Welcome to healthcare Magic! The cancer treatments by radiation and chemotherapy
etc are complicated clinical decisions.
patient need long term follow up and treatment because there can be a relapse of the cancer itself or there may be some complication related to the therapies.
if so these must be detected early and managed as soon as possible and treated diligently at the earliest because delay in these parameters may affect the outcome and survival.
So you should follow the advice of your physician closely and comply with the plan of care.
I hope the advise would be informative and useful for you.