Measurement of neutrons and photons produced during proton therapy

Proton therapy facilities use high-energy proton beams to destroy cancerous cells with greater specificity than photon-based approaches. However, due to the high energy of these protons, secondary radiation is produced through interactions with the patient and surroundings. These secondary neutrons and photons need to be accurately characterized for the benefit of patients and medical personnel. Experiments have been performed at a Chicago Proton Center proton therapy treatment beamline. Continuous-operation pencil beams of 155- and 200-MeV protons were used to irradiate three tissue-equivalent phantoms provided by CIRS Inc: soft tissue, compact bone, and trabecular bone. Secondary particles were detected using an array of organic scintillation detectors: three 7.6-cm diameter by 7.6-cm thick EJ-309 liquid scintillators and one 5-cm diameter by 7.6-cm thick stilbene crystalline scintillator. Pulse shape discrimination was applied to each detector using a charge-integration technique. Preliminary analysis has shown clear separation in the measured neutron and photon pulses.