What is Neutron Therapy?
Neutron therapy is a highly effective form of radiation therapy. Long-term experience with treating cancer has shown that certain tumor types (histologies) are very difficult to kill using conventional radiation therapy. These histologies are classified as being "radioresistant." Neutron therapy specializes in treating inoperable, radioresistant tumors occurring anywhere in the body.

Radiation therapy is the use of penetrating beams of radiation to treat disease. Conventional radiation therapy includes photon (x-ray) and electron radiation, which is available at many clinics and hospitals. These beams are produced by electron accelerators or from radioactive sources such as cobalt. Particle therapy includes protons and neutrons, which are generated using proton accelerators. Radiation therapy is used primarily in the treatment of cancerous tumors.

The basic effect of ionizing radiation is to destroy the ability of cells to divide and grow by damaging their DNA strands. For photon, electron and proton radiation the damage is done primarily by activated radicals produced from atomic interactions. These types of radiation are called low linear-energy-transfer (low LET) radiation. With neutron radiation the damage is done primarily by nuclear interactions. Neutrons are high linear-energy-transfer (high LET) radiation. If a tumor cell is damaged by low LET radiation it has a good chance to repair itself and continue to grow. With high LET radiation such as neutron radiation, the chance for a damaged tumor cell to repair itself is very small.

Because the biological effectiveness of neutrons is so high, the required tumor dose is about one-third the dose required with photons, 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.

History of Neutron Therapy
Sir James Chadwick discovered neutrons in 1932. Just six years later, Dr. Robert Stone began clinical trials treating cancer with neutrons produced by E.O. Lawrence’s cyclotron in Berkeley, California. These trials were terminated because the cyclotron was needed for the war effort during World War II. Clinical research began again in 1965 when Dr. Mary Catterall at Hammersmith Hospital in London began irradiating patients with neutron beams. By 1969, it was clear that for certain tumors, better local control could be achieved using neutron irradiation. Encouraged by these results, the M.D. Anderson Hospital and Tumor Institute in Houston, the Naval Research Laboratory in Washington, D.C., and the University of Washington in Seattle began neutron therapy research. They started treating patients in the early 1970s. During the mid-1970s Chicago-area radiation oncologists, Lionel Cohen, M.D. and Frank Hendrickson, M.D., worked with Dr. Robert R. Wilson (Fermilab Director from 1968 until July 1978) to build the Neutron Therapy Facility (NTF) at Fermilab. Measurements of neutron beam characteristics and dose distributions were completed in 1976; patient treatments were begun September 7, 1976.

One significant finding… was that only neutron beams produced by protons with energies greater than about 60 MeV could produce tumor control with side effects no worse than low LET radiation for deep-seated tumors.

The National Cancer Institute funded the operation of the facility from June 30, 1975, until October 1, 1985. During that period NTF conducted clinical trials to determine the appropriateness of using neutrons to treat various types of cancers. Initial research included using different doses in order to determine the optimum, safe therapeutic dose with minimum treatment-related late side effects. Some of the trials involved randomly assigning eligible patients to receive either the best conventional treatment for their cancer, or neutrons, which at the time were considered to be experimental. This was done only with the patient’s permission. Fermilab’s treatment results using a high-energy neutron beam were combined and analyzed with results from other facilities.