The long range goal of this program is the development and commercialization of proton accelerators suitable for radiation therapy of cancer in hospital or clinical settings. For this purpose the accelerator should have an energy up to 250 Mev, and must be simple, reliable, and inexpensive compared to existing accelerators for physics applications. In addition, with sufficient innovation, it could have beam characteristics which would greatly enhance and simplify its use for the therapy application. Conceptual ideas exist for accelerators with these characteristics and with an estimated construction cost of $1M to $1.5M. The Phase I study would be carried out by experienced accelerator physicists and engineers. It would demonstrate the feasibility of the present conceptual ideas and develop a reliable cost estimate for the medical accelerator. These results would be the basis for attracting capital to produce a prototype accelerator and 2 or 3 units intended for clinical studies in hospitals (such interest presently exists). A Phase II grant request will be submitted to install, commission, and develop the capability of the prototype accelerator, and to transfer the development results to the clinical units. Phase III, supported privately, would make available commercial units.