I was every three months the first year and then on the 6 month schedule the second year. At the end of two years my doctor said see you next year. I questioned if it was too soon to go yearly and he said if I wanted to come in sooner he'd be happy to take my money
I took that as a very reassuring sign that he was confident in my future. Do what ever makes you comfortable, but yearly is a good thing.
Best of luck in your "undetectable" future,
Tom