P. Rodrigues, A. Trindade, L.Peralta, J. Varela GEANT4 Workshop, 2002 30 September – 4 October GEANT4 Medical Applications at LIP P. Rodrigues, A. Trindade, L.Peralta, J. Varela LIP – Lisbon

Overview 1999 2000 2001 2002 Radiotherapy & PEM Radiotherapy & SPECT Use of GEANT4 for medical applications has started at end of 2000 (version 2.0) Work in Radiotherapy has offered a fine opportunite to compare GEANT4 with EGS4 and GEANT3 Recently GEANT4 was adopted by the Portuguese PEM Collaboration 1999 2000 2001 2002 Radiotherapy & PEM Radiotherapy & SPECT Radiotherapy 2003 EGS4 GEANT4 GEANT3

A. Chaves, C. Alves M.C. Lopes GEANT4 Dose Calculation Engine for Radiotherapy In collaboration with: CROC-IPOFG A. Chaves, C. Alves M.C. Lopes C. Oliveira

Homogeneous Phantom Simulation with EGS4 of photon beams produced by a Siemens Mevatron KD2 clinical linear accelerator Phase-space distributions interface with GEANT4 Validation against experimental data: ddepth dose and profile curves 10x10 cm2 Differences 15x15 cm2 Differences 15x15 cm2 10x10 cm2

Photons (LowE) + electrons (Standard) Heterogeneous Phantom Water-styrophoam/bone-water Stringest test on dose calculation algorithms Accuracy of results are highly dependent on electron transport schemes (for Monte Carlo) and approximations (for TPS) GEANT4/GEANT3 comparison with HELAX-TMS and PLATO Water Styrophoam 0.0275 gcm-3 10x10 cm2 Field 5x5 cm2 Field Photons (LowE) + electrons (Standard)

Electron Transport at Low Energies Differences between G4-Standard and G4-Low Energy EM MCNP4b GEANT4 Low GEANT3 GEANT4 Std GEANT4 (Low+Std) Evaluation of electron range for different GEANT4 releases Styrophoam Lead

ROOT Dose AnalysisService Material Parameterization GEANT4 Dose Calculation Engine Phase Space Data User Interface Particle Transport Dose Deposition TPS Volume Contour TPS 3D Dose Matrix CT Images ROOT Dose AnalysisService Material Parameterization

Thorax Irradiation Alderson-Rando anthropomorphic phantom 15 x 15 cm2 lateral single field Voxel size: 0.4 x 0.4 x 10 cm3 21 LiF TLDs (TLD-100) (experimental uncertainty: 3-4%) Comparison with PLATO (2.2.15) and HELAX-TMS (5.0A) 9.8 cm 25 cm PDD Photon beam

Calculated Dose / Measured Dose Thorax Irradiation Calculated Dose / Measured Dose Agreement better than 2% between GEANT4 and TLD dosimeters Differences up to 11% for PLATO near lung-tissue interface

Head Irradiation Voxel: 2 x 2 x 5 mm3 37 CT slices ~ 600k volumes Two lateral opposed fields: 5 x 5 cm2, 10 x 10 cm2 Comparison with PLATO (2.3.3) 11 LiF TLDs for 5 x 5 cm2 27 LiF TLDs for 10 x 10 cm2 Photon beam

Head Irradiation 5 x 5 cm2 Opposed Fields 10 x 10 cm2 Opposed Fields exp. uncertainty: 4% exp. uncertainty: 4% 10 x 10 cm2 Opposed Fields exp. uncertainty: 4% exp. uncertainty: 4%

Differences G4(%)-PLATO(%) Head Irradiation 10x10 cm2 5 x 5 cm2 – Mean deviations 10 x 10 cm2 – Mean deviations Differences G4(%)-PLATO(%) L1

Head Irradiation 10x10 cm2 Profile L1 CT numbers along L1 PLATO: ~25%-45% overestimate dose in and near air cavities Effect of bone structures on dose are present in GEANT4 In some tumours sites (ex: larynx T2/T3-stage) a 5% under dosage will decrease local tumour control probability from ~75% to ~50%

Positron Emission Mammography (PEM)

General PEM Detector Configuration 32 Crystals APD matrix 8 mm LuAP Basic module: 8x4 crystals and APD matrix LuAP(20mm) Module assembly of 8 modules: 256 crystals PEM detector 64 mm 256 crystals FrontEnd Electronics 16 mm 24 modules 3072 crystals Basic requirements: Large solid angle coverage High-density, high-Z and fast crystals Fast data acquisition system 96 mm 128 mm

Heterogeneous phantoms PEM Simulation System Benefits from GEANT4 dose calculation engine code re-use. Under development PhantomFactory MIRD type phantoms CT based phantoms CAD based phantoms Heterogeneous phantoms Homogeneous phantoms PEMsim Detector Design and Optimization DIGITsim Digitization with APD readout simulation Radioactive Decay Generic Source ROOT I/O Reconstruction LMF

Preliminary Results PhantomFactory: 18F decay at Radioactive Decay Module and photon acolinearity annihilation angle 9 mrad ENSDF Data Lu X-ray Escape peak PEMsim: Deposited energy in 2 x 2 x 20 mm3 LuAP crystal Resolution@511 keV = 9%

Preliminary Results – PEM System Sensitivity Head separation distance Distance to center of FOV LuAP thickness Espected value: 20 mm

Summary and Next Steps at LIP… GEANT4 in Radiotherapy: Fine agreement with experimental data, compliant with strict limits Radiotherapy is interesting environment for tuning and testing of GEANT4 Low Energy Models Comparison with other benchmarked MC codes in medical applications Current work: Ongoing development of current PEM simulation code based on GEANT4 (plus test of optical photon transport - R. Moura - LIP/IST) Development and implementation in GEANT4 of a more accurate Bremsstrahlung angular generator for low energies