PubMed · 2477826
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D C Harari, V Parsonnet. 1989. Pacemakers.. https://doi.org/10.1111/j.1540-8159.1989.tb01849.x
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PURPOSE: We evaluated the performance of a new dosimetry module in the LC250 scanning liquid-filled ionization chamber (SLIC) electronic portal imaging device (EPID) for intensity-modulated radiotherapy (IMRT) verification. This module permits one to convert EPID readings to two-dimensional (2D) maps of IMRT dose rate in real time, and to integrate them over time to produce a profile of accumulated dose for treatment verification. METHODS AND MATERIALS: The EPID was calibrated using an iterative procedure, from which a lookup table for dose integration was generated and transferred to the image-acquisition hardware. To evaluate the EPID's integration capability, we investigated the linearity of imaging time (vs. monitor unit [MU]) and integrated dose (vs. planned dose) for static and IMRT fields, in both standard ( approximately 2.7 s/image) and fast ( approximately 1 s/image) synchronous acquisition modes (S- and F-modes). We also compared the EPID-measured profiles with that measured using film and ionization chamber, or calculated from the treatment planning system. For the EPID's patient dose verification capability, we compared the integrated central-axis (CAX) dose with the planned dose for 25 prostate IMRT fields. We also compared the measured relative profiles with the planned ones using a linear regression model, which returns an index sigma (root mean squared error) for the goodness of fit. We identified errors that are either associated with the timing of the EPID-start delay and end truncation, or with the integration process-detector memory effects (decrease in detector's sensitivity with time during the fast continuous acquisition) and beam hold-off effects (the withholding of linac beam pulses when multileaf collimator leaves are not in the correct positions). The CAX doses of static fields were corrected using the ratio of the irradiation time to the imaging time. A linear decay model was proposed to correct the detector memory effect. To investigate the beam hold-off effect, we verified the relative profiles of a five-field prostate IMRT plan for five different MU settings, and correlated the goodness of fit with the percent of beam hold-off. RESULTS: The imaging time is linearly proportional to the given MU with a slope of 0.250 MU/s (ideal slope is 0.250 MU/s) and a R(2) = 1.0. Although the R(2) of the linearity for the measured vs. planned dose is 1.0 for both modes, only the slopes for the S-mode are within 3% of unity. The slopes for the F-mode deviate from unity due to detector memory effects, and are accurately corrected using the linear decay model. The EPID measured profiles agree well (within 2.0%) with the planned dose and profiles for both modes. For the CAX dose of the 25 IMRT fields, the S-mode is within 2% of the planned dose, whereas the F-mode is off significantly (>3%) if not corrected for detector memory effects. For the relative profile verification, lower MU always produces higher sigma for the same mode. The F-mode is more accurate than the S-mode for the same MU; however, the improvement is not proportional to the difference in imaging speed. Analysis of the correlation of the goodness of fit with the percent of beam hold-off indicates that the accuracy of profile verification for the F-mode is predominantly determined by the beam hold-off effect for lower MU. CONCLUSION: The S-mode of LC250 combined with a large MU can be used for the pretreatment verification of IMRT beam delivery with a significant reduction of processing time and computer resources in comparison to off-line processing. Real-time verification during treatment requires the F-mode. Although the detector memory effects encountered in the F-mode can be compensated using the proposed linear decay model, sufficient accuracy for real-time verification requires a resolution of the beam hold-off problem.
BACKGROUND: The aim of this study is to create new ergonomic guidelines for the design of laparoscopic needle holders. METHODS: An ergonomic literature study, observations in the operating room, handle-shaft angle measurements, and anthropometric data were used to compile new ergonomic criteria, specified to the function of a laparoscopic needle holder. Based on these guidelines a new needle holder was designed. The prototype and three currently available needle holders were evaluated according to the new guidelines. In addition, a pelvi-trainer test was done to measure the extreme wrist excursions. RESULTS: The ergonomic evaluation of three commonly used handles and the new prototype indicate that the new handle is an ergonomic improvement in the field of laparoscopic needle holders: only the new handle satisfies all criteria. This is validated by the results of the pelvi-trainer test, which showed that the new prototype significantly (p <0.001) reduced the extreme wrist excursions. CONCLUSION: The new design guidelines for a laparoscopic needle holder result in an ergonomic improvement of the instrument.
Recent years have witnessed a renaissance of fluorescence microscopy techniques and applications, from live-animal multiphoton confocal microscopy to single-molecule fluorescence spectroscopy and imaging in living cells. These achievements have been made possible not so much because of improvements in microscope design, but rather because of development of new detectors, accessible continuous wave and pulsed laser sources, sophisticated multiparameter analysis on one hand, and the development of new probes and labeling chemistries on the other. This review tracks the lineage of ideas and the evolution of thinking that have led to the actual developments, and presents a comprehensive overview of the field, with emphasis put on our laboratory's interest in single-molecule microscopy and spectroscopy.