The GEANT4 simulation toolkit, and how
it could be used for SPECT and PET
simulations
Giovanni Santin
INFN, Trieste & CERN...
MCinNuclearMedicine-Paris16July2001
2
Summary
• Introduction to GEANT4
• Medical applications: DNA, brachytherapy, ...
• P...
MCinNuclearMedicine-Paris16July2001
3
The Geant4 Collaboration
• An international Collaboration of ~100 scientists from >4...
MCinNuclearMedicine-Paris16July2001
4
The role of Geant
• Geant is a simulation tool, that provides a general
infrastructu...
MCinNuclearMedicine-Paris16July2001
5
The transparency
of physics
Advanced functionalities
in geometry, physics, visualisa...
MCinNuclearMedicine-Paris16July2001
6
A look at the past
Physics simulation was handled through
“packages”
– monolithic: e...
MCinNuclearMedicine-Paris16July2001
7
Transparency of Geant4 physics
• No “hard coded” numbers
• Explicit use of units thr...
MCinNuclearMedicine-Paris16July2001
8
Physics processes relevant for medical applications
• Hadronic interactions
– ample ...
MCinNuclearMedicine-Paris16July2001
9
Low Energy Electromagnetic Physics
Geant4
Low Energy
Electromagnetic
package extends...
MCinNuclearMedicine-Paris16July2001
10
Low Energy Electromagnetic Physics
0.01 0.1 1 10
0.1
1
10
Geant4 LowEn
NIST
µ/ρ(cm2...
MCinNuclearMedicine-Paris16July2001
11
Other features relevant for medical
applications
• Powerful tools relevant for comp...
MCinNuclearMedicine-Paris16July2001
12
Code, Examples and Documentation
• Code
– ~1M lines of code, ~2000 classes
(continu...
MCinNuclearMedicine-Paris16July2001
13
Quality Assurance
• Extensive use of Quality
Assurance systems
– fundamental for a ...
MCinNuclearMedicine-Paris16July2001
14
Geometry
Multiple representations
• CGS (Constructed Solid Geometries)
– simple sol...
MCinNuclearMedicine-Paris16July2001
15
Things one can do with Geant4 geometry
One can do
operations with
solids
These figu...
MCinNuclearMedicine-Paris16July2001
16
Geant4 geometry examples
Borexino at Gran Sasso Lab.
Chandra (NASA)
CMS (LHC, CERN)...
MCinNuclearMedicine-Paris16July2001
17
Visualization and UI
• Visualisation
– Various drivers
– OpenGL, OpenInventor, X11,...
MCinNuclearMedicine-Paris16July2001
18
User support
• Wide international user community, in a variety of fields of applica...
MCinNuclearMedicine-Paris16July2001
19
- DNA
Multi-disciplinary Collaboration of
astrophysicists and space scientists
part...
MCinNuclearMedicine-Paris16July2001
20
Geant4 allows a
complete flexible
description of the
real geometry
Brachytherapy
Ra...
MCinNuclearMedicine-Paris16July2001
21
0
30
60
90
120
150
180
• source geometry
• auto-absorption
• encapsulation
• shield...
MCinNuclearMedicine-Paris16July2001
22
Pixel Ionisation
Chamber
Relative dose with 6 MV
photons beam
Dosimetric Studies
G4...
MCinNuclearMedicine-Paris16July2001
23
Bragg Peak of Protons in Water
Magic Cube
Relative dose with
270 MeV protons beam i...
MCinNuclearMedicine-Paris16July2001
24
Geant4 for scatter compensation in Megavoltage 3D CT
• Use GEANT4 to obtain
digital...
MCinNuclearMedicine-Paris16July2001
25
Work in progress
In vivo TLD dosimetry
• Simulation of the energy
deposition of low...
MCinNuclearMedicine-Paris16July2001
26
PET & SPECT simulations with Geant4.
Why not?
• Detailed description of both
– huma...
MCinNuclearMedicine-Paris16July2001
27
• Geant4 is a simulation Toolkit, providing advanced tools for all the domains of
d...
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  • The GEANT4 simulation toolkit, and how easy would it be to use it ...

    1. 1. The GEANT4 simulation toolkit, and how it could be used for SPECT and PET simulations Giovanni Santin INFN, Trieste & CERN, Geneva giovanni.santin@ts.infn.it on behalf of the Geant4 Collaboration MonteCarlo Simulations in Nuclear Medicine 16 - 17 july 2001 - Paris
    2. 2. MCinNuclearMedicine-Paris16July2001 2 Summary • Introduction to GEANT4 • Medical applications: DNA, brachytherapy, ... • PET & SPECT: some ideas and conclusions
    3. 3. MCinNuclearMedicine-Paris16July2001 3 The Geant4 Collaboration • An international Collaboration of ~100 scientists from >40 institutes – wide expertise in a variety of physics and software domains • Manages Geant4 distribution, development and User Support – CERN, KEK, SLAC, TRIUMF, JNL (Common) – ESA, INFN +TERA, Lebedev, IN2P3, Frankfurt Univ. – Atlas, BaBar, CMS, LHCB – COMMON (Serpukov, Novosibirsk, US universities etc.) – possible new memberships under discussion • Based on a Memorandum of Understanding among the parties Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University
    4. 4. MCinNuclearMedicine-Paris16July2001 4 The role of Geant • Geant is a simulation tool, that provides a general infrastructure for – the description of geometry and materials – particle transport and interaction with matter – the description of detector response – visualisation of geometries, tracks and hits • The user develops the specific code for – the primary event generator – the geometrical description of the set-up – the digitisation of the detector response
    5. 5. MCinNuclearMedicine-Paris16July2001 5 The transparency of physics Advanced functionalities in geometry, physics, visualisation etc. Extensibility to satisfy new user requirements thanks to the OO technology Adopts standards wherever available (de jure or de facto) Use of evaluated data libraries Quality Assurance based on sound software engineering Subject to independent validation by a large user community worldwide User support organization by a large international Collaboration of experts Features relevant for medical applicationsFeatures relevant for medical applications
    6. 6. MCinNuclearMedicine-Paris16July2001 6 A look at the past Physics simulation was handled through “packages” – monolithic: either take all of a package or nothing – difficult to understand the physics approach – hard to disentangle the data, their use and the physics modeling
    7. 7. MCinNuclearMedicine-Paris16July2001 7 Transparency of Geant4 physics • No “hard coded” numbers • Explicit use of units throughout the code • Separation between the calculation of cross sections and the generation of the final state • Calculation of cross-sections independent from the way they are accessed (data files, analytical formulae etc.) • Distinction between processes and models • Cuts in range (rather than in energy, as usual) – consistent treatment of interactions near boundaries between materials • Modular design, at a fine granularity, to expose the physics – physics independent from tracking • Public distribution of the code, from one reference repository worldwide • The transparency of the physics implementation contributes to the validation of experimental physics results
    8. 8. MCinNuclearMedicine-Paris16July2001 8 Physics processes relevant for medical applications • Hadronic interactions – ample variety of complementary and alternative models • Multiple scattering – new improved model, taking into account also lateral displacement • Low Energy extensions of electromagnetic interactions – 250 eV electrons, photons – ~ 1 keV positive hadrons, ions – ICRU-compliant and ICRU-consistent – Barkas effect taken into account for antiprotons, negative ions – further extensions and refinements in progress • Radioactive Decay Module – simulation of radioactive sources, including all the secondary emissions • Neutrons – exploiting all the evaluated n data libraries worldwide
    9. 9. MCinNuclearMedicine-Paris16July2001 9 Low Energy Electromagnetic Physics Geant4 Low Energy Electromagnetic package extends the coverage of physics interactions Needed for space and medical applications, ν physics, antimatter searches • down to 250 eV250 eV for electrons and γ • based on the LLNL data libraries • shell effects • down to ~~ 100 eV in the near future • based on Penelope Electron Photon Transport down to ~ 1 keV~ 1 keV for hadrons and ions • Bethe-Bloch above 2 MeV • Ziegler and ICRU parameterisations (with material dependence) • free electron gas model • quantal harmonic oscillator model • charge dependence (Barkas effect) http://www.ge.infn.it/geant4/lowE/
    10. 10. MCinNuclearMedicine-Paris16July2001 10 Low Energy Electromagnetic Physics 0.01 0.1 1 10 0.1 1 10 Geant4 LowEn NIST µ/ρ(cm2/g)inwater Photon Energy (MeV) Photon attenuation coefficient in water Ion ionisation Shell effects Barkas effect Protons, Ziegler
    11. 11. MCinNuclearMedicine-Paris16July2001 11 Other features relevant for medical applications • Powerful tools relevant for complex geometries (CT) – CAD tool front-end – fast algorithms for volume navigation performance – volumes can be parameterised by material • Fast and full simulation in the same environment – detailed handling of physics processes or – possibility of parameterisations for faster processing • Visualisation tools – wide variety functionalities available for all the most common drivers • UI and GUI – user-friendly environement – can be easily tailored according to the user’s needs – GGE and GPE for automatic code generation Ample documentation available from the web
    12. 12. MCinNuclearMedicine-Paris16July2001 12 Code, Examples and Documentation • Code – ~1M lines of code, ~2000 classes (continuously growing) – publicly available from the web • Documentation – 6 manuals – Getting started & installation guide – User guide for application & toolkit developer – Software & physics reference manuals • Examples – distributed with the code – navigation between documentation and examples code – simple detectors – different experiment types – demonstrate essential capabilities
    13. 13. MCinNuclearMedicine-Paris16July2001 13 Quality Assurance • Extensive use of Quality Assurance systems – fundamental for a toolkit of wide public use • Commercial tools – Insure++, Logiscope etc. • C++ coding guidelines – scripts to verify their applications automatically • Code inspections – within working groups and across groups • Testing – Unit testing • in most cases down to class level granularity – Integration testing • sets of logically connected classes – Test-bench for each category • eg.: test-suite of 375 tests for hadronic physics parameterised models – System testing • exercising all Geant4 functionalities in realistic set-ups – Physics testing • comparisons with experimental data – Performance Benchmarks
    14. 14. MCinNuclearMedicine-Paris16July2001 14 Geometry Multiple representations • CGS (Constructed Solid Geometries) – simple solids • STEP extensions – polyhedra, spheres, cylinders, cones, toroids, etc. • BREPS (Boundary REPresented Solids) – volumes defined by boundary surfaces – include solids defined by NURBS (Non-Uniform Rational B-Splines) • External tool for g3tog4 geometry conversion • CAD exchange – interface through ISO STEP (Standard for the Exchange of Product Model Data) • Fields – of variable non-uniformity and differentiability – use of various integrators, beyond Runge-Kutta – time of flight correction along particle transport Role: detailed detector description and efficient navigation
    15. 15. MCinNuclearMedicine-Paris16July2001 15 Things one can do with Geant4 geometry One can do operations with solids These figures were visualised with Geant4 Ray Tracing tool ...and one can describe complex geometries, like Atlas silicon detectors
    16. 16. MCinNuclearMedicine-Paris16July2001 16 Geant4 geometry examples Borexino at Gran Sasso Lab. Chandra (NASA) CMS (LHC, CERN) GLAST (NASA) ATLAS at LHC, CERN
    17. 17. MCinNuclearMedicine-Paris16July2001 17 Visualization and UI • Visualisation – Various drivers – OpenGL, OpenInventor, X11, Postscript, DAWN, OPACS, VRML • User Interfaces – Command-line, Tcl/Tk, Tcl/Java, batch+macros, OPACS, GAG, MOMO • Also choice of User Interfaces: – Terminal (text) or – GUI: Momo (G4), OPACS, Xmotif
    18. 18. MCinNuclearMedicine-Paris16July2001 18 User support • Wide international user community, in a variety of fields of application – HEP and nuclear physics, astrophysics, space sciences, shielding and radioprotection, medical physics, theoretical physics, fine arts etc. • Effective model of user support – granular organisation – provided by a wide network of experts, each one in its domain of expertise – automatic tools for bug notifications – consultancy, requests of enhancements and new developments etc. – priority given to member parties
    19. 19. MCinNuclearMedicine-Paris16July2001 19 - DNA Multi-disciplinary Collaboration of astrophysicists and space scientists particle physicists medical physicists biologists physicians Study of radiation damage at the cellular and DNA level in the space radiation environment (and other applications, not only in the space domain: radiotherapy, radiobiology, ...) http://www.ge.infn.it/geant4/dna/ • capability to model DNA as a “geometry” • capability to handle biochemical processesGeant4 α, C, Fe, ...
    20. 20. MCinNuclearMedicine-Paris16July2001 20 Geant4 allows a complete flexible description of the real geometry Brachytherapy Radioactive sources are used to deposit therapeutic doses near tumors while preserving surrounding healthy tissues 3 mm steel cable 5.0 mm 0.6 mm 3.5 mm 1.1 mmActive Ir-192 Core <E> = 356 keV Courtesy of National Inst. For Cancer Research, Genova, Italy Montecarlo topics: • Dose calculation • Computation of dose deposition kernels for treatment planning dose calculation algorithms based on convolution/superposition methods • Separation of primary, first scatter and multiple scatter components for complex dose deposition models Computation of other model-dependent parameters, e.g. anisotropy function Accurate computation of dose deposition in high gradient regions (i. e. near sources) • Verification of experimental calibrations Naso-pharynx endocavitary treatment
    21. 21. MCinNuclearMedicine-Paris16July2001 21 0 30 60 90 120 150 180 • source geometry • auto-absorption • encapsulation • shielding effects Anisotropy Geant4 Radioactive Decay Module is capable of handling the generation of the whole radioactive chain of the 192 Ir source Isodose curves The simulated source is placed in a 30 cm water box 10.000.000 photons, 1 mm3 voxels 12 h CPU time on Intel Pentium 300 MHz Courtesy of National Inst. For Cancer Research, Genova, Italy Courtesy of National Inst. For Cancer Research
    22. 22. MCinNuclearMedicine-Paris16July2001 22 Pixel Ionisation Chamber Relative dose with 6 MV photons beam Dosimetric Studies G4 vs experimental data Deposited energy vs Depth in water
    23. 23. MCinNuclearMedicine-Paris16July2001 23 Bragg Peak of Protons in Water Magic Cube Relative dose with 270 MeV protons beam in water Deposited energy vs Depth in water Courtesy of INFN & ASP, Torino, Italy and experimental data • Sandwich of 12 parallel plate (25x25) cm2 ionization chambers • Each chamber: • passive material (N2,G10,Mylar) • anode (0.035 mm Cu) • active material (3 mm N2) • passive material • air gap (2 cm, tissue equivalent of adjustable thickness) • Thickness of a chamber as water equivalent ~1.1 mm
    24. 24. MCinNuclearMedicine-Paris16July2001 24 Geant4 for scatter compensation in Megavoltage 3D CT • Use GEANT4 to obtain digitally reconstructed radiographs (DRRs), including full scatter simulation This represents a great improvement over approaches based on ray- casting. • The study of DRRs synthesized by Geant4 allows users to produce a model for scatter compensation of megavoltage radiographs • This will help to produce a more accurate megavoltage 3D CT reconstruction and therefore a more reliable tool for patient positioning and treatment verification • Activity in progress at the Italian National Institute for Cancer Research, Genova • Other possible areas of application of Geant4: – LINAC head simulation – Scatter analysis in total body irradiation
    25. 25. MCinNuclearMedicine-Paris16July2001 25 Work in progress In vivo TLD dosimetry • Simulation of the energy deposition of low energy photons in TLD LiF100 nanodosimeters • Used to calculate dose to patient in radiodiagnostic examinations: • mammography • virtual colonscopy CT image interface Interface between Geant4 and DICOM3 CT scan images format in order to perform in tissue simulation Courtesy of IST, Genova and IRCC Institute for Cancer Research and Treatment, Italy CT slice of a head with the dose deposition of a proton beam obtained with the GEANT code Medical Dept., University of Piemonte Orientale and INFN Torino
    26. 26. MCinNuclearMedicine-Paris16July2001 26 PET & SPECT simulations with Geant4. Why not? • Detailed description of both – human tissues and properties – detector geometry and response (non-linear resolution function of the PET scanner, etc.) • Energy range of Physics processes involved – covered by the G4 standard or – LowEnergy extension of EM processes • Past experience in the medical physics community shows reliability and innovation in G4 simulations • Injected radioactive tracer described by the Radioactive Decay Module • Simulation of patient motion with geometry modification inside the same run
    27. 27. MCinNuclearMedicine-Paris16July2001 27 • Geant4 is a simulation Toolkit, providing advanced tools for all the domains of detector simulation • Geant4 is characterized by a rigorous approach to software engineering • Its areas of application span diverse fields: HEP and nuclear physics, astrophysics and space sciences, medical physics, radiation studies etc. • Geant4 is open to extension and evolution Geant4 physics keeps evolving – with attention to User Requirements – facilitated by the OO approach • An abundant set of physics processes is available, often with a variety of complementary and alternative physics models. Continuos physics validation test. • Geometry description: powerful, accurate and rich • Wide and growing medical user community • User Support granted by the Geant4 Collaboration • G4 URL: http://wwwinfo.cern.ch/asd/geant/geant4.html Summary

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