  This paper introduces a new theory of multiparty session types based on
symmetric sum types, by which we can type non-deterministic orchestration
choice behaviours. While the original branching type in session types can
represent a choice made by a single participant and accepted by others
determining how the session proceeds, the symmetric sum type represents a
choice made by agreement among all the participants of a session. Such
behaviour can be found in many practical systems, including collaborative
workflow in healthcare systems for clinical practice guidelines (CPGs).
Processes using the symmetric sums can be embedded into the original branching
types using conductor processes. We show that this type-driven embedding
preserves typability, satisfies semantic soundness and completeness, and meets
the encodability criteria adapted to the typed setting. The theory leads to an
efficient implementation of a prototypical tool for CPGs which automatically
translates the original CPG specifications from a representation called the
Process Matrix to symmetric sum types, type checks programs and executes them.
