The present study reports on the feasibility, development and test of a slit camera for real time range control in proton therapy by means of prompt gamma imaging. The camera was first optimized and characterized by Monte Carlo simulations with MCNPX. Its performances were evaluated for 100 to 230 MeV proton pencil beams and challenged by a prostate treatment plan. The accuracy of the simulations was assessed by comparison with spectrometry measurements of secondary particles emitted by a PMMA target during proton irradiation at 160 MeV. An excellent agreement was observed when using subtraction methods to isolate the gammas in direct incidence. A first prototype slit camera using the HiCam gamma detector was consequently prepared and tested successfully at 100 and 160 MeV beam energies. Results demonstrate the potential of this new concept for real time range monitoring with millimetre accuracy in pencil beam scanning mode for typical clinical conditions.

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