78 cm
Depth [mm]
0 50 100 150 200
Do
se[%
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Beam range: 13.47 cmModulat ion width: 8.65 cm
Depth [mm]
0 20 40 60 80 100 120 140 160
Do
se[%
]
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20
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Beam rang e: 12.0 cmModulati on wid th: 4.0 cm
Depth [mm]
0 20 40 60 80 100 120 140
Do
se[%
]
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1. RangeandModulation Widthfor each field
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MUcGy
iFactorOutput
ic
calD
Volumefor absolutedosimetry
2. Absolutedosimetryfor each field
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10 Gy15 Gy20 Gy25 Gy30 Gy35 Gy40 Gy45 Gy46 Gy
A SIMPLE EXAMPLE: Para-spinal caseusing 3 fields
CTV
brainstem
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Field PatchingField Patching
• Usefulif targetis closetocritical structures
• Not necessarilyhomogeneousdoseto thetarget for eachbeam(IM!)
• Rangeand penumbrauncertaintiesneedto beconsidered
A
B
C
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PTV
CriticalStructure
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CTV-2
25 Gy30 Gy35 Gy40 Gy45 Gy50 Gy55 Gy60 Gy67 Gy
A COMPLICATED EXAMPLE: Nasopharynx case using14 fields (plus additional photon fields to the lower neck)
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CTV-1CTV-2
ParotidBrainstem
SpinalCord
• GTV 76 Gy– CTV1 60-66 Gy– CTV2 60 Gy
• Nodes54 Gy7/28/2008 16
Treating moving targetswith protons
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• posterior view
• posterior cut
LR
Effect of respiration on dose
© EikeRietzel
• Rescanning• Beam Gating• Real time tumor trackin g with marker s
© ShinishiroMori, MGH 7/28/2008 18
FH Burr Proton Therapy Center (2001FH Burr Proton Therapy Center (2001--))Patient PopulationPatient Population
�� BrainBrain 32%32%�� Spine Spine 23%23%�� ProstateProstate 12%12%�� Skull BaseSkull Base 12%12%�� Head & NeckHead & Neck 7%7%�� Trunk/Extremity Sarcomas Trunk/Extremity Sarcomas
6%6%�� Gastrointestinal Gastrointestinal 6% 6% �� Lung Lung 1%1%
© ThomasDeLaney, MGH
In general,1-3 fields / day/ patientCurrently ~ 45 patients/ day
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TreatmentPlanning
• Passivescatteredprotonbeams• Scannedprotonbeams• Intensity modulatedproton beams• Comparativetreatment plans
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BeamScanningBeamScanning
Beammonitor
IntensityModulated
BeamZ
X
Y
Fast Slow
ScanningMagnets
Pair ofQuads
VacuumChamber
0.8 m
0.6 m
No double scattering systemNo modulator wheelsNo apertureNo range compensator
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Typical SpotBeamin Water
© ErosPedroni, PSI
BeamScanningBeamScanning
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1
2 3
1. Evenly spaced/wei ghted spots
to achieve uniform field
2. 1mm spot erro r due to del ivery
erro r or patie nt moti on.
3. Optimum spaci ng/weighting to
achieve sharper penumbra
Pedroni
© ErosPedroni, PSI
7/28/2008 23© Alf red Smith,MDACC
Dosimetry and QA of pencil beams
• Energy/Range• largenumberof energies required• energyspacingmustprovidedoseuniformity
overall depths• Spot sizeandshape
• spotsize/shapemaydependon energy• spotposition accuracy
• Measurementsrequire methodsfor rapid collectionlargeamounts of data
• Real-timebeaminformation
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Ortho gonal IC array measurem ents performed at different waterdepths using a computer controll ed water column and
compared with calculations.
‘Beam’s-eye-view’ of dosein water
U axis profile
T axis profile
Pedroni, PSI, Switzerlan d
PTCOG 46 Educati onal Worksho p
Ionization Chamber Arra yWater column with 26 smallionization chambers of 0.1 cm3
Dose box
Pedroni, PSI, Swi tzerland
Beam
Mirror
CCDCamera
Scintillating Plate
Scintillating Plate, Mirror andCCD Camera used for pencilbeam scan ning QA.
Spot Pattern Test Uniform Field Scanning Test
M D Ander son Cancer Center
PTCOG 46 Educational Workshop
Scintillating screen viewed with aCCD through a 45° mi rror
– ideal for non ho mogeneousdose dis tribut ions
WER6.65CM
WER7.82CM
W= 6.65 cm
W= 7.82 cm
CalculationMeasurement vs.
Pedroni , PSI, Switzerl and© Alfred Smith,MDACC
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TreatmentPlanning
• Passivescatteredprotonbeams• Scannedprotonbeams• Intensity modulatedprotonbeams• Comparativetreatment plans
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IMPT Treatment PlanningIMPT Treatment Planning
• Braggpeaksof pencil beams aredistributedthroughouttheplanningvolume
• Pencilbeam weights are optimizedfor severalbeamdirectionssimultaneously(inverseplanning)
© Alex Trofimov, MGH
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Intensity-ModulatedProtonTherapy–IMPT
© Alex Trofimov, MGH 7/28/2008 28
TreatmentPlanning
• Passivescatteredprotonbeams• Scannedprotonbeams• Intensity modulatedprotonbeams• Comparativetreatmentplans
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Example(passivescattered protons
vs.photons)
Medulloblastoma
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MedulloblastomaMedulloblastomaProtons Photons
Copyright© MGH/NPTC 2003
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Example(protonsvs. IM photons)
Prostate
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(a)
Dose [Gy]
(b)
Dose [CGE]
(c)
Dose [CGE]
Pass.Sc.Protons
IMRT
IMPT
Prostatecarcinoma:
(GTV + 5mm)to 79.2 Gy
(CTV + 5mm) to 50.4 Gy
© Alex Trofimov, MGH
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Example(protons/ IM protons/ IM photons)
Nasopharynx(caseshown earlier)
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�� protonfieldsprotonfieldsCTV to 59.4CTV to 59.4 GyEGyE (33 x 1.8(33 x 1.8 GyGy))GTV to 70.2GTV to 70.2 GyEGyE (+ 6 x 1.8(+ 6 x 1.8 GyGy))
�� PhotonfieldsPhotonfieldslower neck, nodeslower neck,nodes to 60to 60 GyGy
NN
G
G
A Passive scattered protons(14 proton fields,4 photonfields)
© Alex Trofimov, MGH 7/28/2008 36
B Photon IMRT plan(7 coplanarphotonbeams)
© Alex Trofimov, MGH
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C IMPT plan(4 coplanarproton beams)
© Alex Trofimov, MGH 7/28/2008 38
DVH for target structuresDVH for target structures
Comparable targetcoverage
© Alex Trofimov, MGH
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DVH for somecritical structures
© Alex Trofimov, MGH 7/28/2008 40
Summary
• Proton planningoffers moreoptionsin termsof beamdirectionsandfield shaping thanphotonplanning
• IMRT and 3D protonscanbecomparable interms of doseconformality
• Protonsareableto reducethedoseto mostcritical structurescomparedto photons
• Proton therapyis ableto reducetheintegraldosecomparedto photonsby up to afactor of 3
• IMPT is themethodof choice
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Some remarks on biology
• Neutronsin proton therapy• Theproton RBE
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In tegral dose(protons vs.photons)
Advantage protons !!! Dis-advantage protons ???
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Neutron doseasa function of lateral distance
ZacharatouJarlskogandPaganetti: Int. J. Radiat. Biol. Phys. 2008, in press 7/28/2008 44
Field 1Field 2Field 3
Zacharatou JarlskogandPaganetti:Int. J. Radiat. Biol. Phys. 2008,in press
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From:Annalsof theICRP; ICRP Publication 92; RelativeBiologicalEffectiveness(RBE), QualityFactor (Q), andRadiation Weighting Factor (wR)
Neutron radiation weighting factor
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NCRP Report No. 104,The RelativeBiological EffectivenessNCRP Report No. 104,The RelativeBiological Effectivenessof Radiations of Dif ferent Qualityof Radiations of Diff erent Quality
Neutron RBE asa function of endpoint
Estimates of RBEM for neutron carcinogenesis in mice
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* Basedon experiments at theHarvardcyclotron donein the70’s
RBE in proton therapy:
Clini cal (generic)RBE = 1.1*
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Dose per fractio n [Gy]
1 10
RB
E
0.5
1.0
1.5
2.0
2.5
RBE valuesin vivo (centerof SOBP; relative to 60Co)
Mice data:L ung tolerance,Crypt regeneration,Acute skin reactions,Fibr osarcoma NFSa
1.07 0.12
Paganetti et al.: Int. J. Radiat. Oncol. Biol. Phys.2002; 53, 407-421
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• RBE asa function of LET• becarefulwhenusing theendof rangenext to a critical
structure
• RBE asa function of dose• dosedependency seemsto besmall
• RBE asa function of biological endpoint• variationseems to besmall• Note: RBE for cell kil l canbedifferentthanfor
mutation/carcinogenesis
7/28/2008 50 M.K
räm
er,W
.K.W
eyra
ther
,M.S
chol
z:T
echn
.Can
cer
Res
.Tre
atm
.2,4
27-4
36,2
003
Radiationis moreeffectivewhenenergydepositionsare moreconcentratedin space
RBE asa function of particle energy/ LET
p+
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Thanksto
HanneKooyAlex TrofimovGeorgeChenMartijn EngelsmanJudyAdams
for providing some slidesandfigures