The Dicom toolkit must be installed and then loaded to be used.
It can be installed in GNU Octave directly from octave-forge, or can be installed in an off-line mode via a downloaded tarball.
The toolkit has a dependency on the GDCM library (https://http://gdcm.sourceforge.net/), so it must be installed in order to successfully install the Dicom toolkit.
For fedora: yum install gdcm-devel
For ubuntu: apt install libgdcm2-dev
The toolkit must be then be loaded once per each GNU Octave session in order to use its functionality.
With an internet connection available, the Dicom package can be installed from octave-forge using the following command within GNU Octave:
pkg install -forge dicom
The latest released version of the toolkit will be downloaded and installed.