What exactly is a voxel?

Dear GEANT4 Gurus,

This might be a dumb question but I am having a hard time understanding from my research just what is a voxel. why I want them, how do they affect things, and how do I get them.

In my example, a modified Testem11 to allow gps , I am trying to mimic the results of someone else. Their paper states that “the thickness of the laterally infinite scoring voxel are 0.02R_0, m where R_0 is the continuous slowing down range (CSDA) or the primary electrons”.

I can get my Edep curve to look like there’s for water at 1 MeV, but it is too high in energy by a little more than twice the published amount. I don’t know why this is, and can only assume that it has something to do with the voxels, or if the Max step length still needs to be set to 1% the CSDR, both things I can not seem to figure out despite heavy research. I have been able to match all the other parameters that they described to the best of my knowledge.

I’m very new to GEANT4 and any code involved as I have only been at this for two weeks so I apologize if I am asking stupid questions, but I am trying to get this done asap so I can finish my thesis before Dec.


A voxel is like a pixel, but in three dimensions. Its a basic geometric unit that subdivides whatever object has been voxelized. In some contexts you may have a uniform voxel grid made up of boxes all of the same size, such as is the case for CT/MRI volume information. In other cases, the voxels may not all be the same size if they are purely for optimizing navigation through some geometry, in which case they may be very large voxels in regions that are not near material boundaries, with much smaller voxels near the boundary regions.