Geant4-SPENVIS Geant4-SPENVIS 1 2006/11/08 Pasaden 2006/11/08 Pasaden a Geant4 validation on proton Geant4 validation on proton stopping power stopping power Tsukasa Aso Tsukasa Aso Toyama National College of Maritime T Toyama National College of Maritime T echnology, echnology, JST CREST JST CREST
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Geant4-SPENVIS1 2006/11/08 Pasadena Geant4 validation on proton stopping power Tsukasa Aso Toyama National College of Maritime Technology, JST CREST.
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• 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.
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
• 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”
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
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?
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.
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.
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