arXiv subjects

Reinhard Schulte

Publications and source records attributed to Reinhard Schulte.

12 recordsLinked to original sources

arXiv2026

Toward Ionization Cluster Size Measurements with a Compact Nanodosimeter

Nanodosimetry aims to provide measurable quantities related to the nanoscopic particle track structure, which determines the biological effectiveness of radiation. While simulated nanodosimetry has already demonstrated its potential for radiation treatment planning, the experimental realization of practical nanodosimetric detectors is still in its early stages. In this work, a nanodosimetric prototype operated with low-pressure gas was developed to count ionizations in a nanometer-equivalent sensitive gas volume. Its performance was evaluated experimentally with alpha beams from an Am-241 source in 1 mbar propane gas. The results support the further development of this compact nanodosimeter class, with potential applications in particle therapy, radiation protection, and space radiation dosimetry.

physics.ins-det↗

arXiv2026

Experimental and Monte Carlo Simulation Studies to Investigate the Working Principle of Compact Nanodosimeters

In recent years, compact nanodosimetric detectors based on ion multiplication in low-pressure gas have been developed and gained attention in the scientific community. These detectors use strong electric fields to collect and multiply positive ions produced by the incident radiation in mm-sized cell holes in dielectric materials, achieving a nm-equivalent spatial resolution of the localization of ionization events, when scaled to liquid water at unit density. Their design assumes that ion-impact ionizations of gas molecules within the cell holes dominate signal formation, yet this assumption has lacked direct physical verification. Electron emission from the cell hole walls or the cathode due to ion-impact could also contribute, requiring alternative designs to optimize efficiency. To investigate the relative importance of the possible mechanisms, a nanodosimetric detector featuring a single cell hole with a diameter of 1.5 mm in a dielectric plate was developed. Ion collection and multiplication were achieved by applying a negative high voltage to the glass cathode 0.5 mm below the cell hole, assisted by a low drift field above the plate. A grounded readout electrode with a 0.8 mm hole covers the cell hole to prevent interactions of collected ions with the hole walls. High signal yields in 1 mbar and 2 mbar propane gas were observed and indicated that ion-impact ionizations of the gas molecules could indeed be the primary mechanism for signal induction. Ion-induced secondary electron emission from the cathode was identified as another potential contribution. The compact nanodosimeter setup was further modeled with Geant4-DNA and Garfield++ for deeper insight. The results of these studies are important for understanding and developing a new class of nanodosimeters with potential applications in particle therapy, radiation protection, space dosimetry, and particle physics.

physics.ins-det↗

arXiv2025

The Associated Volume sampling algorithm as an alternative method for the calculation of ionisation cluster size distributions in computational nanodosimetry

In computational nanodosimetry, Monte Carlo Track Structure (MCTS) simulations are employed to calculate ionisation cluster size distributions (ICSDs), which are crucial for characterising mixed radiation fields at the nanoscale. The Uniform Sampling (US) algorithm, commonly used for this purpose, is inefficient when evaluating ICSDs conditioned on clusters exceeding a given size $ν$ threshold. This study investigates a more efficient alternative - the Associated Volume (AV) algorithm - against the US approach for computing conditional ICSDs ($ν\ge 1$) from proton tracks simulated with Geant4-DNA. Two configurations of the AV algorithm were evaluated: the standard AV-Overlap, allowing sensitive volumes to overlap (with a 1/$ν$ correction), and the novel AV-No Overlap, which prevents overlap. We compared the conditional ICSDs, mean cluster size ($M_1$), complementary cumulative frequencies ($F_k$ for $k \in [2,7]$), and overall execution time per run and per event. Deviations exceeding two standard deviations of the mean difference were considered statistically significant. Although statistically significant differences in ICSDs, $M_1$ and $F_k$ were observed, the relative differences in the AV-Overlap rarely exceeded 5%, whereas the No Overlap configuration they ranged from $\lt$ 1% to approximately 15% at the higher $F_k$. Both AV configurations achieved execution times one to two orders of magnitude shorter than the US algorithm. Our findings indicate that the AV-Overlap algorithm may be a preferred alternative for calculating conditional ICSDs and derived nanodosimetric quantities, offering a substantial gain in computational efficiency without compromising accuracy.

physics.comp-ph↗

arXiv2024

Ionization detail parameters and cluster dose: A mathematical model for selection of nanodosimetric quantities for use in treatment planning in charged particle radiotherapy

Objective: To propose a mathematical model for applying Ionization Detail (ID), the detailed spatial distribution of ionization along a particle track, to proton and ion beam radiotherapy treatment planning (RTP). Approach: Our model provides for selection of preferred ID parameters (I_p) for RTP, that associate closest to biological effects. Cluster dose is proposed to bridge the large gap between nanoscopic I_p and macroscopic RTP. Selection of I_p is demonstrated using published cell survival measurements for protons through argon, comparing results for nineteen Ip: N_k; k = 2,3,...,10, the number of ionizations in clusters of k or more per particle, and F_k; k = 1,2,...,10, the number of clusters of k or more per particle. We then describe application of the model to ID-based RTP and propose a path to clinical translation. Main results: The preferred I_p were N_4 and F_5 for aerobic cells, N_5 and F_7 for hypoxic cells. Signifcant differences were found in cell survival for beams having the same LET or the preferred N_k. Conversely, there was no signi?cant difference for F_5 for aerobic cells and F_7 for hypoxic cells, regardless of ion beam atomic number or energy. Further, cells irradiated with the same cluster dose for these I_p had the same cell survival. Based on these preliminary results and other compelling results in nanodosimetry, it is reasonable to assert that I_p exist that are more closely associated with biological effects than current LET-based approaches and microdosimetric RBE-based models used in particle RTP. However, more biological variables such as cell line and cycle phase, as well as ion beam pulse structure and rate still need investigation. Signifcance: Our model provides a practical means to select preferred I_p from radiobiological data, and to convert I_p to the macroscopic cluster dose for particle RTP.

physics.med-ph↗

arXiv2024

A Prototype Scintillator Real-Time Beam Monitor for Ultra-high Dose Rate Radiotherapy

FLASH Radiotherapy (RT) is a potentially new cancer radiotherapy technique where an entire therapeutic dose is delivered in about 0.1 s and at ~1000 times higher dose rate than in conventional RT. For clinical trials to be conducted safely, precise and fast beam monitoring that can generate an out-of-tolerance beam interrupt is required. A FLASH Beam Scintillator Monitor (FBSM) is being developed based in part on a novel proprietary inorganic hybrid scintillator material. The FBSM provides large area coverage, low mass profile, linear response over a broad dynamic range, radiation tolerance, and real-time analysis IEC-compliant fast beam-interrupt signal. This paper includes the design concept and test results from a prototype device in radiation beams that include heavy ions, FLASH level dose per pulse electron beams, anda hospital radiotherapy clinic with electron beams. Results include image quality, response linearity, radiation hardness, spatial resolution, and real-time data processing. The scintillator showed a small -0.02%/kGy signal decrease after a 212 kGy cumulative dose resulting from continuous exposure for 15 minutes at a FLASH compatible dose rate of 234 Gy/s. These tests established the linear response of the FBSM with respect to dose per pulse. Comparison with commercial Gafchromic film indicates that the FBSM produces a high resolution 2D beam image and can reproduce a nearly identical beam profile. At 20 kfps or 50 microsec/frame, the real-time FPGA based computation and analysis of beam position, beam shape, and beam dose takes < 1 microsec.

physics.med-ph↗

arXiv2023

Repair kinetics of DSB-foci induced by proton and helium ion microbeams of different energies

In this work, the induction and repair of radiation-induced 53BP1 foci were studied in human umbilical vein endothelial cells irradiated at the PTB microbeam with protons and α-particles of different energies. The data were analyzed in terms of the mean number of 53BP1 foci induced by the different ion beams. The number of 53BP1 foci found at different times post-irradiation suggests that the disappearance of foci follows first order kinetics. The mean number of initially produced foci shows the expected increase with LET. The most interesting finding of this work is that the absolute number of persistent foci increases with LET but not their fraction. Furthermore, protons seem to produce more persistent foci as compared to α-particles of even higher LET. This may be seen as experimental evidence that protons may be more effective in producing severe DNA lesions, as was already shown in other work, and that LET may not be the best suited parameter to characterize radiation quality

physics.med-ph↗

arXiv2022

Transformative Technology for FLASH Radiation Therapy: A Snowmass 2021 White Paper

Conventional cancer therapies include surgery, radiation therapy, chemotherapy, and, more recently, immunotherapy. These modalities are often combined to improve the therapeutic index. The general concept of radiation therapy is to increase the therapeutic index by creating a physical dose differential between tumors and normal tissues through precision dose targeting, image guidance, and high radiation beams that deliver radiation dose with high conformality, e.g., protons and ions. However, treatment and cure are still limited by normal tissue radiation toxicity, with many patients experiencing acute and long-term side effects. Recently, however, a fundamentally different paradigm for increasing the therapeutic index of radiation therapy has emerged, supported by preclinical research, and based on the FLASH radiation effect. FLASH radiation therapy (FLASH-RT) is an ultra-high dose-rate delivery of a therapeutic radiation dose within a fraction of a second. Experimental studies have shown that normal tissues seem to be universally spared at these high dose rates, whereas tumors are not. The dose delivery conditions are not yet fully characterized. Still, it is currently estimated that large doses of 10 Gy or more delivered in 200 ms or less produce normal tissue sparing effects yet effectively kill tumor cells. There is a great opportunity, but also many technical challenges, for the accelerator community to create the required dose rates with novel and compact accelerators to ensure the safe delivery of FLASH radiation beams.

physics.med-ph↗

arXiv2021

A proton simulator for testing implementations of proton CT reconstruction algorithms on GPGPU clusters

Proton computed tomography (pCT) is an image modality that will improve treatment planning for patients receiving proton radiation therapy compared with the current treatment techniques, which are based on X-ray CT. Reconstruction of a pCT image requires solving a large and sparse system of linear equations, which should be accomplished within a few minutes in order to be clinically practical. Analyzing the efficiency of potentially clinical reconstruction implementations requires multiple quality pCT data sets. The purpose of this paper is to describe the simulator that was developed to generate realistic pCT data sets to be used in testing the efficiency of reconstruction algorithms, in particular string-averaging and block-iterative projection algorithms using sparse matrix formats on General Purpose Graphics Processing Units (GPGPU)s.

physics.med-ph↗

arXiv2018

Derivative-free superiorization with component-wise perturbations

Superiorization reduces, not necessarily minimizes, the value of a target function while seeking constraints-compatibility. This is done by taking a solely feasibility-seeking algorithm, analyzing its perturbations resilience, and proactively perturbing its iterates accordingly to steer them toward a feasible point with reduced value of the target function. When the perturbation steps are computationally efficient, this enables generation of a superior result with essentially the same computational cost as that of the original feasibility-seeking algorithm. In this work, we refine previous formulations of the superiorization method to create a more general framework, enabling target function reduction steps that do not require partial derivatives of the target function. In perturbations that use partial derivatives the step-sizes in the perturbation phase of the superiorization method are chosen independently from the choice of the nonascent directions. This is no longer true when component-wise perturbations are employed. In that case, the step-sizes must be linked to the choice of the nonascent direction in every step. Besides presenting and validating these notions, we give a computational demonstration of superiorization with component-wise perturbations for a problem of computerized tomography image reconstruction.

math.OC↗

arXiv2017

A Real-time Image Reconstruction System for Particle Treatment Planning Using Proton Computed Tomography (pCT)

Proton computed tomography (pCT) is a novel medical imaging modality for mapping the distribution of proton relative stopping power (RSP) in medical objects of interest. Compared to conventional X-ray computed tomography, where range uncertainty margins are around 3.5%, pCT has the potential to provide more accurate measurements to within 1%. This improved efficiency will be beneficial to proton-therapy planning and pre-treatment verification. A prototype pCT imaging device has recently been developed capable of rapidly acquiring low-dose proton radiographs of head-sized objects. We have also developed an advanced, fast image reconstruction software based on distributed computing that utilizes parallel processors and graphical processing units. The combination of fast data acquisition and fast image reconstruction will enable the availability of RSP images within minutes for use in clinical settings. The performance of our image reconstruction software has been evaluated using data collected by the prototype pCT scanner from several phantoms.

physics.med-ph↗

arXiv2014

Performance of Hull-Detection Algorithms For Proton Computed Tomography Reconstruction

Proton computed tomography (pCT) is a novel imaging modality developed for patients receiving proton radiation therapy. The purpose of this work was to investigate hull-detection algorithms used for preconditioning of the large and sparse linear system of equations that needs to be solved for pCT image reconstruction. The hull-detection algorithms investigated here included silhouette/space carving (SC), modified silhouette/space carving (MSC), and space modeling (SM). Each was compared to the cone-beam version of filtered backprojection (FBP) used for hull-detection. Data for testing these algorithms included simulated data sets of a digital head phantom and an experimental data set of a pediatric head phantom obtained with a pCT scanner prototype at Loma Linda University Medical Center. SC was the fastest algorithm, exceeding the speed of FBP by more than 100 times. FBP was most sensitive to the presence of noise. Ongoing work will focus on optimizing threshold parameters in order to define a fast and efficient method for hull-detection in pCT image reconstruction.

cs.CV↗

arXiv2006

Mapping the Sensitive Volume of an Ion-Counting Nanodosimeter

We present two methods of independently mapping the dimensions of the sensitive volume in an ion-counting nanodosimeter. The first method is based on a calculational approach simulating the extraction of ions from the sensitive volume, and the second method on probing the sensitive volume with 250 MeV protons. Sensitive-volume maps obtained with both methods are compared and systematic errors inherent in both methods are quantified.

physics.ins-det↗