I’m having the exact same trouble as posted in this old SLAC hypernews link but there was no publicly available resolution to the reported problem. https://hypernews.slac.stanford.edu/HyperNews/geant4/get/medical_app/412/1/1.html
It seems to me to be a problem with building DCMTK from source. If I obtain DCMTK from my package manager (apt-get install dcmtk on Ubuntu 16.04) and inspect ‘1.dcm’ in the DICOM example using the ‘dcmdump’ executable, it will spit out correctly that the modality of the ‘1.dcm’ file is [CT]; however, it is my understanding I also need the shared libraries such that the GEANT DICOM example can compile correctly; thus the executables from package manager aren’t enough (am I wrong here?)
I tried building DCMTK from source (and tried both versions 3.6.2 and 3.6.5), make sure to enable ‘BUILD_SHARED_LIBS’ in the cmake config but both the DICOM example and ‘dcmdump’ when built from source will incorrectly identify the modality of the example ‘1.dcm’ file as  (amongst many other incorrect tags).
Anyone have an idea of what I’m doing wrong?