Experimental characterization of a diamond detection system for combined dose, LET and RBE assessment in clinical proton beams

<i>Objective.</i>This work presents the first experimental characterization of the DIODE detector, a novel detection system based on single-crystal diamond, designed for simultaneous dosimetric and microdosimetric measurements in clinical proton therapy. The aim is to evaluate its capability to measure absorbed dose, and estimate LET and RBE variations along a clinical proton beam.<i>Approach.</i>The detector was tested under a 70 MeV monoenergetic proton beam at the Trento Proton Therapy Centre. Depth-dose and lateral profiles were compared with EBT3 radiochromic films. Microdosimetric spectra were simultaneously acquired and benchmarked against a mini tissue-equivalent proportional counter (TEPC). Monte Carlo (MC) simulations were also performed to model the experimental setup and the DIODE geometry.<i>Main results.</i>The detector showed linearity with dose with a sensitivity of 0.60 ± 0.01 nC Gy^-1, with a dark current below 0.1 pA, ensuring a good signal-to-noise ratio. Depth-dose profiles matched EBT3 film data and MC simulations, with differences below 2% in peak-to-plateau ratios, indicating limited LET dependence. The dose-mean lineal energyy¯Dclosely agrees with simulated dose-averaged LET values, except in the beam entrance region. In this area,y¯Dvalues were lower than those obtained with the mini-TEPC due to electronic saturation limiting the detection of rare high-LET secondary fragments. Variation in RBE was assessed from the microdosimetric data, based on Loncol's weighting function, which refers to clonogenic cell survival. RBE values ranged from ∼1.1 at the entrance to ∼1.8 in the distal region, consistent with mini-TEPC data and literature RBE₁₀values for V79 and U89 cells. Lateral dose and microdosimetric profiles confirmed high spatial resolution and revealed proton energy variations near the Bragg peak.<i>Significance.</i>The DIODE detector demonstrated reliable performance for simultaneous dosimetric and microdosimetric characterization of clinical proton beams. Its ability to measure dose, and to support LET and RBE assessment through microdosimetric modelling, in a single device, highlights its potential as an advanced tool for beam quality assessment and biologically optimized treatment planning in proton therapy.