A general purpose dosimetric system for brachytherapy

1. 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

2. 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

3. Dose calculation in brachytherapy TPS vs Monte Carlo NB: No commercial software available for superficial brachytherapy with Leipzig applicators • 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

4. The challenge dosimetric system precise 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. User Requirements Calculation of3-D dose distributionin tissue Determination ofisodose 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 physicsinteractions Extension of electromagnetic interactions down to low energies (< 1 keV) Experimental validationof physics involved Microscopic validation of the physics models Macroscopic validation with experimental data specific to the brachytherapic practice

8. 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. Simulation Nucletron Data G. Ghiso, S. Guatelli S. Paolo Hospital Savona experimental mesurements F. Foppiano et al., IST Genova I-125 Distance along Z (mm) 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 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. Effects of source anisotropy Simulation Plato Simulation Plato Data Distance along X (mm) Distance along Z (mm) Results: Effects of source anisotropy Plato-BPS treatment planning algorithm makes some crude approximation ( dependence, no radial dependence) Rely onsimulation for better accuracy than conventional treatment planning software Transverse axis of the source Comparison with experimental data Longitudinal axis of the source Difficult to make direct measurements

13. source 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 of any material (water, tissue, bone, muscle etc.) thanks to the flexibility of Geant4 materials package

14. 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. Abstract Factory design pattern 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 spectrum • Ir-192 source • I-125 source • Configure the source geometry • Ir-192 endocavitary source • I -125 interstitial source • Ir-192 source + Leipzig applicator No commercial general software exists!

16. Dose distribution Analysis of the energy deposit in the phantom resulting from the simulation Isodose curves 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 AIDA + PI Python for analysis for interactivity could be any other AIDA-compliant analysis system

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

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

19. 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!