F. Foppiano, B. Mascialino, M. G. Pia, M. Piergentili Geant4 Simulation of an Accelerator Head for Intensity Modulated RadioTherapy Monte Carlo 2005 Topical Meeting Chattanooga, April 2005

Radiotherapy with external beams A cancer or a tissue near a surgically removed tumour may be irradiated with photons in order to reduce the tumour size or to sterilize the zone Cancer cells are more sensitive to radiation damage compared to healthy cells The goal of radiotherapy is delivering the required therapeutic dose to the tumor area with high precision, while preserving the surrounding healthy tissue Accurate dosimetry is at the basis of radiotherapy treatment planning GANTRY COUCH

Intensity Modulated Radiation Therapy step and shoot Dose distribution more homogeneous within the Planned Target Volume (PTV) Sharper fall-off of dose at PTV boundary Non-homogeneous dose distribution to treat concave surface Progress in 3D medical imaging The exposure of healthy tissue to high doses can be reduced Beam aperture is shaped to the irregular shape of the target Photon fluence is modulated head and neck breast prostate IMRT Conformational technique dynamic technique

Target Primary collimators Vacuum windows Flattening filter Mirror Monitor chamber Secondary collimators Multileaf collimator The LINAC E e =6 MV GANTRY COUCH

Dosimetric system Commercial systems Analytic algorithms Es.: Eclipse, Plato fast, but based on approximations precise Accurate modeling of the experimental set- up Dose distribution in a phantom easy to configure quick Problem Statement determine the dose distribution in a phantom resulting from the head of a linear accelerator

General plan Geant4 AIDA/Anaphe OO technology Specific software process Functionality Design Advanced software Microscopic validation of Geant4 processes (established references - NIST) Dosimetric validation of the system (experimental measurements - IST) validation of the dosimetric system planning and developing the dosimetric system simulationanalysis + DIANE Goodness-of-Fit Statistical Toolkit

Validation of the dosimetric system EXPERIMENTAL MEASUREMENTS Ion chamber PTW flexible Ion chamber PTW flexible Water Phantom PTW MP3 Water Phantom PTW MP3 no MLC (squared fields) no MLC (squared fields) Lateral dose profile Radiographic film Radiographic film Kodak X-Omat V Plexiglass phantom Plexiglass phantom with MLC with MLC Dose distribution in a plane Percent depth dose Isodoses SIMULATION RESULTS

The simulation

Geant4 simulation of the passage of particles through matter  flexibility  openness to extension and evolution  trasparency rigorous software engineering methodologies and OO technology Low Energy Electromagnetic Package Low Energy Accurate dose calculation the geometry of the system and the materials involved (Geometry, Materials), physics interactions of particles through matter (Processes), detector response (Hit, Digits, Read-out geometry), track of the particles (Tracking), to manage the events (Event, Run), visualisation of the detector and of the particles trajectories (Visualization), user interface (Interfaces). < 1 keV

Dosimetric system The analysis produces some histograms from which the user can calculate the Percent Depth Dose (PDD), the lateral profiles at the following depths in the phantom: 15 mm, 50 mm, 100 mm and 200 mm, and the isodoses curves in a plane Gaussian distribution for energy and momentum of primary particles Each pair of jaws can be rotated through an axis perpendicular to the beam axis The user can choose the position of every single leaf phantom jaws flattening filter primary collimator

Dosimetric system Flattening filter MLC Primary collimators and target Multi-leaf collimator phantom MLC jaws primary collimator target

Design  Flexibility  Extensibility  Distributed responsibility Design Pattern Decorator

Software technologies Mapped on ISO Dinamic dimension Based on use cases Rational Unified Process Specific software process for this dosimetric system Software process artifacts based on the Unified Process Static dimension The process was tailored to the specific needs of the project

Specific software process for the dosimetric system Time InceptionElaborationConstructionTransition Vision Use cases User requirements Risk list Requirements analysis Architecture elaboration Implementation Design analysis Test Public deployment of the code Documentation DISCIPLINES: Business Modeling, Requirements, Analysis & Design, Implementation, Test, Deployment, Configuration & Change Management, Project Management, Enviroment. S. Guatelli, B. Mascialino, L. Moneta, I. Papadopouls, A. Pfeiffer, M. G. Pia, M. Piergentili Experience with software process in physics experiments

Microscopic validation of Geant4 processes

Validation of Geant4 electromagnetic models against established references (ICRU - NIST) Simulation of physics quantities in the same experimental set-up as reference data Rigorous quantitative statistical comparison PHYSICAL TEST GOODNESS-OF-FIT TESTING Quantitative statistical analysis - Evaluation of Geant4 physics goodness - How the various Geant4 models behave in the same experimental condition - Systematic data analysis allows to improve the physics models and guarantees the reliability Scope Microscopic validation of Geant4 processes

PhotonPhoton Attenuation Coefficient PhotonPhoton Cross Sections (attenuation coefficients with only one process activated) ElectronElectron CSDA range and Stopping Power (no multiple scattering, no energy fluctuations) Elements: Be, Al, Si, Fe, Ge, Ag, Cs, Au, Pb, U + water Energy range: 1 keV – 10 GeV Geant4 processes pertinent to this application

Microscopic validation of Geant4 processes Physics models under test: Geant4 Standard Geant4 Low Energy - Livermore Geant4 Low Energy – Penelope Reference data: NIST K. Amako, S. Guatelli, V. Ivanchenko, M. Maire, B. Mascialino, K. Murakami, P. Nieminen, L. Pandola, S. Parlati, A. Pfeiffer, M. G. Pia, M. Piergentili, T. Sasaki, L. Urban Precision validation of Geant4 electromagnetic physics G4 LowE PackageQUANTITATIVECOMPARISONS

Validation of the dosimetric system: - lateral dose profiles - depth dose profiles

Experimental measurements with ion chamber IAEA 398 Percent Depth Dose Squared fields 5x5 cm, 10x10 cm, 40x40 cm Ion chamber: PTW Flexible. Water phantom: PTW MP3 Distance (mm) Percent dose PDD 6MV – 10x10 field Distance (mm) Percent dose Lateral profile 6MV – 10x10 field International Atomic Energy Agency

Comparison with experimental data rangeDp-value -84  -60 mm  -48 mm  47 mm  59 mm  84 mm rangeDp-value -56  -35 mm  -22 mm  21 mm  32 mm  36 mm  events  100 CPU days on Pentium IV 3 GHz Lateral profiles B. Mascialino, A. Pfeiffer, M. G. Pia, A. Ribon, P. Viarengo A Toolkit for statistical comparison of data distributions Distance (mm) Percent dose Lateral profile 6MV – 5x5 field – 15mm depth Dosimetric system Experimental data Distance (mm) Percent dose Lateral profile 6MV – 10x10 field – 50mm depth Dosimetric system Experimental data Kolmogorov-Smirnov test Kolmogorov-Smirnov test

Comparison with experimental data D = 0.005; p-value = 1 rangeDp-value 0  14 mm  300 mm Kolmogorov-Smirnov test percent depth dose Percent dose PDD 6MV – 40x40 field Dosimetric system Experimental data Voxels 5mm Depth (mm) Percent dose PDD 6MV – 10x10 field Voxels 5mm Dosimetric system Experimental data

Application of the dosimetric system: - dose distribution in a plane - isodose lines

Experimental measurements with radiographic films Kodak X-Omat V films Scanner VXR16 Dosimetry Pro Software Rit 113 Grey toneOptical densityDose Spatial resolution = 89  m Field used to treat prostate cancer using the MLC

Experimental data and simulation results radiographicfilm Dose distribution in a plane dosimetricsystem dosimetricsystem radiographicfilm Isodose lines dosimetricsystem RIT 113 dosimetricsystem intra-leaf transmission

Conclusions Dosimetric system for IMRT based on Geant4 –reproduces with high accuracy experimental data –can be used to verify treatment plans in a reliable way Open source dosimetric system Geant4 Low Energy electromagnetic package - Validation of physical processes in Geant4 Quantitative comparison with experimental measurements precision This is an Advanced Example of

Activities in progress Phase space Dynamic tecnique Parallelisation For furher J. T. Moscicki, S. Guatelli, M. G. Pia, M. Piergentili Monte Carlo simulation for radiotherapy in a distributed computing environment