Preliminary microdosimetric measurements with ultra-thin 3D silicon detectors of a 62 MeV proton beam

Abstract

In this paper we present the first direct microdosimetric measurements of 62 MeV proton beams using ultra-thin 3D silicon detectors at different depths in a solid-water phantom. The detectors have 3D columnar electrodes that penetrate a 10 µm thick silicon membrane, resulting in a micrometric scale sensitive volume. The 62 MeV proton beam was generated in a cyclotron CYCLONE-110 at Centre de Recherches du Cyclotron (CRC) at Louvain-la-Neuve. The proton beam average energy was modulated with stacked tissue-equivalent solid water layers. The energy loss profile was studied through the Bragg curve and pulse height spectra. The experimental silicon microdosimetric spectra showed the lineal energy dependence along the Bragg curve. This work demonstrates the potential capability of the ultra-thin 3D silicon detectors as 3D detector technology-based microdosimeters.

Silicon 3D Microdetectors for Microdosimetry in Hadron Therapy

“…In particular, two different types of 3D silicon microdosimeters were manufactured at IMB-CNM. The first one belongs to the U3DTHIN architecture [35,37,50,[57][58][59]. On the basis of the preliminary results with U3DTHIN detectors, a novel architecture based on 3D-cylindrical microstructures was proposed and specifically developed for microdosimetry in hadron therapy [32][33][34]36,[38][39][40][41].…”

“…Figure 3 shows some representative pictures of the manufactured U3DTHINs. Taking advantage of their thin sizes (i.e., 10 and 20 µm thicknesses), U3DTHINs were also tested to characterize their potential use in microdosimetry [35,37].…”

“…Figure 4 shows two representative electrical characterization current-voltage (I-V) and capacitance-voltage (C-V) curves: the leakage currents were in the range of 70 ± 10 nA/cm 2 and the capacitances were in the range of 70 ± 10 pF/cm 2 at 10 V (lateral depletion voltage at 5 V). Taking advantage of their thin sizes (i.e., 10 and 20 µm thicknesses), U3DTHINs were also tested to characterize their potential use in microdosimetry [35,37].…”

“…Figure 10a shows the pulse height spectra measured versus the P2251 thickness along the Bragg curve. The low-level discrimination threshold (LLD) was fixed at 75 keV in silicon, the details of which can be found elsewhere [35]. Figure 10b shows the microdosimetry measurements derived from the energy spectra at various depths along the Bragg curve.…”

“…For this purpose, we designed and fabricated novel radiation detectors with both 3D and 3D-cylindrical architectures, which were etched inside the silicon bulk in the National Center of Microelectronics (IMB-CNM, CSIC, Spain). These 3D microstructures were specifically customized for microdosimetry in PT and they overcame some of the technological challenges in this domain, namely the low noise capability, well-defined sensitive volume, high spatial resolution, and pile-up robustness [32][33][34][35][36][37][38][39][40][41]. Both architectures reduce the loss of charge carriers due to trapping effects, the charge collection time, and the voltage required for full depletion compared to planar silicon detectors.…”