I had brain surgery they got over 50% of it why is it a big deal to do radiation on what's left if it's a very slow growing tumor meningomia ?

BIg deal!: You just had Brain surgery, that is a big deal, and statistically, adding radiation treatment to the remaining tumor has the potential to dramatically decrease what is left and prevent further possible complications in the future. Radiation tx has come a long way and they can often pinpoint the beam exactly where they want and need it to go. Best wishes to you.