NEW VERSION OF GDCM and pydicom using conda works like charm:

conda install -c conda-forge -y gdcm
pip install --no-cache-dir git+https://github.com/pydicom/pydicom.git

OLD - keeping for example if somebody finds building GDCM helpful or does not like to use conda

local build/installation instructions

apt-get update
apt install -y python-vtk6 libvtk6-dev cmake-curses-gui checkinstall swig libpython3.6-dev
mkdir gdcm && cd gdcm && git clone --branch release git://git.code.sf.net/p/gdcm/gdcm
mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_FLAGS=-fPIC -DCMAKE_CXX_FLAGS=-fPIC -DGDCM_BUILD_SHARED_LIBS:BOOL=ON -DGDCM_WRAP_PYTHON=ON PYTHON_EXECUTABLE=/usr/local/bin/python3.6 PYTHON_INCLUDE_DIR=/usr/local/lib/python3.6/site-packages/ GDCM_BUILD_SHARED_LIBS=ON GDCM_USE_VTK=ON /gdcm/gdcm
cmake --build . --target install

cp /usr/local/lib/gdcm.py /usr/local/lib/python3.6/site-packages/.
cp /usr/local/lib/gdcmswig.py /usr/local/lib/python3.6/site-packages/.
cp /usr/local/lib/_gdcmswig.so /usr/local/lib/python3.6/site-packages/.
cp /usr/local/lib/libgdcm* /usr/local/lib/python3.6/site-packages/.
ldconfig

INSTALLATION FROM .deb

git clone --branch master https://github.com/HealthplusAI/python3-gdcm.git && cd python3-gdcm && dpkg -i build_1-1_amd64.deb && apt-get install -f
cp /usr/local/lib/gdcm.py /usr/local/lib/python3.6/site-packages/.
cp /usr/local/lib/gdcmswig.py /usr/local/lib/python3.6/site-packages/.
cp /usr/local/lib/_gdcmswig.so /usr/local/lib/python3.6/site-packages/.
cp /usr/local/lib/libgdcm* /usr/local/lib/python3.6/site-packages/.
ldconfig