A novel detector for 4D tracking in particle therapy

An innovative beam monitor for particle therapy applications was developed to count protons and carbon ions in clinical beams and was integrated with a Time-to-Digital Converter (TDC) to add the measurement of particles’ crossing time. The detector exploits strip-segmented planar silicon sensors with an active thickness of a few tens of μm and the front-end electronics is based on a 24-channel ASIC (named ABACUS) for the discrimination of the particles’ signals. The proton counting efficiency shows a dependence on the beam energy because of transversal dimension and pile-up effects, whereas an efficiency between 94 and 98 % with lower energy dependence is found for carbon ions. The time measurements with the TDC allow for the study of the time interval between consecutive particles in one strip, which appears to be compatible with the radio-frequency period of the synchrotron. These results indicate that thin silicon sensors and custom front-end readout with high counting rate capability allow for a full 4D tracking of clinical ion beams, opening the way to future technologies for online monitoring systems.