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The G EANT 4 simulation toolkit, and how it could be used for SPECT and PET simulations

The G EANT 4 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. Summary.

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The G EANT 4 simulation toolkit, and how it could be used for SPECT and PET simulations

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  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. Summary • Introduction to GEANT4 • Medical applications: DNA, brachytherapy, ... • PET & SPECT: some ideas and conclusions MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University

  4. The roleof 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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  5. Features relevant for medical applications The transparency of physics Advanced functionalities in geometry, physics, visualisation etc. Extensibility to satisfy new user requirements thanks to the OO technology Quality Assurance based on sound software engineering MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin Use of evaluated data libraries Subject to independent validation by a large user community worldwide User support organization by a large international Collaboration of experts Adopts standardswherever available (de jure or de facto)

  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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  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 thevalidation of experimental physics results MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  8. Physics processes relevant for medical applications • 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 • Hadronic interactions • ample variety of complementary and alternative models • Radioactive Decay Module • simulation of radioactive sources, including all the secondary emissions MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin • Multiple scattering • new improved model, taking into account also lateral displacement • Neutrons • exploiting all the evaluated n data libraries worldwide

  9. Low Energy Electromagnetic Physics http://www.ge.infn.it/geant4/lowE/ • down to 250 eV for electrons andg • based on the LLNL data libraries • shell effects • down to ~ 100 eV in the near future • based onPenelopeElectron Photon Transport Geant4 Low Energy Electromagnetic package extends the coverage of physics interactions Needed for space and medical applications, n physics, antimatter searches MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin • down to ~ 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)

  10. Low Energy Electromagnetic Physics Protons, Ziegler Shell effects MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin Ion ionisation Barkas effect Photon attenuation coefficient in water

  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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  13. 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 Quality Assurance MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  14. 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 Geometry Role: detailed detector description and efficient navigation MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  15. Things one can do with Geant4 geometry One can do operations with solids These figures were visualised with Geant4 Ray Tracing tool MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin ...and one can describe complex geometries, like Atlas silicon detectors

  16. GLAST (NASA) ATLAS at LHC, CERN Geant4 geometry examples MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin Chandra (NASA) CMS (LHC, CERN) Borexino at Gran Sasso Lab.

  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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  19. - DNA Multi-disciplinary Collaboration of • astrophysicists and space scientists • particle physicists • medical physicists • biologists • physicians a, C, Fe, ... MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin http://www.ge.infn.it/geant4/dna/ 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, ...) • capability to model DNA as a “geometry” • capability to handle biochemicalprocesses Geant4

  20. 5.0 mm Active Ir-192 Core <E> = 356 keV 1.1 mm 0.6 mm 3.5 mm 3 mm steel cable Brachytherapy Radioactive sources are used to deposit therapeutic doses near tumors while preserving surrounding healthy tissues • 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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin Geant4 allows a complete flexible description of the real geometry Courtesy of National Inst. For Cancer Research, Genova, Italy

  21. Anisotropy • source geometry • auto-absorption • encapsulation • shielding effects Courtesy of National Inst. For Cancer Research, Genova, Italy Isodose curves MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin 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 Geant4Radioactive Decay Module is capable of handling the generation of the whole radioactive chain of the 192Ir source

  22. Dosimetric Studies Pixel Ionisation Chamber Relative dose with 6 MV photons beam MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin G4 vs experimental data Deposited energy vs Depth in water

  23. Bragg Peak of Protons in Water Magic Cube Relative dose with 270 MeV protons beam in water Courtesy of INFN & ASP, Torino, Italy MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin • 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 and experimental data Deposited energy vs Depth in water

  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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  25. 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 Work in progress MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin 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 Courtesy of IST, Genova and IRCC Institute for Cancer Research and Treatment, Italy

  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 tracerdescribed by the Radioactive Decay Module • Simulation of patient motion with geometry modification inside the same run MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

  27. Summary • Geant4 is a simulation Toolkit, providing advanced tools for all the domains of detector simulation • Geant4 is characterized by a rigorous approach to softwareengineering • Its areas of application span diverse fields: HEP and nuclearphysics, 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 MC in Nuclear Medicine - Paris 16 July 2001 Geant4 for PET & SPECT G.Santin

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