Arash Darafsheh

Arash Darafsheh
Washington University in St. Louis | WUSTL , Wash U · Department of Radiation Oncology

Associate Professor

About

109
Publications
25,299
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2,009
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Publications

Publications (109)
Article
The clinical translation of FLASH radiotherapy (RT), requires challenges related to dosimetry and beam monitoring of ultra‐high dose rate (UHDR) beams to be addressed. Detectors currently in use suffer from saturation effects under UHDR regimes, requiring the introduction of correction factors. There is significant interest from the scientific comm...
Article
Purpose: To present a proton computed tomography (pCT) reconstruction approach that models the integral depth dose (IDD) of the clinical scanning proton beam into beamlets. Using a multi-layer ionization chamber (MLIC) as the imager, the proposed pCT system and the reconstruction approach can minimize the extra ambient neutron dose and simplify th...
Article
Full-text available
Light microscopy is one of the most powerful techniques for nondestructive real-time imaging of specimens at a resolution beyond the reach of human eyes. However, the spatial resolution of any conventional microscope is fundamentally limited by the diffraction of light waves at the lens aperture. Microsphere-assisted microscopy (MAM) has emerged in...
Article
Full-text available
Additive manufacturing has attracted much attention in the last decade as a principal growing sector of complex manufacturing. Precise layer-by-layer patterning of materials gives rise to novel designs and fabrication strategies that were previously not possible to realize with conventional techniques. Using suitable materials and organized variati...
Article
Full-text available
Research efforts in FLASH radiotherapy have increased at an accelerated pace recently. FLASH radiotherapy involves ultra-high dose rates and has shown to reduce toxicity to normal tissue while maintaining tumor response in pre-clinical studies when compared to conventional dose rate radiotherapy. The goal of this review is to summarize the studies...
Article
Full-text available
Purpose: The purpose of this work is to 1) demonstrate the feasibility of delivering a spread-out Bragg peak (SOBP) proton beam in ultra-high dose rate using a proton therapy synchrocyclotron as a major step toward realizing an experimental platform for preclinical studies, and 2) evaluate the response of four models of ionization chambers in such...
Chapter
Full-text available
Nickel-Titanium (NiTi) shape memory alloys possess 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...
Article
The goal of this study was to develop a Monte Carlo (MC)-based analytical model that can predict the in-room ambient dose equivalent from a Mevion gantry-mounted passively scattered proton system. The Mevion S250 and treatment vault were simulated using the MCNPX MC code. The results of the in-room neutron dose measurements, using an FHT 762 WENDI-...
Article
Purpose: To 1) characterize the fundamental optical and dosimetric properties of the storage phosphor europium doped potassium chloride for quantitative proton dosimetry, and 2) to investigate if its dose radiation response can be described by an analytic radiation transport model. Methods: Cylindrical KCl:Eu2+ dosimeters with dimensions of 6 mm...
Article
The response of GafchromicTM EBT-XD films to proton irradiation using a Mevion S250TM proton therapy system is studied in this work. Film samples from different batches were irradiated with doses from 0.25 Gy to 20 Gy using a Mevion S250 spread-out Bragg peak (SOBP) clinical proton beam. Using a fiber-coupled optical spectrometer, transmission spec...
Article
Purpose: To investigate the inconsistency of recent literature on the effect of magnetic field on the response of radiochromic films, we studied the influence of 0.35 T magnetic field on dosimetric response of EBT3 and EBT-XD GafchromicTM films. Methods: Two different models of radiochromic films, EBT3 and EBT-XD, were investigated. Pieces of fi...
Article
Purpose: To calculate in- and out-of-field neutron spectra and dose equivalent, using Monte Carlo (MC) simulation, for a Mevion gantry-mounted passively scattered proton system in craniospinal irradiation. An analytical model based on the MC calculations that estimates in- and out-of-field neutron dose equivalent from proton CSI was also developed...
Article
Purpose: It has been recently shown that radiotherapy at ultra-high dose rates (>40 Gy/s, FLASH) has a potential advantage in sparing healthy organs compared to that at conventional dose rates. The purpose of this work is to show the feasibility of proton FLASH irradiation using a synchrocyclotron as a first step toward implementing an experimenta...
Article
Full-text available
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...
Article
As the COVID-19 spread continues to challenge the societal and professional norms, radiotherapy around the globe is pushed into an unprecedented transformation. We will discuss how clinical physics has transformed to ascertain safety and quality standards across four facilities around the world through diversity of action, innovation, and scientifi...
Article
Full-text available
Effective treatment delivery in photodynamic therapy (PDT) requires coordination of the light source, the photosensitizer, and the delivery device appropriate to the target tissue. Lasers, light‐emitting diodes (LEDs), and lamps are the main types of light sources utilized for PDT applications. The choice of light source depends on the target locat...
Article
Radiochromic films have been widely studied for clinical dosimetry in conventional external beam radiation therapy. With an increase in practice of proton therapy, such films are being conveniently used; however, their spectroscopic characterization for this modality is lacking. This work investigated the response of the EBT3 radiochromic films irr...
Article
Purpose: The purpose of this study was to investigate the beam quality dependence of the EBT-XD radiochromic films for megavoltage photon and electron beam irradiations by studying their spectral response. Dose, dose rate, and inter-batch dependencies were investigated as well. Methods: EBT-XD and EBT3 radiochromic films were cut into 5 × 5 cm2...
Article
Purpose: The purpose of this study was to investigate the spectral response of the EBT3 radiochromic films to different beam qualities for radiation therapy dosimetry. Dose, dose rate, and interbatch dependencies on the spectral response of the films were investigated as well. Methods: Pieces of EBT3 films placed between layers of solid water ph...
Article
Manifestation of Čerenkov radiation as a contaminating signal is a significant issue in radiation therapy dose measurement by fiber-coupled scintillator dosimeters. To enhance the scintillation signal transmission while minimizing Čerenkov radiation contamination, we designed a fiber probe using a silver-only coated hollow waveguide (HWG). The HWG...
Chapter
Micromachining using laser is a unique fabrication process that provides innovative solution in a myriad of micro-engineering applications for industrial and research purposes. Laser micromachining offers a precise non-contact mode of machining process, which is used in the fabrication of miniature components with intricate geometry. These micro-co...
Article
We studied the characteristics of photonic nanojets formed by dielectric microcylinders over the visible spectrum using FDTD numerical simulations. We varied a wide range of tuning parameters including the refractive indices of the microcylinder and the background medium, size and shape of the microcylinder, and wavelength and state of polarization...
Article
Full-text available
We demonstrated the importance of the refractive index of the background medium containing the microsphere in microsphere-assisted super-resolution microscopy. We performed numerical simulation and showed that the photonic nanojet properties of a microlens can be optimized by adjusting the index of the background medium surrounding it. Our simulati...
Article
Full-text available
We investigate the feasibility of proton therapy dose measurement by using scintillation of a bare silica glass fiber. The emission spectra of the optical fiber at various depths in tissue-mimicking phantoms, irradiated with proton beams of energies 100-225 MeV show two distinct peaks at 460 and 650 nm whose nature is connected with the silica poin...
Article
Full-text available
Purpose: Proton beam dosimetry using bare plastic optical fibers has emerged as a simple approach to proton beam dosimetry. The source of the signal in this method has been attributed to Čerenkov radiation. The aim of this work was a phenomenological study of the nature of the visible light responsible for the signal in bare fiber optic dosimetry o...
Article
Full-text available
This work addresses the shortcomings of the recent paper by Allen et al. [Ann. Phys. (Berlin) 527, 513 (2015)], in which the authors attempted to quantify the spatial resolution and magnification in imaging by using microsphere-embedded films. Their methodology in resolution and magnification analyses is ill-considered and worth discussing. Neglect...
Chapter
Full-text available
This chapter will address the technical and physical aspects of the light sources, delivery devices, and photosensitizers used in ENT photodynamic therapy (PDT). Effective delivery of treatment light to the target tissue requires appropriate matching of the light source to the tissue, the sensitizer, and the delivery device. Lasers, light-emitting...
Article
Purpose:The nature of the background visible light observed during fiber optic dosimetry of proton beams, whether it is due to Cherenkov radiation or not, has been debated in the literature recently. In this work, experimentally and by means of Monte Carlo simulations, we shed light on this problem and investigated the nature of the background visi...
Article
Purpose:Range verification in proton therapy is of great importance. Cherenkov light follows the photon and electron energy deposition in water phantom. The purpose of this study is to investigate the connection between Cherenkov light generation and radiation absorbed dose in a water phantom irradiated with proton beams. Methods:Monte Carlo simula...
Conference Paper
We investigated the feasibility of using fiber optics probes with rare-earth-based phosphor tips for proton beam radiation dosimetry. We designed and fabricated a fiber probe with submillimeter resolution based on TbF3 phosphors and evaluated its performance for measurement of proton beams including profiles and range. The fiber optic probe, embedd...
Article
PDT dose is the product of the photosensitizer concentration and the light fluence in the target tissue. For improved dosimetry during plural photodynamic therapy (PDT), a PDT dose dosimeter was developed to measure both the light fluence and the photosensitizer concentration simultaneously in the same treatment location. Light fluence and spectral...
Article
Full-text available
PDT dose is the product of the photosensitizer concentration and the light fluence in the target tissue. For improved dosimetry during plural photodynamic therapy (PDT), a PDT dose dosimeter was developed to measure both the light fluence and the photosensitizer concentration simultaneously in the same treatment location. Light fluence and spectral...
Conference Paper
We demonstrate that super-resolution imaging of specimens containing sub-diffraction-limited features is feasible by using dielectric microwires fabricated through capillary force lithography followed by photopatterning. As supplementary micron scale cylindrical lenses, we fabricated uniform-sized microwires with and 5 and 10 μm diameters and refra...
Conference Paper
Čerenkov contamination is a significant issue in radiation detection by fiber-coupled scintillators. To enhance the scintillation signal transmission while minimizing Čerenkov contamination, we designed a fiber probe using a silver-only coated hollow waveguide (HWG). The HWG tip with inserted scintillator, embedded in tissue mimicking phantoms, was...
Article
PDT dose is the product of the photosensitizer concentration and the light fluence in the target tissue. For improved dosimetry during plural photodynamic therapy (PDT), a PDT dose dosimeter was developed to measure both the light fluence and the photosensitizer concentration simultaneously in the same treatment location. Light fluence and spectral...
Article
Full-text available
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...
Article
To investigate feasibility of using fiber optics probes with rare-earth-based phosphor tips for proton beam radiation dosimetry. We designed and fabricated a fiber probe with submillimeter resolution (<0.5 mm3) based on TbF3 phosphors and evaluated its performance for measurement of proton beam including profiles and range. The fiber optic probe wi...
Article
To characterize basic performance of plastic scintillator detectors (PSD) array designed for dosimetry of radiation therapy. An in-house PSD array has been developed by placing single point PSD into customized 2D holder. Each point PSD is a plastic scintillating fiber-based detector designed for highly accurate measurement of small radiotherapy fie...
Article
Full-text available
High-index microspheres embedded in elastomer or immersed in liquid allow straightforward super-resolution imaging of biological, metallic, and semiconductor structures.
Conference Paper
We demonstrated super-resolution imaging using microsphere-embedded cover slides. We performed imaging, with resolution improvement by a factor of 2-3, by using barium titanate glass microspheres with diameters ~30-150 μm and refractive index ~1.9-2.1 embedded in a layer of polydimethylsiloxane elastomer placed over the specimen.
Article
We have designed, fabricated, and characterized a fiberoptic probe composed of terbium-based phosphors for ionizing radiation dosimetry. Fiber optic probes consisting of ∼1 mm layer of TbF3 covering the tip embedded in tissue-mimicking phantoms were irradiated with electron beams produced by a medical linear accelerator. Optical spectra of irradiat...
Article
We studied Čerenkov radiation generated in irradiated optical fibers and demonstrated a generic spectroscopic method for separation of Čerenkov radiation from the transmitted signal in fiber optic dosimetry based on the assumption that the recorded signal is a linear superposition of two basis spectra: Čerenkov radiation and characteristic luminesc...
Article
Full-text available
Optical super-resolution imaging is a desirable technique in many fields, including medical and material sciences and nanophotonics. We demonstrated feasibility of optical microscopy, with resolution improvement by a factor of 2-3, by using microsphere-embedded coverslips composed of barium titanate glass microspheres (refractive index n~1.9-2.1) f...
Article
We investigated the optical properties of novel terbium (Tb3+)-doped nanophosphors with various host compounds irradiated by clinical electron, photon, and proton beams for their potential as optical probes. The emission spectra of nanophosphors embedded in tissue-mimicking phantoms were collected by an optical fiber connected to a CCD-coupled spec...
Article
Full-text available
We demonstrated feasibility of super-resolution imaging through high-index microspheres embedded in transparent elastomers. We performed imaging, with resolution improvement by a factor of two, by using implanted barium titanate glass microspheres (diameters ∼30–150 μm and refractive index ∼1.9–2.1) in a thin film of polydimethylsiloxane elastomer...
Article
Full-text available
It is shown that the focusing properties of polystyrene microsphere-chain waveguides (MCWs) formed by sufficiently large spheres (D ≥ 20λ, where D is the sphere diameter and λ is the wavelength of light) scale with the sphere diameter as predicted by geometrical optics. However, this scaling behavior does not hold for mesoscale MCWs with D ≤ 10λ re...
Article
Purpose: Optical properties of terbium (Tb3+)-doped gadolinium trifluoride (GdF3) nanoplates irradiated by electron and photon beams were investigated for their potential as optical probes. The contribution of induced Cerenkov radiation in exciting the nanophosphors was investigated as well. Methods: The emission spectra of Terbium-doped GdF3 dispe...
Article
Purpose: To characterize basic performance of plastic scintillator detectors (PSD) designed for dosimetry of radiation therapy. Methods: The Exradin W1 Scintillator is a plastic scintillating fiber-based detector designed for highly accurate measurement of small radiotherapy fields used in patient plan verification and machine commissioning and QA...
Article
Full-text available
We demonstrate a series of advantages of microsphere-assisted imaging over confocal and solid immersion lens microscopies including intrinsic flexibility, better resolution, higher magnification, and longer working distances. We discerned minimal feature sizes of ̃50-60 nm in nanoplasmonic arrays at the illumination wavelength λ = 405 nm. It is dem...
Article
Full-text available
Vitreoretinal surgery is performed using mechanical dissection that sometimes results in iatrogenic complications, including vitreous hemorrhage, retinal breaks, incomplete membrane delamination, retinal distortion, microscopic damage, etc. An ultraprecise laser probe would be an ideal tool for cutting away pathologic membranes; however, the depth...
Article
Full-text available
Using numerical modeling, it is shown that chains of dielectric spheres and cylinders act as polarizers. The mechanism is based on gradual filtering of periodically focused modes with a certain polarization propagating with minimal losses due to Brewster angles conditions, whereas orthogonally polarized modes are strongly attenuated. It is shown th...
Conference Paper
Full-text available
It is shown that super-resolution microscopy can be performed by using dielectric microcylinders. We used silica (n ~ 1.46) optical fibers, chemically etched down to ~ 7 μm diameter, placed on top of a commercial Blu-ray® disk. We clearly resolved one-dimensional arrays of 200 nm width stripes separated by 100 nm width grooves. Potential applicatio...
Conference Paper
Full-text available
We show that microsphere-assisted microscopy, where liquid-immersed barium titanate glass (n ~ 1.9) beads with diameters of several microns are employed, has superior optical resolution compared to the confocal microscopy. The resolution advantage of microsphere-assisted microscopy stems from an ability of high-index microspheres to pick spatial di...
Thesis
Full-text available
In my Ph.D. work, I investigated novel optical phenomena in individual and arrays of dielectric microspheres and microcylinders. I addressed the challenging problem of overcoming the diffraction-limit in optical microscopy and invented the immersed microsphere-assisted super-resolution imaging technique. I demonstrated that high-index microspheres...
Article
Full-text available
Vitreoretinal surgery is performed using mechanical dissection that sometimes results in iatrogenic complications, including vitreous hemorrhage, retinal breaks, incomplete membrane delamination, retinal distortion, microscopic damage, etc. The laser probe would be an ideal tool for cutting away pathologic membranes, however the depth of surgery sh...
Article
Full-text available
It is shown that microsphere-chain waveguides have strong polarization-dependent attenuation properties that can be used for developing passive filters of radially polarized beams. By using numerical modeling, it is demonstrated that the principle of operation of such devices is based on filtering periodically focused modes in chains of dielectric...