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Geant4-SPENVISGeant4-SPENVIS 112006/11/08 Pasadena2006/11/08 Pasadena
Geant4 validation on proton stopping Geant4 validation on proton stopping powerpower
Tsukasa AsoTsukasa AsoToyama National College of Maritime Technology,Toyama National College of Maritime Technology,
JST CRESTJST CREST
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 22
IntroductionIntroduction
• The validation of proton physics models with respect to The validation of proton physics models with respect to reference data is a critical issuereference data is a critical issue
• Proton physics is fundamental for space and medical Proton physics is fundamental for space and medical applicationapplication– i.e. Proton radiation therapy demands rigorous i.e. Proton radiation therapy demands rigorous
comparisons for patient’s safetycomparisons for patient’s safety– Position determination < 1 mmPosition determination < 1 mm– Dose determination < 5 %Dose determination < 5 %
• Bragg peak distribution must agree between the simulation Bragg peak distribution must agree between the simulation and the measurementand the measurement– Bragg peak consists of many physics processes such as Bragg peak consists of many physics processes such as
ionization, multiple scattering, hadronic process etc.ionization, multiple scattering, hadronic process etc.
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 33
Bragg peak and processesBragg peak and processes
• (1) Ionisation energy loss(1) Ionisation energy loss
• (2) (2) (1)(1)+Energy fluctuation+Energy fluctuation
• (3) (3) (2)(2)+Multiple Coulomb Scattering+Multiple Coulomb Scattering
• (4) (4) (3)(3)+Hadron elastic scattering+Hadron elastic scattering
• (5) (5) (4)(4)+Hadron inelastic scattering+Hadron inelastic scattering
• Stopping power ~ RangeStopping power ~ Range
• Excitation energy of material Excitation energy of material
• Best interaction modelsBest interaction models
• Peak position (Range)Peak position (Range)
• Width of peakWidth of peak
• Peak to Plateau ratio Peak to Plateau ratio
Proton Bragg peak in Water
Observables Basis of observable quantities
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 44
Previous worksPrevious works
Using Low energy EM with SRIM2000, transition energy 10 MeV.
Range cut 3 micron.100 micron sliced geometry
Lines : PSTAR NISTRed symbols: Simulation
• ValidationValidation– ““Comparison of Geant4 Electromagnetic Physics Models Against the NIST ReferenComparison of Geant4 Electromagnetic Physics Models Against the NIST Referen
ce Data” had already been published in IEEE TNS 52-4(2005)910-918, K.Amako ce Data” had already been published in IEEE TNS 52-4(2005)910-918, K.Amako et al., under the condition without multiple scattering and energy fluctuationset al., under the condition without multiple scattering and energy fluctuations
• Our previous workOur previous work– “Verification of the Dose Distributions
with Geant4 Simulation for Proton Therapy” ,IEEE TNS, 52-4(2005) 896-901
• The agreement is better than 0.1%, 0.3%, and 0.2% for water, lead, and aluminum, respectively
• There was a long story to reachthese results
• It must be understood systematically
G4v7
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 55
This workThis work
• Study of more detail comparison concentrating on proton stopping Study of more detail comparison concentrating on proton stopping power for power for sub-millimetersub-millimeter scale consistency scale consistency
– Proton range validation to NIST/ICRU reference valueProton range validation to NIST/ICRU reference value
Using SUsing Stopping power modelstopping power models
Range cut / step limit dependencies Range cut / step limit dependencies
Std EM and Low EM differencesStd EM and Low EM differences
The validation is done in terms of “Proton range”The validation is done in terms of “Proton range”
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 66
Electromagnetic physics models in Electromagnetic physics models in Geant4Geant4
Multiple scatteringBremsstrahlungIonisationAnnihilationPhotoelectric effectCompton scatteringRayleigh effectgamma conversione+e- pair productionSynchrotron radiationtransition radiationCherenkovRefractionReflectionAbsorptionScintillationFluorescenceAuger
Standard EM
LowEnergy EM
• Many choice of stopping power Many choice of stopping power parameterisations for protonsparameterisations for protons
Specialized according to - the particle type - energy range of process
ICRU composite material ~ 11 Al_2O_3, CO_2, CH_4, (C_2H_4)_N-Polyethylene, (C_2H_4)_N-Polypropylene, (C_8H_8)_N, C_3H_8, SiO_2, H_2OH_2O, H_2O-Gas, Graphite
Bethe-Bloch formula
Below 2 MeV by default
Proton Ionisation:: Stopping power
e+e-/gamma down to Ek~100 eV
e+e-/gamma down to Ek~1 keV
NIST for NIST material(G4_Water) [v8.x]ICRU49 (ChemicalFormula)Bragg rule (ICRU49 element)
Below 2 MeV by default
Below 2 MeV by defaultZiegler1977 (Bragg rule)ICRU49 (ChemicalFormula)Ziegler1985 (Bragg rule)SRIM2000 (Bragg rule)Bragg rule (ICRU49 element)
• Geant4 electromagnetic Geant4 electromagnetic processesprocesses
Energy fluctuation model
dE/dX tableIonisation energy loss =+
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 77
Range study(1) : Validation of stopping Range study(1) : Validation of stopping powerpower• 100 microns sliced water phantom100 microns sliced water phantom• 200 MeV proton200 MeV proton• CSDA rangeCSDA range
– Only Ionisation processOnly Ionisation process• Multiple scattering, Hadronic interaction (Elastic/Inelastic)Multiple scattering, Hadronic interaction (Elastic/Inelastic)
are turned offare turned off• Range cut is set to 3 micronRange cut is set to 3 micron
– Count number of protons in each layerCount number of protons in each layerdz = 100 micron
200 MeV proton
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 88
Comparison of STD EM with Low EMComparison of STD EM with Low EM
e-,e+,gamma = 3um RED G4hIonisation BLK G4hLowEnergyIonisation
w/o ChemicalFormula(“H_2O”)NuclearStoppingOffi.e. Bragg rule is applied
200 MeV proton
ICRU 259.6mm
w/ MeanExcitationEnergy = 75eV (ICRU)
Depth in water (mm)
Pro
ton
sur
viva
l pro
babi
lity
G4v7
Low energy EM process gives consistent range with NIST PSTAR prediction
Standard EM process gives shorter range than NIST PSTAR prediction
Under specified circumstances :
Discussion will be back later,but let’s adopt Low EM for study
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 99
Comparison of stopping power Comparison of stopping power functionsfunctions
200 MeV protonin Water
ICRU49 259.6mm
G4v7 G4hLowEnergyIonisation BLK: Bragg rule NuclearStoppingOff BLU: ICRU H_2O parameterization NuclearStoppingOff GRN: ICRU H_2O parameterization NuclearStoppingOn
diff. ~ 500 micronLow EM : Bragg rule or ICRU param.?
Low energy EM process + ICRU parameterization function for water
Depth in water(mm)
Pro
ton s
urv
ival pro
babili
ty
But why?
Low energy EM process + ICRU Bragg rule
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1010
Proton Range in water - Ionization Loss Table -Proton Range in water - Ionization Loss Table -
En
erg
y L
oss
(M
eV
/mm
)
KinE (MeV)
E_tr=2MeV
Bethe-BlochAt low energy region,RED: Bragg ruleGRN: ICRU49 param. function
G4hLowEnergyIonisation
Energy loss with ICRU49 parameterisationtends to be overestimated than Bragg rule’s calculationat the kinetic energy range from 100s MeV to 1 MeV.
Rat
io o
f Ene
rgy
Loss
(%
)
KinE (MeV)
G4v7
Energy loss in Bethe-Bloch formulais factored to ensure a smooth transitionto the low energy model.
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1111
Correction Factor: ParamBCorrection Factor: ParamB
G4v8.1.p01
The collection factor to the Bethe-Bloch formula is called as “ParamB” in low energy EM.
i.e. eloss *= (1+paramB*kinetic_energy/Transition_energy)
Stopping power function connectivity
-0.02
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0 2 4 6 8 10 12Transition Energy (MeV)
Cor
rect
ion
fact
or
LowE SRIM2000LowE ICRU param.LowE ICRU Bragg ruleStd. ICRU param.Std. ICRU Bragg ruleStd. G4WATER NIST
SRIM2000with 10 MeV cutoff was used in
our previous study
Smooth connectivity of stopping power
parameterization is desirable for precise
range calculation
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1212
Range cut and step size dependenceRange cut and step size dependence• Range cutRange cut may be set by users according to expected simulation accuracy. may be set by users according to expected simulation accuracy.
– ( Step limit can be set by users, but normally it is limited by geometry. )( Step limit can be set by users, but normally it is limited by geometry. )– The assurance of simulated result should be kept consistent within the accuracyThe assurance of simulated result should be kept consistent within the accuracy
• We observed a systematic variation of simulated range compared to the expected value fWe observed a systematic variation of simulated range compared to the expected value from the production cut.rom the production cut.– The range of The range of 200 MeV200 MeV proton becomes about 3 mm longer than NIST prediction by a proton becomes about 3 mm longer than NIST prediction by a
pplying a looser production cut. pplying a looser production cut.
200MeV Proton, ICRU predicts259.6mm
G4hLowEnergyIonisation No ChemicalFormula NuclearStoppingOff
Geometry: Sliced in 100um thickness
500um100um 50um 10um 5um 3um 1um
Su
rviv
ed p
roto
n p
rob
abili
ty
Depth in Water ( mm )
Production Cut
G4v7
We have to applyvery tiny productioncut in order to getreasonable result?
diff. ~ 3 mm
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1313
Range study(2): Range cut and Step limit Range study(2): Range cut and Step limit optimizationoptimization
• Bulk Water ( no geometrical slices )Bulk Water ( no geometrical slices )• 190 MeV proton190 MeV proton• Range cut dependence: 0.015, 0.050, 0.1, 0.5, 1 mmRange cut dependence: 0.015, 0.050, 0.1, 0.5, 1 mm• Step limit dependence: 0.01, 0.015, 0.020, 0.040, 0.050,Step limit dependence: 0.01, 0.015, 0.020, 0.040, 0.050,
0.100, 0.500, 1.0 mm 0.100, 0.500, 1.0 mm
190 MeV proton
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1414
Production Cuts
234
235
236
237
238
239
240
241
242
0.01 0.1 1
Production Cut (mm)
Pro
ton
Ran
ge (m
m)
Step. 0.01mm
Step. 0.05mm
Step.0.10mm
Step.0.50mm
Step.1mm
Step.0.04mm
Step.0.03mm
Step.0.02
Step. Default
NIST 237.7mm
Step Limits
diff = 6 mm
diff = 3 mm
Only 10um Step Limit reproduces NIST range.The range is independent to the production cutin this case.
Proton Range in bulk waterProton Range in bulk water
G4v7
G4hLowEnergyIonisation SRIM2000p blow 10 MeV190MeV proton
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1515
Proton Range in bulk waterProton Range in bulk water
Step limits
237
237.5
238
238.5
239
239.5
240
240.5
241
241.5
0.01 0.1 1Step limit length (mm)
Pro
ton
Ran
ge (
mm
)
Prod.1mmProd.0.5mmProd.0.1mmProd.0.05mmProd.0.015mm
NIST 237.7mm
Simulated Range changes with the step limit size.Range becomes longest when step limit is around 100um.
G4v7
G4hLowEnergyIonisation SRIM2000p 10 MeV
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1616
Energy fluctuation: ElectronicLossFluctuation()Energy fluctuation: ElectronicLossFluctuation()
(Fluctuated Eloss) - ( Eloss by dE/dX ) [keV]
if( EnlossFlucFlag && 0.0 < eloss && finalT > MinKineticEnergy) { // now the electron loss with fluctuation eloss = ElectronicLossFluctuation(particle, couple, eloss, step) ; if(eloss < 0.0) eloss = 0.0; finalT = kineticEnergy - eloss - nloss; } Eloss by dE/dX Table
Eloss dE/dX = 0.21 MeV / 500um
Eloss dE/dX = 0.0417 MeV / 100um
Eloss dE/dX = 0.00417 MeV / 10umThese values aretypical for 225MeVproton
Mean value of these distributions are:
-7.163 (keV)/500um-1.244(keV)/100um
-0.01013(keV)/10um
Fluctuated Eloss
RangeCut=10mm
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1717
Range with or without Energy fluctuationRange with or without Energy fluctuation
• G4hLowEnergyhIonisationG4hLowEnergyhIonisation• 225 MeV proton in Water225 MeV proton in Water• Range cut = 10 mmRange cut = 10 mm
313.0
314.0
315.0
316.0
317.0
318.0
319.0
320.0
321.0
322.0
323.0
0.001 0.01 0.1 1 10 100 1000
Step limits(mm)
Ran
ge (m
m)
LowEM SRIM2000 w/ o Efluc
LowEM SRIM2000 w/ EFluc
Without energy fluctuation, LowEM hIoni. reproduces NIST range at the step size below 5 mm.Energy fluctuation obviously distorts energy deposition with the underestimation.
1.00
10.00
100.00
1000.00
10000.00
100000.00
1000000.00
0.001 0.01 0.1 1 10 100 1000
Step Limits(mm)N
umbe
r of
cal
ls
NUserStepNLowEhIoni
NIST 317.4mm
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1818
Low EM or Std EMLow EM or Std EM
e-,e+,gamma = 3um RED G4hIonisation BLK G4hLowEnergyIonisation
w/o ChemicalFormula(“H_2O”)NuclearStoppingOffi.e. Bragg rule is applied
200 MeV proton
ICRU49 259.6mm
w/ MeanExcitationEnergy = 75eV (ICRU)
Depth in water (mm)
Pro
ton
sur
viva
l pro
babi
lity
G4v7
Low energy EM process gives consistent range with NIST PSTAR prediction
Standard EM process gives shorter range than NIST PSTAR prediction
What is the source of problem?
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 1919
Range with or without energy fluctuationRange with or without energy fluctuationRange Study
313.0
314.0
315.0
316.0
317.0
318.0
319.0
320.0
321.0
322.0
323.0
0.001 0.01 0.1 1 10 100 1000StepLimit (mm)
Ran
ge (m
m)
LowE SRIM w/ o EflucStd ICRU w/ o EflucStd NIST w/ o EflucStd ICRU w/ o Fluc (BINS)
With Energy Fluctuation
313.0
314.0
315.0
316.0
317.0
318.0
319.0
320.0
321.0
322.0
323.0
0.001 0.01 0.1 1 10 100 1000Step Limits (mm)
Ran
ge (m
m)
LowE SRIM w/ EFlucStd ICRU param. w/ EFlucStd G4NIST w/ EFluc
Std EM uses G4UniversalFluctuationLowE EM uses G4hLowEnergyIonisation::ElectronicFluctuation() Both calculation based on “Energy loss in thin layers in GEANT4”,NIM A362(1995)416-422. But the implementation is slightly different.
0.1keV-100TeV 120bin=>0.1keV-1GeV 36000bins
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 2020
SummarySummary• Source of problem and desired improvementsSource of problem and desired improvements
– Importing stopping power functionImporting stopping power function• Interconnectivity to the Bethe-Bloch formulaInterconnectivity to the Bethe-Bloch formula
– ~10% difference causes ~500um shift of range in water~10% difference causes ~500um shift of range in water
Should Geant4 be capable to import user’s stopping power functioShould Geant4 be capable to import user’s stopping power function? or Need to ensure non-stress way for interpolationn? or Need to ensure non-stress way for interpolation
– Energy fluctuation modelEnergy fluctuation model• Calculation model does not stable at around 100 micron step sizeCalculation model does not stable at around 100 micron step size
– Underestimation of energy loss makes the range longerUnderestimation of energy loss makes the range longer
Need to fix the unstable behaviorNeed to fix the unstable behavior– dE/dX table resolution might be neededdE/dX table resolution might be needed
• The fine binning The fine binning – It changes expected range about 1 mmIt changes expected range about 1 mm
Table binning should be adjustable for the applicationTable binning should be adjustable for the application
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 2121
Accuracy versus Execution time?Accuracy versus Execution time?
• Geometry: Sliced in 100um thicknessGeometry: Sliced in 100um thickness• 225MeV proton225MeV proton• ProductionCut=1mm,StepLimit=DefaultProductionCut=1mm,StepLimit=Default
– Range 322.2mmRange 322.2mm– CPU 915.89s/10000evCPU 915.89s/10000ev
• ProductionCut=1mm,StepLimit=10umProductionCut=1mm,StepLimit=10um– RangeRange 317.487mm317.487mm– CPU CPU 56095609s/10000evs/10000ev
• ProductionCut=3um, StepLimit=DefaultProductionCut=3um, StepLimit=Default– Range 317.787mmRange 317.787mm– CPU CPU 99219921s/10000eVs/10000eV
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 2222
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 2323
0.01
0.1
10.01 0.1 1
Step Limits (mm)
Ave
rage
ste
p le
ngth
(m
m)
Prod.1mmProd.0.5mmProd.0.1mmProd.0.05mmProd.0.015mm
Step Limits を 10um にすると、ProductionCut 15um と同じ意味になる
2006/11/08 Pasadena2006/11/08 Pasadena Geant4-SPENVISGeant4-SPENVIS, , Tsukasa AsoTsukasa Aso TNCMTTNCMT 2424
Proton range in waterProton range in waterRange in Si
165.0
166.0
167.0
168.0
169.0
170.0
171.0
0.001 0.01 0.1 1 10 100 1000
Step Limit (mm)
Ran
ge (m
m)
Std NIST w/ o FlucStd NIST w/ Fluc