code: def vt2vtk_file(vessel_tree, outfile, text_label=None, lc_all="C"):
      
  
      polyData = vt2polyData(vessel_tree, text_label=text_label)
      if lc_all is not None:
          import locale
          locale.setlocale(locale.LC_ALL, 'C')
      writer = vtk.vtkPolyDataWriter()
      writer.SetFileName(outfile)
      try:
          writer.SetInputData(polyData)
      except:
          logger.warning("old vtk is used")
          writer.SetInput(polyData)
      writer.Write()
      return polyData
docs: vessel_tree structure
      :param vessel_tree:  vt structure
      :param outfile: filename with .vtk extension
      :param text_label: text label like 'porta' or 'hepatic_veins'
      :param lc_all: LC_ALL locale settings. Controls float numbers
          format (dot or colon). If is set to "C" dot is used.
          If None is used no processing is done
      :return: