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Fast neutron therapy utilizes high energy neutrons typically greater than 20 MeV to treat cancer....

Fast neutron therapy utilizes high energy neutrons typically greater than 20 MeV to treat cancer. Most fast neutron therapy beams are produced from proton beams impinging upon beryllium targets. Radiation therapy of cancers is based upon the biological response of cells to ionizing radiation. Tumor cells typically lack effective repair mechanisms, so if radiation is delivered in small sessions, a process known as fractionation, normal tissue will have time to repair itself. This repair of normal tissue means that there is a therapeutic ratio between cancer cells and normal cells. In addition, different types of ionizing radiation will produce different effects upon cells. A comparison of neutrons with X-rays illustrates the differences. X-rays are the most common form of radiation used to treat cancer. Both neutrons and X-rays are uncharged; for this reason they are referred to as indirectly ionizing radiation. The biological effect of neutrons or X-rays is due almost completely to the secondary electrons that they produce when they interact with a patient's tissue. When therapeutic energy X-rays (1 to 25 MV) interact with cells in human tissue, they do so mainly by Compton