The brachytherapy advanced example Susanna Guatelli (CERN/INFN) Geant4 Users Workshop CERN 14th November 2002 http://cern.ch/geant4/geant4.html

Brachytherapy Radioactive sources deliver therapeutic doses near tumors, while preserving surrounding healthy tissues Brachytherapy is a medical therapy used for cancer treatment Interstitial brachytherapy prostate I-125 Endocavitary brachytherapy uterus, vagina, lungs Ir-192 source Superficial brachytherapy skin Leipzig Applicator

approximate dose calculation the source is approximated to a point Software characteristics for brachytherapy precision reproduction of the real geometry and tissues (CT ) calculation speed simple to use ( for hospitals !) Calculation of dose delivered to tissue All the tissues are approximated to water Analytical calculation methods Commercial software available es.: Variseed V 7, Prowes Disadvantages approximate dose calculation density insensitive the source is approximated to a point Advantage high speed dose calculation

Project software for dose calculation 3D dose distribution calculation Isodose curves Simulation Geant4 Analysis AIDA/Anaphe Monte Carlo method Accurate physical process simulation Test to guarantee the quality of the software Precision Real geometry reproduction Accurate description of the geometry Possibility to interface the sofware to CT Graphical visualization + user interface Dose distribution analysis ( eg. isodose curves ) Simple to use Use in hospitals Parallelisation Access to calculation distributed resources Calculation speed Expansive to new functionalities Public access Other user requirements

Development of the project Sofware planning and development Tests Test from a microscopic point of view (on e- ranges) Test the dose distribution of the interstitial source Isoseed I-125 Experimental mesurements functionalities design Software Process (USDP ) Brachytherapic Application Dose distribution calculation Isodose curves in different brachytherapic techniques Results and future Technology Transfer

Design of the brachytherapy example run Primary Particles physics Energy deposit detector analysis visualization geometry and materials event User Interfaces

Comparison with the protocol data Software tests Test of Geant4 e- electromagnetic processes Microscopic test e- CSDA range simulations for different absorber materials Comparison of different physical models (Standard/Low Energy) Comparison with protocol data (Report ICRU 37) CSDA range Test of the dose distribution of Bebig-Isoseed I-125 dose distribution 2 Comparison with the protocol data

CSDA range test design Primary particles Physics Range Detector

Test: CSDA range e- delivered from the centre of the box Range = distance between the origin and the point where the kinetic energy of e- is zero Beryllium Max step fixed No secondary particles No energy loss fluctuations No multiple scattering Geant4 packages Low Energy / Standard

Materials of interest to medical physics Test results Materials Beryllium Berillium elements Materials of interest to medical physics Beryllium Aluminum Gold Lead Uranium Water Soft tissue Muscle Bone Geant4 packages Low Energy / Standard simulate ranges with good accuracy (~ %)

Dose distribution test design Primary particles Physics Energy deposit Detector

Dose distribution test Bebig Isoseed I-125 at the center of the phantom Source composition structure Geometry Random generation point and direction in the radionuclide, Decay gamma energy spectrum Primary particles Cut in range= 100 mm electromagnetic processes for e+, e-, gamma E (keV) Prob. 27.4 0.784 31.4 0.17 35.5 0.046 Physics Track geometry and dose calculation geometry are separated (voxels = 1 mm3) CPU Optimisation 2D histogram: energy deposit in the plane containing the source analysis dose

Dose distribution results mm simulation TG43 The simulation results are NOT in agreement with protocol data

Protocol data Performed with dosimeters LiF Lif wide range of use Low spatial resolution Critical measurements (delicate methodology of use of Lif) Measurement in plexiglass Measurements performed in water Better spatial resolution(~ 0.5 mm) Disadvantage : reduced range of use in comparison with LiF Experimental measurement of dose distribution with the use of films misura diretta

Experimental measurements d = 3.1+/- 0.2 mm Optimisation of the experimental set-up film dose measurements of a single source characterised by different exposure time (2, 9 , 12, 30 minutes) Water phantom The measurements disagree with the protocol data and agree with Geant4 simulation Experimental measurements protocol MC protocol

Consequences Experimental measurements results The results of this work would affect strongly the clinical activity In depth studies will be performed

Generalisation of the software Functionality 3D dose distribution Isodose curves Choice of the materials of the phantom Graphical visualisation Possibility to interface the system to CT source composition geometry, materials, spectrum Abstract Factory Use of abstract classes Radioactive source definition thanks to the design pattern: Abstract Factory Generalisation + Specific aspects of the source Parametrisation of the volumes in the geometry Parametrisation function: volume material Interface to CT Simulation result: energy deposit Analysis: dose distribution and isodose curves Dosimetry

Interstitial brachytherapy Results: Interstitial brachytherapy Source Bebig Isoseed I-125 0.16 mGy =100% isodose curves The results can be generalised to more sources located in the phantom

Endocavitary brachytherapy Superficial brachytherapy Results: Endocavitary brachytherapy Source MicroSelectron-HDR Results: Superficial brachytherapy Leipzig Applicator

Parallelisation and distributed calculation Speed is a fundamental requirement for software used in clinical practice MC simulations were never used until now in clinical practice due to the long calculation time Intermediate system between applications and GRID Parallelisation Access to distributed computing resources First results: factor ~30 increase in speed (conference Siena 2002) Possibility to run the brachytherapy example simulation + analysis via web? Look at A. Mantero Thesis

Results of my simulation Technology Transfer Particle physics software aids space and medicine Geant4 is a showcase example of technology transfer from particle physics to other fields such as space and medical science […]. CERN Courier, June 2002 Results of my simulation

Conclusions Software In collaboration with 3D dose calculation Accurate simulation of physics Realistic experimental configuration Possibility to interface the system to CT Applicable to all brachytherapic techniques Exstensive GRID compatible New and original Unità Operativa di Fisica Sanitaria, Savona IT Division, CERN Geant4 collaboration Anaphe team INFN In collaboration with Example of collaboration between different environments: Hospital activities and High Energy physics