arXiv subjects

Albert Hirtl

Publications and source records attributed to Albert Hirtl.

14 recordsLinked to original sources

arXiv2026

Spectacular - A Modular DAQ System for Microdosimetry

Particle therapy using light ions like protons, helium ions or carbon ions enables precise tumor targeting with enhanced biological effectiveness while minimizing damage to healthy tissue. Successful treatment planning depends not only on the absorbed dose but also on quality of the radiation, as quantified by the linear energy transfer (LET). Microdosimetry provides a direct experimental determination of such quantities by measuring the energy deposited per incoming particle in micrometer-sized solid-state detectors representing the relevant biological scales. However, the small signal amplitudes and high particle rates in therapeutic ion beams challenge existing readout systems, which are not sufficiently optimized for reliable operation with respect to pileup and signal-to-noise ratio (SNR). To address this, a modular data acquisition (DAQ) system was developed to accelerate the design of custom readout electronics and sensor characterization in microdosimetry and related spectroscopic applications. Centered around a Xilinx Zynq system-on-chip, it combines real-time processing, high-bandwidth streaming, and high-resolution digitization (16 bit at 100 MSas$^{-1}$) to enable advanced digital signal processing. The platform integrates programmable power supplies, a bias-voltage filter, test-pulse generators, and flexible I/O. Detector and preamplifier front-ends are hosted on interchangeable daugtherboards connected via a standardized interface, allowing different hardware configurations and readout algorithms to be evaluated on the same platform. The Spectacular DAQ system was successfully tested at the MedAustron ion therapy facility with custom charge-sensitive amplifiers and a diamond microdosimeter. First results demonstrate the feasibility and provide a proof-of-concept for potential future applications in clinical practice.

physics.ins-det↗

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↗

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↗

arXiv2025

A double multi-turn injection scheme for generating mixed helium and carbon ion beams at medical synchrotron facilities

The low relative charge-to-mass ratio offset of 0.065% between fully ionized helium-4 and carbon-12 ions enables simultaneous acceleration in hadron therapy synchrotrons. At the same energy per mass, helium ions exhibit a stopping range approximately three times greater than carbon ions. They can therefore be exploited for online range verification downstream of the patient during carbon ion beam irradiation. One possibility for creating this mixed beam is accelerating the two ion species sequentially through the LINAC and subsequently "mixing" them at injection energy in the synchrotron with a double multi-turn injection scheme. This work reports the first successful generation, acceleration, and extraction of a mixed helium and carbon ion beam using this double multi-turn injection scheme, which was achieved at the MedAustron therapy accelerator in Austria. A description of the double multi-turn injection scheme, particle tracking simulations, and details on the implementation at the MedAustron accelerator facility are presented and discussed. Finally, measurements of the mixed beam at delivery in the irradiation room using a radiochromic film and a low-gain avalanche diode (LGAD) detector are presented.

physics.acc-ph↗

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↗

arXiv2025

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↗

arXiv2023

First experimental time-of-flight-based proton radiography using low gain avalanche diodes

Ion computed tomography (iCT) is an imaging modality for the direct determination of the relative stopping power (RSP) distribution within a patient's body. Usually, this is done by estimating the path and energy loss of ions traversing the scanned volume via a tracking system and a separate residual energy detector. This study, on the other hand, introduces the first experimental study of a novel iCT approach based on time-of-flight (TOF) measurements, the so-called Sandwich TOF-iCT concept, which in contrast to any other iCT system, does not require a residual energy detector for the RSP determination. A small TOF-iCT demonstrator was built based on low gain avalanche diodes (LGAD), which are 4D-tracking detectors that allow to simultaneously measure the particle position and time-of-arrival with a precision better than 100um and 100ps, respectively. Using this demonstrator, the material and energy-dependent TOF was measured for several homogeneous PMMA slabs in order to calibrate the acquired TOF against the corresponding water equivalent thickness (WET). With this calibration, two proton radiographs (pRad) of a small aluminium stair phantom were recorded at MedAustron using 83 and 100.4MeV protons. Due to the simplified WET calibration models used in this very first experimental study of this novel approach, the difference between the measured and theoretical WET ranged between 37.09 and 51.12%. Nevertheless, the first TOF-based pRad was successfully recorded showing that LGADs are suitable detector candidates for TOF-iCT. While the system parameters and WET estimation algorithms require further optimization, this work was an important first step to realize Sandwich TOF-iCT. Due to its compact and cost-efficient design, Sandwich TOF-iCT has the potential to make iCT more feasible and attractive for clinical application, which, eventually, could enhance the treatment planning quality.

physics.med-ph↗

arXiv2022

Novel ion imaging concept based on time-of-flight measurements with low gain avalanche detectors

Treatment planning in ion beam therapy requires accurate knowledge of the relative stopping power (RSP) distribution within the patient. Currently, RSP maps are obtained via conventional x-ray computed tomography (CT) by converting the measured attenuation coefficients of photons into RSP values for ions. Alternatively, to avoid conversion errors that are inherent to this method, ion computed tomography (iCT) can be used since it allows determining the RSP directly. In typical iCT systems, which usually consist of a tracking system and a separate residual energy detector, the RSP is obtained by measuring the particle trajectory and the corresponding water equivalent path length (WEPL) of single ions travelling through the patient. Within this work, we explore a novel iCT approach which does not require a residual energy detector. Instead, the WEPL is estimated indirectly by determining the change in time of flight (TOF) due to the energy loss along the ion's path. For this purpose, we have created a Geant4 model of a TOF-iCT system based on low gain avalanche detectors (LGADs), which are fast 4D-tracking detectors that can measure the time of arrival and position of individual particles with high spatial and time precision. To assess the performance of this TOF-iCT concept, we determined the RSP resolution and accuracy for different system settings using the Catphan CTP404 sensitometry phantom. Within the set of investigated system parameters, the lower limit of the RSP accuracy was found at 0.91%, demonstrating the proof-of-principle of this novel TOF-iCT concept. The main advantage of using this approach is that it could potentially facilitate clinical integration due to its compact design, which, however, requires experimental verification and an improvement of the current WEPL calibration procedure.

physics.med-ph↗

arXiv2021

Feasibility study of a proton CT system based on 4D-tracking and residual energy determination via time-of-flight

For dose calculations in ion beam therapy, it is vital to accurately determine the relative stopping power (RSP) distribution within the treated volume. Currently, RSP values are extrapolated from Hounsfield units (HU), measured with x-ray computed tomography (CT), which entails RSP inaccuracies due to conversion errors. A suitable method to improve the treatment plan accuracy is proton computed tomography (pCT). A typical pCT system consists of a tracking system and a separate residual energy (or range) detector to measure the RSP distribution directly. This paper introduces a novel pCT system based on a single detector technology, namely low gain avalanche detectors (LGADs). LGADs are fast 4D-tracking detectors, which can be used to simultaneously measure the particle position and time with precise timing and spatial resolution. In contrast to standard pCT systems, the residual energy is determined via a time-of-flight (TOF) measurement between different 4D-tracking stations. The design parameters for a realistic proton computed tomography system based on 4D-tracking detectors were studied and optimized using Monte Carlo simulations. The RSP accuracy and RSP resolution were measured inside the inserts of the CTP404 phantom to estimate the performance of the pCT system. After introducing a dedicated calibration procedure for the TOF calorimeter, RSP accuracies < 0.6 % could be achieved. Furthermore, the design parameters with the strongest impact on the RSP resolution were identified and a strategy to improve RSP resolution is proposed.

physics.med-ph↗

arXiv2021

A Proton Computed Tomography Demonstrator for Stopping Power Measurements

Particle therapy is an established method to treat deep-seated tumours using accelerator-produced ion beams. For treatment planning, the precise knowledge of the relative stopping power (RSP) within the patient is vital. Conversion errors from x-ray computed tomography (CT) measurements to RSP introduce uncertainties in the applied dose distribution. Using a proton computed tomography (pCT) system to measure the SP directly could potentially increase the accuracy of treatment planning. A pCT demonstrator, consisting of double-sided silicon strip detectors (DSSD) as tracker and plastic scintillator slabs coupled to silicon photomultipliers (SiPM) as a range telescope, was developed. After a significant hardware upgrade of the range telescope, a 3D tomogram of an aluminium stair phantom was recorded at the MedAustron facility in Wiener Neustadt, Austria. In total, 80 projections with 6.5x10^5 primary events were acquired and used for the reconstruction of the RSP distribution in the phantom. After applying a straight-line approximation for the particle path inside the phantom, the most probable value (MPV) of the RSP distribution could be measured with an accuracy of 0.59%. The RSP resolution inside the phantom was only 9.3% due to a limited amount of projections and measured events per projection.

physics.med-ph↗

arXiv2021

Commissioning of low particle flux for proton beams at MedAustron

MedAustron is a synchrotron-based particle therapy centre located in Wiener Neustadt, Austria. It features three irradiation rooms for particle therapy, where proton beams with energies up to 252.7 MeV and carbon ions of up to 402.8 MeV/u are available for cancer treatment. In addition to the treatment rooms, MedAustron features a unique beamline exclusively for non-clinical research (NCR). This research beamline is also commissioned for proton energies up to 800 MeV, while available carbon ion energies correspond to the ones available in the clinical treatment rooms. Based on the requirements for particle therapy, all irradiation rooms offer particle rates of up to 10^9 particles/s for protons and 10^7 particles/s for carbon ions. However, for research purposes, lower particle fluxes are required and were therefore commissioned for the NCR beamline. Three particle flux settings with particle rates ranging from ~2.4x10^3 particles/s to ~5.2x10^6 particles/s were established for seven proton energies below 252.7 MeV. In addition to the particle rate, the spot sizes and beam energies were measured for these settings. Furthermore, three low flux settings for 800 MeV protons with particle rates ranging from ~2x10^3 particles/s to ~1.3x10^6 particles/s were commissioned. Since the commissioned low flux settings are in a regime well below the limits of the available standard beam diagnostics, setting up the beam under these new operational conditions entirely relied on the use of external detectors. Furthermore, a beam position measurement based alignment without using the standard beam profile monitors was performed for 800 MeV protons.

physics.acc-ph↗

arXiv2013

New Approaches for Improvement of TOF-PET

We present results of simulations on the influence of photon propagation and the Cherenkov effect on the time resolution of LSO:Ce scintillators. The influence of the scintillator length on the coincidence time resolution is shown. Furthermore, the impact of the depth of interaction on the time resolution, the light output and the arrival time distribution at the photon detector is simulated and it is shown how these information can be used for time walk correction.

physics.ins-det↗

arXiv2004

High Resolution He-like Argon And Sulfur Spectra From The PSI ECRIT

We present new results on the X-ray spectroscopy of multicharged argon, sulfur and chlorine obtained with the Electron Cyclotron Resonance Ion Trap (ECRIT) in operation at the Paul Scherrer Institut (Villigen, Switzerland). We used a Johann-type Bragg spectrometer with a spherically-bent crystal, with an energy resolution of about 0.4 eV. The ECRIT itself is of a hybrid type, with a superconducting split coil magnet, special iron inserts which provides the mirror field, and a permanent magnetic hexapole. The high frequency was provided by a 6.4 GHz microwave emitter. We obtained high intensity X-ray spectra of multicharged F-like to He-like argon, sulfur and chlorine with one 1s hole. In particular, we observed the $1s2s^{3}S_1 \to 1s^2^{1}S_0 M1$ and $1s2p^{3}P_2 \to 1s^2^{1}S_0 M2$ transitions in He-like argon, sulfur and chlorine with unprecedented statistics and resolution. The energies of the observed lines are being determined with good accuracy using the He-like M1 line as a reference.

physics.atom-ph↗

arXiv2001

Vortices in the SU(2)-Higgs model -- Vortices and the covariant adjoint Laplacian

Vortices in the SU(2)--Higgs model: The presence of a fundamental Higgs in the SU(N)-Higgs model yields color screening at some finite distance. Whereas the transition to the Higgs "phase" is accompanied by a suppression of projected center vortices, there is nearly no influence of color screening on the vortex properties in the confined "phase". Hence the behavior of the Wilson loop can be described in both phases within the vortex picture of confinement. Vortices and the covariant adjoint Laplacian: Laplacian center gauge is a method to localize center vortices in SU(N) gauge theory. We show that the eigenvectors of the covariant adjoint Laplacian identify vortices for a special class of gauge field configurations. However, for Monte Carlo generated configurations, modified approaches are required.

hep-lat↗