Verification of the Dose Verification of the Dose Distributions with Geant4 Distributions with Geant4 Simulation Simulation for Proton Therapy for Proton Therapy Tsukasa Aso (Toyama College of Maritime Tec Tsukasa Aso (Toyama College of Maritime Tec h.) h.) A.Kimura (JST CREST) A.Kimura (JST CREST) S.Tanaka ( Ritsumeikan Univ.) S.Tanaka ( Ritsumeikan Univ.) H.Yoshida (Naruto Univ.) H.Yoshida (Naruto Univ.) N.Kanematsu (NIRS) N.Kanematsu (NIRS) T.Sasaki (KEK) T.Sasaki (KEK) T.Akagi (HIBMC) T.Akagi (HIBMC) This work This work is partly supported by Core Resea is partly supported by Core Resea rch rch for Evaluational Science and Technology (CRES for Evaluational Science and Technology (CRES T) of T) of the Japan Science and Technology (JST) the Japan Science and Technology (JST)
Transcript
Verification of the Dose Verification of the Dose Distributions with Geant4 Distributions with Geant4
Simulation Simulation for Proton Therapyfor Proton Therapy
Tsukasa Aso (Toyama College of Maritime Tech.)Tsukasa Aso (Toyama College of Maritime Tech.)A.Kimura (JST CREST)A.Kimura (JST CREST)
This workThis work is partly supported by Core Research is partly supported by Core Research for Evaluational Science and Technology (CREST) of for Evaluational Science and Technology (CREST) of
the Japan Science and Technology (JST)the Japan Science and Technology (JST)
Bragg peak characteristics is suitable for the radio-therapeutic treatment of tumorBragg peak characteristics is suitable for the radio-therapeutic treatment of tumors.s.
NIRS, National Cancer Center, HIBMC, Tsukuba-U in JAPANNIRS, National Cancer Center, HIBMC, Tsukuba-U in JAPAN Request to develop simulation tools forRequest to develop simulation tools for
Designing beam delivery systemDesigning beam delivery system Validate or Proposing a treatment planningValidate or Proposing a treatment planning
These efforts are employed by the approaches, so far,These efforts are employed by the approaches, so far, Experimental measurements (Trustable but hard to do everything)Experimental measurements (Trustable but hard to do everything) Analytical calculations (Model limitation for simplicity )Analytical calculations (Model limitation for simplicity )
Simulation Tools is possible to includeSimulation Tools is possible to include Complex geometrical effectComplex geometrical effect Material varietyMaterial variety Different Physics processes for comparisonDifferent Physics processes for comparison
However, in order to apply simulation tools for the hadron therapy, However, in order to apply simulation tools for the hadron therapy, it has to reproduce the dose profiles for patient safety.it has to reproduce the dose profiles for patient safety.
=> Comparison of result is nesseary.=> Comparison of result is nesseary.
This talk gives a comparison of simulation with the measurement of proton bThis talk gives a comparison of simulation with the measurement of proton beams at HIBMC including the validation of the beam delivery system as well eams at HIBMC including the validation of the beam delivery system as well as the dose distributions.as the dose distributions.
HIBMC: HIBMC: Hyogo Ion Beam Medical CenterHyogo Ion Beam Medical Center Hyogo Ion Beam Medical CenterHyogo Ion Beam Medical Center
located at Harima Science Garden City, Hyogo,located at Harima Science Garden City, Hyogo,JAPAN.JAPAN.
Therapeutic beam is extracted from SynchrotronTherapeutic beam is extracted from Synchrotron 150,190,230 MeV proton150,190,230 MeV proton 250,320 MeV/u Carbon ion 250,320 MeV/u Carbon ion
Five treatment rooms, including two Gantry nozzles,Five treatment rooms, including two Gantry nozzles,those are up to 3.0 m in length, and 16 cm square irradithose are up to 3.0 m in length, and 16 cm square irradiation field.ation field.
Spring8
Hyogo Ion Beam Medical CenterTreatment Room ofisocentric rotating Gantry(Only for Protons)
Based on GEANT4All beam line elements in HIBMC Gantry NozzleConfiguration param. in ASCII file Easy reconfiguration w/o recomplieWobbling magnetic field is set for each one of primary protonsMaterial parameters taken from NIST databaseIonization: Low Energy extension Bethe-Bloch + SRIM2000 swicthed at 10 MeV kinetic energy.hadronic: LHEP_PRECO_HP Pre-equilibrium decay model. Geant4 educational package
Range of Protons in waterRange of Protons in water
(mm)
First of all, we have examined the range of proton in water. Our simulation uses G4hLowEnergyIonisation with low energy electro-magneticprocesses. In the low energy hadrons ionization process, the energy loss functionbelow the kinetic energy of 2 MeV is changed according to the setting of “ChemicalFormula”. If ChemicalFormula is set to “H_2O”, the energy loss is derived from the fit function of the ICRU, while it is not set, the energy loss is calculated from the sum of electronic stopping power of the elements in thematerial.
Pro
ton
rate
ChemicalFormula=“”
ChemicalFormula=“H_2O”
200MeV protons
ICRU 259.6mm
If we dose not set the ChemicalFormula, simulatedrange is consistent with ICRUvalue.
But with the setting ofChemicalFormula=“H_2O”,the simulated range becomeshorter.
For smooth connection at 2 MeV,the BetheBloch value is multipliedby the factor (ParamB).
We changed the energy losscalculation at the region from0.8 to 2 MeV to use the sumof electronic stopping powerin G4hParamterisedLossModel.
G4 used the correction factor “paramB” in the G4hLowEnergyIonisation Class.But the correction factor becomes large in Water ， so that the range become shorterthan the measured value.
Range of proton in Water Range of proton in Water 150MeV
157.8mm
190MeV
237.8mm
230MeV
329.5mm
NIST PSTAR program calculation based on continuous-slowing-downapproximation, with ICRU Report49(1993) ICRU 150MeV - 157.7 mm 190MeV - 237.7 mm 230MeV - 329.1 mm
After the modification of the energy loss calculation, the G4hLowEnergyIonisationcan reproduce the range of proton in watergiven by the ICRU Report.
Ranges of proton are obtained in the simulationby switching off all processes except for ionization process.
As a reference, the PSTAR program (National Institute of Standards and Technology, NIST) was used for comparison.
The ranges obtained from Geant4 simulationare good agreement with reference values. The agreement is better than 0.1%, 0.3%, and 0.2%for water, lead, and aluminum, respectively.
Material Validation: Range of Material Validation: Range of protonsprotons
Beam line elements Beam line elements tuning/validationtuning/validation Wobbling radiusWobbling radius
Standard Deviation ~ 14mm
Wobbling trace w/o scatter
190 MeV
Beam dispersion by scatterBeam dispersion by scatter
Wobbling radius ~ 99 mm
Beam dispersion w/o wobbling
The magnetic fields of a pair of wobbling magnets are adjusted to fit a radius of circular trace in the measurement. Then a set of wobbling fields is randomly changed for each one of primary protons in the simulation. The primary beam dispersion at the nozzle entrance is derived from the comparison with measurements and included in the simulation, where parallel beam and Gaussian shape intensity are assumed.
-1.5% -3%
Thickness in measurement1.6mm 150MeV2.5mm 190MeV3.5mm 230MeV
Dose verification(1): Bragg Dose verification(1): Bragg peakpeakIn order to compare two distributions,
the following procedure is performed.(1)Depth-dose distributions are normalizedat the peak position.(2) The Simulated distribution is fitted by the measured distributions with a displacement (a) and normalization (b) fitting parameters as f(z) = b D(z+a).
a = -1.02+-0.08 mmb = 0.96+-0.01
a = -1.22+-0.10 mmb = 0.97+-0.01
a = -1.86+-0.13 mmb = 0.97+-0.01
Difference is about 2~3%
The depth-dose distributions agree each other better than 4% accuracy.
Range modulation: Bar ridge filterRange modulation: Bar ridge filter Bar ridge filter is used as the range-modulating system in order to obtain Spread Out Bragg Peak (SOBP). The ridge filter made of aluminum has 24 bars with the pitch of 5mm. It is processed within an accuracy of 30 um by the micro fabrication technique. The ridge filters used to produce SOBP at Gantry Nozzle were designed and built for 150 MeV and 190 MeV beams, respectively.
The height of ridges is about 4cm and 6cm for 9cm width and 12cm width SOBP, respectively.
Proton Energy
w/o Ridge Filter
w/ Ridge Filterfor 9cm SOBP
1717
Dose Verification(2): SOBPDose Verification(2): SOBPNormalization and fitting procedure are performed at the same manner with Bragg peak comparison.
a=-1.03+-0.51b=0.99+-0.02
a=-1.15+-0.50b=0.99+-0.02
a=-0.05+-0.36b=1.00+-0.02
a=-0.07+-0.35b=0.99+-0.02
The shape of the SOBP is similar to the measurements. For 12cm width SOBP, fan beam effect is clearly reproduced.There are some discrepancy, but those are less than 4 % at the maximum.
The small bump in the measurement isthought to be a fan beam effect which isnever seen at the analytical calculationwith the parallel beam approximation
SummarySummary The GEANT4 based simulation for proton therapy has been developed.The GEANT4 based simulation for proton therapy has been developed. The obtained dose distributions are agree well better than 4 % The obtained dose distributions are agree well better than 4 %
difference with the measured value at HIBMC.difference with the measured value at HIBMC. The results are derived from only the simple assumption of beam spot The results are derived from only the simple assumption of beam spot
size at nozzle entrance. The use of realistic beam profile will improve size at nozzle entrance. The use of realistic beam profile will improve the simulation.the simulation.
Further development is processed.Further development is processed. DICOM interface has already available. DICOM interface has already available. The plastic phantom DICOM data will be simulated and compared The plastic phantom DICOM data will be simulated and compared
with the treatment system predictions.with the treatment system predictions.
DiscussionDiscussion Displacement of Bragg peak positionDisplacement of Bragg peak position
Measurement systematic error, Measurement systematic error, Not sure, but ~500um, by the comparison of w/ Not sure, but ~500um, by the comparison of w/
wobbling and w/o wobbling.wobbling and w/o wobbling.Simulation shows about 500um shift due to wobbling, Simulation shows about 500um shift due to wobbling, but measured data is not.but measured data is not.
Beam energy ambiguity,Beam energy ambiguity, Not sure. But peak shifts roughly 1mm/0.5MeV.Not sure. But peak shifts roughly 1mm/0.5MeV.
Energy resolution of the synchrotron is thought to be Energy resolution of the synchrotron is thought to be 0.1%.0.1%.If the beam energy shift about 0.3~0.5% higher, it is If the beam energy shift about 0.3~0.5% higher, it is consistent.consistent.
