An experimental unit for fast neutron radiotherapy

The possible application of 14 MeV neutrons produced by the deuterium-tritium reaction to radiotherapy is discussed. The basic neutron generator is a sealed tube device developed by the Services Electronic Research Laboratory and this is described, as is also an associated shielding and collimating system. It is shown that the neutron beams produced by this device are adequately defined for radiotherapy. The dose-rate at the end of the collimator is equivalent to about 5 rads/minute of X rays. Percentage depth doses for a limited range of field sizes have been measured at 50, 75 and 100 cm SSD, and the values are intermediate between these for 250 kVp X rays and 60Co γ rays. It is shown that there is a slight “build-up” effect at the surface, extending to a depth of 2 mm.