Neutrons are sub-atomic particles. They are usually produced by bombarding a beryllium target with protons. Protons are positively charged sub-atomic particles produced in a cyclotron. Neutrons can be used to treat certain tumours. The property of neutrons which differentiates this therapy from most others is that it damages cells using high linear-energy-transfer (high LET). If a tumour cell is damaged by low LET radiation it has a good chance to repair itself and continue to grow. With high LET radiation, the chance for a damaged tumour cell to repair itself is very small.
Because the biological effectiveness of neutrons is so high, the required tumour dose is about one-third the dose required with photons (x rays), electrons or protons. A full course of neutron therapy is delivered in only 10 to 12 treatments, compared to 30 – 40 treatments needed for low LET radiation. Side effects for fast neutron therapy are similar to those of low LET therapy. Their severity depends on the total dose delivered and the general health of the patient. Effects on normal tissues are minimized by careful computerized treatment planning for CT-based, conformal therapy.