1. The application of GEANT4 simulation code to the verification of a brachytherapy calibration procedure F. Foppiano 1, S. Garelli 1, P. Moresco 1, G. Paoli 1, S. Agostinelli 2 1 Istituto Nazionale per la Ricerca sul Cancro di Genova, Italia 2 INFM and Dipartimento di Fisica di Genova, Italia With the collaboration of Maria Grazia Pia 3 and Matteo Tropeano 4 3 Istituto Nazionale di Fisica Nucleare di Genova, Italia 4 Dipartimento di Fisica di Genova, Italia

2. Brachytherapy facility installed at National Cancer Institute of Genova: Microselectron High Dose Rate (HDR) afterloading system 192 Ir source = 356 keV

3. calibration certificate Every new source is supplied by Mallinckrodt Medical B.V. Holland with a calibration certificate that specifies the air kerma rate measure at a distance of 1 m with uncertainty of ±5 % For every new source we perform calibration following the protocol for The Basic Dosimetry with Brachitherapy Sources of the Italian Association of Biomedical Physics (AIFB) using a 0.6 cc Capintec chamber we measure the air kerma rate using a well - type chamber PTW Freiburg For every new source

4. internal absorption and source encapsulation The Microselectron HDR Treatment Planning System (PLATO), in order to account for the internal absorption and source encapsulation uses a list of anisotropy correction factors F i ( ) where is the longitudinal axial angle

5. Geant4simulation medical Geant4 is a new toolkit for the simulation of the passage of particles through matter. Its application areas include high energy physics and nuclear experiments, medical, accelerator and space physics studies. It is based on Object Oriented technology and has been developed using the C++ computer language. Our application anisotropy correction factors of 192 Ir source transverse axis energy deposition in water verification of the calibration procedure of 192 Ir source

6. Geant4 As a first test for Geant4 application we perform the simulation of attenuation coefficient in different material of interest 1.000.000 photons generated 120 sec on an Intel PC 300 MHz

7. Anisotropy cell dimension: 1 mm 3 number of photons generated: 10.000.000 simulation time: 12 h on a Intel PC 300 MHz

8. Energy deposition in water cell dimension: 1 mm 3 number of photons generated: 10.000.000 simulation time: 12 h on a Intel PC 300 MHz

9. Future developments Geant4 Use of the new Geant4 low energy model Conclusions Simulation of air kerma rate Isodose distribution around shielded and unshielded applicators Geant4 We have developed a procedure to test Geant4 toolkit, which provides a modern Montecarlo implementation and robust physics modelling. Geant4 We have found a very interesting field of application for Geant4 in brachytherapy.