Set password for a specific topic/branch in phpbb 3?

Question

phpBB

I have an admin account, FTP and database access.
There was a need to restrict access to the flesh to one, the only user in the topic.
There will be consultations for patients.
I just don’t want to, only for this purpose to create a closed section, for the sake of one topic.
Maybe some plugins can achieve this or regular means?
Thanks in advance.