G Santin Geant 4 for PET SPECT MC

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 The GEANT 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 Geant 4 Collaboration Monte. Carlo Simulations in Nuclear Medicine 16 - 17 july 2001 - Paris

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 Summary • Introduction to GEANT 4 • Medical applications: DNA, brachytherapy, . . . • PET & SPECT: some ideas and conclusions 2

G. Santin Geant 4 for PET & SPECT The Geant 4 Collaboration • An international Collaboration of ~100 scientists from >40 institutes – wide expertise in a variety of physics and software domains • Manages Geant 4 distribution, development and User Support MC in Nuclear Medicine - Paris 16 July 2001 – CERN, KEK, SLAC, TRIUMF, JNL (Common) – ESA, INFN +TERA, Lebedev, IN 2 P 3, Frankfurt Univ. – Atlas, Ba. Bar, 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 3

G. Santin Geant 4 for PET & SPECT The role of Geant • Geant is a simulation tool, that provides a general infrastructure for – the description of geometry and materials MC in Nuclear Medicine - Paris 16 July 2001 – 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 4

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 Features relevant for medical applications The transparency of physics Extensibility to satisfy new user requirements thanks to the OO technology Subject to independent validation by a large user community worldwide Adopts standards wherever available (de jure or de facto) Advanced functionalities in geometry, physics, visualisation etc. Quality Assurance based on sound software engineering Use of evaluated data libraries User support organization by a large international Collaboration of experts 5

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 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 6

G. Santin Geant 4 for PET & SPECT Transparency of Geant 4 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. ) MC in Nuclear Medicine - Paris 16 July 2001 • 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 7

G. Santin Physics processes relevant for medical applications Geant 4 for PET & SPECT • Low Energy extensions of electromagnetic interactions – – – 250 e. V electrons, photons ~ 1 ke. V positive hadrons, ions ICRU-compliant and ICRU-consistent Barkas effect taken into account for antiprotons, negative ions further extensions and refinements in progress MC in Nuclear Medicine - Paris 16 July 2001 • Radioactive Decay Module – simulation of radioactive sources, including all the secondary emissions • Multiple scattering – new improved model, taking into account also lateral displacement • Hadronic interactions – ample variety of complementary and alternative models • Neutrons – exploiting all the evaluated n data libraries worldwide 8

G. Santin Low Energy Electromagnetic Physics MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT http: //www. ge. infn. it/geant 4/low. E/ • down to 250 e. V for electrons and g Geant 4 • based on the LLNL data libraries • shell effects Low Energy Electromagnetic package extends the coverage of physics interactions Needed for space and medical applications, physics, antimatter searches n • down to ~ 100 e. V in the near future • based on Penelope Electron Photon Transport down to ~ 1 ke. V for hadrons and ions • Bethe-Bloch above 2 Me. V • Ziegler and ICRU parameterisations (with material dependence) • free electron gas model • quantal harmonic oscillator model • charge dependence (Barkas effect) 9

Protons, Ziegler Geant 4 for PET & SPECT G. Santin Low Energy Electromagnetic Physics MC in Nuclear Medicine - Paris 16 July 2001 Shell effects Ion ionisation Photon attenuation coefficient in water Barkas effect 10

MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT G. Santin 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 11

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 Code, Examples and Documentation • Code – ~1 M 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 12

G. Santin Geant 4 for PET & SPECT Quality Assurance • Extensive use of Quality Assurance systems – fundamental for a toolkit of wide public use • Commercial tools MC in Nuclear Medicine - Paris 16 July 2001 – 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 Geant 4 functionalities in realistic set -ups – Physics testing • comparisons with experimental data – Performance Benchmarks 13

G. Santin Geometry MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT Role: detailed detector description and efficient navigation 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 g 3 tog 4 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 14

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 Things one can do with Geant 4 geometry One can do operations with solids These figures were visualised with Geant 4 Ray Tracing tool . . . and one can describe complex geometries, like Atlas silicon detectors 15

G. Santin MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT GLAST (NASA) Geant 4 geometry examples Chandra (NASA) ATLAS at LHC, CERN CMS (LHC, CERN) Borexino at Gran Sasso Lab. 16

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 Visualization and UI • Visualisation – Various drivers – Open. GL, Open. Inventor, X 11, 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 (G 4), OPACS, Xmotif 17

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 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 18

MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT G. Santin - DNA Multi-disciplinary Collaboration of Ô Ô Ô astrophysicists and space scientists particle physicists medical physicists biologists physicians a, C, Fe, . . . http: //www. ge. infn. it/geant 4/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, . . . ) Geant 4 • capability to model DNA as a “geometry” • capability to handle biochemical processes 19

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 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) Naso-pharynx endocavitary treatment • Verification of experimental calibrations 5. 0 mm Active Ir-192 Core <E> = 356 ke. V 1. 1 mm 0. 6 mm Geant 4 allows a complete flexible description of the real geometry 3. 5 mm 3 mm steel cable Courtesy of National Inst. For Cancer Research, Genova, Italy 20

MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT G. Santin Anisotropy • source geometry • auto-absorption • encapsulation • shielding effects Courtesy of National Inst. For Cancer Research, Genova, Italy Isodose curves The simulated source is placed in a 30 cm water box 10. 000 photons, 1 mm 3 voxels 12 h CPU time on Intel Pentium 300 MHz Courtesy of National Inst. For Cancer Research Geant 4 Radioactive Decay Module is capable of handling the generation of the whole radioactive chain of the 192 Ir source 21

G. Santin MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT Dosimetric Studies Pixel Ionisation Chamber Relative dose with 6 MV photons beam G 4 vs experimental data Deposited energy vs Depth in water 22

G. Santin Geant 4 for PET & SPECT Bragg Peak of Protons in Water Magic Cube Relative dose with 270 Me. V protons beam in water MC in Nuclear Medicine - Paris 16 July 2001 Courtesy of INFN & ASP, Torino, Italy and experimental data Deposited energy vs Depth in water • Sandwich of 12 parallel plate (25 x 25) cm 2 ionization chambers • Each chamber: • passive material (N 2, G 10, Mylar) • anode (0. 035 mm Cu) • active material (3 mm N 2) • passive material • air gap (2 cm, tissue equivalent of adjustable thickness) • Thickness of a chamber as water equivalent ~1. 1 mm 23

G. Santin Geant 4 for scatter compensation in Megavoltage 3 D CT MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT • Use GEANT 4 to obtain digitally reconstructed radiographs (DRRs), including full scatter simulation This represents a great improvement over approaches based on raycasting. • • The study of DRRs synthesized by Geant 4 allows users to produce a model for scatter compensation of megavoltage radiographs This will help to produce a more accurate megavoltage 3 D 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 Geant 4: – LINAC head simulation – Scatter analysis in total body irradiation 24

G. Santin Geant 4 for PET & SPECT MC in Nuclear Medicine - Paris 16 July 2001 Work in progress In vivo TLD dosimetry • Simulation of the energy deposition of low energy photons in TLD Li. F 100 nanodosimeters • Used to calculate dose to patient in radiodiagnostic examinations: · · mammography virtual colonscopy CT image interface Interface between Geant 4 and DICOM 3 CT scan images format in order to perform in tissue simulation 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 25

G. Santin Geant 4 for PET & SPECT simulations with Geant 4. Why not? • Detailed description of both – human tissues and properties – detector geometry and response (non-linear resolution function of the PET scanner, etc. ) MC in Nuclear Medicine - Paris 16 July 2001 • Energy range of Physics processes involved – covered by the G 4 standard or – Low. Energy extension of EM processes • Past experience in the medical physics community shows reliability and innovation in G 4 simulations • Injected radioactive tracer described by the Radioactive Decay Module • Simulation of patient motion with geometry modification inside the same run 26

MC in Nuclear Medicine - Paris 16 July 2001 Geant 4 for PET & SPECT G. Santin Summary • Geant 4 is a simulation Toolkit, providing advanced tools for all the domains of detector simulation • Geant 4 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. • Geant 4 is open to extension and evolution evolving Geant 4 physics keeps – 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 • User Support granted by the Geant 4 Collaboration • G 4 URL: http: //wwwinfo. cern. ch/asd/geant 4. html Wide and growing medical user community 27