Can queries to boost's rtree be done from parallel threads?

I have two modules in application. Module1 owns and builds boost::geometry::index::rtree. Module2 makes queries to Module1, which are passed to RTree. Now I want to speed up and have several Module2 instances, which make queries to one Module1 instance, and work separately. I am 100% sure, that while any Module2 working RTree does not change.

Tl;dr:

Is it safe to make queries to boost::geometry::index::rtree from different threads, if I am 100% sure, that no thread modifies RTree?