The GEANT4 simulation toolkit_ and how easy would it be to use it by suchenfz


									The GEANT4 simulation toolkit, and how
 it could be used for SPECT and PET

               Giovanni Santin
      INFN, Trieste & CERN, Geneva
           on behalf of the Geant4 Collaboration

        MonteCarlo Simulations in Nuclear Medicine
                 16 - 17 july 2001 - Paris

Geant4 for PET & SPECT

                                              • Introduction to GEANT4

                                              • Medical applications: DNA, brachytherapy, ...
MC in Nuclear Medicine - Paris 16 July 2001

                                              • PET & SPECT: some ideas and conclusions

Geant4 for PET & SPECT

                                                       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.
MC in Nuclear Medicine - Paris 16 July 2001

                                                   –   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
                                                                       IHEP Protvino
                                                                       MEPHI Moscow                                       3
                                                                       Pittsburg University

                                                                    The role of Geant
Geant4 for PET & SPECT

                                              • 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
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                                                 – 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


                                                   Features relevant for medical applications
Geant4 for PET & SPECT

                                                             The transparency
                                                                                              Advanced functionalities
                                                                 of physics
                                                                                        in geometry, physics, visualisation etc.

                                                 Extensibility to
                                                                                                          Quality Assurance
                                                 satisfy new user
                                                                                                           based on sound
                                               requirements thanks
                                                                                                         software engineering
                                              to the OO technology
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                                                                                                            Use of evaluated
                                              Subject to independent
                                                                                                             data libraries
                                               validation by a large
                                                 user community
                                                    worldwide                                          User support
                                                                                                  organization by a large
                                                  Adopts standards wherever available                   international
                                                  (de jure or de facto)                           Collaboration of experts


                                                            A look at the past
Geant4 for PET & SPECT

                                              Physics simulation was handled through
                                              – monolithic: either take all of a package or
MC in Nuclear Medicine - Paris 16 July 2001

                                              – difficult to understand the physics approach
                                              – hard to disentangle the data, their use and
                                                the physics modeling


                                                    Transparency of Geant4 physics
                                              • No “hard coded” numbers
Geant4 for PET & SPECT

                                              • 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
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                                              • Cuts in range (rather than in energy, as usual)
                                                   – consistent treatment of interactions near boundaries between
                                              • Modular design, at a fine granularity, to expose the physics
                                                   – physics independent from tracking
                                              • Public distribution of the code, from one reference repository
                                              •   The transparency of the physics implementation contributes to the
                                                  validation of experimental physics results                          7

                                               Physics processes relevant for medical applications
                                                     • Low Energy extensions of electromagnetic interactions
Geant4 for PET & SPECT

                                                         –   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
MC in Nuclear Medicine - Paris 16 July 2001

                                                               • Multiple scattering
                                                                    – new improved model, taking into account also lateral
                                              • Hadronic interactions
                                                 – ample variety of complementary and alternative models
                                                             • Neutrons
                                                                 – exploiting all the evaluated n data libraries worldwide   8

                                                            Low Energy Electromagnetic Physics
Geant4 for PET & SPECT

                                                                                • down to 250 eV for electrons and g
                                              Geant4                                • based on the LLNL data libraries
                                                                                    • shell effects
                                              Low Energy
                                                                                • down to ~ 100 eV in the near future
                                              Electromagnetic                       • based on Penelope Electron Photon
                                              package extends the                   Transport
MC in Nuclear Medicine - Paris 16 July 2001

                                              of physics interactions

                                              Needed for space and             down to ~ 1 keV for hadrons and ions
                                              medical applications,
                                              n physics, antimatter                • Bethe-Bloch above 2 MeV
                                              searches                             • Ziegler and ICRU parameterisations
                                                                                       (with material dependence)
                                                                                   • free electron gas model
                                                                                   • quantal harmonic oscillator model
                                                                                   • charge dependence (Barkas effect)


                                                                                                Low Energy Electromagnetic Physics

                                                                                                                                               Protons, Ziegler
Geant4 for PET & SPECT

                                                                              Shell effects
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                                                                                                               Geant4 LowEn
                                                                        10                                     NIST

                                                                                                                              Ion ionisation
                                               / (cm 2 /g) in water



                                                                              0.01        0.1              1        10
                                                                                     Photon Energy (MeV)

                                                    Photon attenuation coefficient                                             Barkas effect
                                                               in water                                                                                           10
                                                            Other features relevant for medical

                                              • Powerful tools relevant for complex geometries (CT)
Geant4 for PET & SPECT

                                                  –   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
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                                              • 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

                                                               Code, Examples and Documentation

                                              •   Code
Geant4 for PET & SPECT

                                                  – ~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
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                                                  – Software & physics reference manuals
                                              •   Examples
                                                  – distributed with the code
                                                  – navigation between documentation and examples code
                                                  – simple detectors
                                                  – different experiment types
                                                  – demonstrate essential capabilities


                                                                               Quality Assurance
Geant4 for PET & SPECT

                                                                                           •   Testing
                                              • Extensive use of Quality                        – Unit testing
                                                Assurance systems                                   • in most cases down to class
                                                  – fundamental for a toolkit of                      level granularity
                                                    wide public use                             – Integration testing
                                                                                                    • sets of logically connected
                                              •   Commercial tools                                    classes
                                                  – Insure++, Logiscope etc.                    – Test-bench for each
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                                                  C++ coding guidelines
                                                                                                    • eg.: test-suite of 375 tests
                                                  – scripts to verify their applications              for hadronic physics
                                                    automatically                                     parameterised models
                                              •   Code inspections                              – System testing
                                                  – within working groups and across                • exercising all Geant4
                                                    groups                                            functionalities in realistic
                                                                                                – Physics testing
                                                                                                    • comparisons with
                                                                                                      experimental data
                                                                                                – Performance Benchmarks

                                                          Role: detailed detector description and efficient navigation
Geant4 for PET & SPECT

                                              Multiple representations
                                              •   CGS (Constructed Solid Geometries)      • CAD exchange
                                                   – simple solids                            – interface through ISO STEP
                                              •   STEP extensions                               (Standard for the Exchange
                                                   – polyhedra, spheres, cylinders,             of Product Model Data)
                                                       cones, toroids, etc.               • Fields
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                                              •   BREPS (Boundary REPresented
                                                                                              – of variable non-uniformity
                                                                                                and differentiability
                                                   – volumes defined by boundary
                                                       surfaces                               – use of various integrators,
                                                   – include solids defined by NURBS            beyond Runge-Kutta
                                                       (Non-Uniform Rational B-Splines)       – time of flight correction
                                              •   External tool for g3tog4 geometry             along particle transport


                                              Things one can do with Geant4 geometry
Geant4 for PET & SPECT

                                                             One can do
                                                           operations with
                                                          These figures were
                                                            visualised with
                                                          Geant4 Ray Tracing
MC in Nuclear Medicine - Paris 16 July 2001

                                                           ...and one can
                                                         describe complex
                                                       geometries, like Atlas
                                                         silicon detectors


                                                                            Geant4 geometry examples
                                                  GLAST (NASA)
Geant4 for PET & SPECT

                                                                                                      Chandra (NASA)
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                                                                               ATLAS at   LHC, CERN

                                                                                                                       CMS (LHC, CERN)

                                              Borexino at Gran Sasso Lab.


                                                       Visualization and UI

                                              • Visualisation
Geant4 for PET & SPECT

                                                   – Various drivers
                                                   – OpenGL, OpenInventor, X11,
                                                     Postscript, DAWN, OPACS,

                                              • User Interfaces
                                                   – Command-line, Tcl/Tk,
MC in Nuclear Medicine - Paris 16 July 2001

                                                     Tcl/Java, batch+macros,
                                                     OPACS, GAG, MOMO
                                              •   Also choice of User Interfaces:
                                                   – Terminal (text) or
                                                   – GUI: Momo (G4), OPACS, Xmotif


                                                                          User support
Geant4 for PET & SPECT

                                              •   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
MC in Nuclear Medicine - Paris 16 July 2001

                                                   –   automatic tools for bug notifications
                                                   –   consultancy, requests of enhancements and new developments etc.
                                                   –   priority given to member parties

                                                                       - DNA

                                              Multi-disciplinary Collaboration of
Geant4 for PET & SPECT

                                                   astrophysicists and space scientists
                                                   particle physicists
                                                                                             a, C, Fe, ...
                                                   medical physicists
                                                   biologists
                                                   physicians
MC in Nuclear Medicine - Paris 16 July 2001

                                                    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”
                                                 Geant4             • capability to handle biochemical processes           19

                                              Radioactive sources are used to deposit
                                              therapeutic doses near tumors while
Geant4 for PET & SPECT

                                              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                                       Naso-pharynx endocavitary treatment
                                                           Computation of other model-dependent parameters, e.g. anisotropy
                                                           Accurate computation of dose deposition in high gradient regions (i.
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                                                          e. near sources)

                                                • Verification of experimental calibrations
                                                                                                  5.0 mm

                                                                                                                                                        Geant4 allows a
                                                                                Active Ir-192 Core                                        1.1 mm       complete flexible
                                                                                                                                    0.6 mm
                                                                                <E> = 356 keV                                                          description of the
                                                                                                                                                            real geometry
                                                                                                     3.5 mm
                                                   3 mm steel cable
                                                        Courtesy of National Inst. For Cancer Research, Genova, Italy
G.Santin                                                                     90
                                                            120                             60
                                                                                                                  • source geometry
                                                    150                                                 30
                                                                                                                  • auto-absorption
Geant4 for PET & SPECT

                                                                                                                  • encapsulation
                                              180                                                             0   • shielding effects
                                              Courtesy of National Inst. For Cancer Research, Genova, Italy

                                                                         Isodose curves
                                                                   The simulated source is
MC in Nuclear Medicine - Paris 16 July 2001

                                                                   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

                                              Geant4 Radioactive Decay Module
                                              is capable of handling the generation of the whole radioactive chain of
                                              the 192Ir source                                                                                                                 21

                                                           Dosimetric Studies
Geant4 for PET & SPECT

                                                                         Pixel Ionisation
                                                                         Relative dose with 6 MV
                                                                             photons beam
MC in Nuclear Medicine - Paris 16 July 2001

                                              experimental data
                                                                  Deposited energy vs

                                                                  Depth in water                   22

                                                           Bragg Peak of Protons in Water
Geant4 for PET & SPECT

                                                                                              Magic Cube
                                                                                            Relative dose with
                                                                                         270 MeV protons beam in
                                                                                         Courtesy of INFN & ASP, Torino, Italy
MC in Nuclear Medicine - Paris 16 July 2001

                                                                                   • Sandwich of 12 parallel plate (25x25)
                                                                                   cm2 ionization chambers
                                                                                   • Each chamber:
                                                                                         • passive material (N2,G10,Mylar)
                                                                                         • anode (0.035 mm Cu)
                                                       and experimental data             • active material (3 mm N2)
                                                                                        • passive material
                                                                                        • air gap (2 cm, tissue equivalent
                                                                                         of adjustable thickness)
                                              Deposited energy vs Depth in water   • Thickness of a chamber as water
                                                                                   equivalent ~1.1 mm

                                                  Geant4 for scatter compensation in Megavoltage 3D CT
                                              •   Use GEANT4 to obtain
                                                  digitally reconstructed
Geant4 for PET & SPECT

                                                  radiographs (DRRs),
                                                  including full scatter
                                                  This represents a great
                                                  improvement over
                                                  approaches based on ray-
MC in Nuclear Medicine - Paris 16 July 2001

                                              •   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
                                                    –    LINAC head simulation
                                                    –    Scatter analysis in total body irradiation

                                                                               Work in progress
Geant4 for PET & SPECT

                                                                                                           CT image interface
                                              In vivo TLD dosimetry
                                                                                                                 Interface between Geant4 and
                                              • Simulation of the energy                                         DICOM3 CT scan images
                                                deposition of low energy                                         format in order to perform in
                                                photons in TLD LiF100                                            tissue simulation
MC in Nuclear Medicine - Paris 16 July 2001

                                              • Used to calculate dose to
                                                patient in radiodiagnostic
                                                                                                                                               CT slice of a head
                                                examinations:                                                                                  with the dose
                                                    mammography                                                                               deposition of a proton
                                                                                                                                               beam obtained with
                                                    virtual colonscopy                                                                        the GEANT code

                                                                                                                                               Medical Dept., University of
                                                                                                                                               Piemonte Orientale and INFN

                                                              Courtesy of IST, Genova and IRCC Institute for Cancer Research and Treatment, Italy

                                                           PET & SPECT simulations with Geant4.
                                                                       Why not?
Geant4 for PET & SPECT

                                              • 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
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                                                   – 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


                                              •   Geant4 is a simulation Toolkit, providing advanced tools for all the domains of
                                                  detector simulation
Geant4 for PET & SPECT

                                              •   Geant4 is characterized by a rigorous approach to software
                                              •   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
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                                                   – 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
                                              •   Geometry description: powerful, accurate and rich
                                              •   Wide and growing medical user community
                                              •   User Support granted by the Geant4 Collaboration
                                              •   G4 URL:

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