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. He received board certification by the American Board of Radiology in 1950. On his return to Madison, he practiced initially with Dr. Larry Littig, before starting his own practice serving small hospitals in Darlington and Dodgeville and opening his own office in the Tenney Building at 110 East Main Street in Madison. This practice evolved into Madison Radiologists, S.C. and at the time of his departure in 1973 in addition to an office at 20 S. Park St. in Madison, served St. Mary's Hospital Medical Center, St. Clare's Hospital, Baraboo, and General Hospital Sauk City as well as the hospitals in Darlington and Dodgeville. He opened a new private office practice, Stiennon Radiology Group at One South Park St in Madison in 1975 and continued to practice in association with his two radiologist sons until his retirement in 2001. Community activities He was a flutist and chamber music exponent, regularly assembling chamber music groups at his home. He served on a steering committee chaired by Leo T. Crowley which worked to raise funds for the Diocesan Holy Name Seminary Radiation treatment center He opened the Radiation Center, the first private medical center to treat cancer patients with a betatron, at 2716 Marshall Court in the Village of Shorewood Hills a suburb of Madison, Wisconsin, in 1957. The facility employed one of the first Allis-Chalmers 25 MeV Betatrons and brought the era of modern megavoltage radiation therapy to the Madison area. Evenings the machine was used to analyze industrial castings, including some related to the Titan Missile. The Longitudinal Muscle in Esophageal Disease He published a book, The Longitudinal Muscle in Esophageal Disease about his conclusions concerning the esophagus obtained from a lifetime of experience in radiology. Among his conclusions was that achalasia and barrett's esophagus are not