arXiv subjects

Dieter Röhrich

Publications and source records attributed to Dieter Röhrich.

10 recordsLinked to original sources

arXiv2023

Exploration of Differentiability in a Proton Computed Tomography Simulation Framework

Objective. Algorithmic differentiation (AD) can be a useful technique to numerically optimize design and algorithmic parameters by, and quantify uncertainties in, computer simulations. However, the effectiveness of AD depends on how "well-linearizable" the software is. In this study, we assess how promising derivative information of a typical proton computed tomography (pCT) scan computer simulation is for the aforementioned applications. Approach. This study is mainly based on numerical experiments, in which we repeatedly evaluate three representative computational steps with perturbed input values. We support our observations with a review of the algorithmic steps and arithmetic operations performed by the software, using debugging techniques. Main results. The model-based iterative reconstruction (MBIR) subprocedure (at the end of the software pipeline) and the Monte Carlo (MC) simulation (at the beginning) were piecewise differentiable. Jumps in the MBIR function arose from the discrete computation of the set of voxels intersected by a proton path. Jumps in the MC function likely arose from changes in the control flow that affect the amount of consumed random numbers. The tracking algorithm solves an inherently non-differentiable problem. Significance. The MC and MBIR codes are ready for the integration of AD, and further research on surrogate models for the tracking subprocedure is necessary.

physics.med-ph↗

arXiv2022

Toward the End-to-End Optimization of Particle Physics Instruments with Differentiable Programming: a White Paper

The full optimization of the design and operation of instruments whose functioning relies on the interaction of radiation with matter is a super-human task, given the large dimensionality of the space of possible choices for geometry, detection technology, materials, data-acquisition, and information-extraction techniques, and the interdependence of the related parameters. On the other hand, massive potential gains in performance over standard, "experience-driven" layouts are in principle within our reach if an objective function fully aligned with the final goals of the instrument is maximized by means of a systematic search of the configuration space. The stochastic nature of the involved quantum processes make the modeling of these systems an intractable problem from a classical statistics point of view, yet the construction of a fully differentiable pipeline and the use of deep learning techniques may allow the simultaneous optimization of all design parameters. In this document we lay down our plans for the design of a modular and versatile modeling tool for the end-to-end optimization of complex instruments for particle physics experiments as well as industrial and medical applications that share the detection of radiation as their basic ingredient. We consider a selected set of use cases to highlight the specific needs of different applications.

physics.ins-det↗

arXiv2021

The charge sensitivity calibration of the upgraded ALICE Inner Tracking System

The ALICE detector is undergoing an upgrade for Run 3 at the LHC. A new Inner Tracking System (ITS) is part of this upgrade. The upgraded ALICE ITS features the ALPIDE, a Monolithic Active Pixel Sensor. Due to IC fabrication variations and radiation damages, the threshold values for the ALPIDE chips in ITS need to be measured and adjusted periodically to ensure the quality of data. The calibration is implemented within the ALICE Online-Offline (O$^2$) Computing System, thus it runs in the same framework as the normal operations. This paper describes the concept and first implementation of the charge sensitivity scanning procedures for the upgraded ALICE ITS in the ALICE O$^2$ System, and demonstrates the first results of the scanning of the data taken from the installed ITS.

physics.ins-det↗

arXiv2020

Remote Configuration of the ProASIC3 on the ALICE Inner Tracking System Readout Unit

A Large Ion Collider Experiment (ALICE) is one of the four major experiments conducted at the CERN Large Hadron Collider (LHC). The ALICE detector is currently undergoing an upgrade for the upcoming Run 3 at the LHC. The new Inner Tracking System (ITS) sub-detector is part of this upgrade. The front-end electronics of the ITS is composed by 192 Readout Units, installed in a radiation environment. Single Event Upsets (SEUs) in the SRAM-based Xilinx Kintex Ultrascale FPGAs used in the ITS readout represent a real concern. To clear SEUs affecting the Kintex configuration memory, a secondary Flash-based Microsemi ProASIC3E (PA3) FPGA is used. This device configures and continuously scrubs the Xilinx FPGA while data-taking is ongoing, which avoids accumulation of SEUs. The communication path to the RUs is via the radiation hard Gigabit Transceiver (GBT) system on 100 m long optical links. The PA3 is reachable via the GBT Slow Control Adapter (GBT-SCA) ASIC using a dedicated JTAG bus driving channel. During the course of Run 3, it is foreseeable that the FPGA design of the PA3 will require upgrades to correct possible issues and add new functionality. It is therefore mandatory that the PA3 itself can be configured remotely, for which a dedicated software tool is needed. This paper presents the design and implementation of the distributed tools to re-configure remotely the PA3 FPGAs.

physics.ins-det↗

arXiv2020

Proton Tracking Algorithm in a Pixel-Based Range Telescope for Proton Computed Tomography

Proton Computed Tomography (CT) is a prototype imaging modality for the reconstruction of the Relative Stopping Power of a patient, for more accurate calculations of the dose distributions in proton therapy dose planning. The measurements needed for the reconstruction of a proton CT image are: i) each initial proton vector incident on the imaged object, ii) each proton vector incident on the front face of the detector and iii) the stopping depth of each proton in the detector. In this study, a track reconstruction algorithm is adapted for a planned pixel-based particle-tracking range telescope for proton CT, called the Digital Tracking Calorimeter (DTC). The algorithm is based on the track-following scheme, in which a growing track searches for deeper-laying activated pixels, while minimizing the accumulated angular change. The algorithm is applied to Monte Carlo-simulated output of the DTC, showing that the DTC is able to reconstruct the tracks and find the depths of up to several hundred simultaneous proton tracks.

physics.med-ph↗

arXiv2019

Effects of Proton Irradiation on 60 GHz CMOS Transceiver Chip for Multi-Gbps Communication in High-Energy Physics Experiments

This paper presents the experimental results of $17~MeV$ proton irradiation on a $60~GHz$ low power, half-duplex transceiver (TRX) chip implemented in $65~nm$ CMOS technology. It supports short range point-to-point data rate up to $6~Gbps$ by employing on-off keying (OOK). To investigate the irradiation hardness for high energy physics applications, two TRX chips were irradiated with total ionizing doses (TID) of $74~kGy$ and $42~kGy$ and fluence of $1.4~\times$10$^{14}~ N_{eq}/cm^2$ and $0.8~\times$10$^{14}~N_{eq}/cm^2$ for RX and TX modes, respectively. The chips were characterized by pre- and post-irradiation analogue voltage measurements on different circuit blocks as well as through the analysis of wireless transmission parameters like bit error rate (BER), eye diagram, jitter etc. Post-irradiation measurements have shown certain reduction in performance but both TRX chips have been found operational through over the air measurements at $5~Gbps$. Moreover, very small shift in the carrier frequency was observed after the irradiation.

physics.ins-det↗

arXiv2017

A comparison of proton ranges in complex media using GATE/Geant4, MCNP6 and FLUKA

The Monte Carlo (MC) simulation method is a powerful tool for radiation physicists, and several general-purpose software packages are commonly applied in a myriad of different radiation physics fields today. In medical physics, charged particle detectors for proton Computed Tomography are under development, a modality introduced in order to increase the accuracy of proton radiation therapy. MC simulations are helpful during the development and optimization phase of such detector systems. In order to justify the usage of MC for such purposes, the simulation output must be validated against experimental or theoretical data, or even cross-checked between different MC software packages. In this study, we compare three general-purpose MC software packages (GATE/Geant4, MCNP6 and FLUKA) with respect to how they predict the spatial distribution of the stopping position of protons. They are compared to each other and to semi-empirical data, using the mean proton range, the longitudinal and lateral variation of individual proton ranges, and the fraction of primary protons lost to nuclear interactions. This comparison is performed in two homogeneous materials and in a detector geometry designed for proton Computed Tomography. The three MC software packages agree well, and sufficiently reproduce the semi-empirical data. Some discrepancies are observed, such as less lateral beam spreading in GATE/Geant4, and a small deficiency in the MCNP6 proton range in water: This is consistent with previously published data. Due to the general agreement, the choice of simulation framework may be made on personal preferences. It is important to note that the choice of physics packages, simulation parameter settings and material definitions are important aspects when performing MC simulations, both during the preparation, execution and interpretation of the simulation results.

physics.med-ph↗

arXiv2017

Accuracy of parameterized proton range models; a comparison

An accurate calculation of proton ranges in phantoms or detector geometries is crucial for decision making in proton therapy and proton imaging. To this end, several parameterizations of the range-energy relationship exist, with different levels of complexity and accuracy. In this study we compare the accuracy four different parameterizations models: Two analytical models derived from the Bethe equation, and two different interpolation schemes applied to range-energy tables. In conclusion, a spline interpolation scheme yields the highest reproduction accuracy, while the shape of the energy loss-curve is best reproduced with the differentiated Bragg-Kleeman equation.

physics.med-ph↗

arXiv2017

Proton tracking in a high-granularity Digital Tracking Calorimeter for proton CT purposes

Radiation therapy with protons as of today utilizes information from x-ray CT in order to estimate the proton stopping power of the traversed tissue in a patient. The conversion from x-ray attenuation to proton stopping power in tissue introduces range uncertainties of the order of 2-3% of the range, uncertainties that are contributing to an increase of the necessary planning margins added to the target volume in a patient. Imaging methods and modalities, such as Dual Energy CT and proton CT, have come into consideration in the pursuit of obtaining an as good as possible estimate of the proton stopping power. In this study, a Digital Tracking Calorimeter is benchmarked for proof-of-concept for proton CT purposes. The Digital Tracking Calorimeteris applied for reconstruction of the tracks and energies of individual high energy protons. The presented prototype forms the basis for a proton CT system using a single technology for tracking and calorimetry. This advantage simplifies the setup and reduces the cost of a proton CT system assembly, and it is a unique feature of the Digital Tracking Calorimeter. Data from the AGORFIRM beamline at KVI-CART in Groningen in the Netherlands and Monte Carlo simulation results are used to in order to develop a tracking algorithm for the estimation of the residual ranges of a high number of concurrent proton tracks. The range of the individual protons can at present be estimated with a resolution of 4%. The readout system for this prototype is able to handle an effective proton frequency of 1 MHz by using 500 concurrent proton tracks in each readout frame, which is at the high end range of present similar prototypes. A future further optimized prototype will enable a high-speed and more accurate determination of the ranges of individual protons in a therapeutic beam.

physics.med-ph↗

arXiv2015

Thin silicon strip detectors for beam monitoring in Micro-beam Radiation Therapy

Microbeam Radiation Therapy (MRT) is an emerging cancer treatment that is currently being developed at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. This technique uses a highly collimated and fractionated X-ray beam array with extremely high dose rate and very small divergence, to benefit from the dose-volume effect, thus sparing healthy tissue. In case of any beam anomalies and system malfunctions, special safety measures must be installed, such as an emergency safety shutter that requires continuous monitoring of the beam intensity profile. Within the 3DMiMic project, a novel silicon strip detector that can tackle the special features of MRT, such as the extremely high spatial resolution and dose rate, has been developed to be part of the safety shutter system. The first prototypes have been successfully fabricated, and experiments aimed to demonstrate their suitability for this unique application have been performed. Design, fabrication and the experimental results as well as any identified inadequacies for future optimisation are reported and discussed in this paper.

physics.ins-det↗