1,720,957 research outputs found
Evaluation of a novel anthropomorphic thorax phantom with a dynamic lung using 4DCT
No full textPurpose/Objective: Four-dimensional computed tomography (4DCT) has revolutionized the radiation therapy field by allowing visualization and tracking of movements in the target volume and organs at risk, leading to more accurate treatment procedures. However, the image quality and accuracy of quantitative information could be affected by severe artifacts arising from regular or irregular breathing and motion artifacts. These image quality measurements are mostly performed using phantoms, which do not represent entirely the complexities and motion of patients. Recently, the 3D-printing technology has been introduced into radiotherapy that allows for increased customization and generating anthropomorphic dynamic/deformable phantoms. This study aims to evaluate the 4DCT image quality and proof-of-concept of an in-house developed realistic dynamic/deformable phantom in terms of tumor trajectory and motion artifacts, which allows for more realistic motion evaluation than with more commonly used simplistic phantoms. Material/Methods: A novel anthropomorphic thorax phantom (Figure 1A) was manufactured with fused deposition modeling (FDM) printing by using tissue-equivalent materials that represented soft tissue, lung tissue and bone. These materials were selected based on the effective atomic number and relative electron density. The soft tissue structure was based on CT images of a real patient with, in addition, tissue-equivalent bone such as spine and ribs and a deformable and compressible lung, including bronchi and tumors with accurate mechanical properties for realistic compression. The compression was performed by a developed electronic lung compression system (LCS), that simulated realistic respiration induced breathing motion. This system was connected to a static chest movement system (CMS; Figure 1B). The latter system was used to connect the ANZAI belt and allowed to track the breathing phases by the 4DCT system. A snippet of the respiratory curve is shown in Figure 2A. Images were acquired in static 3DCT (reference volume) and 4DCT. The image acquisition was performed on a SOMATOM Definition Drive CT scanner (Siemens Healthineers) with a tube voltage of 120 kVp (Qr40). This scanner used a phase-based sorting algorithm to reconstruct at specific breathing phases (0% inhale, 25% inhale, 50% inhale, 75% inhale, 100% inhale, 75% exhale, 50% exhale, 25% exhale). The scan parameters for the 4DCT were chosen based on clinical practice and included a pitch of 0.14 s, a field-of-view of 500 mm and a CTDIvol of 22 mGy. In addition, reconstruction was performed with 3 mm slice thickness. In evaluation, two tumors that had different volumes(tumor 1 and 2; Figure 1A) were assessed by quantifying the center of mass and volume between the respiratory phases. In addition, the amplitude between the different tumors was evaluated to demonstrated the realistic motion induced by the LCS
Evaluation of a novel anthropomorphic thorax phantom with a dynamic lung using 4DCT
No full textPurpose/Objective: Four-dimensional computed tomography (4DCT) has revolutionized the radiation therapy field by allowing visualization and tracking of movements in the target volume and organs at risk, leading to more accurate treatment procedures. However, the image quality and accuracy of quantitative information could be affected by severe artifacts arising from regular or irregular breathing and motion artifacts. These image quality measurements are mostly performed using phantoms, which do not represent entirely the complexities and motion of patients. Recently, the 3D-printing technology has been introduced into radiotherapy that allows for increased customization and generating anthropomorphic dynamic/deformable phantoms. This study aims to evaluate the 4DCT image quality and proof-of-concept of an in-house developed realistic dynamic/deformable phantom in terms of tumor trajectory and motion artifacts, which allows for more realistic motion evaluation than with more commonly used simplistic phantoms. Material/Methods: A novel anthropomorphic thorax phantom (Figure 1A) was manufactured with fused deposition modeling (FDM) printing by using tissue-equivalent materials that represented soft tissue, lung tissue and bone. These materials were selected based on the effective atomic number and relative electron density. The soft tissue structure was based on CT images of a real patient with, in addition, tissue-equivalent bone such as spine and ribs and a deformable and compressible lung, including bronchi and tumors with accurate mechanical properties for realistic compression. The compression was performed by a developed electronic lung compression system (LCS), that simulated realistic respiration induced breathing motion. This system was connected to a static chest movement system (CMS; Figure 1B). The latter system was used to connect the ANZAI belt and allowed to track the breathing phases by the 4DCT system. A snippet of the respiratory curve is shown in Figure 2A. Images were acquired in static 3DCT (reference volume) and 4DCT. The image acquisition was performed on a SOMATOM Definition Drive CT scanner (Siemens Healthineers) with a tube voltage of 120 kVp (Qr40). This scanner used a phase-based sorting algorithm to reconstruct at specific breathing phases (0% inhale, 25% inhale, 50% inhale, 75% inhale, 100% inhale, 75% exhale, 50% exhale, 25% exhale). The scan parameters for the 4DCT were chosen based on clinical practice and included a pitch of 0.14 s, a field-of-view of 500 mm and a CTDIvol of 22 mGy. In addition, reconstruction was performed with 3 mm slice thickness. In evaluation, two tumors that had different volumes(tumor 1 and 2; Figure 1A) were assessed by quantifying the center of mass and volume between the respiratory phases. In addition, the amplitude between the different tumors was evaluated to demonstrated the realistic motion induced by the LCS
Development of a novel 3D-printed dynamic anthropomorphic thorax phantom for evaluation of four-dimensional computed tomography
No full textBackground and purpose: In radiotherapy, the image quality of four-dimensional computed tomography (4DCT) is often degraded by artifacts resulting from breathing irregularities. Quality assurance mostly employ simplistic phantoms, not fully representing complexities and dynamics in patients. 3D-printing allows for design of highly customized phantoms. This study aims to validate the proof-of-concept of a realistic dynamic thorax phantom and its 4DCT application. Materials and methods: Using 3D-printing, a realistic thorax phantom was produced with tissue-equivalent materials for soft tissue, bone, and compressible lungs, including bronchi and tumors. Lung compression was facilitated by motors simulating customized breathing curves with an added platform for application of monitoring systems. The phantom contained three tumors which were assessed in terms of tumor motion amplitude. Three 4DCT sequences and repeated static images for different lung compression levels were acquired to evaluate the reproducibility. Moreover, more complex patient-specific breathing patterns with irregularities were simulated. Results: The phantom showed a reproducibility of +/- 0.2 mm and +/- 0.4 mm in all directions for static 3DCT images and 4DCT images, respectively. Furthermore, the tumor close to the diaphragm showed higher amplitudes in the inferior/superior direction (13.9 mm) than lesions higher in the lungs (8.1 mm) as observed in patients. The more complex breathing patterns demonstrated commonly seen 4DCT artifacts. Conclusion: This study developed a dynamic 3D-printed thorax phantom, which simulated customized breathing patterns. The phantom represented a realistic anatomy and 4DCT scanning of it could create realistic artifacts, making it beneficial for 4DCT quality assurance or protocol optimization
Preliminary design and evaluation of a 3D-printed phantom for gynecological brachytherapy dosimetry audits
No full textBaarmoederhalskanker blijft een belangrijke oorzaak van kankergerelateerde sterfte in lage- en middeninkomenslanden, waar de toegang tot radiotherapie en consistente quality assurance (QA) beperkt is. High-dose-rate brachytherapie (BT), een belangrijk onderdeel van de curatieve behandeling, vereist een hoge geometrische nauwkeurigheid, maar gestandaardiseerde QA-instrumenten ontbreken vaak. Deze masterproef stelt de ontwikkeling, met behulp van 3D-printing, van een reproduceerbaar en kosteneffectief QA-fantoom voor gynaecologische BT voor. Commerciële BT-applicatoren werden gereconstrueerd via computertomografie (CT) en omgezet in Computer Aided Design (CAD)- modellen. Testfantomen werden vervaardigd met behulp van Fused Deposition Modeling (FDM) met polylactide (PLA) voor rigide en thermoplastisch polyurethaan (TPU) voor flexibele karakteristieken. Het model werd geëvalueerd door middel van geometrische analyse, testen met inbrenging van de applicator en beeldcompatibiliteit met CT. Geometrische afwijkingen van het CAD-model bleven kleiner dan de resolutie van de CT. CT-compatibiliteit, structurele integriteit en betrouwbaarheid bij dosimetrische testen werden bevestigd. Deze resultaten tonen de bruikbaarheid aan van goedkoop 3D-printen voor QA-toepassingen in BT. De ontwikkelde workflow biedt een schaalbare oplossing voor klinische centra met beperkte middelen en draagt bij aan verbeterde consistentie en veiligheid in de klinische praktijk
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
Experimental Evaluation of the HS-RP200 Optical Fiber Scintillator for Dosimetry in Clinical and Preclinical Radiotherapy
No full textNauwkeurige en real-time dosimetrie blijft een uitdaging binnen de moderne radiotherapie, vooral bij het gebruik van diverse bestralingsmodaliteiten en opstellingen. Dit onderzoek evalueert de HYPERSCINT RP200 (HS-RP200) optische vezel-scintillatordetector (OFS) als flexibel en betrouwbaar dosimetriesysteem voor klinische en preklinische radiotherapie. Het doel was het bepalen van de reproduceerbaarheid, lineariteit en nauwkeurigheid in verschillende toepassingen. De HS-RP200 werd onder gestandaardiseerde omstandigheden getest in vier modaliteiten: MV LINAC (Varian TrueBeam), HDR-brachytherapie (Bravos afterloader), elektronische brachytherapie (Axxent Xoft) en preklinische X-stralenbestraling (MultiRad 225). Voor de nauwkeurigheidsbepaling werden de OFS-metingen vergeleken met alaninedosimetrie en radiochromische film als referentiemethoden.
Bij de LINAC- en HDR-metingen vertoonde de detector uitstekende reproduceerbaarheid (minder dan 1%) en lineariteit (afwijking minder dan 1%). De nauwkeurigheid kwam goed overeen met alaninedosimetrie, terwijl bij filmdosimetrie afwijkingen door veroudering werden vastgesteld. Voor Xoft bleef de reproduceerbaarheid binnen 1% en toonde de PDD-analyse goede overeenstemming met de theorie. In MultiRad bleef de reproduceerbaarheid binnen 1%, was de lineariteit sterk en stemden de resultaten goed overeen met alanine. Deze bevindingen bevestigen de HS-RP200 als een nauwkeurige en betrouwbare real-time dosimeter voor uiteenlopende radiotherapietoepassingen
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
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