I am searching for source code to segment Lung in CT images using watershed algorithm. Please let me know if you find any website / source code.
Watershed algorithm – CT Lung segmentation
4.1k Views Asked by user523582 AtThere are 4 best solutions below

Relevant algorithms:
morphological watershed method (Meyer)
modified watershed algorithm (Beucher, Meyer)
gradient descent or rainfall algorithm (Osma-Ruiz)
watershed immersion algorithm (Vincent-Soille)
Some Source code here

The Insight Toolkit is a comprehensive image processing framework for segmentation and registration of medical images.
There are many specialised algorithms for processing medical images, including the Watershed algorithm. Some of the examples are very similar to what you describe.
I strongly recommend reading the ITK Software Guide book before undertaking such a significant project.
Furthermore, it is very important to choose a library that correctly deals with medical images and the special attributes and requirements they have (for example, patient orientation, anisotropic voxels, etc). Most libraries do not handle these aspects correctly, while ITK has been designed from the ground up to support all the complexities of medical imaging applications.
Wikipedia might help.