[Principle of neutron teletherapy with the Soviet U-120 cyclotron]

The authors present the results of their clinical developments on fast neutron irradiation of malignant tumors on the low-flow cyclotron U-120. The technique involved design of complexes provided with the sources of fast neutrons based on beryllium, gas deuterium and beryllium-deuterium targets. The spectrometry and dosimetry measurements of collimated bunches of fast neutrons have shown that the mean energies of neutrons from beryllium and gas deuterium targets are 6.0 and 11.5 MeV, while the absorbed doses are 0.8 and 0.5 sGy/min X microA. The increase of the local power of the biological dose inside the phantom irradiated by the collimated bunch of fast neutrons is shown to be due to intermediate energy neutrons, the contribution of which to the spectrum of fast neutrons increases with the decrease of their mean energy. The problems of selection of the sources of fast neutrons for neutron therapy are discussed.