1. From the Mayo Clinic Translational Interventional Electrophysiology Laboratory (H.I.L., M.T., K.D.P., S.B.J., S.J.A., D.L.P.) and Department of Radiation Oncology (A.J.D., J.J.K., L.S., S.E.A., J.T.C., R.C.M., M.G.H.), Mayo Clinic, Rochester, MN; and Texas Center for Proton Therapy, Irving (L.S.).