Room: Exhibit Hall | Forum 7
Purpose: The direct measurement of each beam particle is proposed as a new paradigm for the monitoring of clinical ion beams. To this aim, the results on clinical proton beams of Ultra Fast Silicon Detectors (UFSDs)-based devices are reported.
Methods: The capability to detect single protons and the outstanding time resolution (tenths of ps) provided by UFSDs are exploited to develop two monitoring devices. The first one directly counts individual protons up to 10â?¹ p/cmÂ²s, using strip detectors. Strips of 2mmÂ² area each and active thickness of 50 Î¼m were produced in two geometries (30 mm and 15 mm length). Different doping modalities were tested to study radiation hardness at expected clinical fluences. A dedicated VLSI readout chip (>100MHz/strip) has been designed and produced, and dedicated pileup mitigation algorithms, to be implemented in the readout chain, are under study. The second device measures protonsâ€™ time-of-flight (TOF) between two UFSDs in a telescope configuration, using the constant fraction algorithm to compensate for time-walk effects. From measured TOF values, the corresponding beam energies are obtained through an analytical approximation validated with Geant4. Following preliminary tests with UFSD pads, dedicated strip sensors were produced and thinned to 100 Î¼m, covering an area of 4x4 mmÂ². Combinatorial methods to identify coincidences among strips are being studied.
Results: The tests on clinical proton beams (both synchrotron and cyclotron) showed: counter prototype pileup inefficiency lower than 1% at 100 MHz/cmÂ², and an error smaller than 1 MeV in the energy estimation at 228 MeV and 97 cm distance between sensors.
Conclusion: These promising results encourage moving from beam monitoring based on gas detectors to single particle tracking based on solid state detector technology. This approach has the potential to overcome the limits of current beam monitors, fostering the clinical use of advanced delivery techniques.