1. 1 COMPARISON BETWEEN PLATO ISODOSE DISTRIBUTION OF A 192 IR SOURCE AND THOSE SIMULATED WITH GEANT4 TOOLKIT F. Foppiano 1, S. Agostinelli 1, S. Garelli 1, G. Paoli 1, M. Bevegni 1, M.G. Pia 2, P. Franzone 1, T. Scolaro 1, L. Andreucci 1 1 National Cancer Institute and 2 Physics Dept. of Genova foppiano@hp380.ist.unige.it

2. 2 Brachytherapy facility At the National Cancer Institute of Genova Ir-192 brachytherapy treatments are performed by a High Dose Rate (HDR) Microselectron afterloading unit. For the treatment planning we use Plato BPS, v 1.2.3 software

3. 3 Monte Carlo for brachytherapy Monte Carlo simulation topics for brachytherapy: oDose calculation n Computation of dose deposition kernels for treatment planning dose calculation algorithms based on convolution/superposition methods n Separation of primary, first scatter and multiple scatter components for complex dose deposition models / Computation of other model-dependent parameters, e.g. anisotropy function / Accurate computation of dose deposition in high gradient regions (i. e. near sources) oVerification of experimental calibration procedures

4. 4

5. 5 GEANT4 Low Energy Electromagnetic Physics Further extensions are in progress Relevant for medical, space science, astrophysics etc. applications Geant4 Low Energy Electromagnetic package extends the coverage of physics interactions 250 eV down to 250 eV for electrons and photons based on the LLNL data libraries shell effects ~ 1 keV down to ~ 1 keV for hadrons and ions Bethe-Block above 2 MeV Ziegler and ICRU parameterisations (with material dependence) free electron gas model quantal harmonic oscillator model charge dependence (Barkas effect)

6. 6 Geant4 tests: simulation of  Simulated water  (attenuation coefficient) Geant4 versus NIST data with Geant4 Standard electromagnetic package and Low Energy extension

7. 7 Description of  -Selectron 192 Ir source ]Geant4 allows complete flexible description of the real geometry ] 192 Ir energy spectrum l currently described as monochromatic at 356 keV l will soon be described by the new GEANT4 RadioactiveDecay class

8. 8 Simulation of dose deposition in water ]The simulated source is positioned in a 30 cm water box ]The dose deposition is investigated in the longitudinal plane ]Plane is partitioned in 1 million 1mm 3 voxels ]A minimum of 10 millions photons are generated on the 4  solid angle Longitudinal plane partitioned in cells  -Selectron 192 Ir source

9. 9 Results: PDD

10. 10 Results: Isodoses distribution

11. 11 Conclusions and future goals ]Monte Carlo simulation is useful in brachytherapy both to obtain model- dependent parameters and to verify experimental data ]Geant4 offers reliable particle-matter Monte Carlo simulation within a flexible modern object-oriented toolkit ]We have used Geant4 to simulate  coefficients and a commercial brachytherapy source with full dose deposition calculation ]Geant4 simulated dose deposition has been compared with Plato BPS calculations and has been found to be consistent /More realistic description of 192 Ir source energy spectrum with the new Geant4 RadioactiveDecay class /Simulation of shielded and Leipizig brachytherapy applicators Future goals