Nishan Shrestha - Academia.edu (original) (raw)

Papers by Nishan Shrestha

Research paper thumbnail of Clostridioides difficile PCR Positivity on Successive Days after Treatment Initiation

ABSTRACTAmong 1282 patients with a positive Clostridioides difficile PCR test who were retested w... more ABSTRACTAmong 1282 patients with a positive Clostridioides difficile PCR test who were retested within 14 days, the proportion of positive tests rapidly decreased on successive days within the first week since initiation of treatment. Between days 7 and 14 after treatment initiation, approximately 25% of tests remained positive.

Research paper thumbnail of A phantom-based study and clinical implementation of brainlab’s treatment planning system for radiosurgical treatments of arteriovenous malformations

Biomedical Physics & Engineering Express

Purpose. Development of a simple, phantom-based methodology allowing for pilot applications for t... more Purpose. Development of a simple, phantom-based methodology allowing for pilot applications for the Elements TPS cranio-vascular module and clinical implementation prior to AVM treatments. Methods. A customized phantom was developed to be visible in MRI and CT images. High resolution digital subtraction angiograms (DSAs) and CT images of the phantom were acquired and imported into the Brainlab Elements treatment planning system. A clinical treatment plan with 5 arcs was generated in cranial vascular planning module and delivered to the phantom using a Varian TrueBeam STx Linac equipped with HD-MLCs and Brainlab ExacTrac imaging system for non-coplanar setup verification. The delivered dose was verified using a calibrated ionization chamber placed in the phantom. Upon verification of the TPS workflow, three patients with AVM who have been treated to date at our center using the Brainlab’s cranial vascular module for AVM are presented here for retrospective review. Results. The differ...

Research paper thumbnail of Further developments in 2D optically stimulated luminescence dosimetry based on Al2O3 and MgB4O7

The objective of this work is to explore potential improvements in 2D OSL dosimetry. These includ... more The objective of this work is to explore potential improvements in 2D OSL dosimetry. These include the introduction of Tikhonov regularization in the pixel bleeding algorithm, which was investigated based both on simulated data as well as experimental results obtained using a 6 MV linear accelerator (linac) and an Accuray CyberKnife. The feasibility of using of Al2O3:C and Al2O3:C,Mg for its application in dosimetry in the presence of magnetic fields was tested. Finally, initial results of newly developed MgB4O7:Ce,Li films for 2D optically stimulated luminescence dosimetry are presented. indings and Conclusions: The results show that the implementation of Tikhonov regularization improves the image noise and resolves the directional dependence in the OSL images when compared to the Least Squares algorithm. The initial measurements of offcentral ray ratios (OCR), output factors (OF's), and tissue phantom ratios (TPR) in CyberKnife shows good agreement with the measurements using the commercial stereotactic diode. The initial tests using the Al2O3 OSLD's in MR linac show that the detectors do not attenuate the beam, independent of angle of irradiation within 1.4%. The gamma analysis of IMRT treatment plans and the OSL images show a good passing rate for both 3%-3 mm and 2%-2 mm gamma criteria. The initial studies of MgB4O7:Ce,Li films demonstrate the possibility of 2D dosimetry for radiotherapy applications with many advantages over Al2O3:C or Al2O3:C,Mg films. MBO films show no pixel bleeding in the OSL images, has a linear dose response up to 10 Gy with steep dose gradients, has background equivalent dose of <0.5 mGy. However, it suffers from fading and sensitization. In conclusion, this work demonstrates OSL films have huge potential for its 2D dosimetry in both small fields and MR guided radiotherapy especially with development of new OSL materials to overcome the challenges with the current OSL materials.

Research paper thumbnail of The DOSIS 3D Project Onboard the International Space Station - Status and Science Overview of 6 years of measurements (2012 - 2018)

Research paper thumbnail of An analysis of rice-based farming practices in Valderrama, Antique, The Philippines

7-L fl3ifinrp of animals in Lubrub based on the f irst survey 7.2 Percentage of animals under pas... more 7-L fl3ifinrp of animals in Lubrub based on the f irst survey 7.2 Percentage of animals under pasagod/pahonol 7-3 Reproductive performances of native and hybrid pigs in six barangay of Valderrama 8-L Age distribution of the sampre respondents of the main survey 8.2 Level of schooting of respondents 9.3 Payment of harveéter and thresher 8.4 Àctive barangay under DÀR 8-5 Bank rending cónditions for smalr borrowers 8.6 cumnulatÍve numbers of animais-ài=i".="d by DÀ, in Valderrama municipality since 19g0 8.7 Markets freguenteà Uy farmers xvl

Research paper thumbnail of Development of an in Vivo Dosimetry System Using Radiophotoluminescence from Silver-doped Phosphate Glass for Radiotherapy Applications

The goal of this project was to determine the potential of using radiophotoluminescence (RPL) fro... more The goal of this project was to determine the potential of using radiophotoluminescence (RPL) from silver-doped phosphate glass as a real-time, in vivo dosimeter in radiation therapy. Our objective is to develop a portable RPL reader and identify the technical difficulties and potential solutions to decide on the feasibility of such system. Two different setups were built to characterize the material luminescence properties, such as the excitation/emission wavelength, to select proper optical filters for the system. The stimulation and detection components of the system were characterized to understand the overall stability of the system. Additional material characteristics, including the dose build up effect, were also studied. Based on these studies a qualitative model for the RPL properties was proposed. The results show that that the diode laser when operated in QCW mode is limited by the laser rise and fall time, which needs to be taken in to account when taking time discrimina...

Research paper thumbnail of Clostridioides difficile PCR Positivity on Successive Days after Treatment Initiation

ABSTRACTAmong 1282 patients with a positive Clostridioides difficile PCR test who were retested w... more ABSTRACTAmong 1282 patients with a positive Clostridioides difficile PCR test who were retested within 14 days, the proportion of positive tests rapidly decreased on successive days within the first week since initiation of treatment. Between days 7 and 14 after treatment initiation, approximately 25% of tests remained positive.

Research paper thumbnail of A phantom-based study and clinical implementation of brainlab’s treatment planning system for radiosurgical treatments of arteriovenous malformations

Biomedical Physics & Engineering Express

Purpose. Development of a simple, phantom-based methodology allowing for pilot applications for t... more Purpose. Development of a simple, phantom-based methodology allowing for pilot applications for the Elements TPS cranio-vascular module and clinical implementation prior to AVM treatments. Methods. A customized phantom was developed to be visible in MRI and CT images. High resolution digital subtraction angiograms (DSAs) and CT images of the phantom were acquired and imported into the Brainlab Elements treatment planning system. A clinical treatment plan with 5 arcs was generated in cranial vascular planning module and delivered to the phantom using a Varian TrueBeam STx Linac equipped with HD-MLCs and Brainlab ExacTrac imaging system for non-coplanar setup verification. The delivered dose was verified using a calibrated ionization chamber placed in the phantom. Upon verification of the TPS workflow, three patients with AVM who have been treated to date at our center using the Brainlab’s cranial vascular module for AVM are presented here for retrospective review. Results. The differ...

Research paper thumbnail of Further developments in 2D optically stimulated luminescence dosimetry based on Al2O3 and MgB4O7

The objective of this work is to explore potential improvements in 2D OSL dosimetry. These includ... more The objective of this work is to explore potential improvements in 2D OSL dosimetry. These include the introduction of Tikhonov regularization in the pixel bleeding algorithm, which was investigated based both on simulated data as well as experimental results obtained using a 6 MV linear accelerator (linac) and an Accuray CyberKnife. The feasibility of using of Al2O3:C and Al2O3:C,Mg for its application in dosimetry in the presence of magnetic fields was tested. Finally, initial results of newly developed MgB4O7:Ce,Li films for 2D optically stimulated luminescence dosimetry are presented. indings and Conclusions: The results show that the implementation of Tikhonov regularization improves the image noise and resolves the directional dependence in the OSL images when compared to the Least Squares algorithm. The initial measurements of offcentral ray ratios (OCR), output factors (OF's), and tissue phantom ratios (TPR) in CyberKnife shows good agreement with the measurements using the commercial stereotactic diode. The initial tests using the Al2O3 OSLD's in MR linac show that the detectors do not attenuate the beam, independent of angle of irradiation within 1.4%. The gamma analysis of IMRT treatment plans and the OSL images show a good passing rate for both 3%-3 mm and 2%-2 mm gamma criteria. The initial studies of MgB4O7:Ce,Li films demonstrate the possibility of 2D dosimetry for radiotherapy applications with many advantages over Al2O3:C or Al2O3:C,Mg films. MBO films show no pixel bleeding in the OSL images, has a linear dose response up to 10 Gy with steep dose gradients, has background equivalent dose of <0.5 mGy. However, it suffers from fading and sensitization. In conclusion, this work demonstrates OSL films have huge potential for its 2D dosimetry in both small fields and MR guided radiotherapy especially with development of new OSL materials to overcome the challenges with the current OSL materials.

Research paper thumbnail of The DOSIS 3D Project Onboard the International Space Station - Status and Science Overview of 6 years of measurements (2012 - 2018)

Research paper thumbnail of An analysis of rice-based farming practices in Valderrama, Antique, The Philippines

7-L fl3ifinrp of animals in Lubrub based on the f irst survey 7.2 Percentage of animals under pas... more 7-L fl3ifinrp of animals in Lubrub based on the f irst survey 7.2 Percentage of animals under pasagod/pahonol 7-3 Reproductive performances of native and hybrid pigs in six barangay of Valderrama 8-L Age distribution of the sampre respondents of the main survey 8.2 Level of schooting of respondents 9.3 Payment of harveéter and thresher 8.4 Àctive barangay under DÀR 8-5 Bank rending cónditions for smalr borrowers 8.6 cumnulatÍve numbers of animais-ài=i".="d by DÀ, in Valderrama municipality since 19g0 8.7 Markets freguenteà Uy farmers xvl

Research paper thumbnail of Development of an in Vivo Dosimetry System Using Radiophotoluminescence from Silver-doped Phosphate Glass for Radiotherapy Applications

The goal of this project was to determine the potential of using radiophotoluminescence (RPL) fro... more The goal of this project was to determine the potential of using radiophotoluminescence (RPL) from silver-doped phosphate glass as a real-time, in vivo dosimeter in radiation therapy. Our objective is to develop a portable RPL reader and identify the technical difficulties and potential solutions to decide on the feasibility of such system. Two different setups were built to characterize the material luminescence properties, such as the excitation/emission wavelength, to select proper optical filters for the system. The stimulation and detection components of the system were characterized to understand the overall stability of the system. Additional material characteristics, including the dose build up effect, were also studied. Based on these studies a qualitative model for the RPL properties was proposed. The results show that that the diode laser when operated in QCW mode is limited by the laser rise and fall time, which needs to be taken in to account when taking time discrimina...