Unfortunately, the area where the gallbladder is lcoated is not always well visualized on CT scans. There are several possible causes for a "calcification" in the area where the gallbladder used to be (most of them are benign).
As I am not involved in your care, and as I cannot review your CT scans, your best bet is to see a GI specialist for further evaluation.
Sincerely/ Robert A. Wascher, MD, FACS
www.doctorwascher.com
www.oncoguard.com