It is unclear from your question how exactly is represented your point cloud in the DICOM image stack.
I suppose the points are pixels in the slices that have a particular color. In this case, the ITK Software Guide has a fully documented example about how to extract a surface from a 3D DICOM image: It is chapter "6.11 Extracting Surfaces" (link to the book).
This example uses an ITK filter that performs a thresholding step to isolate your points and then performs the surface extraction.
It is not exactly what you are asking for though: this example outputs a mesh instead of a set of points. However, in ITK a mesh is a kind of point set (class vtkMesh derives from vtkPointset) so you can get your cloud of points from there.
See also chapters "4.2 PointSet" and "4.3 Mesh" in the same book.
I hope this helps.