The proof of concept of a new device, capable of determining in a few seconds the energy of clinical proton beams by measuring the time of flight (ToF) of protons, is presented. The prototype ...consists of two thin ultra fast silicon detector (UFSD) pads, aligned along the beam direction in a telescope configuration and readout by a digitizer. The method developed for extracting the energy at the isocenter from the measured ToF, validated by Monte Carlo simulations, and the procedure used to calibrate the system are also presented and discussed in detail. The prototype was tested at the Centro Nazionale di Adroterapia Oncologica (CNAO, Pavia, Italy), at several beam energies, covering the entire clinical range, and using different distances between the sensors. The measured beam energies were benchmarked against the nominal CNAO energy values, obtained during the commissioning of the centre from the measured ranges in water. Deviations of few hundreds of keV have been achieved for all considered proton beam energies for distances between the two sensors larger than 60 cm, indicating a sensitivity to the corresponding beam range in water smaller than the clinical tolerance of 1 mm. Moreover, few seconds of irradiation were necessary to collect the required statistics. These preliminary results indicate that a telescope of UFSDs could achieve in a short time the accuracy required for the clinical application and therefore encourage further investigations towards the improvement and the optimization of the present prototype.
Beam monitoring in particle therapy is a critical task that, because of the high flux and the time structure of the beam, can be challenging for the instrumentation. Recent developments in thin ...silicon detectors with moderate internal gain, optimized for timing applications (Ultra Fast Silicon Detectors, UFSD), offer a favourable technological option to conventional ionization chambers. Thanks to their fast collection time and good signal-to-noise ratio, properly segmented sensors allow discriminating and counting single protons up to the high fluxes of a therapeutic beam, while the excellent time resolution can be exploited for measuring the proton beam energy using time-of-flight techniques. We report here the results of the first tests performed with UFSD detector pads on a therapeutic beam. It is found that the signal of protons can be easily discriminated from the noise, and that the very good time resolution is confirmed. However, a careful design is necessary to limit large pile-up inefficiencies and early performance degradation due to radiation damage.
Background: The total yields of direct Single-Strand Breaks (SSBs) and Double -Strand Breaks (DSBs) in proton energies varying from 0.1 to 40 MeV were calculated. While other studies in this fleld ...have not used protons with energy less than 0.5 MeV, our results show interesting and complicated behavior of these protons. Materials and Methods: The simulation has been done using the Geant4-DNA toolkit. An atomic model of DNA geometry was simulated. Simulations were performed with a source in the Z-axis direction at the cell nucleus entrance with protons at energies of 0.1-1 MeV in 0.1 MeV steps, 5 MeV, and 10-40 MeV in 10 MeV steps. Results: The calculated SSB yields decreased from 60.08 (GbpGy)-1 for 0.1 MeV proton energy to 49.52 (GbpGy) -1 for 0.5 MeV proton energy, and then it increased to 54.35 (GbpGy)-1 in 40 MeV. The DSB yields decreased from 4.32 (GbpGy)-1 for 0.1 MeV proton energy to 1.03 (GbpGy)-1 for 40-MeV protons. The DSB yields for energies less than 0.5 MeV was about 56%, and for the other energy levels, it was 44%. As for SSB yields, 35% of the breaks arose from protons with an energy of fewer than 0.5 MeV and 65% from higher energies. Conclusion: It was found that the proton ranges with an energy less than 0.5 MeV are smaller than the cell size (10 pm), and 100% of the energy is deposited in the cell region. Then protons with these energies are the best choice to increase the number of DSBs.
Fast procedures for the beam quality assessment and for the monitoring of beam energy modulations during the irradiation are among the most urgent improvements in particle therapy. Indeed, the online ...measurement of the particle beam energy could allow assessing the range of penetration during treatments, encouraging the development of new dose delivery techniques for moving targets. Towards this end, the proof of concept of a new device, able to measure in a few seconds the energy of clinical proton beams (from 60 to 230 MeV) from the Time of Flight (ToF) of protons, is presented. The prototype consists of two Ultra Fast Silicon Detector (UFSD) pads, featuring an active thickness of 80 um and a sensitive area of 3 x 3 mm2, aligned along the beam direction in a telescope configuration, connected to a broadband amplifier and readout by a digitizer. Measurements were performed at the Centro Nazionale di Adroterapia Oncologica (CNAO, Pavia, Italy), at five different clinical beam energies and four distances between the sensors (from 7 to 97 cm) for each energy. In order to derive the beam energy from the measured average ToF, several systematic effects were considered, Monte Carlo simulations were developed to validate the method and a global fit approach was adopted to calibrate the system. The results were benchmarked against the energy values obtained from the water equivalent depths provided by CNAO. Deviations of few hundreds of keV have been achieved for all considered proton beam energies for both 67 and 97 cm distances between the sensors and few seconds of irradiation were necessary to collect the required statistics. These preliminary results indicate that a telescope of UFSDs could achieve in a few seconds the accuracy required for the clinical application and therefore encourage further investigations towards the improvement and the optimization of the present prototype.
PDF
