MRI question

two months ago, i had an mri to see if the radiation and chemotherapy was having any effect on the astrocytoma (grade II, involving right parietal lobe and both sides of my thalamus)  I was diagnosed in April 2007.  Two months ago, the doctor said it was stable but that there was a bright spot that they couldn't identify - the biopsy was inconclusive.  The bright spot is small.  This past month I had another MRI to see what the situation is.  I know that these types of tumors cannot ever be totally eradicated, but my question is this.  The MRI only showed the bright spot with no change and the original tumor - total size of a baseball - did not show on the MRI.  I know this is great news and I'm very excited, but since the tumor can never be totally eradicated, what could happen next?  Since it was a slow growing tumor, whivh the doctor believes could have been there since I was a child, could it take another 30-40 yers for it to grow back or will the cells that are still remaining come back sooner than that?  Is it possible that if they do come back, that I could be dealing with another form of brain cancer and, if so, what could those be?  Any help from the medical community would be greatly appreciated.  Thank you and have a good day, survivor42