1. 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

2. 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

3. 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

4. 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

5. 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
gcm-3
10x10 cm2 Field
5x5 cm2 Field
Photons (LowE) + electrons (Standard)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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%

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

13. 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%

14. Positron Emission Mammography (PEM)

15. 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

16. 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

17. 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
keV = 9%

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

19. 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