1. From the Department of Radiology, Mayo Clinic, 13400 E Shea Blvd, Scottsdale, AZ 85259 (W.F.S.); Department of Radiology (I.R., V.G., R.V.) and Department of Diagnostic Medical Physics and Radiation Safety (M.H.), AdventHealth, Altamonte Springs, Fla; and Varian Medical Systems, Atlanta, Ga (P.P.).