1,721,072 research outputs found
Response to "comment on 'Helium ions for radiotherapy? Physical and biological verifications of a novel treatment modality' "[Med. Phys. 43, 1995-2004 (2016)]
No full textFLASH radiotherapy with carbon ion beams
No full textFLASH radiotherapy is considered a new potential breakthrough in cancer treatment. Ultra-high dose rates (>40 Gy/s) have been shown to reduce toxicity in the normal tissue without compromising tumor control, resulting in a widened therapeutic window. These high dose rates are more easily achievable in the clinic with charged particles, and clinical trials are, indeed, ongoing using electrons or protons. FLASH could be an attractive solution also for heavier ions such as carbon and could even enhance the therapeutic window. However, it is not yet known whether the FLASH effect will be the same as for sparsely ionizing radiation when densely ionizing carbons ions are used. Here we discuss the technical challenges in beam delivery and present a promising solution using 3D range-modulators in order to apply ultra-high dose rates (UHDR) compatible with FLASH with carbon ions. Furthermore, we will discuss the possible outcome of C-ion therapy at UHDR on the level of the radiobiological and radiation chemical effects
Advancing the modeling in particle therapy: From track structure to treatment planning
No full textWe present a series of implementations on Monte Carlo track structure level which might have an impact on treatment planning for particle therapy. We evaluated the effect of multiple ion scattering and radical diffusion on the nanoscopic radial dose. Our cross section database for electron interactions was extended to be able to predict the sensitizing effect of gold nanoparticles in particle therapy. We also implemented LiF as a possible target for efficiency calculations of thermoluminescent detectors (TLDs). © 2013 Elsevier Ltd
Kill painting of hypoxic tumors with multiple ion beams
No full textWe report on a novel method for simultaneous biological optimization of treatment plans for hypoxic tumors using multiple ion species. Our previously introduced kill painting approach, where the overall cell killing is optimized on biologically heterogeneous targets, was expanded with the capability of handling different ion beams simultaneously. The current version (MIBO) of the research treatment planning system TRiP98 has now been augmented to handle 3D (voxel-by-voxel) target oxygenation data. We present a case of idealized geometries where this method can identify optimal combinations leading to an improved peak-to-entrance effective dose ratio. This is achieved by the redistribution of particle fluences, when the heavier ions are preferentially forwarded to hypoxic target areas, while the lighter ions deliver the remaining dose to its normoxic regions. Finally, we present an in silico skull base chordoma patient case study with a combination of 4 He and 16 O beams, demonstrating specific indications for its potential clinical application. In this particular case, the mean dose, received by the brainstem, was reduced by 3%-5% and by 10%-12% as compared to the pure 4 He and 16 O plans, respectively. The new method allows a full biological optimization of different ion beams, exploiting the capabilities of actively scanned ion beams of modern particle therapy centers. The possible experimental verification of the present approach at ion beam facilities disposing of fast ion switch is presented and discussed
Low-energy electron transport in non-uniform media
No full textWe simulated the transport of low and medium energy electrons with energies between 1.26 eV and 10 keV in non-uniform carbon targets using the track structure Monte Carlo code TRAX which has several applications in biophysics and radiation physics. Cross sections for electrons incident on carbon have been critically assessed. Furthermore the code has been extended to handle non-uniform targets allowing a complex geometry description. Solid state targets, which are commonly used as targets in electron spectrometers and other devices can be non-uniform, e.g. have highly irregular surfaces or pinholes. The resulting electron spectra can be significantly affected by these non-uniformities. We reproduce experimental data obtained by GSI's Toroid electron spectrometer using thin solid state foils as targets. This unique experiment was designed to gain further insight in the emission and transport of low energy electrons in solids to improve the description of microscopic energy deposition. The realistic implementation of non-uniform targets in TRAX was verified by comparison with available experimental data. The increased backscattering due to the roughness of an unpolished target in comparison with polished ones could be reproduced as well as secondary electron spectra from the Toroid. © 2013 Elsevier B.V. All rights reserved
Simulations of dose enhancement for heavy atom nanoparticles irradiated by protons
No full textA possible dose enhancement effect by proton or electron irradiation in the vicinity of nanoparticles consisting of different high Z atomic materials has been investigated using the track structure Monte Carlo code TRAX. In the simulations, Fe, Ag, Gd, Pt and Au nanoparticles (r = 22 and 2 nm) were irradiated with monoenergetic proton beams at energies of therapeutic interest (2, 80 and 300 MeV) and 44 keV electrons. Due to the large number of electrons in atoms with high atomic numbers, many electrons can be released in Auger cascades in addition to the primary ionization process. The potential additional nanoscopic radial dose contributions in the presence of metallic nanoparticles are assessed by comparison with liquid water and water simulated with the same density as the metallic materials. We find a noticeable impact of Auger electrons emitted from the nanoparticles. Special focus has been given to the assessment of complete sets of low-energy electron cross sections for the nanoparticle materials. © 2014 Institute of Physics and Engineering in Medicine
Overview of recent advances in treatment planning for ion beam radiotherapy ∗
No full textTo achieve practical calculations of dose delivery in ion beam radiotherapy, the physical models of beam propagation need to be properly implemented and supplemented by models describing the complex mechanisms of radiation damage in the biological tissues. TRiP98 is the first and most advanced treatment planning system for particles, in which physical and biological models have been incorporated to develop a clinically applicable tool for dose optimization and delivery. We report our recent advances in TRiP98 code development, in particular towards hypoxia-driven and multi-modal dose optimization. We also discuss the present needs and possible extensions of our models for which input from nanoscale physics is required
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
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