Purpose: A new system to measure the energy of clinical proton beams was developed. It is based on the precise measurement of the protons' time of flight (TOF) and a self-calibration procedure. Results from preliminary validation tests will be presented.
Methods: A telescope was built using two Ultra-Fast Silicon Detectors segmented in 2.2 mm2 strips and mounted on dedicated 8-channels front-end readout boards. A high-precision positioning system allows the TOF measurement at different configurations. Two linear stages are used for the transversal alignment of the second sensor while a third, 1 m long, linear stage moves one sensor to change the distance from 30 to 95 cm along the beam direction (axes Z). This displacement is measured with 10 µm of accuracy using an absolute optical encoder. The 16 signals from strips were acquired with a 5Gs/s digitizer and processed with a MALTAB application. To validate the self-calibration procedure, measurements were performed with a clinical proton beam at 7 different energies (69, 72, 104, 142, 183, 223, and 227 MeV), 4 distances (40, 60, 80 and 95 cm) and 12 milliseconds of data from 30 seconds of acquisition time.
Results: The linear interpolations of the averaged TOFs as a function of the distance shown deviations of a few hundred keV for most of the energies and all the distances, corresponding to less than 1 mm range difference. The consistent energy values obtained for the four distances reflect the good calibration of the system.
Conclusion: A new system able to measure independently the proton beam energy in a few seconds has been developed. This new technology, fast and precise, would radically improve the commissioning operations and could introduce new methods for beam control and validation in particle therapy.
Funding Support, Disclosures, and Conflict of Interest: We kindly acknowledge the following funding agencies and collaborations: INFN - CSN V (MoVeIT project); Dipartimenti di Eccellenza, Universita' degli Studi di Torino (ex L. 232/2016, art. 1, cc. 314,337); Ministero della Ricerca, PRIN 2017, progetto 2017L2XKTJ 4DInSiDe.