Prompt-γ production of 220 MeV/u 12C ions interacting with a PMMA target

The radiation used in particle therapy treatments produces secondary particles, either neutral or charged, when interacting with the patient body. The particles that exit from the body can be used to provide a fast feedback on the treatment plans. Here we report the measurements of prompt-γ ray fluxes produced by the interaction of a 220 MeV/u carbon ion beam at GSI, Darmstadt, with a polymethyl methacrylate (PMMA) target. The photons were detected by means of an array of LYSO crystals, allowing for a measurement of time of flight and released energy. Different angular configurations were explored, placing the prompt-γ detector at 60°, 90°, and 120° with respect to the primary beam direction. The prompt-γ energy spectra have been obtained for the different angular configurations after having taken into account the detector resolution by means of an unfolding procedure tuned with a dedicated Monte Carlo simulation. The integrated fluxes (over the full 4π solid angle), in the 2-10 MeV prompt-γ ray energy range, at 60°, 90° and 120°, are measured as Φγ(60°) = (6.7±1.7) × 10-3 sr-1, Φγ(90°) = (6.3±2.1) × 10-3 sr-1 and Φγ(120°) = (4.4±1.1) × 10-3 sr-1 respectively