I slept with my cellphone for 2 years. after i stopped using cellphone, does hypothetical risk for brain tumor still exist, if i stopped using phone?

No risk: In my opinion, the claim that there is even a "hypothetical" risk is silly. Cell phones don't produce the kind of radiation the causes cancer. If they did, the research piranhas would have demonstrated it by now -- it's how you get famous. The big study had more brain tumors on the side opposite to where the phone was held. Stop worrying over this stuff and enjoy your phone.

Cell phones emit: Radiofrequency waves, a form of nonionizing radiation. The current evidence between nonionizing radiation and cancer is not strong enough to be considered causal and needs to be investigated further. Individuals who are concerned about radiofrequency exposure can limit their exposure, including using an ear piece and limiting cell phone use, particularly children.