Energy Spectra in the NAC Proton Therapy Beam

In order to tailor a proton beam for radiation therapy several beam modification devices are used which affect both the dose distribution and the energy spectrum of the beam. Knowledge of the proton spectra is helpful for optimising the beam delivery system and for comparison with theoretical calculations. Proton elastic scattering has been used to measure spectra in the NAC 200 MeV clinical beam. A polyethylene scatterer is located at the treatment isocentre. Two scintillator detector ?E/E telescopes are placed symmetricaly about the beam axis such that the energy of both the scattered and recoil protons is half the incident beam energy. Multiparameter data acquisition and analysis are used to determine the coincident summed spectra under various irradiation conditions.