Creating mask around points

Hello. I need to create a lung mask by points. I have succeeded in making a lung mask for a particular time slice but I need to make a loop for making the masks for all the DICOM scans of the patient. These 'points' are basically the bone structures in the DICOM image which will change at each time slice. Here is what I need to do:

I can filter out the bone part (blue) by changing the HU Values. That is pretty much done. What I need is to join all these blue points in such a way that it creates a mask(yellow) so that I can separate it as an ROI from the original image. Also, the other bone part (on far left and right) should not be included in the mask.

Any help would be greatly appreciated.