Dielectric-Backed Aperture Resonators for X-band Depth-Limited in Vivo EPR Nail Dosimetry
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Applied Magnetic Resonance
ORIGINAL PAPER
Dielectric‑Backed Aperture Resonators for X‑band Depth‑Limited in Vivo EPR Nail Dosimetry Oleg Grinberg1 · Jason W. Sidabras3,4 · Dmitriy Tipikin1 · Vladimir Krymov1 · Steven G. Swarts2 · Harold M. Swartz1 Received: 24 June 2020 / Revised: 18 August 2020 / Published online: 25 September 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract A new resonant geometry for X-band in vivo electron paramagnetic resonance (EPR) nail dosimetry has been developed, fabricated, and tested. The dielectricbacked aperture resonator (DAR) was specifically designed for depth-limited surface spectroscopy. The DAR improves EPR sensitivity of surface samples with sub-millimeter thicknesses by at least a factor of 20 compared to other aperture resonator designs. The increase in EPR sensitivity was achieved using a non-resonant dielectric slab which is placed on the aperture inside the cavity. The dielectric slab provides an increased microwave magnetic field, while minimizing the problematic resonance conditions of the aperture. It has been shown that the DAR provides sufficient sensitivity to make biologically-relevant measurements both in vitro and in vivo. This work demonstrates that in vivo tests with an equivalent dosimetry sensitivity of approximately 1.4 Gy are feasible. Plausible ways to further increase the sensitivity are discussed, such as, the introduction and simulations of a DAR based on a semi-spherical TE011 geometry.
1 Introduction There is a need for rapid screening methods to assess for the exposure to ionizing radiation after an incident in which clinically-significant doses may have occurred. These methods are essential to guide efficient treatments based on an individual’s radiation dose in the range that could lead to acute radiation syndrome [1–3]. Rapid * Oleg Grinberg [email protected] 1
Geisel School of Medicine at Dartmouth, Hanover, NH 03755, USA
2
Department of Radiation Oncology, University of Florida, Gainesville, FL 32610, USA
3
Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53211, USA
4
EPR Research Group, Max Planck for Chemical Energy Conversion, 45468 Mülheim an der Ruhr, Germany
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screening methods must provide the ability to triage large populations quickly, be minimally invasive, and identify individuals who may have received exposures of 2 Gy or more. Significant effort has been devoted to develop electron paramagnetic resonance (EPR) as a technique that would provide retrospective dosimetry screening [4–6]. Teeth, fingernails, and toenails have been demonstrated as viable in vitro and in vivo EPR dosimetry assays, providing a dose estimate based on a radiationinduced EPR signal (RIS) that reflects the extent of exposure to ionizing radiation [7–9]. We focus this work on fingernail and toenail assays, while the methods provided here are also feasible on tooth measurements with little modification. The technical approach of in vitro nail dosimet
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