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[%

]

0

20

40

60

80

100

120

Beam range: 13.47 cmModulat ion width: 8.65 cm

Depth [mm]

0 20 40 60 80 100 120 140 160

Do

se[%

]

0

20

40

60

80

100

120

Beam rang e: 12.0 cmModulati on wid th: 4.0 cm

Depth [mm]

0 20 40 60 80 100 120 140

Do

se[%

]

0

20

40

60

80

100

120

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

5050

PTV

CriticalStructure

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7/28/2008 13© Marc Bussiere, MGH 7/28/2008 14

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


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7/28/2008 33© Alex Trofimov, MGH 7/28/2008 34

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)


B Photon IMRT plan(7 coplanarphotonbeams)


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C IMPT plan(4 coplanarproton beams)


DVH for target structuresDVH for target structures

Comparable targetcoverage


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DVH for somecritical structures


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+

7/28/2008 51

Thanksto

HanneKooyAlex TrofimovGeorgeChenMartijn EngelsmanJudyAdams

for providing some slidesandfigures

treatment planning - aapm

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