I think the OP said the tumor is meningioma, not melanoma. From what I've read, meningiomas are almost always benign and, though surgery is the best course, radiation can and has been successful (at least in humans) in prolonging quality life.
If it was my 14-year-old dog, as long as he/she was in good health otherwise (given its age), I'd give radiation a shot.
Thanks Ivy, it was 15 years ago for dad, but only 2 years ago for my Rama dog. Hope your friends furkid doesn't have the melanoma and that the radiation helps. It's always so hard to know what to do. Especially when you just want your loved one to feel better.