Comment # 2 on bug 1167431 from Johannes Segitz

the package is currently broken. /etc/orthanc is owned by root, but orthanc
tries to create OrthancStorage in there, which fails since it's already running
as the unprivileged user. This can be changed in Resources/Configuration.json
AFAIU. This should be moved to /var anyways, /etc is not the right place for
this

While you're at it you can enable hardenings in the systemd unit like
PrivateTmp=true
ProtectSystem=strict
ProtectHome=true
ProtectKernelModules=true
ProtectKernelTunables=true
ProtectControlGroups=true
MountFlags=private
NoNewPrivileges=true
PrivateDevices=true
MemoryDenyWriteExecute=true
that shouldn't be an issue with this type of service