Ramamurthy,
RT alone will not be sufficient to eliminate agressive cells.
Surgery even though it has some harsh realities removes potential breeding grounds for more malignant cells.
You state that your tumor has disappeared and ask if you can only have the RT. Cancer is different in every individual and treatment is different in every individual.
Get as many opinions as you feel you need and ask the doctors the questions you have asked here. When you are satisified with the answers then choose the treatment that you feel is best for you.
All the best,
Mike