.9 is well, well below normal. If they were climbing a full point I would worry more. It is good that you are watching them closely. Cat scans are routinely done every 6 months for monitoring purposes. Once you get past a certain time, they get less frequent.
Ask your doctor what he/she feels is the plan. For example: every 6 months until you hit 3 years with no evidence of disease then once a year? They do have a plan but you need to ask.
I get scanned every 3 months but my CEA seems to be climbing back up. Slow climb but still climbing. My next CT scan will tell me more about what the heck is going on inside.
Good luck and it sounds like you're doing great.
Welcome to our group...not a group we really want to join but so glad to have found.