Radiotherapy is unique as a medical specialty in that it depends upon physical sources of energy deposition within tissues to bring about profound and complex biological changes for the purpose of eradicating cancerous growths. Thus, it has the broadest interface with both physical and biological sciences of any clinical discipline. It is for this reason that progress in radiotherapy is continually stimulated by advances in bothphysical and biological sciences. In recent years, increasing attention has been focused on high energy particle radiations as possible additions to the therapeutic armamentarium, in an effort to improve the results obtainable with x and y radiations. The purpose of this paper is to discuss how some accelerator produced radiations, fast neutrons and Π mesons, might be of potential value to radiotherapy.