Hi,
alternative with API Revit
import sys
import clr
clr.AddReference('ProtoGeometry')
import Autodesk.DesignScript.Geometry as DS
clr.AddReference('RevitAPI')
import Autodesk
from Autodesk.Revit.DB import *
clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager
doc = DocumentManager.Instance.CurrentDBDocument
clr.AddReference("RevitNodes")
import Revit
clr.ImportExtensions(Revit.GeometryConversion)
topo = UnwrapElement(IN[0])
slabShape = topo.GetSlabShapeEditor()
pair_vertices = [p.EndPoints for p in slabShape.SlabShapeCreases if p.CreaseType == SlabShapeCreaseType.Boundary]
OUT = [DS.Line.ByStartPointEndPoint(vertA.Position.ToPoint(), vertB.Position.ToPoint()) for vertA, vertB in pair_vertices]