A novel dual-mode tracking device for on-line dose monitoring in hadron therapy

Hadron therapy is a technique for cancer treatment that exploits ion beams (mostly protons and carbons). Due to the shape of the hadron energy deposition pattern, dose releases are more localized with respect to radiotherapy. Hadron therapy is thus particularly suitable to treat tumors close to critical organs. A critical issue is the monitoring accuracy of the dose released by the beam to the patient. We present the design of a dual-tracking device capable of on-line dose monitoring through the detection of prompt photons and charged particles produced by the interactions of the beam in the patient tissues whose emission shapes are correlated to spatial dose release and to the Bragg peak. The dosimeter, whose design has been optimized using Monte Carlo simulations, is composed of a tracker made of six scintillating fiber stations followed by a layer of plastic scintillator (electron shield) and a lyso pixellated crystal to detect photons. A first tracker layer has been assembled and is under test. A complete simulation and reconstruction software has been developed to estimate the achievable spatial resolution. Charged particles are reconstructed using the fiber planes and those identified as protons are back-traced to determine the point of origin. Prompt photons are reconstructed exploiting their Compton interactions by combining the spatial and energy measurements from the tracker for the electron and from the lyso for the photon. For a real hadrotherapeutic treatment the achievable resolution is of the order of ten (few) millimeters using the neutral (charged) component.