  No fast neutron therapy facility has been built with optimized beam quality
based on a thorough understanding of the neutron spectrum and its resulting
biological effectiveness. A study has been initiated to provide the information
necessary for such an optimization. Monte Carlo studies will be used to
simulate neutron energy spectra and LET spectra. These studies will be
bench-marked with data taken at existing fast neutron therapy facilities.
Results will also be compared with radiobiological studies to further support
beam quality optimization. These simulations, anchored by this data, will then
be used to determine what parameters might be optimized to take full advantage
of the unique LET properties of fast neutron beams. This paper will present
preliminary work in generating energy and LET spectra for the Fermilab fast
neutron therapy facility.
