Voxel Density and Dose in DICOM Example

Hello, good day everyone. In the Dicom example, when I print the density associated with each voxel on the screen, some of them show a density equal to zero, but they still register dose and deposited energy. Is this possible? Attached is part of the output:

Voxel | Dose | Edep | Material | Density
0 0 0 Air 0
1 0 0 Air 0
2 0 0 Air 0
3 2.03809e-09 0.00076953 Air 0
4 2.53917e-09 0.000958723 Air 0
5 0 0 Air 0
6 0 0 Air 0
7 0 0 Air 0
8 4.90349e-09 0.00185143 Air 0
9 0 0 Air 0
10 0 0 Air 0
11 0 0 Air 0
12 0 0 Air 0
13 0 0 Air 0.01204
14 7.19753e-09 0.0027176 Air 0.0110367
15 0 0 Air 0.0110367
16 0 0 Air 0.01204
17 0 0 Air 0.0100333
18 0 0 Air 0.0100333
19 0 0 Air 0.0110367
20 0 0 Air 0.00802667
21 3.98354e-10 0.000150408 Air 0.00802667