One thing's for sure, don't go to "Chinese Massage" behind LuLu Hypermarket.

I don't know about registered medical-type massage therapists, but most likely the better hotels e.g. Marriott, Four Seasons, and Ritz Carlton, have spas with good masseurs and masseusses.

Of course in Qatar only women massage women, and men massage men, so if you are used to good deep pressure from a male therapist at home, find a big woman here! ;o)