Due to its high sensitivity to anatomical changes, particle therapy will only unfold its full potential together with a functioning online range verification. We present a detector concept making use of a large fraction of the secondary particles available by hybrid prompt gamma-ray and fast neutron imaging. The system is expected to exhibit a high detection sensitivity to these particles, a high time, energy and position resolution, excellent pulse shape discrimination, and a small footprint. It comprises a quasi-monolithic organic detector array consisting of novel organic scintillators with dual-ended silicon photomultiplier light read-out and fast digitizers. The reconstruction of the proton range from the events registered by the detector is based on gamma/neutron scatter kinematics, cone back-projection and maximum likelihood expectation maximization. Multiple studies are currently ongoing investigating the feasibility of this concept on an experimental and simulation level. A first Monte Carlo simulation study involving realistic patient data and an idealized detector has revealed that a range-shift sensitivity of 1 mm per spot is attainable for clinical spot weights. These results demonstrate the potential of particle treatment verification by fast neutrons and prompt gamma-rays and strengthen the potential of this hybrid system for clinical application.
