akoo, I've never heard the exact phrase "patchy enhancement" used before. You should ask your doctor for clarification. But it sounds to me like your tumor is probably showing signs of necrosis -- a very good thing. Here's why:
A live tumor shows up white (enhanced) with contrast agent applied during an MRI. As the tumor begins to die (following radiation treatment), the dead tissue shows up black (not enhanced). This black and white spottiness (parts of the tumor still alive, parts of it dead), I would think, is what your doctor is probably referring to when they note "patchy enhancement."
It's important to note that dead scar tissue also shows up white in an MRI with contrast. That's because scar tissue has no vascularity (blood flow). So, the usual progression of a tumor that's been irradiated is for it show in MRIs with contrast as at first all-white then spotty (black and white patches) and then finally all-white again, as the dead tissue finally becomes scar tissue. Some people's tumors never show the blotchy phase, presumably because it occurred between MRI sessions, yet their tumor's growth, in the overwhelming number of cases, is nevertheless halted.