Fast-prompt gamma imaging for the online monitoring of the ion range in hadron therapy

International audienceThe French collaboration ClaRyS is developing fast detectors for online ion range monitoring to reduce treatment uncertainties in hadron therapy. Prompt gamma imaging (PGI), based on the detection of prompt gamma rays following nuclear reactions along the ion track, is a promising technique for the real time verification of ion range, especially when time of flight (TOF) is used to discriminate the prompt gamma rays issued from the patient from the large background of secondary radiation [1].A Compton Camera prototype has been developed by CLaRyS for PGI. Using Compton kinematics, the photon emission point is reconstructed using either an iterative process, or, if the camera is used in conjunction with a beam-tagging hodoscope, an analytic process involving the intersection of a line and a cone. The iterative reconstruction yielded a precision of 2 mm in the measured range for a 160 MeV proton pencil beam incident on a PMMA phantom. Whilst much quicker than the iterative reconstruction, the analytic reconstruction is less precise, but may be improved using TOF with 100 ps resolution or less. This has been studied by means of a Monte Carlo simulation.CLaRyS has recently acquired a fast photon counting Temporal camera developed by Damavan Imaging [2]. Although originally conceived for standalone nuclear dismantling operations, the custom Temporal Compton camera readout will be synchronized with the readout of a beam hodoscope. The camera is undergoing characterisation to investigate its suitability to be used as an online range monitor in hadron therapy.Results from the two studies will be presented and discussed.[1] J. Krimmer et al., Nuclear Inst. and Methods in Physics Research, A 878 (2018) 58–73[2] http://damavan-imaging.com/temporal-delta-compton-camera