This paper focuses on boundary surface based ray casting. In general the boundary surface based ray casting is processed in two stages. In the first stage, boundary surfaces are found and stored into buffers. In the second stage, the distance between the viewpoint and the voxels of the area of interest is calculated by projecting boundary surfaces on the view plane, and then the traverse of the volume data space with the distance is started. Our approach differs from the general boundary surface ray casting in its first stage. In contrast to the typical boundary surface based ray casting where all boundary surfaces of volume data are stored into buffers, in our proposal, they are projected on the planes aligned to the axis of volume data coordinates and these projected data are stored into 6-depth buffers. Such a maneuver shortens the time for ray casting, and reduces memory usage because it can be carried out independently from the amount of the volume data.