A general purpose dosimetric system for brachytherapy 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 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

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

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

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

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

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

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

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

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

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

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

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

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

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!

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

Interstitial brachytherapy 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

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

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!