Calibration method and performance of a time‐of‐flight detector to measure absolute beam energy in proton therapy

Abstract

BackgroundThe beam energy is one of the most significant parameters in particle therapy since it is directly correlated to the particles’ penetration depth inside the patient. Nowadays, the range accuracy is guaranteed by offline routine quality control checks mainly performed with water phantoms, 2D detectors with PMMA wedges, or multi‐layer ionization chambers. The latter feature low sensitivity, slow collection time, and response dependent on external parameters, which represent limiting factors for the quality controls of beams delivered with fast energy switching modalities, as foreseen in future treatments. In this context, a device based on solid‐state detectors technology, able to perform a direct and absolute beam energy measurement, is proposed as a viable alternative for quality assurance measurements and beam commissioning, paving the way for online range monitoring and treatment verification.PurposeThis work follows the proof of concept of an energy monitoring system for clinical proton beams, based on Ultra Fast Silicon Detectors (featuring tenths of ps time resolution in 50 μm active thickness, and single particle detection capability) and time‐of‐flight techniques. An upgrade of such a system is presented here, together with the description of a dedicated self‐calibration method, proving that this second prototype is able to assess the mean particles energy of a monoenergetic beam without any constraint on the beam temporal structure, neither any a priori knowledge of the beam energy for the calibration of the system.MethodsA new detector geometry, consisting of sensors segmented in strips, has been designed and implemented in order to enhance the statistics of coincident protons, thus improving the accuracy of the measured time differences. The prototype was tested on the cyclotron proton beam of the Trento Protontherapy Center (TPC). In addition, a dedicated self‐calibration method, exploiting the measurement of monoenergetic beams crossing the two telescope sensors for different flight distances, was introduced to remove the systematic uncertainties independently from any external reference.ResultsThe novel calibration strategy was applied to the experimental data collected at TPC (Trento) and CNAO (Pavia). Deviations between measured and reference beam energies in the order of a few hundreds of keV with a maximum uncertainty of 0.5 MeV were found, in compliance with the clinically required water range accuracy of 1 mm.ConclusionsThe presented version of the telescope system, minimally perturbative of the beam, relies on a few seconds of acquisition time to achieve the required clinical accuracy and therefore represents a feasible solution for beam commission, quality assurance checks, and online beam energy monitoring.

Consistency of Faraday cup and ionization chamber dosimetry of proton fields and the role of nuclear interactions

“…The novel method of the current study substitutes the strong dependence on MC by the range measurement and its conversion to the proton kinetic energy. This uncertainty is according to Table 1 about 0.4% (k = 1), which is in line with the experimental validations of Moyers et al 59 and Vignati et al 60 So the novel method replaces a contribution of the uncertainty of at least 1.5% with one of 0.4%.…”

Stopping power and range estimations in proton therapy based on prompt gamma timing: motion models and automated parameter optimization

“…The simulation has shown good agreement with experimental data in Ferrero et al (2023). The thin silicon detectors tag single particles with a time resolution of 30 ps (Vignati et al 2023) and the PG-detectors show a time resolution of 124 ps (Ferrero et al 2022a). Therefore, the resulting coincidence time resolution is only slightly larger than the 106 ps applied in this work.…”