Biological characterization of a high energy neutron beam for radiation therapy

In anticipation of the use of the Naval Research Laboratory (NRL) 35-MeV neutron facility for radiotherapy by the Middle Atlantic Neutron Therapy Association (MANTA), RBE values were obtained for a diversity of biological end points. Animals were exposed to neutrons at a dose-rate of approximately 60 rads/min, in Lucite exposure chambers which also served as scattering material. Parallel experiments were performed, using the same exposure apparatus, in which animals were exposed to 60Co gamma rays given at approximately 100 rads/min. RBE values were found as follows: mouse LD50/5 1.68; mouse LD50/30 1.80; mouse endogenous spleen colonies, 1.58; mouse thymic involution (ED50) 1.45; mouse splenic involution (ED50), 1.40; chick LD50/30 hour 1.81.