Mitigating disruptions, and scalability of radiation oncology physics work during the COVID-19 pandemic

PURPOSE: The COVID-19 pandemic has led to disorder in work and livelihood of a majority of the modern world. In this work, we review its major impacts on procedures and workflow of clinical physics tasks, and suggest alternate pathways to avoid major disruption or discontinuity of physics tasks in the context of small, medium, and large radiation oncology clinics. We also evaluate scalability of medical physics under the stress of social distancing . METHODS: Three models of facilities characterized by the number of clinical physicists, daily patient throughput, and equipment were identified for this purpose. For identical objectives of continuity of clinical operations, with constraints such as social distancing and unavailability of staff due to system strain, however with the possibility of remote operations, the performance of these models was investigated. General clinical tasks requiring on-site personnel presence or otherwise were evaluated to determine the scalability of the three models at this point in the course of disease spread within their surroundings. RESULTS: The clinical physics tasks within three models could be divided into two categories. The former, which requires individual presence, include safety-sensitive radiation delivery, high dose per fraction treatments, brachytherapy procedures, fulfilling state and nuclear regulatory commission\u27s requirements, etc. The latter, which can be handled through remote means, include dose planning, physics plan review and supervision of quality assurance, general troubleshooting, etc. CONCLUSION: At the current level of disease in the United States, all three models have sustained major system stress in continuing reduced operation. However, the small clinic model may not perform if either the current level of infections is maintained for long or staff becomes unavailable due to health issues. With abundance, and diversity of innovative resources, medium and large clinic models can sustain further for physics-related radiotherapy services

Optical super-resolution and periodical focusing effects by dielectric microspheres

Optical microscopy is one of the oldest and most important imaging techniques; however, its far-field resolution is diffraction-limited. In this dissertation, we proposed and developed a novel method of optical microscopy with super-resolution by using high- index dielectric microspheres immersed in liquid and placed on the surface of the structures under study. We used barium titanate glass microspheres with diameters of D~2-220 µm and refractive indices n~1.9-2.1 to discern minimal feature sizes ~?/4 (down to ~?/7) of various photonic and plasmonic nanostructures, where ? is the illumination wavelength. We studied the magnification, field of view, and resolving power, in detail, as a function of sphere sizes. We studied optical coupling, transport, focusing, and polarization properties of linear arrays of dielectric spheres. We showed that in arrays of spheres with refractive index n=v3, a special type of rays with transverse magnetic (TM) polarization incident on the spheres under the Brewster’s angle form periodically focused modes with radial polarization and 2D period, where D is the diameter of the spheres. We showed that the formation of periodically focused modes in arrays of dielectric spheres gives a physical explanation for beam focusing and extraordinarily small attenuation of light in such chains. We showed that the light propagation in such arrays is strongly polarization- dependent, indicating that such arrays can be used as filters of beams with radial polarization. The effect of forming progressively smaller focused beams was experimentally observed in chains of sapphire spheres in agreement with the theory. We expanded the concept of periodically focused modes to design a practical device for ultra-precise contact-mode laser tissue-surgery, with self-limiting ablation depth for potential application in retina surgery. By integrating arrays of dielectric spheres with infrared hollow waveguides and fibers, we fabricated prototypes of the designs and tested them with an Er:YAG laser. Furthermore, we proposed another design based on conical arrays of dielectric spheres to increase the coupling efficiency of the probe

Spectroscopic Separation of Čerenkov Radiation in High-Resolution Radiation Fiber Dosimeters

We have investigated Čerenkov radiation generated in phosphor-based optical fiber dosimeters irradiated with clinical electron beams. We fabricated two high-spatial resolution fiber-optic probes, with 200 and 400  μm core diameters, composed of terbium-based phosphor tips. A generalizable spectroscopic method was used to separate Čerenkov radiation from the transmitted signal by the fiber based on the assumption that the recorded signal is a linear superposition of two basis spectra: characteristic luminescence of the phosphor medium and Čerenkov radiation. We performed Monte Carlo simulations of the Čerenkov radiation generated in the fiber and found a strong dependence of the recorded Čerenkov radiation on the numerical aperture of the fiber at shallow phantom depths; however, beyond the depth of maximum dose that dependency is minimal. The simulation results agree with the experimental results for Čerenkov radiation generated in fibers. The spectroscopic technique used in this work can be used for development of high-spatial resolution fiber micro dosimeters and for optical characterization of various scintillating materials, such as phosphor nanoparticles, in ionizing radiation fields of high energy

Optical super-resolution and periodical focusing effects by dielectric microspheres

Optical microscopy is one of the oldest and most important imaging techniques; however, its far-field resolution is diffraction-limited. In this dissertation, we proposed and developed a novel method of optical microscopy with super-resolution by using high-index dielectric microspheres immersed in liquid and placed on the surface of the structures under study. We used barium titanate glass microspheres with diameters of D~2-220 μm and refractive indices n∼1.9-2.1 to discern minimal feature sizes ∼λ/4 (down to ∼λ/7) of various photonic and plasmonic nanostructures, where λ is the illumination wavelength. We studied the magnification, field of view, and resolving power, in detail, as a function of sphere sizes. We studied optical coupling, transport, focusing, and polarization properties of linear arrays of dielectric spheres. We showed that in arrays of spheres with refractive index [special characters omitted], a special type of rays with transverse magnetic (TM) polarization incident on the spheres under the Brewster's angle form periodically focused modes with radial polarization and 2D period, where D is the diameter of the spheres. We showed that the formation of periodically focused modes in arrays of dielectric spheres gives a physical explanation for beam focusing and extraordinarily small attenuation of light in such chains. We showed that the light propagation in such arrays is strongly polarization-dependent, indicating that such arrays can be used as filters of beams with radial polarization. The effect of forming progressively smaller focused beams was experimentally observed in chains of sapphire spheres in agreement with the theory. We studied optical coupling,transport, focusing, and polarization properties of linear arrays of dielectric spheres. We showed that in arrays of spheres with refractive index n=ã3, a special type of rays with transverse magnetic (TM) polarization incident on the spheres under the Brewster's angle form periodically focused modes with radial polarization and 2D period, where D is the diameter of the spheres. We showed that the formation of periodically focused modes in arrays of dielectric spheres gives a physical explanation for beam focusing and extraordinarily small attenuation of light in such chains. We showed that the light propagation in such arrays is strongly polarization-dependent, indicating that such arrays can be used as filters of beams with radial polarization. The effect of forming progressively smaller focused beams was experimentally observed in chains of sapphire spheres in agreement with the theory

Dielectric microspheres enhance microscopy resolution mainly due to increasing the effective numerical aperture

Abstract Microsphere-assisted microscopy utilizing a microsphere in immediate proximity of the specimen boosts the imaging resolution mainly as a result of an increase in the effective numerical aperture of the system

Monte Carlo modeling of a triple photon energy absorptiometry technique

Introduction: Osteoporosis is a bone disease in which there is a reduction in the amount of bone mineral content leading to an increase in the risk of bone fractures. The affected individuals not only have to go through lots of pain and suffering but this disease also results in high economic costs to the society due to a large number of fractures.  A timely and accurate diagnosis of this disease makes it possible to start a treatment and thus preventing bone fractures as a result of osteoporosis. Radiographic methods are particularly well suited for in vivo determination of bone mineral density (BMD) due to the relatively high x-ray absorption properties of bone mineral compared to other tissues. Materials and Methods: Monte Carlo simulation has been conducted to explore the possibilities of triple photon energy absorptiometry (TPA) in the measurement of bone mineral content. The purpose of this technique is to correctly measure the bone mineral density in the presence of fatty and soft tissues. The same simulations have been done for a dual photon energy absorptiometry (DPA) system and an extended DPA system. Results: Using DPA with three components improves the accuracy of the obtained result while the simulation results show that TPA system is not accurate enough to be considered as an adequate method for the measurement of bone mineral density. Discussion: The reason for the improvement in the accuracy is the consideration of fatty tissue in TPA method while having attenuation coefficient as a function of energy makes TPA an inadequate method. Conclusion: Using TPA method is not a perfect solution to overcome the problem of non uniformity in the distribution of fatty tissue

Laser welding of nickel-titanium (NiTi) shape memory alloys

Nickel-titanium (NiTi) shape memory alloys (SMAs) with outstanding shape memory and superelasticity effects are interesting candidates for a multitude of applications ranging from small-scale structures, such as microsensors and stents, to large-scale components used in aviation and automotive industries. After a mechanical deformation, SMAs can resume their initial shape which makes them an ideal candidate material to be used in smart components for various applications. A practical method for joining similar and dissimilar NiTi SMAs is laser welding. However, the thermal effect associated with the laser welding procedure influences the transformation temperature of the welded parts that will significantly impact their super elasticity and/or shape memory effect characteristics. This chapter deals with the microstructural, metallurgical, and mechanical investigations of the laser welding process as well as suggesting effective methods to improve the functionality of the welded parts of NiTi alloys

4D printing of shape memory polylactic acid (PLA)

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