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Boron neutron capture therapy (BNCT) is an experimental form of radiotherapy that utilizes a neutron beam that interacts with boron injected to a patient. BNCT depends on the interaction of slow neutrons with boron-10 to produce alpha particles and lithium nuclei, without producing other types of ionizing radiation. Patients are first given an intravenous injection of a boron-10 tagged chemical that preferentially binds to tumor cells. In clinical trials performed so far the neutrons are created in a nuclear reactor, but particle accelerators may also be used to collide protons into targets made of lithium or beryllium. The neutrons pass through a moderator, which shapes the neutron energy spectrum suitable for BNCT treatment. Before entering the patient the neutron beam is shaped by a beam collimator. While passing through the tissue of the patient, the neutrons are slowed by collisions and become low energy thermal neutrons. The thermal neutrons undergo reaction with the boron-10 nuclei, forming a compound nucleus (excited boron-11) which then promptly disintegrates to lithium-7 and an alpha particle. Both the alpha particle and the lithium ion produce closely spaced ionizations in the immediate vicinity of the reaction, with a range of approximately 10 micrometres, or one cell diameter. This technique is advantageous since the radiation damage occurs over a short range and thus normal tissues can be spared. BNCT has been experimentaly tested primarily as an alternative treatment for malignant brain tumors called glioblastomas. Although there are reports of some successful outcomes, this approach has not yet been shown to be superior to other current therapies. Hence, BNCT has not entered routine clinical use.
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