The New Particles and Their Application in Medicine

Abstract

In recent years there has been increasing interest in the use of “new” particle beams for various medical applications. The particles being used, fast neutrons, protons, helium ions, negative pions, and heavy ions, have in fact been known and studied by nuclear and high-energy physicists for over forty years. They are new only in the sense that, until recently, the medical community has had little experience with them in the clinic. One of the particles, the neutron, is not really new even to radiotherapy. In the late thirties Stone et al. treated 226 patients using cyclotron-produced neutrons (1940), but they discontinued therapy five years later because of unexpected severe late reactions (Stone, 1948). It was not until the sixties that it became generally recognized that neutron irradiation is relatively more effective compared to x-rays at the lower doses per fraction used in therapy than at the higher single doses commonly used in animal and cell experiments. This difference in effectiveness becomes even more important at the lower doses encountered in radiation protection, and it is interesting that it played an inhibiting role in the early days of particle radiotherapy (Brennan and Phillips, 1971).