F. Foppiano, B. Mascialino, M. G. Pia, M. Piergentili

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

2. 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 isdelivering the required therapeutic dose to the tumor area with high precision,while preserving the surrounding healthy tissue GANTRY COUCH Accurate dosimetry is at the basis of radiotherapy treatment planning

3. Intensity Modulated Radiation Therapy new Progress in 3D medical imaging • Beam aperture is shaped to the irregular shape of the target • Photon fluence is modulated 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 dynamic technique Conformational technique head and neck breast prostate The exposure of healthy tissue to high doses can be reduced IMRT

4. The LINAC • Mirror • Monitor chamber • Secondary collimators • Multileaf collimator • Target • Primary collimators • Vacuum windows • Flattening filter GANTRY COUCH Ee=6 MV

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

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

7. Validation of the dosimetric system SIMULATION RESULTS EXPERIMENTAL MEASUREMENTS • Radiographic film Kodak X-Omat V • Plexiglass phantom • with MLC • Ion chamber PTW 31002 flexible • Water Phantom PTW MP3 • no MLC (squared fields) Lateral dose profile Dose distribution in a plane Percent depth dose Isodoses

8. The simulation

9. Geant4 simulation of the passage of particles through matter Accurate dose calculation Low Energy Electromagnetic Package Low Energy < 1 keV rigorous software engineering methodologies and OO technology • flexibility • openness to extension and evolution • trasparency • 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 thedetector and of the particles trajectories (Visualization), • user interface (Interfaces).

10. Dosimetric system • 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 primary collimator • The analysis produces some histograms from which the user can calculate the Percent Depth Dose (PDD), thelateral profiles at the following depths in the phantom: 15 mm, 50 mm, 100 mm and 200 mm, and the isodoses curves in a plane jaws flattening filter phantom

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

12. Design Design Pattern Decorator • Flexibility • Extensibility • Distributed responsibility

13. Software technologies iterative and incremental approach Based on use cases Software process artifacts Mapped on ISO 15504 Rational Unified Process Dinamic dimension based on the Unified Process Specific software process for this dosimetric system Static dimension The process was tailored to the specific needs of the project

14. Specific software process for the dosimetric system Time Inception Elaboration Construction Transition 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

15. Microscopic validation of Geant4 processes

16. - 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 • 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 Quantitative statistical analysis PHYSICAL TEST GOODNESS-OF-FIT TESTING

17. Geant4 processes pertinent to this application • Photon Attenuation Coefficient • Photon Cross Sections (attenuation coefficients with only one process activated) • ElectronCSDA 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

18. Physics models under test: • Geant4 Standard • Geant4 Low Energy - Livermore • Geant4 Low Energy – Penelope G4 LowE Package • Reference data: • NIST Microscopic validation of Geant4 processes QUANTITATIVE COMPARISONS 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

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

20. PDD 6MV – 10x10 field Lateral profile 6MV – 10x10 field Percent dose Percent dose Distance (mm) Distance (mm) Experimental measurements with ion chamber Percent Depth Dose Squared fields 5x5 cm, 10x10 cm, 40x40 cm Water phantom: PTW MP3 Ion chamber: PTW 31002 Flexible. IAEA 398 International Atomic Energy Agency

21. Lateral profile 6MV – 10x10 field – 50mm depth Dosimetric system Experimental data Dosimetric system Experimental data Percent dose Percent dose Distance (mm) Distance (mm) Lateral profiles Lateral profile 6MV – 5x5 field – 15mm depth Comparison with experimental data  1010 events  100 CPU days on Pentium IV 3 GHz Kolmogorov-Smirnov test B. Mascialino, A. Pfeiffer, M. G. Pia, A. Ribon, P. Viarengo A Toolkit for statistical comparison of data distributions

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

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

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

25. intra-leaf transmission dosimetric system RIT 113 radiographic film dosimetric system dosimetric system RIT 113 Experimental data and simulation results radiographic film dosimetric system Dose distribution in a plane Isodose lines

26. 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

27. Activities in progress • Phase space • Dynamic tecnique • Parallelisation J. T. Moscicki, S. Guatelli, M. G. Pia, M. Piergentili Monte Carlo simulation for radiotherapy in a distributed computing environment For furher informations: Michela.Piergentili@ge.infn.it