1. A general purpose dosimetric system for brachytherapy
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

2. Brachytherapy Techniques:
Radioactive sources are used to deposit therapeutic doses near tumors, while preserving surrounding healthy tissues
Techniques:
endocavitary
lung, vagina, uterus
interstitial
prostate
superficial
skin

3. Dose calculation in brachytherapy
TPS vs Monte Carlo
Based on analytical methods
Approximation in source dosimetry
Uniform material: water
Full source description: physics + geometry
CT based
Precision
Speed
Fast and reliable (FDA)
Ages…
Each software is specific to one technique and one type of source
TPS is expensive
(~ hundreds K $/euro)
Cost
Virtually no cost
NB: No commercial software available for superficial brachytherapy with Leipzig applicators

4. The challenge dosimetric system precise general purpose
Develop a
general purpose
realistic geometry
and material modeling
with the capability of
interface to CT images
with a
user-friendly interface
low cost at
adequate speed for clinical usage
performing at

5. Design run Primary particles Physics Energy deposit Detector Analysis
Visualisation
Experimental set-up
Events
User Interface

6. 2. Accurate model of the real experimental set-up
User Requirements
Calculation of 3-D dose distribution in tissue
Determination of isodose curves
Based on Monte Carlo methods
Accurate description of physics interactions
Experimental validation of physics involved
1. Precision
2. Accurate model of the real experimental set-up
Realistic description of geometry and tissue
Possibility to interface to CT images
Simple user interface + Graphic visualisation
Elaboration of dose distributions and isodoses
3. Easy configuration
for hospital usage
Parallelisation (Talk: Monte Carlo Simulation for radiotherapy in a distributed environment, 19th April, Monte Carlo 2005) and access to distributed computing resources
4. Speed
Transparent, open to extension and new functionality, publicly accessible
5. Other requirements

7. 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

8. Verification of Geant4 physics: once for all
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

9. Dosimetric validation in the experimental context for simple set-ups
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
experimental mesurements
G. Ghiso, S. Guatelli
S. Paolo Hospital Savona
I-125
Distance along Z (mm)
Simulation
Nucletron
Data
F. Foppiano et al., IST Genova
Ir-192
Ir-192

10. 2. Accurate model of the real experimental set-up
Radioactive source
Spectrum (192Ir, 125I)
Geometry
Patient
Phantom with realistic material model
Possibility to interface the system to CT images

11. 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
Ir-192 source + applicator
for superficial brachytherapy

12. Results: Effects of source anisotropy
Plato-BPS treatment planning algorithm makes some crude approximation
( dependence,
no radial dependence)
Distance along X (mm)
Simulation
Plato
Data
Rely on simulation for better accuracy than conventional treatment planning software
Distance along Z (mm)
Effects of source anisotropy
Simulation
Plato
Transverse axis of the source
Comparison with experimental data
Longitudinal axis of the source
Difficult to make direct measurements

13. Phantom with realistic material model
Possibility to interface the system to CT images
Modeling a phantom
Modeling geometry and materials from CT data through a DICOM interface
source
of any material
(water, tissue, bone, muscle etc.)
thanks to the flexibility of Geant4 materials package

14. General purpose system
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

15. any source type Abstract Factory design pattern Configuration of
Source spectrum and geometry transparently interchangeable
Configuration of
any brachytherapy technique
any source type
through an Abstract Factory
to define geometry, primary spectrum
Abstract Factory
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!

16. Results: Dosimetry Simulation of energy deposit through
Geant4 Low Energy Electromagnetic package
to obtain accurate dose distribution
Production threshold: 100 mm
2-D histogram
with energy deposit
in the plane containing the source
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

17. Interstitial brachytherapy
Dosimetry
Interstitial brachytherapy
Bebig Isoseed I-125 source
0.16 mGy =100%
Isodose curves

18. Dosimetry Dosimetry Endocavitary brachytherapy
Superficial brachytherapy
MicroSelectron-HDR source
Leipzig applicator

19. adequate for clinical use
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

20. 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.)

21. 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...)

22. 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!