Development of a diamond hodoscope for online ion range monitoring in hadrontherapy
Résumé
The ballistic property of ion beams is a key issue in hadrontherapy. Online ion range assessment during treatment would permit to fully exploit this advantage. In this context, Prompt-Gamma (PG) imaging using a Compton camera has been proposed by the French CLaRyS collaboration. The originality of the system is the use of a beam-tagging hodoscope that would provide temporal and spatial information on the incoming ions. This hodoscope at first relied on an array of scintillating fibres. To reach higher counting rate and a timing resolution of 100 ps, the collaboration has initiated recently the development of a diamond hodoscope. (CLaRyS Ultra Fast Timing). Diamond were selected for their very fast response and radiation hardness. Initially, for characterization purposes, pad detectors made of Chemical Vapor Deposition (CVD) single-crystal and polycrystalline diamonds as well as Diamonds grown On Iridium (DOI) were built. Then, to satisfy the position-sensitive criterion in the hodoscope prototyping, double-side stripped demonstrators were designed and assembled with custom discrete current preamplifiers at LPSC in Grenoble. Both pad and strip detectors have been characterized under various irradiation conditions. At GANIL, a 18 ps RMS Time-Of-Flight resolution has been obtained between a single-crystal and a DOI pad detectors with 95 MeV/u 12C ions. The same two detectors exhibit a 59 ps RMS Time-Of-Flight resolution when tested with 68 MeV protons in ARRONAX-Nantes. Single 68 MeV proton detection efficiency has been evaluated with two 1 cm² pad detectors: one polycrystalline and one DOI. The results are respectively 92% and 50%. Finally, stripped sensors were tested with a 8.5 keV pulsed X-Ray micro-beam at European Synchrotron Radiation Facility. A 100% detection efficiency and a 103 ps RMS time resolution were measured at several strips crossings with the polycrystalline sample. In conclusion, present results encourage, in a near future, the development of a larger area prototype made of four diamonds in a mosaic arrangement and read by a dedicated and integrated fast readout electronics currently developed at LPSC.
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