1,720,967 research outputs found
An accurate model for the computation of the dose of protons in water
No full textPurpose: The accurate and fast calculation of the dose in proton radiation therapy is an essential ingredient for successful treatments. We propose a novel approach with a minimal number of parameters. Methods: The approach is based on the exact calculation of the electromagnetic part of the interaction, namely the Moliere theory of the multiple Coulomb scattering for the transversal 1D projection and the Bethe-Bloch formula for the longitudinal stopping power profile, including a gaussian energy straggling. To this e.m. contribution the nuclear proton-nucleus interaction is added with a simple two-parameter model. Then, the non gaussian lateral profile is used to calculate the radial dose distribution with a method that assumes the cylindrical symmetry of the distribution
On the lateral dose profile of 4He beams in water
No full textPURPOSE: We investigate the possibility to improve the accuracy of the lateral dose profile for 4He beams with a novel approach, by extending an already validated model for proton beams to heavier ions.
METHODS: The full Moliere theory for the Coulomb multiple scattering is applied to the case of 4He beams, with a complete separation of the electromagnetic and of the nuclear contributions in the calculation of the total dose. The latter is described with only three free parameters.
RESULTS: The accuracy of the results compared with Monte Carlo predictions already validated with experimental data is comparable with other studies at low energy, but improves by a factor 2 at high energy. In addition the found solution is more stable with respect to (multi-) Gaussian and other parameterizations. This result makes this method of interest for applications to Treatment Planning Systems (TPS) in ion beam therapy.
CONCLUSIONS: We propose a model, named MONETalpha (MOdel of ioN dosE for Therapy for alpha), for the calculation of the lateral dose of 4He beams in water that allows fast and accurate dose calculations by requiring a small data base of parameters as input.
Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved
On Molière and Fermi-Eyges scattering theories in hadrontherapy
No full textWe consider the evaluation of lateral spread distributions of charged particle beams at therapeutic energies, due to an absorber in the form of a homogeneous slab or of a stack. We show that the Molière theory has the same degree of flexibility as the Fermi-Eyges, but is much more accurate and does not present particular computing difficulties with the energy loss formula we have employed. It is also shown that the non-Gaussian shape of the projected one dimensional (1D) distributions is not a complication for passing from the projected to the spatial two-dimensional (2D) distribution, if one assumes circular symmetry. All the calculations are compared with the results of the FLUKA code. The nuclear interaction is not considered here, because it is outside of the scope of this work. © 2017 Institute of Physics and Engineering in Medicine
Radiobiological damage by space radiation: extension of the BIANCA model to heavy ions up to iron, and pilot application to cosmic ray exposure
No full text: Space research seems to be object of a renewed interest, also considering that human missions to the Moon, and possibly Mars, are being planned. Among the risks affecting such missions, astronauts' exposure to space radiation is a major concern. In this work, the question of the evaluation of biological damage by Galactic Cosmic Rays (GCR) was addressed by a biophysical model called BIophysical ANalysis of Cell death and chromosome Aberrations (BIANCA), which simulates the induction of cell death and chromosome aberrations by different ions. While previously BIANCA has been validated for calculating cell death along hadrontherapy beams up to oxygen, herein the approach was extended up to Fe ions. Specifically, experimental survival curves available in literature for V79 cells irradiated by Si-, Ne-, Ar- and Fe-ions were reproduced, and a reference radiobiological database describing V79 cell survival as a function of ion type (1 ⩽Z⩽ 26), energy and dose was constructed. Analogous databases were generated for Chinese hamster ovary hamster cells and human skin fibroblasts, finding good agreement between simulations and data. Concerning chromosome aberrations, which are regarded as radiation risk biomarkers, dicentric data in human lymphocytes irradiated by heavy ions up to iron were reproduced, and a radiobiological database allowing calculation of lymphocyte dicentric yields as a function of dose, ion type (1 ⩽Z⩽ 26) and energy was constructed. Following interface between BIANCA and the FLUKA Monte Carlo transport code, a feasibility study was performed to calculate the relative biological effectiveness (RBE) of different GCR spectrum components, for both dicentrics and cell death. Fe-ions, although representing only 10% of the total absorbed dose, were found to be responsible for about 35%-40% of the RBE-weighted dose. Interestingly, the RBE for dicentrics was higher than that for cell survival. More generally, this work shows that BIANCA can calculate RBE values for cell death and lymphocyte dicentrics not only for ion therapy, but also for space radiation
Healthy Tissue Damage Following Cancer Ion Therapy: A Radiobiological Database Predicting Lymphocyte Chromosome Aberrations Based on the BIANCA Biophysical Model
No full textChromosome aberrations are widely considered among the best biomarkers of radiation health risk due to their relationship with late cancer incidence. In particular, aberrations in peripheral blood lymphocytes (PBL) can be regarded as indicators of hematologic toxicity, which is a major limiting factor of radiotherapy total dose. In this framework, a radiobiological database describing the induction of PBL dicentrics as a function of ion type and energy was developed by means of the BIANCA (BIophysical ANalysis of Cell death and chromosome Aberrations) biophysical model, which has been previously applied to predict the effectiveness of therapeutic-like ion beams at killing tumour cells. This database was then read by the FLUKA Monte Carlo transport code, thus allowing us to calculate the Relative Biological Effectiveness (RBE) for dicentric induction along therapeutic C-ion beams. A comparison with previous results showed that, while in the higher-dose regions (e.g., the Spread-Out Bragg Peak, SOBP), the RBE for dicentrics was lower than that for cell survival. In the lower-dose regions (e.g., the fragmentation tail), the opposite trend was observed. This work suggests that, at least for some irradiation scenarios, calculating the biological effectiveness of a hadrontherapy beam solely based on the RBE for cell survival may lead to an underestimation of the risk of (late) damage to healthy tissues. More generally, following this work, BIANCA has gained the capability of providing RBE predictions not only for cell killing, but also for healthy tissue damage
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
- …
