Particle tracking, recognition and LET evaluation of out-of-field proton therapy delivered to a phantom with implants

This study evaluates the composition of scattered particles in proton therapy near titanium dental implants. Using a therapeutic conformal proton beam, the experiment was conducted on a head phantom implanted with Ti and plastic inserts. A MiniPIX Timepix3 hybrid pixel detector was used to detect scattered radiation behind the tumor during irradiation. Algorithms trained with artificial intelligence (AI) were used to recognize particles and decompose the radiation field. Measurements were collected at two beam angles (0° and 60°), and AI identified protons, electrons & photons, and fast neutrons. Scattered radiation with Ti implants was mainly electrons and photons (52.2%), while plastic implants showed higher proton contributions (65.4%). LET spectra ranged from 0.01 to 7.5 keV/μm. Low-LET was mostly from electrons and photons, and high-LET from protons and ions. The findings help quantify out-of-field radiation risks, supporting safer, more precise treatment validation.

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