Characterization of secondary neutron production during proton therapy

Proton therapy facilities use high-energy proton beams to destroy cancerous cells. In this approach, secondary radiation is produced due to proton interactions with the patient and surrounding materials. This secondary radiation field, which includes both neutrons and photons, must be accurately characterized in order to determine its effect on patients and medical personnel. The MCNPX-PoliMi code has been used to characterize the secondary neutrons produced during proton irradiation of radiation therapy phantoms. Measurements have been performed at the Loma Linda University Medical Center proton therapy research beamline in order to validate the Monte Carlo models. Proton beams of 155- and 200-MeV were used to irradiate a variety of phantoms and the secondary particles were detected using organic liquid scintillators. These detectors are sensitive to fast neutrons and gamma rays. Pulse shape discrimination was used to classify each detected pulse as either a neutron or a gamma ray. Preliminary analysis has shown good agreement between the simulations and the measurements.