How to retrieve Menu Items from Custom Field of Incident

Summary

need to retrieve key/value pairs frm a custom field of INCIDENT

Content

The custom field "Incident.CustomFields.c.specialty is of the menu type

I need to query the menu items (key / value) in order to populate a plain HTML select menu.

The context is a PHP script which resices in the FILE MANAGER / Custom Scripts forder

Thanks in adavance!