I am wondering if accusations put into an employment file, though unsubstantiated can be subject to a libel suit?

I work with high school students and due to some personality conflict with one of the administrators, have been subject to false accusations being put into my employment reviews and ultimately employment file. There have been statements made that I know would cause any future employer to question or even reject me as a candidate for a job should I seek another position. At first, I signed all documents to be placed in my file because there were opposing statements made by colleagues on my behalf. These documents would seem to contradict the others when assessing my job performance. This past school year I refused to sign my performance review because it was so blatantly laced with falsehoods. It has gotten to the point that I am being treated for a stress condition.