Orateur
Description
1 Introduction
In 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 of
the 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).
2 Material and methods
The 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 signal
conversion 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.
3 Results
This 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-Flight
gamma 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.
