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3,326 results on '"Singh, Ashok"'

40. Evaluation of gross target volumes in CECT vs MRI in head and neck cancer and its implication on concordance indices and dose-volume parameters of IMRT treatment plan

Author

Deshmukh, Milind, Jain, Bharati M., Singh, Ashok, Kalbande, Pallavi, Tayade, Atul, and Datta, Niloy R.

Subjects
Magnetic resonance imaging -- Comparative analysis, CT imaging -- Comparative analysis, Head and neck cancer -- Diagnosis -- Physiological aspects -- Care and treatment, Health
Abstract

Background: Although radiotherapy treatment planning (RTP) for head and neck cancers (HNCs) is based on contrast enhanced computed tomography (CECT), soft tissue contrasts are better evident on magnetic resonance imaging (MRI). We therefore evaluated dose-volume histogram (DVH) parameters along with concordance index (ConI), conformity index (CI), and homogeneity index (HI) of planning target volume (PTV) of GTV delineated on CECT vs MRI in HNCs enrolled for intensity modulated radiotherapy (IMRT). Methodology: Forty consecutive HNCs were enrolled in this study. All underwent CECT and MRI simulations with immobilization devices. GTVp and GTVn were delineated independently on CECT and MRI images. Corresponding MRI volumes were then copied to CECT. IMRT plans were generated on the CECT incorporating PTV margins. DVH parameters of PTVpn for both CECT and MRI were compared. In addition, mean (±SD) percentage difference of GTVp, GTVn, GTVpn, ConI, CI, and HI were evaluated using paired t-test. Results: The GTVp (P = 0.005), GTVn (P = 0.009), and GTVpn (P < 0.001) delineated on MRI were found to be significantly larger than GTV delineated on CECT. In eight patients, GTV outlined on CECT were larger than MRI. Significant mean differences in CECT vs MRI of CI (P < 0.001), HI (P < 0.001), ConI (P < 0.001), and DVH parameters (D[sub.2], D[sub.95], D[sub.98], V[sub.95], and V[sub.100] all P < 0.001; D50: P = 0.009) were noted. Conclusion: The GTVs and corresponding PTVs were significantly larger on MRI compared to CECT. This resulted in significant differences in DVH parameters, CI, ConI, and HI. This could be improved by co-registered MRI-CECT volumes during routine IMRT treatment planning for HNCs. Keywords: CECT, concordance indices, MRI, Author(s): Milind Deshmukh [1]; Bharati M. Jain [1]; Ashok Singh [1]; Pallavi Kalbande [1]; Atul Tayade [2]; Niloy R. Datta (corresponding author) [1] INTRODUCTION Cancer represents an immense and growing [...]

Published
2024
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41. Synergistic Niobium Doped Two-Dimensional Zirconium Diselenide: An Efficient Electrocatalyst for O$_2$ Reduction Reaction

Author

Singh, Ashok and Pakhira, Srimanta

Subjects
Condensed Matter - Materials Science
Abstract

The development of high-activity and low-price cathodic catalysts to facilitate the electrochemical sluggish O$_2$ reduction reaction (ORR) is very important to achieve the commercial application of fuel cells. Here, we have investigated the electrocatalytic activity of two-dimensional single-layer Nb-doped zirconium diselenide (2D Nb-ZrSe$_2$) towards ORR by employing the dispersion corrected Density Functional Theory (DFT-D) method. Through our study, we computed structural properties, electronic properties, and energetics of the 2D Nb-ZrSe$_2$ and ORR intermediates to analyze the electrocatalytic performance of the 2D Nb-ZrSe$_2$. The electronic properties calculations depict that the 2D monolayer ZrSe$_2$ has a large band gap of 1.48 eV, which is not favorable for the ORR mechanism. After the doping of Nb, the electronic band gap vanishes and 2D Nb-ZrSe$_2$ acts as a conductor. We studied both the dissociative and associative pathways through which the ORR can proceed to reduce the oxygen molecule (O$_2$). Our results show that the more favorable path for O$_2$ reduction on the surface of the 2D Nb-ZrSe$_2$ is the 4e$^-$ associative path. The detailed ORR mechanisms (both associated and dissociative) have been explored by computing the changes of Gibbs free energy ({\Delta}G). All the ORR reaction intermediate steps are thermodynamically stable and energetically favorable. The free energy profile for the associative path shows the downhill behavior of the free energy vs. the reaction steps, suggesting that all ORR intermediate structures are catalytically active for the 4e$^-$ associative path and a high 4e$^-$ reduction pathway selectivity. Therefore, 2D Nb-ZrSe$_2$ is a promising catalyst for the ORR which can be used as an alternative ORR catalyst compared with expensive platinum (Pt).

Published
2023

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