There is no standard protocal. It depends on your stage, on your doctors policy, on what is going on in your blood and on you.
I have Stage IV colon to liver. I get bloodwork and a CT every six months. I had 1 colonoscopy 1 year after my surgery.
I know other Stage IV's who are no longer seeing their doctor after finishing their chemo.
As a Stage IV, I'd rather get a CT every 6 months then not. About a year ago I also had an MRCP (basically an MRI of my abdomen) to find out why my liver enzymes are still high. But, it didn't answer any questions.
Since some studies showed that PET scans aren't that effective in detecting cancer, some insurance companies dropped it.
So it's up to the patient to be informed and also to decide what you want to do. Some people are scared of the radiation they get from CT's and therefore don't get one. I initially had to pay for my colonoscopy, but when they found something, the insurance company picked it up.