Characterization of a beam-tagging hodoscope for hadrontherapy monitoring

National audienceIntroductionIn a context where ion beam therapy faces uncertainties concerning ion range verification, solutions for real-time monitoring are investigated. Among them, some exploit the prompt-gammas (PG) emissions [?]. A Compton and a collimated camera coupled to a beam-tagging hodoscope, made of two scintillating fibres planes, are under development within the CLaRyS collaboration. The beam-tagging hodoscope is designed to provide the time-of-arrival of the ions, which is useful to reduce the background, mainly induced by neutrons. The specifications ofthe detector are a detection efficiency over 90% for coincidence events in the two planes, with a time resolution below 2 ns FWHM, at counting rates up to 100 MHz. The performance of the beam-tagging hodoscope has been assessed in terms of detection efficiency, time resolution, multiplicity and radiation hardness during experiments at GANIL (Caen) and the Mediterranean Protontherapy Institute (Nice).Material and methodsThe final version of the beam-tagging hodoscope is composed of two parallel planes of 1 mm2 square-section polystyrene scintillating fibres, oriented perpendicular one to the other, and transverse to the beam direction.Each plane contains 128 fibres, which gives an active area of 128 x 128 mm2. Fibres are readout on both sides by 8 Hamamatsu multi-anode photomultiplier tubes (PMTs) H8500C. Each PMT is linked to a front-end (FE) card via a 64-channel connector. The main components of this card are two 32-channel readout ASICs, a signal-processing FPGA, a single-channel optical transceiver and an RJ45 connector. The data are then sent from the FPGA to the back-end card (AMC40) of a μTCA acquisition system [2], with a specific protocol [?, 3, 4].For the performance tests a smaller hodoscope with 32 fibres per plane has also been developed in order to use a single acquisition board to collect all the data of the two planes. Each fibre plane is readout by a single ASIC.The setup used during the experiments consists in inserting the beam-tagging hodoscope between two plastic scintillators (PSs) located about 5 cm upstream and downstream. The external trigger is provided by the coincidence signal generated from the PSs when a proton impinges the hodoscope. The analog to logic signalconversion is performed in a NIM module. When the PSs counting rate limit is reached, a PS placed out of the beam and calibrated at low beam intensity was used to monitor the beam intensity.ResultsThis hodoscope successfully provided 2D images of proton beams with a detection efficiency larger than 98% with logical OR condition between the two fibre planes. The detection efficiency with a coincidence between the two planes is close to 75% for beam intensities up to ~ 1 MHz. Moreover, the timing resolution is around 1.5 ns FWHM. Radiation damage was studied with 95 MeV/u carbon ions at GANIL, where fluences up to 1013 ions/cm2 were shown to (temporarily) decrease the detection efficiency by 10%. Overall, the performance show that such a technology is viable for beam monitoring during hadrontherapy. Further improvements of the ASIC developed for the front-end electronics boards are foreseen to reach the counting rate capabilities of the specifications (100 MHz).References[1] J. Krimmer, D. Dauvergne, J.M. Létang, and E. Testa, Prompt-gamma monitoring in hadrontherapy: A review., Nucl. Instrum. Meth. A, 878 (2018) pg. 58-73[2] J.-P. Cachemiche, P.-Y. Duval, F. Hachon, R. Le Gac, and F. Marin, Study for the LHCb upgrade read-out board., J. Instrum., 5 (2010) pg. C12036[3] X. Chen, B. Carlus, C. Caplan, L. Caponetto, J.-P. Cachemiche, D. Dauvergne, R. Della-Negra, M. Fontana, L. Gallin-Martel, D. Lambert, G.-N. Lu, M. Magne, H. Mathez, C. Morel, G. Montarou, M. Rodo, E. Testa, and Y. Zoccarato, A data acquisition system for a beam-tagging hodoscope used in hadrontherapy moni-toring., in IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), Atlanta, GA, USA, pg. 1-4, Oct 2017.[4] C. Caplan, O. Allegrini, J. . Cachemiche, B. Carlus, X. Chen, D. Dauvergne, R. Della-Negra, M. Fontana, L. Gallin-Martel, M. . Gallin-Martel, J. Hérault, D. Lambert, G. . Lu, M. Magne, H. Mathez, G. Montarou, C. Morel, M. Rodo Bordera, E. Testa, and Y. Zoccarato, A μTCA back-end firmware for data acquisition and slow control of the CLaRyS Compton camera., in IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) Manchester, United Kingdom, pg. 1-4, Oct 2019.[5] X. Chen, O. Allegrini, B. Carlus, C. Caplan, L. Caponetto, J. P. Cachemiche, S. Curtoni, D. Dauvergne, R. Della Negra, M. Fontana, L. Gallin-Martel, M.-L. Gallin-Martel, J. Hérault, D. Lambert, G.-N. Lu, M. Magne, S. Marcatili, H. Mathez, C. Morel, G. Montarou, E. Testa, and Y. Zoccarato, A Time-of-Flightgamma camera data acquisition system for hadrontherapy monitoring., in IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), Manchester, United Kingdom, pg. 1-4 Oct 2019