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Microdosimetry has been traditionally performed through gaseous proportional counters, although in recent years different solid-state microdosimeters have been proposed and constructed for this task. In this paper, we analyze the response of solid-state devices of micrometric size with no intrinsic gain developed by CNM-CSIC (Spain). There are two major aspects of the operation of these devices that affect the reconstruction of the probability distributions and momenta of stochastic quantities related to microdosimetry. For micrometric volumes, the drift and diffusion of the charge carriers gives rise to a partial charge collection efficiency in the peripheral region of the depleted volume. This effect produces a perturbation of the reconstructed pulse height (i.e. imparted energy) distributions with respect to the actual microdosimetric distributions. The relevance of this deviation depends on the size, geometry and operating conditions of the device. On the other hand, the electronic noise from the single-event readout set-up poses a limit on the minimum detectable lineal energy when the microdosimeter size is reduced. This article addresses these issues to provide a framework on the physical constraints for the design and operation of solid-state microdosimeters.

Microdosimetry has been traditionally performed through gaseous proportional counters, although in recent years different solid-state microdosimeters have been proposed and constructed for this task. In this paper, we analyze the response of solid-state devices of micrometric size with no intrinsic gain developed by CNM-CSIC (Spain). There are two major aspects of the operation of these devices that affect the reconstruction of the probability distributions and momenta of stochastic quantities related to microdosimetry. For micrometric volumes, the drift and diffusion of the charge carriers gives rise to a partial charge collection efficiency in the peripheral region of the depleted volume. This effect produces a perturbation of the reconstructed pulse height (i.e. imparted energy) distributions with respect to the actual microdosimetric distributions. The relevance of this deviation depends on the size, geometry and operating conditions of the device. On the other hand, the electronic noise from the single-event readout set-up poses a limit on the minimum detectable lineal energy when the microdosimeter size is reduced. This article addresses these issues to provide a framework on the physical constraints for the design and operation of solid-state microdosimeters.

Cancer is a broad term that defines a very large number of different diseases that are characterized by certain common traits. The most common way of treating cancer is using radiation to kill the tumoral cells. In 1946, Robert Wilson proposed the use of heavier charged particles for therapy, giving birth to the field of Particle Therapy. In order to provide the correct amount of radiation it is necessary to assess the properties of the beam and characterise the beam quality (i.e. particle type and energy spectra) by means of dosimetric and microdosimetric measurements. This thesis are the results from research in the field of microdosimetry and silicon detectors for hadrontherapy done at the Molecular Imaging and Medical Physics group of the University of Santiago de Compostela (USC) from 2014 to 2019 and describes the different silicon devices employed for measuring the radiation quality of particle beams, with an electrical characterisation of the different silicon detectors, the comparison of the data obtained with theoretical results by means of Monte Carlo simulations, and a study on the limitations of these particular detection systems.

[Introduction] Use of solid-state sensors for measuring microdosimetric quantities has been increasing recently due to advantages such as its size, portability and its lack of high voltage biasing to work properly. However, these devices do not lack drawbacks; drift and diffusion phenomena affect partial charge collection, modifying the microdosimetric spectra depending on the geometry of the site, operation conditions and readout electronic noise. [Methods] Drift and diffusion processes are very relevant when micrometric active sites are considered. A perturbation in the pulse height detected spectrum respect to the ideal imparted energy within the considered site geometry is produced. Effects in silicon micro-dosimeters built by IMB-INM (CSIC, Spain) were evaluated. To parametrize the charge collection effi ciency an IBIC test at CNA (Seville, Spain) was performed and results were compared with TCAD simulations. The device model used together with FLUKA Monte Carlo simulations has been compared with experimental micro-dosimetric spectra of a clinical 12C ion beam at Fondazione CNAO (Pavia, Italy). [Results] Smeared Monte Carlo spectra reproduce the main features of the experimental spectra taken with the silicon microdosimeters affected by partial charge collection events. The perturbation on the frequency and dose averaged lineal energy as a function of micro-dosimeter size was evaluated. Additionally, the minimum detectable lineal energy for no intrinsic gain devices was evaluated considering a general model of readout electronics as a function of the fl uence averaged mass thickness of solid-state micro-dosimeters. [Conclusions] Solid-state devices can be employed to measure microdosimetric spectra, but large collection and electronic noise pose limitations on their performance. The perturbation on the microdosimetric spectra has been evaluated in this work to set a general benchmark for the expected performance of a micro-dosimeter depending on geometry and se

Purpose: The aim of this study was to present a novel 2041 liquid-filled ionization chamber array for high-resolution verification of radiotherapy treatments. Materials and Methods: The prototype has 2041 ionization chambers of 2.5 × 2.5 mm2 area filled with isooctane. The detection elements are arranged in a central square grid of 43 × 43, totally covering an area of 107.5 × 107.5 mm2. The central inline and cross-line are extended to 227 mm and the diagonals to 321 mm to be able to perform profile measurements of large fields. We have studied stability, pixel response uniformity, dose rate dependence, depth and field size dependence and anisotropy. We present results for output factors, tongue-and-groove, garden fence, small field profiles, irregular fields, and verification of dose planes of patient treatments. Results: Comparison with other detectors used for small field dosimetry (SFD, CC13, microDiamond) has shown good agreement. Output factors measured with the device for square fields ranging from 10 × 10 to 100 × 100 mm2 showed relative differences within 1%. The response of the detector shows a strong dependence on the angle of incident radiation that needs to be corrected for. On the other hand, inter-pixel relative response variations in the 0.95–1.08 range have been found and corrected for. The application of the device for the verification of dose planes of several treatments has shown gamma passing rates above 97% for tolerances of 2% and 2 mm. The verification of other clinical fields, like small fields and irregular fields used in the commissioning of the TPS, also showed large passing rates. The verification of garden fence and tongue-and-groove fields was affected by volume-averaging effects. Conclusions: The results show that the liquid filled ionization chamber prototype here presented is appropriate for the verification of radiotherapy treatments with high spatial resolution. Recombination effects do not affect very much the verification of rel