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Lee, S

Publications and source records attributed to Lee, S.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

SU-E-T-335: Transit Dosimetry for Verification of Dose Delivery Using Electronic Portal Imaging Device (EPID)

Purpose: To evaluate the effectiveness of transit dose, measured with an electronic portal imaging device (EPID), in verifying actual dose delivery to patients. Methods: Plans of 5 patients with lung cancer, who received IMRT treatment, were examined using homogeneous solid water phantom and inhomogeneous anthropomorphic phantom. To simulate error in patient positioning, the anthropomorphic phantom was displaced from 5 mm to 10 mm in the inferior to superior (IS), superior to inferior (SI), left to right (LR), and right to left (RL) directions. The transit dose distribution was measured with EPID and was compared to the planed dose using gamma index. Results: Although the average passing rate based on gamma index (GI) with a 3% dose and a 3 mm distance-to-dose agreement tolerance limit was 94.34 % for the transit dose with homogeneous phantom, it was reduced to 84.63 % for the transit dose with inhomogeneous anthropomorphic phantom. The Result also shows that the setup error of 5mm (10mm) in IS, SI, LR and SI direction can Result in the decrease in values of GI passing rates by 1.3% (3.0%), 2.2% (4.3%), 5.9% (10.9%), and 8.9% (16.3%), respectively. Conclusion: Our feasibility study suggests that the transit dose-based quality assurance may provide information regarding accuracy of dose delivery as well as patient positioning.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-484: A New Method of Aligning Patient Setup Lasers in Radiation Therapy

Purpose: To develop a new method to align the patient setup lasers in radiation therapy and examine its validity and effectiveness. Methods: The new laser alignment method was realized by a device composed of both a metallic base plate and few acrylic transparent plates with a cross hair line on each of them. The holders of radiochromic films were prepared in the device to find a radiation isocenter. The right laser positions could be found optically by matching the shadows of all the cross hairs in the gantry head and the device. The repeatability and reproducibility (R and R) of laser alignments and the dependency of the alignment on the position error of the light source were evaluated by comparing the standard deviations and the means of the measured laser positions. After aligning the lasers optically, a radiation isocenter was found by a collimator spoke shot and the gantry spoke shot, and then the lasers were parallely translated to the isocenter. Results: In the R and R test, the standard deviation was 1.14 mm for the new method whereas it was 1.49 mm or 2.76 mm for the conventional method with either high- or low-precision levels. In the test of the dependency on the position error of the light source, the mean laser position was shifted by 5.3 mm corresponding to the shift of the light source, 4.8 mm for the new method, but for the conventional method the laser position was shifted more than 7 times than that. The positional shift could be corrected by a parallel translation to the isocenter in the new method. Conclusion: A new laser alignment method was devised for radiation therapy and tested successfully. The method enabled us to align the lasers easily and accurately without repetition, and all lasers could be finally aligned to the radiation isocenter.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

SOWFA Super-Controller: A High-Fidelity Tool for Evaluating Wind Plant Control Approaches

This paper presents a new tool for testing wind plant controllers in the Simulator for Offshore Wind Farm Applications (SOWFA). SOWFA is a high-fidelity simulator for the interaction between wind turbine dynamics and the fluid flow in a wind plant. The new super-controller testing environment in SOWFA allows for the implementation of the majority of the wind plant control strategies proposed in the literature.

17 WIND ENERGY↗
DOE OSTI2012

Plasma focus ion beam fluence and flux-Scaling with stored energy

Measurements on plasma focus ion beams include various advanced techniques producing a variety of data which has yet to produce benchmark numbers [A Bernard et al., J. Mosc. Phys. Soc. 8, 93-170 (1998)]. This present paper uses the Lee Model code [S Lee, http://www.plasmafocus.net (2012)], integrated with experimental measurements to provide the basis for reference numbers and the scaling of deuteron beams versus stored energy E{sub 0}. The ion number fluence (ions m{sup -2}) and energy fluence (J m{sup -2}) computed as 2.4-7.8 Multiplication-Sign 10{sup 20} and 2.2-33 Multiplication-Sign 10{sup 6}, respectively, are found to be independent of E{sub 0} from 0.4 to 486 kJ. Typical inductance machines (33-55 nH) produce 1.2-2 Multiplication-Sign 10{sup 15} ions per kJ carrying 1.3%-4% E{sub 0} at mean ion energy 50-205 keV, dropping to 0.6 Multiplication-Sign 10{sup 15} ions per kJ carrying 0.7% E{sub 0} for the high inductance INTI PF.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Effects of laser energy fluence on the onset and growth of the Rayleigh-Taylor instabilities and its influence on the topography of the Fe thin film grown in pulsed laser deposition facility

The effect of laser energy fluence on the onset and growth of Rayleigh-Taylor (RT) instabilities in laser induced Fe plasma is investigated using time-resolved fast gated imaging. The snow plow and shock wave models are fitted to the experimental results and used to estimate the ablation parameters and the density of gas atoms that interact with the ablated species. It is observed that RT instability develops during the interface deceleration stage and grows for a considerable time for higher laser energy fluence. The effects of RT instabilities formation on the surface topography of the Fe thin films grown in pulsed laser deposition system are investigated (i) using different laser energy fluences for the same wavelength of laser radiation and (ii) using different laser wavelengths keeping the energy fluence fixed. It is concluded that the deposition achieved under turbulent condition leads to less smooth deposition surfaces with bigger sized particle agglomerates or network.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Coded aperture imaging of fusion source in a plasma focus operated with pure D{sub 2} and a D{sub 2}-Kr gas admixture

The coded aperture imaging (CAI) technique has been used to investigate the spatial distribution of DD fusion in a 1.6 kJ plasma focus (PF) device operated in, alternatively, pure deuterium or deuterium-krypton admixture. The coded mask pattern is based on a singer cyclic difference set with 25% open fraction and positioned close to 90 Degree-Sign to the plasma focus axis, with CR-39 detectors used to register tracks of protons from the D(d, p)T reaction. Comparing the coded aperture imaging proton images for pure D{sub 2} and D{sub 2}-Kr admixture operation reveals clear differences in size, density, and shape between the fusion sources for these two cases.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗