  This paper reviews the main types of radio-frequency powering systems which
may be used for medical applications. It gives the essentials on vacuum tubes,
including tetrodes, klystrons, and inductive output tubes, and the essentials
on transistors. The basics of combining systems, splitting systems, and
transmission lines are discussed. The paper concludes with a case study
specific to medical applications, including overall efficiency and cost
analysis regarding the various available technologies.
