Hello,
No, Orthanc does not support multi-tenancy. The rationale is that Orthanc being lightweight, multiple Orthanc servers can easily be started, even on the same host.
In your example, you would have to start 4 different instances of Orthanc. You could however connect these 4 instances of Orthanc to the same PostgreSQL server with 4 separate databases. In such a setup, multi-tenancy would be brought through PostgreSQL.
On a related topic, make sure to read the following page:
HTH,
Sébastien-