A Computational Dosimetric Comparison between Mcnpx and Attila of the Mammosite Radiation Therapy System

The need for more accurate radiation therapy treatment planning is driving improvements in radiation transport calculations. In particular, the inclusion of patient specific anatomy and tissue density heterogeneities will be very important, particularly for treatment modalities that involve strong material discontinuities. The study presented here compares the application of the deterministic code Attila and Monte Carlo code MCNPX to an absorbed dose calculation for an implanted MammoSite breast cancer radiation therapy system in conjunction with the Varian VariSource VS2000 iridium-192 high dose rate source. An initial simplified model was developed in each code consisting of the VS2000 centered in a 30 cm diameter sphere of water where total dose deposition over the volume was calculated. For this scenario, the codes compared to each other within 3% difference. Phantom models of the MammoSite and VS2000 sources in water were then used to compare physics modeling between Attila and MCNPX and showed agreement within 1-2%. A final model using patient computed tomography data in Attila provided absorbed dose gradients through anatomical structures, presenting an introduction to the unique brachytherapy treatment planning capabilities of Attila.