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Background: Ion beam therapy allows for a substantial sparing of normal tissues and higher biological efficacy. Synthetic single crystal diamond is a very good material to produce high‐spatial‐resolution and highly radiation hard detectors for both dosimetry and microdosimetry in ion beam therapy. Purpose: The aim of this work is the design, fabrication and test of an integrated waterproof detector based on synthetic single crystal diamond able to simultaneously perform dosimetric and microdosimetric characterization of clinical ion beams. Methods: The active elements of the integrated diamond device, that is, dosimeter and microdosimeter, were both realized in a Schottky diode configuration featured by different area, thickness, and shape by means of photolithography technologies for the selective growth of intrinsic and boron‐doped CVD diamond. The cross‐section of the sensitive volume of the dosimetric element is 4 mm2 and 1 μm‐thick, while the microdosimetric one has an active cross‐sectional area of 100 × 100 μm2 and a thickness of about 6.2 μm. The dosimetric and microdosimetric performance of the developed device was assessed at different depths in a water phantom at the MedAustron ion beam therapy facility using a monoenergetic uniformly scanned carbon ion beam of 284.7 MeV/u and proton beam of 148.7 MeV. The particle flux in the region of the microdosimeter was 6·107 cm2/s for both irradiation fields. At each depth, dose and dose distributions in lineal energy were measured simultaneously and the dose mean lineal energy values were then calculated. Monte Carlo simulations were also carried out by using the GATE‐Geant4 code to evaluate the relative dose, dose averaged linear energy transfer (LETd), and microdosimetric spectra at various depths in water for the radiation fields used, by considering the contribution from the secondary particles generated in the ion interaction processes as well. Results: Dosimetric and microdosimetric quantities were measured by the developed prototype with relatively low noise (∼2 keV/μm). A good agreement between the measured and simulated dose profiles was found, with discrepancies in the peak to plateau ratio of about 3% and 4% for proton and carbon ion beams respectively, showing a negligible LET dependence of the dosimetric element of the device. The microdosimetric spectra were validated with Monte Carlo simulations and a good agreement between the spectra shapes and positions was found. Dose mean lineal energy values were found to be in close agreement with those reported in the literature for clinical ion beams, showing a sharp increase along the Bragg curve, being also consistent with the calculated LETd for all depths within the experimental error of 10%. Conclusions: The experimental indicate that the proposed device can allow enhanced dosimetry in particle therapy centers, where the absorbed dose measurement is implemented by the microdosimetric characterization of the radiation field, thus providing complementary results. In addition, the proposed device allows for the reduction of the experimental uncertainties associated with detector positioning and could facilitate the partial overcoming of some drawbacks related to the low sensitivity of diamond microdosimeters to low LET radiation. [ABSTRACT FROM AUTHOR]

Objective. Microdosimetry is gaining increasing interest in particle therapy. Thanks to the advancements in microdosimeter technologies and the increasing number of experimental studies carried out in hadron therapy frameworks, it is proving to be a reliable experimental technique for radiation quality characterisation, quality assurance, and radiobiology studies. However, considering the variety of detectors used for microdosimetry, it is important to ensure the consistency of microdosimetric results measured with different types of microdosimeters. Approach. This work presents a novel multi-thickness microdosimeter and a methodology to characterise the radiation quality of a clinical carbon-ion beam. The novel device is a diamond detector made of three sensitive volumes (SVs) of different thicknesses: 2, 6 and 12 µ m. The SVs, which operate simultaneously, were accurately aligned and laterally positioned within 3 mm. This alignment allowed for a comparison of the results with a negligible impact of the SVs alignment and their lateral positioning, ensuring the homogeneity of the measured radiation quality. An experimental campaign was carried out at MedAustron using a carbon-ion beam of typical clinical energy (284.7 MeV u -1 ). Main results. The measurement results allowed for a meticulous interpretation of its radiation quality, highlighting the effect of the SV thickness. The consistency of the microdosimetric spectra measured by detectors of different thicknesses is discussed by critically analysing the spectra and the differences observed. Significance. The methodology presented will be highly valuable for future experiments investigating the effects of the target volume size in radiobiology and could be easily adapted to the other particles employed in hadron therapy for clinical (i.e. protons) and for research purposes (e.g. helium, lithium and oxygen ions)., (Creative Commons Attribution license.)