Microdosimetry performance of the first multi-arrays of 3D-cylindrical microdetectors

The present work reports on the microdosimetry measurements performed with the two first multi-arrays of microdosimeters with the highest radiation sensitive surface covered so far. The sensors are based on new silicon-based radiation detectors with a novel 3D cylindrical architecture. Each system consists of arrays of independent microdetectors covering 2 mm × 2 mm and 0.4 mm × 12 cm radiation sensitive areas, the sensor distributions are arranged in layouts of 11 × 11 microdetectors and 3 × 3 multi-arrays, respectively. We have performed proton irradiations at several energies to compare the microdosimetry performance of the two systems, which have different spatial resolution and detection surface. The unitcell of both arrays is a 3D cylindrical diode with a 25 μ m diameter and a 20 μ m depth that results in a welldefined and isolated radiation sensitive micro-volume etched inside a silicon wafer. Measurements were carried out at the Accélérateur Linéaire et Tandem à Orsay (ALTO) facility by irradiating the two detection systems with monoenergetic proton beams from 6 to 20 MeV at clinical-equivalent fluence rates. The microdosimetry quantities were obtained with a spatial resolution of 200 μ m and 600 μ m for the 11 × 11 system and for the 3 × 3 multi-array system, respectively. Experimental results were compared with Monte Carlo simulations and an overall good agreement was found. The good performance of both microdetector arrays demonstrates that this architecture and both configurations can be used clinically as microdosimeters for measuring the lineal energy distributions and, thus, for RBE optimization of hadron therapy treatments. Likewise, the results have shown that the devices can be also employed as a multipurpose device for beam monitoring in particle accelerators.