Congratulations on your successful one year scan. I, like you, had a subtotal removal, but mine was 95% to 97% of the tumor. My surgeon told me it was likely I would need gamma at some point in the future, but there was the possibility I would not. My residual tumor was stable at one year, at two and a half years remained that way. My next scan is set for the 4 year mark.
House recently published a paper on follow ups on subtotal removals. The study compared complete removals with near total and subtotal removals and concluded the regrowth rates were substantially higher for incomplete removals versus complete, but that the need for actual re-treatment was "infrequent." Followed for up to 5 years, there was regrowth of 21% and 22% in the incomplete removals but re-treatment was required in 2% and 10% for near total and subtotal removals respectively.
Regrowth itself does not necessarily mean we require further treatment immediately. Good luck