If you can diagnose from the source code that’s great.
But just FYI if you are able to run Slicer on the machine you can run vtk examples too. If you download the example linked above to /tmp/SampleRayCast.py, and then give it a .vtk volume file as an argument it should work for you like this example:
~/Downloads/Slicer-4.11.20210226-linux-amd64/bin/PythonSlicer /tmp/SampleRayCast.py ~/Documents/MRHead.vtk
(here I made MRHead.vtk by downloading the MRHead from the SampleData module and saving it as .vtk format.)