Transcript The GEANT4 simulation toolkit, and how easy would it be to

The GEANT4 simulation toolkit, and how
it could be used for SPECT and PET
simulations
Giovanni Santin
INFN, Trieste & CERN, Geneva
[email protected]
on behalf of the Geant4 Collaboration
MonteCarlo Simulations in Nuclear Medicine
16 - 17 july 2001 - Paris
G.Santin
Geant4 for PET & SPECT
MC in Nuclear Medicine - Paris 16 July 2001
Summary
• Introduction to GEANT4
• Medical applications: DNA, brachytherapy, ...
• PET & SPECT: some ideas and conclusions
2
G.Santin
Geant4 for PET & SPECT
MC in Nuclear Medicine - Paris 16 July 2001
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
3
G.Santin
Geant4 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
Geant4 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
MC in Nuclear Medicine - Paris 16 July 2001
Geant4 for PET & SPECT
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
Geant4 for PET & SPECT
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.)
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
Geant4 for PET & SPECT
• 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
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
Geant4 for PET & SPECT
http://www.ge.infn.it/geant4/lowE/
• down to 250 eV for electrons and g
Geant4
Low Energy
Electromagnetic
package extends the
coverage
of physics interactions
Needed for space and
medical applications,
n physics, antimatter
searches
• 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 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)
9
G.Santin
Low Energy Electromagnetic Physics
Geant4 for PET & SPECT
Protons, Ziegler
Geant4 LowEn
NIST
10
Ion ionisation
 / (cm 2 /g) in water
MC in Nuclear Medicine - Paris 16 July 2001
Shell effects
1
0.1
0.01
0.1
1
10
Photon Energy (MeV)
Photon attenuation coefficient
in water
Barkas effect
10
MC in Nuclear Medicine - Paris 16 July 2001
Geant4 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
Geant4 for PET & SPECT
MC in Nuclear Medicine - Paris 16 July 2001
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
12
G.Santin
Geant4 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 Geant4
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
Geant4 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 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
14
G.Santin
Geant4 for PET & SPECT
MC in Nuclear Medicine - Paris 16 July 2001
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
15
GLAST (NASA)
MC in Nuclear Medicine - Paris 16 July 2001
Geant4 for PET & SPECT
G.Santin
Geant4 geometry examples
Chandra (NASA)
ATLAS at
LHC, CERN
CMS (LHC, CERN)
Borexino at Gran Sasso Lab.
16
G.Santin
Geant4 for PET & SPECT
MC in Nuclear Medicine - Paris 16 July 2001
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
17
G.Santin
Geant4 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
Geant4 for PET & SPECT
G.Santin
- DNA
Multi-disciplinary Collaboration of
 astrophysicists and space scientists
 particle physicists
 medical physicists
 biologists
 physicians
a, C, Fe, ...
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, ...)
Geant4
• capability to model DNA as a “geometry”
• capability to handle biochemical processes
19
G.Santin
Geant4 for PET & SPECT
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
Naso-pharynx endocavitary treatment
 Computation of other model-dependent parameters, e.g. anisotropy
MC in Nuclear Medicine - Paris 16 July 2001
function
 Accurate computation of dose deposition in high gradient regions (i.
e. near sources)
• Verification of experimental calibrations
5.0 mm
Active Ir-192 Core
<E> = 356 keV
3.5 mm
3 mm steel cable
Courtesy of National Inst. For Cancer Research, Genova, Italy
1.1 mm
0.6 mm
Geant4 allows a
complete flexible
description of the
real geometry
20
G.Santin
90
120
MC in Nuclear Medicine - Paris 16 July 2001
Geant4 for PET & SPECT
150
Anisotropy
60
30
180
0
• 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
10.000.000 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
G.Santin
MC in Nuclear Medicine - Paris 16 July 2001
Geant4 for PET & SPECT
Dosimetric Studies
Pixel Ionisation
Chamber
Relative dose with 6 MV
photons beam
G4
vs
experimental data
Deposited energy vs
Depth in water
22
G.Santin
Geant4 for PET & SPECT
Bragg Peak of Protons in Water
Magic Cube
Relative dose with
270 MeV 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 (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
23
G.Santin
Geant4 for scatter compensation in Megavoltage 3D CT
MC in Nuclear Medicine - Paris 16 July 2001
Geant4 for PET & SPECT
•
Use GEANT4 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
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
24
G.Santin
Geant4 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 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
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
Geant4 for PET & SPECT
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.)
MC in Nuclear Medicine - Paris 16 July 2001
• 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
26
G.Santin
Geant4 for PET & SPECT
MC in Nuclear Medicine - Paris 16 July 2001
Summary
•
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
evolving
Geant4 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
•
Wide and growing medical user community
•
User Support granted by the Geant4 Collaboration
•
G4 URL: http://wwwinfo.cern.ch/asd/geant/geant4.html
27