CT-BASED MONTE-CARLO SIMULATION TOOL FOR DOSIMETRY PLANNING AND ANALYSIS

The Los Alamos code MCNP4A (Monte Carlo N-Particle version 4A) is curr ently used to simulate a variety of problems ranging from nuclear reac tor analysis to boron neutron capture therapy. A graphical user interf ace has been developed that automatically sets up the MCNP4A geometry and radiation source requirements for a three-dimensional Monte Carlo simulation using computed tomography data. The major drawback for this dosimetry system is the amount of time to obtain a statistically sign ificant answer. A specialized patch file has been developed that optim izes photon particle transport and dose scoring within the standard MC NP4A lattice geometry. The transport modifications produce a performan ce increase (number of histories per minute) of approximately 4.7 base d upon a 6 MV point source centered within a 30 x 30 x 30 cm(3) lattic e water phantom and 1 x 1 x 1 mm(3) voxels. The dose scoring modificat ions produce a performance increase of approximately 470 based upon a tally section of greater than 1 x 10(4) lattice elements and a voxel s ize of 5 mm(3). Homogeneous and heterogeneous benchmark calculations p roduce good agreement with measurements using a standard water phantom and a high-and low-density heterogeneity phantom. The dose distributi on from a typical mediastinum treatment planning setup is presented fo r qualitative analysis and comparison versus a conventional treatment planning system. (C) 1998 American Association of Physicists in Medici ne.