The major effect of ionizing radiation in cells is to destroy the ability of cells to divide by damaging their DNA strands. Extensive researches are leading to an understanding that the characteristics of high LET radiations such as fast neutrons and low LET radiations like protons, photons and electrons are different; because of different types of their interactions with tissue. Low LET radiations mostly damage tissue by producing free radicals. Oxygen has an effect of enhancing free radical formation in cells. Indeed hypoxic cells, which exist in malignant tumors, are radio resistant under irradiation with low LET radiations. In contrast, neutron interacts with tissue primarily via nuclear interactions, so its biological effectiveness is not affected on the presence of oxygen. The required dose to kill the same number of cancerous cells by neutrons is about one third in comparison with photons. Clinical reports show that a full course of treatment with neutrons consists of 12 treatment sessions, compared to 30-40 treatments with photons or electrons. In conclusion, in this review we describe which cancers or tumors could be better treated with neutrons. We also refer to whether neutrons could be used for diagnosis.

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