Also consider the @surf_to_vol_spackle program. That wraps 3dSurf2Vol but fills in holes missed by the projection.
https://afni.nimh.nih.gov/pub/dist/doc/program_help/@surf_to_vol_spackle.html
https://discuss.afni.nimh.nih.gov/t/schaefer-atlas-for-dti-tractography/3252/1