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Abstract — Most Monte Carlo simulations can be parallelized, or at least easily distributed. However, the parallelization of such programs is not mainstream. In this paper, we propose good practices to distribute a Monte Carlo simulation for computed tomography. We apply this to large edifices (such as volcanoes or pyramids) and give a particular focus on performances. The work included first the optimization of an existing sequential prototype and second the use of reliable parallel random streams. The optimized parallel version runs on a Symmetric Multi-Processor (SMP) and shows a fine and scalable speedup. The cumulated optimizations (sequential and parallel) enabled a speedup of 400X on a 32 cores SMP. Keywords- distributed computing, parallel random numbers