Radiation therapy has made marked progress following introduction of high energy X rays

gamma rays and electron beams. Nevertheless

there still remains a substantial numbers of patients suffering from the failure of local tumor control. The high LET radiations including fast neutrons

heavy ions and negative pions might be expected to offer a therapeutic gains as compared to those as mentioned above. The rationale for introducing fast neutron therapy mainly is its radiobiological properties that are potentially superior to those of photons and electrons. The tumor types or sites for which a benefit is observed are outlined . Results of clinical trials of high LET radiations therapy are also listed.