1,720,990 research outputs found
EPR/alanine dosimetry in Stereotactic Radiosurgery treatments through Helical Tomotherapy
No full textIntracranial stereotactic radiosurgery (SRS) is a technique to deliver an ablative radiation dose with an extremely sharp dose gradient to small brain tumors. This tecnique allows to deliver high doses of radiation to the tumor sparing the surrounding healthy tissue.
In this study the accuracy of the dose delivered in a SRS session by a non conventional radiotherapy machine, the TomoTherapy Hi-Art System, was investigated using an "end-to-end" test. This is perfomed by means of alanine Electron Paramagnetic Resonance (EPR) pellets. The response of these dosimeters is compared to that of gafchromic films which are particularly suitable for twodimensional dose verification providing accurate estimate of the distribution and of the gradients of the absorbed dose.
Dose verifications were made using alanine dosimeters placed in an antropomorphic head phantom (Alderson Rando Phantom) under different treatment conditions in case of both single and multiple brain tumors. 1.25mm slice kVCT scan of the phantom was used to generate SRS plans on the TomoTherapy Planning Station platform, prescribing dose at the 95% isodose level of the "PTV" using different combinations of pitch and Modulation Factor. Before each session a MVCT was performed for setup verification.
Commercial alanine dosimeters (Synergy Health, Germany) were irradiated in various positions of the phantom. EPR measurements were carried out through Bruker ECS106 spectrometer working at about 9.7 GHz.
The dose values measured through alanine dosimeters and gafchromic films show a good agreement with the dose values calculated by the TomoTherapy Treatment Planning System, for both organs at risk and tumors.
Alanine absolute dose measurements showed to be useful for the dosimetric validation of HT SRS treatments
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
Dosimetric analysis of phenolic solid state pellets exposed to radio-therapeutic photon and electron beams through electron spin resonance technique=Analisi dosimetrica di composti fenolici irradiati con fasci clinici di fotoni ed elettroni tramite spettroscopia di risonanza di spin elettronico
No full textPurpose: Among the various dosimetric techniques used for characterizing the radiation beams used in radiation therapy, the electron spin resonance (ESR) arouses increasing interest for applications in various therapy procedures. In this work we report the ESR investigation of particular phenol compounds exposed to clinical photon and electron beams [1].
Materials and methods: Pellets were produced by mixing Phenol (IRGANOX 1076® Sigma Aldrich) and paraffin (10% by weight).
The irradiations of dosimeters were performed with photon and electron beams with absorbed doses ranging from 0 to 13 Gy. Basic dosimetric properties of phenolic dosimeters, such as reproducibility, dose-response, sensitivity, linearity and dose rate dependence were investigated. Finally, the dosimeters were tested by measuring the depth dose profile of a 6 MV photon beam.
ESR measurements were performed through an X band spectrometer. Readout parameters were optimized to maximize the signal without excessive spectrum distortions.
Results: .A satisfactory intra-batch reproducibility of the ESR signal of the manufactured dosimeters was obtained. The analysis of the ESR signal as function of absorbed dose highlights that the response of this material is linear in the investigated dose range and is independent of the beam energy. Reliable and accurate assessment of the dose was achieved, independently of the dose rate. The minimum detectable dose was evaluated equal to approximately 0.6 Gy as effect to the presence of a no-negligible background signal that deserves further investigations.
Conclusion: The observed features, along with the tissue-equivalence of IRGANOX 1076® and the stability of the ESR signal, make these dosimeters promising materials for ESR dosimetric applications in radiotherapy
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
Phenol compounds for EPR dosimetry in radiation therapy
No full textAmong the various dosimetric techniques used for characterizing the radiation beams used in radiation therapy, the electron paramagnetic resonance (EPR) arouses increasing interest for applications in various therapy procedures [1]. Free radicals are known to be produced when a compound is irradiated with ionizing radiations. The concentration of radiation-induced free radicals is proportional to the absorbed dose and this allows for dosimetric measurements through EPR technique which able to quantitatively determine the radical concentration [2]. Our research group has started an investigation of the EPR response of some phenols compounds for possible EPR dosimetric applications suitable features, such as high efficiency of radiation-matter energy transfer and radical stability at room temperature [3-5].
In this work we report the EPR investigation of IRGANOX 1076 pellets and thin films exposed to various type of radiation beams (clinical photon and electron beams, neutron-photon mixed field).
Phenols are compounds possessing a benzene ring attached to a OH group. After irradiation the final product is a stable phenoxy radical. The stability of such radical can be improved by adding other alkyl chains which can be attached to the benzene ring. In particular, the phenol octadecyl-3-(3,5-ditert. butyl-4-hydroxyphenyl)-propionate (IRGANOX 1076) gave interesting results. Moreover, its high molecular weight, the low volatility and the compatibility with the dosimeter binding material (wax) are advantages with respect to lower molecular weight phenols. Photon and electron irradiations at various energies were performed with clinical LINAC. Thermal neutron irradiations were performed at the thermal neutron column at the Triga Mark II reactor of Pavia (Italy). EPR dosimeters were readout by means of a Bruker ECS106 spectrometer equipped with a TE102 rectangular cavity at room temperature.
The dosimetric features of these EPR dosimeters were investigated and the results regarding the dependence on microwave power and modulation amplitude are reported. The dependence on beam type and energy, the detection limits for various beam typologies, signal stability after irradiation were analyzed. The dose response was found to be linear for all beams used in the dose range analyzed.
The possibility of obtaining depth dose profile was investigated.
In conclusion, the phenols show radiometric features that designate it as a new material for EPR
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