How to get the proper shape from 3d OCT volume rendering

Operating system: Mac OS X
Slicer version: 4.10.1
Expected behavior: Trying to interactively build a 3d model from a stack of circular OCT images from an airway. The boundaries are not very well defined.
Actual behavior: In the 3d volume it shows up as a volumetric cylinder, how to make it in the shape I want, i.e. an actual airway?

You can reconstruct Cartesian volume from circular OCT images (see discussion here) and then you can use Segment Editor to create a 3D model.