Transcript Seminario Geant4 INFN

http://www.ge.infn.it/geant4
A general purpose dosimetric
system for brachytherapy
S. Chauvie0,1 S. Agostinelli2, F. Foppiano2,
S. Garelli2,
S. Guatelli1, M.G. Pia1
INFN1
National Institute for Cancer Research, IST Genova2
AO S Croce e Carle, Cuneo0
20th April 2005,
Monte Carlo 2005, Chattanooga, USA
Brachytherapy
Radioactive sources are used to deposit
therapeutic doses near tumors, while
preserving surrounding healthy tissues
Techniques:
endocavitary
–
lung, vagina, uterus
interstitial
–
prostate
superficial
–
skin
Dose calculation in brachytherapy
TPS
vs
Based on analytical methods
Approximation in source
dosimetry
Uniform material: water
Precision
Fast and reliable (FDA)
Speed
Each software is specific
to one technique and one
type of source
TPS is expensive
(~ hundreds K $/euro)
Cost
Monte Carlo
Full source description:
physics + geometry
CT based
Ages…
Virtually no cost
NB: No commercial software available for superficial brachytherapy with Leipzig applicators
The challenge
precise
Develop a
general purpose
with the capability of
dosimetric
system
realistic geometry
and material modeling
interface to CT images
with a
at
performing at
user-friendly interface
low cost
adequate speed for clinical usage
Design
run
Primary particles
Physics
Energy
deposit
Detector
Analysis
Visualisation
Experimental set-up
Events
User Interface
User Requirements
Calculation of 3-D dose distribution in tissue
Determination of isodose curves
1. Precision
Based on Monte Carlo methods
Accurate description of physics interactions
Experimental validation of physics involved
2. Accurate model of the
real experimental set-up
Realistic description of geometry and tissue
Possibility to interface to CT images
3. Easy configuration
for hospital usage
4. Speed
Simple user interface + Graphic visualisation
Elaboration of dose distributions and isodoses
Parallelisation (Talk: Monte Carlo Simulation for
radiotherapy in a distributed environment, 19th April, Monte
Carlo 2005) and access
to distributed computing
resources
5. Other requirements
Transparent, open to extension and new
functionality, publicly accessible
1. Precision
Based on Monte Carlo methods
Accurate description of physics interactions
Extension of electromagnetic interactions
down to low energies (< 1 keV)
Experimental validation of physics involved
Microscopic validation of the physics models
Macroscopic validation with experimental data
specific to the brachytherapic practice
Microscopic validation of the physics models
Verification of Geant4 physics: once for all
Geant4 Low Energy Package for photons and electrons
Geant4 Standard Package for positrons
Validation of the Geant4 physics models with respect to
experimental data and recognised reference data
Results summerised in “Comparison of Geant4
electromagnetic physics models against the NIST reference
data”, submitted to IEEE Transactions on Nuclear Science
Talk: Precision Validation of Geant4 electromagnetic physics,
20th April, Monte Carlo 2005
Macroscopic validation with experimental data
specific to the brachytherapic practice
Dosimetric validation in the experimental context for simple set-ups
Comparison to:
manufacturer data,
protocol data,
original experimental data
Simulation
Simulazione
Nucletron
Nucletron
Data
Misure
1,2
F. Foppiano et al., IST Genova
1,0
Ir-192
I-125
Ir-192
G. Ghiso, S. Guatelli
S. Paolo Hospital Savona
Dose %
0,8
0,6
0,4
0,2
experimental
mesurements
0,0
0
10
20
30
Distance
along
Z (mm)
Distanza
lungo
Z (mm)
40
50
2. Accurate model of the real
experimental set-up
Radioactive source
Spectrum (192Ir,
Geometry
125I)
Patient
Phantom with realistic material model
Possibility to interface the system to CT images
Geometry
Precise geometry and material model of any type of source
• Iodium core
• Air
• Titanium capsule tip
• Titanium tube
Iodium core
I-125 source for interstitial brachytherapy
Iodium core:
Inner radius :0
Outer radius: 0.30mm
Half length:1.75mm
Titanium tube:
Outer radius:0.40mm
Half length:1.84mm
Air:
Outer radius:0.35mm
half length:1.84mm
Titanium capsule tip:
Box
Side :0.80mm
5.0 mm
0.6 mm
3.5 mm
3 mm steel cable
Active Ir-192 Core
1.1 mm
Ir-192 source + applicator
for superficial brachytherapy
Results: Effects of source anisotropy
Plato-BPS treatment
planning algorithm makes
some crude approximation
( dependence,
no radial dependence)
Rely on simulation for
better accuracy than
conventional treatment
planning software
Simulazioni
Plato
Misure
2,5
Simulazioni
Plato
2,5
2,0
Dose %
Dose %
2,0
1,5
1,0
Simulation
Plato
Data
0,5
Effects of
source
1,5
1,0
Simulation
Plato
0,5
anisotropy
0,0
0,0
-40
-30
-20
-10
0
10
20
30
Distanza lungo X (mm)
Distance along X (mm)
40
-40
-30
-20
-10
0
10
20
30
40
Distanza lungo Z (mm)
Distance along Z (mm)
Transverse axis of the source
Longitudinal axis of the source
Comparison with experimental data
Difficult to make direct measurements
Phantom with realistic material model
Possibility to interface the system to CT images
Modeling a phantom
source
of any material
(water, tissue, bone, muscle etc.)
thanks to the flexibility of Geant4 materials package
Modeling geometry
and materials from
CT data through a
DICOM interface
3. Easy configuration
for hospital usage
General purpose system
For any brachytherapy technique
Object Oriented Technology
Software system designed in terms of Abstract Interfaces
For any source type
Abstract Factory design pattern
Source spectrum and geometry transparently interchangeable
Abstract Factory design pattern
Source spectrum and geometry transparently interchangeable
Configuration of
any brachytherapy
technique
Abstract Factory
any source type
through an Abstract
Factory
to define geometry,
primary spectrum
Configure the source geometry
Ir-192 endocavitary source
I -125 interstitial source
Ir-192 source + Leipzig applicator
Configure the source spectrum
Ir-192 source
I-125 source
No commercial general software exists!
Results: Dosimetry
Simulation of energy deposit through
Geant4 Low Energy Electromagnetic package
to obtain accurate dose distribution
2-D histogram
with energy deposit
in the plane containing
the source
Production threshold: 100 mm
Analysis of the energy
deposit in the phantom
resulting from the simulation
Dose distribution
Isodose curves
AIDA + PI
Python
for analysis
for interactivity
could be any other AIDA-compliant analysis system
Dosimetry
Interstitial brachytherapy
Bebig Isoseed I-125 source
0.16 mGy =100%
Isodose curves
Dosimetry
Dosimetry
Endocavitary brachytherapy
Superficial brachytherapy
MicroSelectron-HDR source
Leipzig applicator
4.Speed
adequate for clinical use
Parallelisation
Transparent configuration in sequential or
parallel mode
Access to distributed computing resources
Transparent access to the GRID through an
intermediate software layer
Talk: Monte Carlo Simulation for radiotherapy in a distributed environment,
19th April, Monte Carlo 2005
5. Other requirements
Transparency
Design and code publicly distributed
Physics and models exposed through OO design
Openness to extension and new functionality
OO technology: plug-ins for other techniques
Treatment head
Beam line for hadrontherapy
...
Publicly accessible
Application code released with Geant4
Based on open source code (Geant4, AIDA etc.)
Extension and evolution
Configuration of
any brachytherapy technique
any source type
System extensible
to any source configuration
without changing
the existing code
General dosimetry system for radiotherapy
extensible to other techniques
plug-ins for external beams
(factories for beam, geometry, physics...)
Summary
A precise dosimetric system, based on Geant4
– Accurate physics, geometry and material modeling, CT interface
A general dosimetric system for brachytherapy
– Possibility of extensions to other radiotherapic techniques
Full dosimetric analysis
– AIDA + PI or other AIDA - compliant analysis tools
Fast performance
– parallel processing (look: Monte Carlo Simulation for radiotherapy
in a distributed environment, 19th April, Monte Carlo 2005)
Access to distributed computing resources
– GRID (look: Monte Carlo Simulation for radiotherapy in a
distributed environment, 19th April, Monte Carlo 2005)
Beware: R&D prototype!