Towards real-time beam monitoring and quality assurance of proton beams using radioluminescent silica fiber

Objective. Due to the emergence of ultra-high dose rate proton therapy techniques, the need for advanced in-vivo dosimetry tools able to monitor such beams has become more critical. This study evaluates the potential of silica optical fibers as real-time scintillating detectors for quality assurance of scattered and scanned pulsed proton beams at high and standard dose rates. Approach. The radioluminescence (RL) of short pieces of thin Gd³⁺-, Ce³⁺-, and N-doped silica fibers was studied focusing on their response to dose rate and energy, and their ability to perform depth-dose measurements, and for pencil beam scanning proton beams, spot size evaluation and real-time beam monitoring. The fibers response was evaluated in a continuous scattered proton beam and a synchrocyclotron scanned pulsed proton beam. Main Results. Up to 130 Gy.s-1, fibers response was linear as a function of dose rate. For both proton beams, range was measured with less than 1.1 mm deviation with the three fibers, despite scintillation quenching from 63 to 226 MeV. With the same data, spot size was estimated with less than 0.3 mm difference from the reference, taking advantage of the real-time RL acquisitions for scanned beams. Also, characterization of synchrocyclotron specific dose delivery by repainting, was investigated. Fibers were able to measure the relative dose contribution of each painting, according to the system log-files (less than 2% difference). Moreover, the ability of the system to resume properly the irradiation after beam interruption was validated in real-time through fibers acquisitions and were correlated to the system log-files. Significance. RL-based silica fiber sensors appeared to be viable detectors for proton beam quality assurance (proton range, spot size) at standard and high dose rates despite showing scintillation quenching and showed potential for real-time dosimetry for scanned proton beams and log-files QA, in addition to high dose rate proton beams.