O. Arthur Stiennon, Jr. (November 9, 1919 in Green Bay, Wisconsin – January 10, 2003 in Madison, Wisconsin) was a clinical radiologist, inventor, radiation treatment pioneer, software and real estate developer in Madison, Wisconsin. He attended the University of Wisconsin–Madison, graduating Phi Beta Kappa in 1941. He received his M.D. at the University of Wisconsin in 1943 under the wartime accelerated program. He served an internship at the Royal Victoria Hospital in Montreal, P.Q., Canada. After serving in the United States Army from 1944-1947, he served a residency in Diagnostic and Therapeutic Radiology at the University of Michigan Hospitals in Ann Arbor, Michigan.