plateforme de calcul pour les sciences du vivant lydia maigne gate/g4 meeting collaboration -...
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Plateforme de Calcul pour les Sciences du Vivant
http://clrpcsv.in2p3.fr
1Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge
Electron Dose point kernels calculations in water using GATE/G4.8
GATE/G4 collaboration meeting, 12-09-07
Lydia Maigne (LPC, Clermont-Ferrand), [email protected]
Credits: Cheick Thiam (LPC, Clermont-Ferrand), Nicolas Chouin, Ludovic Ferrer (Inserm, Nantes),
Michel Maire (G4 collaboration)
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 2
DPK calculations methodology
drr
Simulations characteristics:
-Isotropic point source
-Monoenergetic emission, 5M e- generated
-Scoring of the dose in a spherical water phantom of 400 mm in diameter containing 22 spherical shells each of thickness of 0.05 rE
-Cut of 2 kev on e-
-Standard EM package
2( / , ) 4 ( , ) /E Ej r r E r D r E r E
Formalism to calculate the dose (Berger and TG43): fraction of emitted energy that is deposited in a spherical shell of scaled radius r/rE to r/rE + d(r/rE).
With: r being the radial distance to the middle of the spherical shells, rE the nominal CSDA range the density of the medium, D(r,E) the dose per incident particle at distance r.
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 3
Comparisons G4 versions and other Monte Carlo
4 MeV
1 MeV
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 4
Comparisons:Cuts, detector volumes, EM packages
4 MeV 4 MeV Large volume Spherical shells
4 MeV
Problems but where do they come from??
By considering a large volume of water: Cut values have a non negligeable influenceBy considering spherical shells:Changes on cut values have no influence
Results obtained with a cut value of 2 keV(0.0043 mm) in a large volume of water givecomparable results to spherical shells.
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 5
Solutions
• Important modifications to simulate the dose deposited:– No more spherical shells– Use of a large sphere in water
Z
Y
X
drrdrr
Modifications in the code of GATE: To fix the maximal step length on electron transport, StepMax
To obtain an homogeneous distribution of the dose deposited along the step
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 6
Control the step length « StepMax »
GEANT4 class to manage the step « G4Step.cc »
In GATE: Addition of the class « GateStepMax » to call « GateSteppingAction » and « G4Step » classes: Consequence in GATE macros, add the following command line: # StepMax Control !!! /gate/StepMax/stepMax 7 µm
Consequence on the dose deposited by electrons: No influence, results stay the same
So, what to do?.....
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 7
Control the energy deposited along the step
Modification of the « GateSteppingAction.cc » class:
GEANT4: By default, energy is deposited at the end of the step: "Post-step point"
-Random distribution of energy deposited along the step -Continue energy loss along the trajectory - Enable to fit well the dose deposited inside a volume
Energy deposited
Energy deposited
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 8
Results: 100 keV
100 keV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 9
Results: 3 MeV
3 MeV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 10
Comparisons GATE versus other MC codes
50 keV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 11
Comparisons GATE versus other MC codes
100 keV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 12
Comparisons GATE versus other MC codes
1 MeV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 13
Comparisons GATE versus other MC codes
2 MeV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 14
Comparisons GATE versus other MC codes
3 MeV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 15
Comparisons GATE versus other MC codes
4 MeV, standard
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Plateforme de Calcul pour les Sciences du Vivant
Lydia Maigne GATE/G4 meeting collaboration - 12/09/07 - Hebden Bridge 16
Conclusions
- Random deposition of the energy along the step is the the most important parameter to change in the simulation to obtain reliable results
- Comparisons show:- Deviation less than 1% between GATE and Berger results for
50, 100 keV and 1 MeV- Deviation less than 0.5% with other Monte Carlo
- GATE and G4 are now trusted and well validated for dose deposited by electrons especially for very high dose gradient on short distances.