1,721,614 research outputs found
A novel surface imaging system for patient positioning and surveillance during radiotherapy A phantom study and clinical evaluation
No full textBackground. The use of optical surface positioning to support or replace X-ray-based image-guided radiotherapy (IGRT) may reduce patient exposure to extra dose. In specifically designed phantom tests, we analyzed the potential of a new scanning device preclinically. The system's clinical performance was evaluated in comparison to cone-beam computed tomography (CBCT) in a prospective study. Materials and methods. We first evaluated the scanning performance in terms of accuracy and reproducibility using phantom tests. An institutional review board (IRB)-approved clinical evaluation encompassing 224 fractions in 13 patients treated in three different regions (head and neck, thorax, pelvis) was then performed. Patients were first positioned using CBCT and then scanned with the Catalyst(TM) (C-RAD, Uppsala, Sweden) optical system to define the resulting difference vector. Results. Individual system settings are necessary for different scanning conditions. Reproducibility tests with phantoms showed a mean difference of 0.25 +/- 0.21 cm. Accuracy tests showed a mean difference of less than 0.52 +/- 0.41 cm. Considering all patients, clinical data showed residual target position differences between Catalyst(TM) (surface-driven) and CBCT (target-driven) systems within 0.07 +/- 0.28 cm/-aEuro parts per thousand 0.13 +/- 0.40 cm/0.15 +/- 0.36 cm/0.11 +/- 1.57A degrees/-aEuro parts per thousand 0.43 A +/- 1.68/-aEuro parts per thousand 0.10 A +/- 1.67A degrees (lateral/longitudinal/vertical/rotation/roll/pitch). Conclusion. Scanning quality depends on the color and shape of the scanned surface. Upon prospective clinical evaluation, excellent agreement between target- and contour driven positioning was observed. Catalyst(TM) may reduce CBCT scan frequency in patients where tumor location is fixed relative to the surface
Clinical evaluation of a commercial surface-imaging system for patient positioning in radiotherapy
No full textLaser scanning-based patient surface positioning and surveillance may complement image-guided radiotherapy (IGRT) as a nonradiation-based approach. We investigated the performance of an optical system compared to standard kilovoltage cone-beam computed tomography (CBCT) and its potential to reduce the number of daily CBCTs. We analyzed the patient positioning of 153 treatment fractions in 21 patients applied to three different treatment regions. Patients were first scanned with CBCT, shifted to the optimal isocenter position, and an optical scan was performed to verify the matching in relation to CBCT. For the head-and-neck region, the lateral/longitudinal/vertical/rotational/roll and pitch shift was 0.9 +/- 1.8 mm/-2.7 +/- 3.8 mm/-0.8 +/- 3.6 mm/0.0 +/- 1.1A degrees/-0.5 +/- 2.1A degrees/0.2 +/- 1.6A degrees. For the thorax, the lateral/longitudinal/vertical/roll and pitch shift was -1.2 +/- 3.6 mm/0.8 +/- 5.1 mm/0.8 +/- 4.3 mm/0.6 +/- 1.4A degrees/0.1 +/- 0.9A degrees/0.3 +/- 1.0A degrees. For the pelvis, the respective values were -2.5 +/- 4.1 mm/4.6 +/- 7.3 mm/-5.1 +/- 7.4 mm/0.3 +/- 1.1A degrees/-0.5 +/- 1.0A degrees/0.3 +/- 2.1A degrees. In total, the recorded disagreement was -1.0 +/- 3.6 mm/1.0 +/- 6.3 mm/-1.8 +/- 5.9 mm/0.3 +/- 1.2A degrees/-0.3 +/- 1.5A degrees/0.2 +/- 1.7A degrees. This analysis showed good agreement between the optical scanner approach and CBCT. The optical system holds potential to ensure precise patient positioning and reduced CBCT frequency in tumor locations with fixed relation to surface structures
Intensity modulated radiosurgery of brain metastases with flattening filter-free beams
No full textPurpose: Flattening filter free (FFF) irradiation potentially reduces treatment delivery time in radiosurgery thus eliminating intrafraction motion and increasing patient comfort. We compared plan quality and efficiency of VMAT and IMRT plans for FFF- and standard delivery for brain metastases with single fraction doses of 20 Gy and validated the dosimetric accuracy of the FFF delivery. Material and Methods: CT data of 15 patients with brain metastases were included in this study. For every patient, 2 IMRT- and 2 VMAT-plans were created using a high-resolution MLC with two different delivery modes (6 MV standard vs. 6 MV FFF). Plan quality and efficiency was assessed by analysis of conformity, homogeneity, dose gradients, treatment delivery time and number of monitor units (MU). Dosimetric evaluation was performed for 10 FFF plans with radiochromic film and ion chamber. Results: Plan quality was similar for both approaches. FFF provided a mean treatment time reduction of 51.5% with similar MU for VMAT and IMRT for this low-modulation paradigm. The dosimetric validations showed an absolute dose deviation of +0.93 +/- 0.99% and gamma-index analysis (3%/3 mm and 3%/1 mm) resulted in agreement of 99.08 +/- 1.58% respectively 93.46 +/- 2.41%. Conclusion: FFF radiosurgery is an efficient technique for intensity modulated hypofractionated or single fraction treatments with similar plan quality when compared to flattened beams at reduced treatment time. (C) 2013 Elsevier Ireland Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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