Computer generation of dose distributions for a fast-neutron therapy beam.

A system has been developed for the computer generation of dose distributions for the MANTA-NRL fast-neutron radiotherapy beam. This program is based on scatter-air ratio (SAR) techniques. A method has been developed to unfold the effect of the neutron-beam profile in the derivation of SARs so that the SARs obtained are those which would be derived if the beam profile were flat. Tables of zero-area tissue-air ratios and SARs are presented. Comparisons of calculated and measured dose distributions are shown. An empirical correction to the usual SAR methods was required to obtain agreement between calculated and measured dose distributions at source-to-skin distances (SSD) which are different from the SSD at which the SAR are derived.