Physical Dosimetry and Instrumentation for Low-Energy Proton Irradiation of Primates

The object of this program was to develop a method to irradiate primates with whole-body exposures to proton beams in the energy range from 5 to 28 MeV. A system to expand the external beam of the Oak Range Isochronous Cyclotron was devised. The spatial distribution of the beam was uniform within ±5% over a 20 × 40-cm rectangle, and for all energies above 5 MeV the energy resolution was less than 1.8 MeV full width at half maximum. The proton beam was extremely stable; all beam profiles were basically identical, and the center of the beam did not vary over 3 cm in any direction. A variable-volume ionization chamber was designed and fabricated for use in remotely measuring the relative intensity of the flux. Flux values were measured with a Faraday cup, and surface-dose calculations were made from tabulated values of 1/ρ dE/dX for muscle. The dose values were accurate within ±8% for all energies used except 5 MeV, where the energy straggling made the uncertainty ±10%. In all, 90 primates were irradiated at 28, 21, 14, or 5 MeV and given doses ranging from 500 to 2000 rads.