http www ge infn itgeant 4 A general

http: //www. ge. infn. it/geant 4 A general purpose dosimetric system for brachytherapy S. Chauvie 0, 1 S. Agostinelli 2, F. Foppiano 2, S. Garelli 2, S. Guatelli 1, M. G. Pia 1 INFN 1 National Institute for Cancer Research, IST Genova 2 AO S Croce e Carle, Cuneo 0 20 th 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: 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 Develop a precise general purpose with the capability of with a at performing at dosimetric system realistic geometry and material modeling interface to CT images user-friendly interface low cost adequate speed for clinical usage

Design run Primary particles Physic s Energy deposit Detector Visualisation Experimental set-up Events User Interface Analysi s

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, 19 th 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 ke. V) 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 Geant 4 physics: once for all Geant 4 Low Energy Package for photons and electrons Geant 4 Standard Package for positrons Validation of the Geant 4 physics models with respect to experimental data and recognised reference data Results summerised in “Comparison of Geant 4 electromagnetic physics models against the NIST reference data”, submitted to IEEE Transactions on Nuclear Science Talk: Precision Validation of Geant 4 electromagnetic physics, 20 th 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 F. Foppiano et al. , IST Genova Ir-192 I-125 Ir-192 G. Ghiso, S. Guatelli S. Paolo Hospital Savona experimental mesurements Distance along Z (mm) Simulation Nucletron Data

2. Accurate model of the real experimental set-up Radioactive source Spectrum (192 Ir, Ir Geometry 125 I) I 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 I-125 source for interstitial brachytherapy Iodium core: Inner radius : 0 Outer radius: 0. 30 mm Half length: 1. 75 mm Titanium tube: Outer radius: 0. 40 mm Half length: 1. 84 mm Air: Outer radius: 0. 35 mm half length: 1. 84 mm Titanium capsule tip: Box Side : 0. 80 mm • Iodium core • Air • Titanium capsule tip • Titanium tube Ir-192 source + applicator for superficial

Results: Effects of source anisotropy Plato-BPS treatment planning algorithm makes some crude approximation ( dependence, no radial dependence) Simulation Plato Data Rely on simulation for better accuracy than conventional treatment planning software Distance along X (mm) Simulation Plato Effects of source anisotrop y 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 Geant 4 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

Results: Dosimetry Simulation of energy deposit through Geant 4 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 m. Gy =100% Isodose curves

Dosimetry Endocavitary brachytherapy Superficial brachytherapy Micro. Selectron-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, 19 th 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 Geant 4 Based on open source code (Geant 4, AIDA etc. )

Extension and evolution Configuration of any brachytherapy technique System extensible to any source configuration without changing the existing code any source type 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 Geant 4 – 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, 19 th April, Monte Carlo 2005) Access to distributed computing resources – GRID (look: Monte Carlo Simulation for radiotherapy in a distributed environment, 19 th April, Monte Carlo 2005) Beware: R&D prototype!