New accelerating method for photon transport in Monte Carlo simulation

In Monte Carlo simulation, photon transport requires calculating the distance from the location of the photon to the nearest boundary of each uniform attenuating medium along its path of travel, and comparing the distance with the length of its path generated in the simulation. In this paper, we propose a new method which omits the calculation of the location of the exiting point of the photon and of the distance between the exit point and the original position. The method only checks the medium of the voxel existing along with the path of the photon transport. If the medium is different from that in the voxel which the photon emitted, then we calculate the location of the entry point in the voxel, and the length of the path is compared with the mean free path length generated by a random number. Simulations by means of an MCAT phantom show that the ratios of the calculation time were 1.0 for the voxel based method, 0.51 for the proposed method with a 256×256×256 matrix image and the effectiveness was confirmed