We propose the development of a very compact, rotating-wave electron beam accelerator (RWA) for x-ray radiotherapy applications. The proposed accelerator employs a very short accelerating structure to accelerate a low-energy electron beam to a final energy of 6 MeV in a highly efficient manner. The RWA offers twice the efficiency of conventional small accelerators in addition to having a greater degree of simplicity and a more compact design. Based on its high efficiency and compactness, we estimate a reduction in the price of the entire system by a factor of 2. In Phase I we conducted a complete design of the RWA for radiotherapy applications including experimental testing of the RWA cavity as well as a large number of computer simulations and a conceptual RWA design. Our successful Phase I design studies corroborate our initial estimates and show that the RWA should be perfectly suited for medical applications while providing a substantial cost reduction when compared to conventional machines. We are now ready to proceed with the development of a 6 MeV accelerator system during Phase II. Once fully developed, the rotating-wave accelerator could be the basis for a new class of very compact 6 MeV radiotherapy accelerators that should be affordable for small clinics and hospitals around the country. We anticipate that this compact accelerator will be able to provide 6 MeV electron beams for applications such as radiotherapy, sterilization of medical devices, food processing, and pollution control, among others. The proposed accelerator will be more compact, more power efficient and more affordable than conventional small accelerators. ? ? ? ?