MONTE CARLO SIMULATION OF AN Ir-192 BRACHYTHERAPY SOURCE SPECTRA, GEOMETRY AND ANYSOTROPY FACTORS USING GEANT4 CODE

In brachytherapy cancer treatments, methods for calculation of dose delivered to tumours and organs have been continuously improved. The goal of those calculations is the maximization of dose deposition in the target volume, while minimizing the deposition in the healthy tissues. The use of interstitial brachytherapy sources follows the recommendations of AAPM REPORT N degrees 51. The present work is based on Monte Carlo simulations with GEANT4. An Iridium-192 MicroSelectron HDR source was simulated and the geometry of dose deposition in media and primary spectra were obtained. Calculations also include photon-fluence distributions at two radial distances and accumulated air Kerma. A matrix of radial and angular coordinates was constructed, obtaining the Geometry Factor G(r,theta), the Anisotropy Function F(r,theta) and the Radial Dose Function g(r,theta) needed for dosimetry calculations, adopting the AAPM REPORT N degrees 51 recommendations. A cubic arrangement of sources was simulated as an example of multi-source isodose calculation.