DICOM
It supports reading of DICOM data, and it is possible to manipulate the threshold and extract the surface model.
Volume Paint
Volume Paint can efficiently create surface models from volume segmentation processing using a paint interface from 3D medical images (DICOM).
Models can be extracted as they are colored by operations such as fill and brush.
Fill
You can color the connected parts and fix the threshold, like a paint tool fill.
Brush
You can change the threshold partially with the brush tool to extract a detailed surface model.