VMC is a computer program that simulates the irradiation of the human body by external sources. It uses a voxel phantom produced at Yale University and the Monte Carlo technique to simulate the emission of photons by a point, ground, cloud source or X ray source. It then transports the photons through the human body phantom and calculates the dose to each body region.
For the simulation of the human body, a voxel phantom with a format of 488 “slices” each of 192 x 96 picture elements was used. The size of each voxel is 3.6 mm x 3.6 mm x 3.6 mm and there are 8.994.816 million voxels in the phantom. The voxel phantom is derived from a whole body magnetic resonance image (MRI) scan and was obtained from the Yale University voxel phantom library which is maintained by I. George Zubal, Ph.D. The voxel phantoms in this library are freeware, and may be obtained through George Zubal at George.Zubal@Yale.Edu. The Yale voxel phantom was modified at the IRD so as to maintain only the tissues relevant for the calculation of the effective dose, as defined in ICRP 60.
VMC is a Monte Carlo code designed specifically for voxel geometries and has an extensive graphic output. It is written in Visual Basic. As the energies of the radionuclides of interest for external dose calculations during most occupational exposure or accident situations fall in the range of 0.02 – 1.5 MeV, only photoelectric and Compton interactions were considered. The Monte Carlo code uses the RANMAR random number generator, with a period of approximately 10^30 random numbers.