arXiv subjects

Giulio Magrin

Publications and source records attributed to Giulio Magrin.

6 recordsLinked to original sources

arXiv2026

A frontend ASIC for Microdosimetry

Recent clinical evidence shows a correlation between linear energy transfer (LET) and tumor control in carbon ion radiotherapy. This prompts the direct inclusion of LET into the treatment planning. Currently, LET is mainly extracted from simulations. Good clinical practice requires adopting measurement routines that correlate with LET, such as microdosimetry. In this work, we describe an application-specific integrated circuit (ASIC) for reading out microdosimeteric sensors. The ASIC is designed for input capacitances up to 3 pF. It contains four readout channels, each with a different saturation charge ranging from 75 fC to 3.2 pC. In the 75 fC range, at 1 pF input capacitance and a shaping time of 1 microseconds, the ASIC has an equivalent noise contribution (ENC) below 15 electrons at ambient temperature. This low noise level is expected to enable new measurement possibilities, including the assessment of microdosimetric proton spectra in the low-LET region of the entrance channel, as well as studying the contribution of delta electrons.

hep-ex↗

arXiv2026

Measurements of the micro-spill structure of medical cyclotron and synchrotron beams and its impact on pulse pileup

Detector characterization and instrumentation testing are often performed at cyclotron and synchrotron facilities, many of which were originally developed for medical applications in cancer therapy. For particle physics experiments requiring a single-particle resolution, pileup can significantly degrade data quality, making precise knowledge of the beam time structure essential for selecting appropriate readout parameters. However, such information is often unavailable from the facilities and challenging to determine experimentally. Here, we report measurements of the spill time structure at two medical accelerator facilities using a silicon carbide (SiC) particle sensor coupled to a high-frequency readout system. Owing to its high carrier saturation velocity and the tolerance to large bias voltages, SiC is well suited for fast readout and measurements requiring precise timing. Using a 6 GHz readout with custom SiC diodes, we characterize the micro-spill structure of both cyclotron and synchrotron beams on a sub-nanosecond timescale. The measured arrival-time distributions exhibit modulation with the accelerator RF frequencies, reflecting features of the extraction process. The resolved micro-spill structure enables quantitative estimation of pileup contributions and provides design constraints for future readout electronics. The presented results emphasize the importance of the characterization of the beam time-structure characterization for the development of precise readout systems.

physics.ins-det↗

arXiv2025

Characterizing the Delivered Spill Structure of Medical Proton and Carbon-Ion Beams at MedAustron using a High Frequency Silicon Carbide Readout

Medical synchrotrons are often used for testing instrumentation in high-energy physics or non-clinical research in medical physics. In many applications of medical synchrotrons, such as microdosimetry and ion imaging, precise knowledge of the spill structure and instantaneous particle rate is crucial. Conventional ionization chambers, while omnipresent in clinical settings, suffer from limitations in charge resolution and integration time, making single-particle detection at high dose rates unfeasible. To address these limitations, we present a beam detection setup based on a silicon carbide (SiC) sensor and a monolithic microwave integrated circuit (MMIC), capable of detecting single particles with a full width at half maximum (FWHM) pulse duration of 500 ps. At the MedAustron ion therapy center, we characterized the spill structure of proton and carbon-ion beams delivered to the irradiation room beyond the timescale of the maximum ion revolution frequency in the synchrotron. The resulting data offer valuable insights into the beam intensity at small time scales and demonstrate the capabilities of SiC-based systems for high-flux beam monitoring.

physics.ins-det↗

arXiv2024

Exploring Offline Pileup Correction to Improve the Accuracy of Microdosimetric Characterization in Clinical Ion Beams

Microdosimetry investigates the energy deposition of ionizing radiation at microscopic scales, beyond the assessment capabilities of macroscopic dosimetry. This contributes to an understanding of the biological response in radiobiology, radiation protection and radiotherapy. Microdosimetric pulse height spectra are usually measured using an ionization detector in a pulsed readout mode. This incorporates a charge-sensitive amplifier followed by a shaping network. At high particle rates, the pileup of multiple pulses leads to distortions in the recorded spectra. Especially for gas-based detectors, this is a significant issue, that can be reduced by using solid-state detectors with smaller cross-sectional areas and faster readout speeds. At particle rates typical for ion therapy, however, such devices will also experience pileup. Mitigation techniques often focus on avoiding pileup altogether, while post-processing approaches are rarely investigated. This work explores pileup effects in microdosimetric measurements and presents a stochastic resampling algorithm, allowing for offline simulation and correction of spectra. Initially it was developed for measuring neutron spectra with tissue equivalent proportional counters and is adapted for the use with solid-state microdosimeters in a clinical radiotherapy setting. The algorithm was tested on data acquired with solid-state microdosimeters at the MedAustron ion therapy facility. The successful simulation and reduction of pileup counts is achieved by establishing of a limited number of parameters for a given setup. The presented results illustrate the potential of offline correction methods in situations where a direct pileup-free measurement is currently not practicable.

physics.med-ph↗

arXiv2024

Microdosimetry of a clinical carbon-ion pencil beam at MedAustron -- Part 1: experimental characterization

This paper characterizes the microdosimetric spectra of a single-energy carbon-ion pencil beam at MedAustron using a miniature solid-state silicon microdosimeter to estimate the impact of the lateral distribution of the different fragments on the microdosimetric spectra. The microdosimeter was fixed at one depth and then laterally moved away from the central beam axis in steps of approximately 2 mm. The measurements were taken in both horizontal and vertical direction in a water phantom at different depths. In a position on the distal dose fall-off beyond the Bragg peak, the frequency-mean and the dose-mean lineal energies were derived using either the entire range of y-values, or a sub-range of y values, presumingly corresponding mainly to contributions from primary particles. The measured microdosimetric spectra do not exhibit a significant change up to 4 mm away from the beam central axis. For lateral positions more than 4 mm away from the central axis, the relative contribution of the lower lineal-energy part of the spectrum increases with lateral distance due to the increased partial dose from secondary fragments. The average values yF and yD are almost constant for each partial contribution. However, when all particles are considered together, the average value of yF and yD varies with distance from the axis due to the changing dose fractions of these two components varying by 30 % and 10 % respectively up to the most off axis vertical position. Characteristic features in the microdosimetric spectra providing strong indications of the presence of helium and boron fragments have been observed downstream of the distal part of the Bragg peak. We were able to investigate the radiation quality as function of off-axis position. These measurements emphasize variation of the radiation quality within the beam and this has implications in terms of relative biological effectiveness.

physics.med-ph↗

arXiv2018

Microdosimetry in ion-beam therapy: studying and comparing outcomes from different detectors

Experimental studies of microdosimetry in therapeutic ion beams have been performed using several detectors. The differences among them lie on the shapes, the site sizes, and the material. Coin-shaped solid-state detectors made of silicon or diamond with thickness varying from 0.3 to 10 microns, as well as proportional counters with spherical and cylindrical sensitive volumes filled with tissue-equivalent gas are the microdosimeters used in therapeutic proton and carbon-ion beams. One goal of microdosimetry in the clinical environment is providing repeatable specification of the radiation quality of the radiation field. A methodology should be developed to provide, independently from the heterogeneous information collected with the different detectors, a detector-independent specification of the radiation quality. Historically the specification of the radiation quality is provided either, in terms of Linear Energy Transfer (LET) or in terms of lineal energy, y. First this study focuses on identifying the correlation between the distributions of LET and the lineal energy spectra as well as the correspondence between their mean values calculated in frequency and in dose. The evaluation is based on the method of LET analysis described by Kellerer making the adaptation to the peculiarities of the therapeutic ion-beam where the pristine irradiation is unidirectional and made of a single type of mono-energetic ions. The second objective of this study is to interpret the spectrum collected by a slab and estimate what the spectrum would be if it was collected by a detector different in shape, material, or size. An example confirms the method starting from the simulated lineal energy spectrum obtained for carbon ions in a slab detector of graphite and converting it to the spectruma that would be obtained in the same radiation field for spherical, cylindrical, and slab detector made of water.

physics.ins-det↗