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Trofimov, Alexei

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Trofimov

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Alexei

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Trofimov, Alexei
Author's Publications: search.filters.isAuthorOfPublication.79b76e1c-fd06-44da-9b3f-b484831b8a92

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    Improved Quantum Sensing with a Single Solid-State Spin via Spin-to-Charge Conversion
    (American Physical Society (APS), 2019-06-03) Jaskula, Jean-Christophe; Shields, Brendan; Bauch, Erik; Lukin, Mikhail; Trofimov, Alexei; Walsworth, Ronald
    Efficient optical read-out of single, solid-state electronic spins at room temperature is a key challenge for nanoscale quantum sensing. Nitrogen-vacancy color centers in diamond have a fast optical spin-state read-out mechanism, but it provides little information in a single shot, because the spin state is destroyed before many photons can be collected. Recently, a technique based on spin-to-charge conversion (SCC) was demonstrated that circumvents this problem by converting the spin state to a long-lived charge state. Here, we study how the choice of spin read-out technique impacts the performance of a single nitrogen-vacancy center in bulk diamond for quantum-sensing applications. Specifically, we show that the SCC technique results in an order-of-magnitude reduction in spin read-out noise per shot and a factor of 5 increase in ac-magnetometry sensitivity compared with the conventional optical read-out method. Crucially, these improvements are obtained for a low collection efficiency and bulk diamond geometry, which opens up the SCC technique to a wide array of sensing applications. We identify applications where single-shot spin read-out noise, rather than sensitivity, is the limiting factor (e.g., low duty cycle pulsed sequences in biomagnetometry involving long dead times).
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    Interfractional Variations in the Setup of Pelvic Bony Anatomy and Soft Tissue, and Their Implications on the Delivery of Proton Therapy for Localized Prostate Cancer
    (Elsevier BV, 2011) Trofimov, Alexei; Nguyen, Paul; Efstathiou, Jason; Wang, Yi; Lu, Hsiao-Ming; Engelsman, Martijn; Merrick, Scott; Cheng, Chee-Wai; Wong, James R.; Zietman, Anthony
    Purpose To quantify daily variations in the anatomy of patients undergoing radiation therapy for prostate carcinoma, to estimate their effect on dose distribution, and to evaluate the effectiveness of current standard planning and set-up approaches employed in proton therapy. Methods We used series of CT data, which included the pre-treatment scan, and between 21 and 43 in-room scans acquired on different treatment days, from 10 patients treated with intensity-modulated radiation therapy at Morristown Memorial Hospital. Variations in femur rotation angles, thickness of subcutaneous adipose tissue, and physical depth to the distal surface of the prostate for lateral beam arrangement were recorded. Proton dose distributions were planned with the standard approach. Daily variations in the location of the prescription iso-dose were evaluated. Results In all 10 datasets, substantial variation was observed in the lateral tissue thickness (standard deviation of 1.7–3.6 mm for individual patients, variations of over 5 mm from the planning CT observed in all series), and femur rotation angle (standard deviation between 1.3–4.8°, with the maximum excursion exceeding 10° in 6 out of 10 datasets). Shifts in the position of treated volume (98% iso-dose) were correlated with the variations in the lateral tissue thickness. Conclusions Analysis suggests that, combined with image-guided set-up verification, the range compensator expansion technique prevents loss of dose to target due to femur rotation and soft tissue deformation, in the majority of cases. Anatomic changes coupled with the uncertainties of particle penetration in tissue restrict possibilities for margin reduction in proton therapy of prostate cancer.
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    Assessing Residual Motion for Gated Proton-Beam Radiotherapy
    (Oxford University Press (OUP), 2007) Sharp, Gregory; Lu, Hsiao-Ming; Trofimov, Alexei; Tang, Xiaoli; Jiang, Steve B.; Turcotte, Julie; Gierga, David; Chen, George; Hong, Theodore
    Gated radiation therapy is a promising method for improving the dose conformality of treatments to moving targets and reducing the total volume of irradiated tissue. Target motion is of particular concern in proton beam radiotherapy, due to the finite range of proton dose deposition in tissue. Gating allows one to reduce the extent of variation, due to respiration, of the radiological depth to target during treatment delivery. However, respiratory surrogates typically used for gating do not always accurately reflect the position of the internal target. For instance, a phase delay often exists between the internal motion and the motion of the surrogate. Another phenomenon, baseline drifting refers to a gradual change in the exhale position over time, which generally affects the external and internal markers differently. This study examines the influence of these two physiological phenomena on gated radiotherapy using an external surrogate.