Monte Carlo investigation of electron fluence perturbation in MRI-guided radiotherapy beams using six commercial radiation detectors

With the integration of MRI-linacs to the clinical workflow, the understanding and characterization of detector response in reference dosimetry in magnetic fields are required. The magnetic field perturbs the electron fluence (Fe), and the degree of perturbation depends on the irradiation conditions and the detector type. This work evaluates the magnetic field impact on the electron fluence spectra in several detectors to provide a deeper understanding of detector response in these conditions. Monte Carlo calculations of Fe are performed in six detectors (solid-state: PTW60012 and PTW60019, ionization chambers: PTW30013, PTW31010, PTW31021, and PTW31022) placed in water and irradiated by an Elekta Unity 7 MV FFF photon beam with small and reference fields, at 0 T and 1.5 T. Three chamber-axis orientations are investigated: parallel or perpendicular (two possibilities: FL towards the stem or the tip) to the magnetic field and perpendicular to the beam. One orientation for the solid-state detector is studied: parallel to the beam and perpendicular to the magnetic field. Additionally, Fe spectra are calculated in modified detector geometries to identify the underlying physical mechanisms behind the fluence perturbations. The total Fe is reduced up to 1.24% in the farmer chamber, at 1.5 T, in the parallel orientation. The interplay between the gyration radius and the farmer chamber cavity length significantly affects Fe in the perpendicular orientation; the total fluence varies up to 5.12% in magnetic fields. For the small-cavity chambers, the maximal variation in total Fe is 0.19%, for the reference field, in the parallel orientation. . In contrast, significant small-field effects occur; the total Fe is reduced between 9.86% to 14.50% at 1.5T (with respect to 0T) depending on the orientation. The magnetic field strongly impacted the solid-state detectors in both field sizes, probably due to the high-density extracameral components. The maximal reductions of total Fe are 15.06±0.09% (silicon) and 16.00±0.07% (microDiamond). This work provides insights into detector response in magnetic fields by illustrating the interplay between several factors causing dosimetric perturbation effects: 1) chamber and magnetic field orientation, 2) cavity size and shape, 3) extracameral components, 4) air gaps and their asymmetry, 5) electron energy. Low-energy electron trajectories are more susceptible to change in magnetic fields, and generally, they are associated with detector response perturbation.

Advantages and Requirements in Time Resolving Tracking for Astroparticle Experiments in Space

A large-area, solid-state detector with single-hit precision timing measurement will enable several breakthrough experimental advances for the direct measurement of particles in space. Silicon microstrip detectors are the most promising candidate technology to instrument the large areas of the next-generation astroparticle space borne detectors that could meet the limitations on power consumption required by operations in space. We overview the novel experimental opportunities that could be enabled by the introduction of the timing measurement, concurrent with the accurate spatial and charge measurement, in Silicon microstrip tracking detectors, and we discuss the technological solutions and their readiness to enable the operations of large-area Silicon microstrip timing detectors in space.

Direct detection of 5-MeV protons by flexible organic thin-film devices

The direct detection of 5-MeV protons by flexible organic detectors based on thin films is here demonstrated. The organic devices act as a solid-state detector, in which the energy released by the protons within the active layer of the sensor is converted into an electrical current. These sensors can quantitatively and reliably measure the dose of protons impinging on the sensor both in real time and in integration mode. This study shows how to detect and exploit the energy absorbed both by the organic semiconducting layer and by the plastic substrate, allowing to extrapolate information on the present and past irradiation of the detector. The measured sensitivity, S = (5.15 ± 0.13) pC Gy−1, and limit of detection, LOD = (30 ± 6) cGy s−1, of the here proposed detectors assess their efficacy and their potential as proton dosimeters in several fields of application, such as in medical proton therapy.

3-D thermal and radiation-matter interaction simulations of a SiC solid-state detector for neutron flux measurements in JSI TRIGA Mark II research reactor

Neutron detection is a relevant topic in the field of nuclear instrumentation. It is at the heart of the concerns for fusion applications (neutron diagnostics, measurements inside the Test Blanket Modules TBM) as well as for fission applications (in-core and ex-core monitoring, neutron mapping or safety applications in research reactors). Moreover, due to the even more harsh conditions of the future experimental reactors such as the Jules Horowitz Reactor (JHR) or International Thermonuclear Experimental Reactor (ITER), neutron detectors need to be adapted to high neutron and γ fluxes, high nuclear heating rates and high temperatures. Consequently, radiation and temperature hardened sensors with fast response, high energy resolution and stability in a mixed neutron and γ environment are required. All these requirements make wide-bandgap semiconductors and, more precisely, Silicon Carbide (SiC) serious candidates due to their intrinsic characteristics in such extreme environments. Thus, since the last decades, SiC-based detectors are developed and studied for neutron detection in various nuclear facilities. In this paper, a SiC-based neutron detector is 3-D designed and studied through thermal and radiation-matter interaction numerical simulations for a future irradiation campaign at the Jožef Stefan Institute TRIGA Mark II research reactor in Slovenia. Firstly, this paper presents the scientific background and issues of our SiC-based detectors. In a second part the 3-D geometry is shown. Thereafter, the 3-D numerical thermal simulation results are reported. Finally, the 3-D numerical radiation/matter interaction simulations results are presented.

Evaluation of an organ-based tube current modulation tool in pediatric CT examinations

Objectives To investigate the effect of an organ-based tube current modulation (OTCM) technique on organ absorbed dose and assess image quality in pediatric CT examinations. Methods Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old were used. Standard head and thorax acquisitions were performed with automatic tube current modulation (ATCM) and ATCM+OTCM. Dose calculations were performed by means of Monte Carlo simulations. Radiation dose was measured for superficial and centrally located radiosensitive organs. The angular range of the OTCM exposure window was determined for different tube rotation times (t) by means of a solid-state detector. Image noise was measured as the standard deviation of the Hounsfield unit value in regions of interest drawn at selected anatomical sites. Results ATCM+OTCM resulted in a reduction of radiation dose to all radiosensitive organs. In head, eye lens dose was reduced by up to 13% in ATCM+OTCM compared with ATCM. In thorax, the corresponding reduction for breast dose was up to 10%. The angular range of the OTCM exposure window decreased with t. For t = 0.4 s, the angular range was limited to 74° in head and 135° for thorax. Image noise was significantly increased in ATCM+OTCM acquisitions across most examined phantoms (p < 0.05). Conclusions OTCM reduces radiation dose to exposed radiosensitive organs with the eye lens and breast buds exhibiting the highest dose reduction. The OTCM exposure window is narrowed at short t. An increase in noise is inevitable in images located within the OTCM-activated imaged volume. Key Points • In pediatric CT, organ-based tube current modulation reduces radiation dose to all major primarily exposed radiosensitive organs. • Image noise increases within the organ-based tube current modulation enabled imaged volume. • The angular range of the organ-based tube current modulation low exposure window is reduced with tube rotation time.

Detection of partially overlapped masses in mammograms

<span>Breast cancer remains one of the major causes of cancer deaths among women. For decades, screening mammography has been one of the most common methods for early cancer detection and diagnosis. Digital mammography images are created by applying a small burst of x-rays that pass through the breast to a solid-state detector, which transmits the electronic signals to a computer to form a digital image. However, due to projection, some mass areas may be partially covered, which makes them difficult to be interprated. This paper addresses the issue of potential mass regions being distorted by other normal breast tissues, which will negatively affect some of the features being extracted from the mass and in turn deteriorate the classification accuracy. The goal was to estimate the overlapped parts of the mass border using Euclidean distance in order to give more accurate results in next stages. The presented method achieved 95.744% region sensitivity at 0.333 False Positive per Image (FPI), outperforming other researches in this branch of mammography analysis.</span>

GEANT 4 Simulation of the Helios E6 - Proton Contamination of Relativistic Electron Measurements

&lt;p&gt;The Helios mission consisted of two almost identical spacecraft in highly elliptic orbits launched in 1974 (Helios A) and 1976 (Helios B). Until Parker Solar Probes first perihelion, Helios B was the first spacecraft to reach a distance of 0.29 AU to the Sun. One of its instruments is the Experiment 6 (E6) which was designed and built at the Christian-Albrechts-University Kiel in order to measure ions (protons up to iron) in the energy range of 1.3 MeV/nucleon up to several GeV/nucleon and electrons in the energy range from 0.3 to about 8 MeV. The instrument relies on the dE/dx-E and on the dE/dx-Cherenkov method for stopping and penetrating particles, respectively. Electrons are separated from ions by the signal in the first 100 &amp;#181;m thick solid state detector. Any particle that does not trigger this detector is identified as an electron. Since the solid state detectors are not working perfectly, a significant part of protons is identified as electrons. Here, we present a new method to correct the electron measurements for the cross talk based on detailed instrument simulations.&lt;/p&gt;