Is it possible to do research, in your PhD, on the same topic that you did for your Master's dissertation?
Researching the same topic for a Ph.D. as a Masters is entirely possible, and not necessarily even all that unusual (it depends on how you define "same").  If the Masters is a first set of results on the topic, and the Ph.D. then pursues a significant advance thereupon, that would be an entirely reasonable progression of research.