1,721,033 research outputs found
Distribuzione di radicali liberi in dosimetri EPR irradiati con radiazioni di diverso LET
No full textIn questo lavoro abbiamo analizzato la distribuzione spaziale dei radicali liberi osservati in dosimetri di tartrato di ammonio esposti a vari fasci di radiazione (protoni da 19.3
M e V , fotoni gamma del ^°Co e ioni carbonio da 62 MeV/nucleone). Lo studio è stato effettuato sia tramite Electron Spin Resonance in onda continua che tramite Electron Spin Echo ( E S E ) decay analysis che forniscono informazioni rispettivamente sulla concentrazione macroscopica e microscopica d i radicali liberi.
U n a più approfondita indagine della distribuzione d i radicali liberi
all'interno dei dosimetri è stata condotta attraverso l a tecnica Doublé Electron-Electron Resonance ( D E E R ) che è i n grado di misurare distanze (1.5-8 nm) tra radicali nei solidi
Radiation-induced telomere length variations in normal and in Nijmegen Breakage Syndrome cells
No full textPurpose: The meiotic recombination protein 11 (MRE11), radiation sensitive 50 (RAD50) and nibrin (NBN) are members of the MRE11/RAD50/NBN (MRN) complex which plays a fundamental role in the double-strand break damage response, including DNA damage sensing, signalling and repair after exposure to ionizing radiations. In addition the MRN complex is involved in the mechanisms regulating telomere length maintenance. Based on our previous results indicating that, in contrast to X-rays, high linear energy transfer (LET) radiations were able to elongate telomeres, we investigated the behavior of cells mutated in components of the MRN complex after exposure either to 62 MeV carbon-ions (50 keV/mm, at cell surface) or X-rays. Materials and methods: Epstein Barr Virus (EBV)-transformed lymphoblastoid cell lines (LCL) established from normal, heterozygous for the NBN gene, homozygous for either mutant/deleted NBN, RAD50 or ataxia telangiectasia mutated (ATM) genes were irradiated with 4 Gy, with telomere length being evaluated 24 h later or in time course-experiments up to 15 days later. The induction of telomeric sister chromatid exchanges (T-SCE) was measured as a hallmark of homologous directed recombinational repair. Results: NBN and RAD50 mutated cells failed to elongate telomeres that instead occurred in the remaining cell lines as a response only to high-LET irradiation. Also, a kinetic study with 0.5-4 Gy up to 15 days from irradiation confirmed that NBN gene was indispensable for telomere elongation. Furthermore, such an elongation, was accompanied by an increased frequency of sister chromatid exchanges at telomeres (T-SCE). In contrast, the induction of genomic sister chromatid exchanges (G-SCE) occurred for carbon-ions irrespective of NBN gene status. Conclusions: We speculate that the MRN is necessary to process a subclass of high-LET radiation-induced complex DNA damage through a recombinational-repair mediated mechanism which in turn is responsible for telomere elongatio
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
In Vitro sub-lethal and non-targeted effects on normal human cells along the Bragg curve for different ion beams.
No full textLinear Energy Transfer (LET) is the main physical parameter to compare charged particles to photons and predict their higher effectiveness. Damage complexity governs cellular radioresponse and reflects how energy is deposited by ions as described by the Bragg curve. It is likely to change along penetration depth and with track structure. Hence, ion beams of different Z but similar LET may differ radiobiologically. Construction of “biological” Bragg curves may improve modeling of ion action. There are also uncertainties on non-cancer effects of relevance in hadrontherapy. In fact, most experimental data are almost exclusively on tumour lethality and the Spread-Out Bragg Peak (SOBP), overlooking sub-lethal damage on normal cells at various positions along the Bragg curve. Further, little is known on non-targeted effects (NTE) by ion-irradiated normal cells expressing long-term sub-lethal damage. We studied Stress-Induced Premature Senescence (SIPS) by -galactosidase assay and chromosome aberrations (CA) by WCP-FISH and mFISH along the Bragg curve for several ion beams on 3 cell lines (AG01522 fibroblasts, MCF-10A breast epithelial cells, endothelial HUVEC cells). NTE occurrence was studied by medium-transfer from irradiated prematurely senescing cells at time points after irradiation on MCF10A and breast cancer epithelial MCF7 cells. To explore changing biological effectiveness along the Bragg curve we used up to 20 MeV 12C and 16O beams at a 3-MV Tandem accelerator (Department of Physics, Naples); and 60 MeV/u 16O and 20Ne beams at INFN-LNS cyclotron, Catania. Data show SIPS being effectively induced by ions, with a clear dependence on ion type and Bragg curve position, persisting for 2 months post exposure. CA data indicate a similar dependence, and the elevated frequency of complex-type CA agrees with these aberrations being a cytogenetic signature of high-LET ions. However, incidence of CA and SIPS point to a significantly greater efficiency of ion beams compared to x-rays even at very high LETs, contrary to the notion of a close-to-unity RBE above 200 keV/m. Onset of SIPS at ion beam entrance may have important implications for hadrontherapy patients. We also observed a significant bystander effect by senescing cells manifesting itself with an increase in tumour cell proliferation, in accord with reports of a Senescence-Associated Secretory Phenotype. Geant4 Monte-Carlo modeling is under way to correlate ion-track structure with such results
Relative biological effectiveness variation along monoenergetic and modulated Bragg peaks of a 62-MeV therapeutic proton beam: A preclinical assessment
No full textThe biological optimization of proton therapy can be achieved only through a detailed evaluation of relative biological effectiveness (RBE) variations along the full range of the Bragg curve. The clinically used RBE value of 1.1 represents a broad average, which disregards the steep rise of linear energy transfer (LET) at the distal end of the spread-out Bragg peak (SOBP). With particular attention to the key endpoint of cell survival, our work presents a comparative investigation of cell killing RBE variations along monoenergetic (pristine) and modulated (SOBP) beams using human normal and radioresistant cells with the aim to investigate the RBE dependence on LET and intrinsic radiosensitvity. Methods and Materials Human fibroblasts (AG01522) and glioma (U87) cells were irradiated at 6 depth positions along pristine and modulated 62-MeV proton beams at the INFN-LNS (Catania, Italy). Cell killing RBE variations were measured using standard clonogenic assays and were further validated using Monte Carlo simulations and the local effect model (LEM). Results We observed significant cell killing RBE variations along the proton beam path, particularly in the distal region showing strong dose dependence. Experimental RBE values were in excellent agreement with the LEM predicted values, indicating dose-averaged LET as a suitable predictor of proton biological effectiveness. Data were also used to validate a parameterized RBE model. Conclusions The predicted biological dose delivered to a tumor region, based on the variable RBE inferred from the data, varies significantly with respect to the clinically used constant RBE of 1.1. The significant RBE increase at the distal end suggests also a potential to enhance optimization of treatment modalities such as LET painting of hypoxic tumors. The study highlights the limitation of adoption of a constant RBE for proton therapy and suggests approaches for fast implementation of RBE models in treatment planning
A PET Prototype for "In-Beam" Monitoring of Proton Therapy
No full textThe in-beam PET is a novel PET application to image the β + activity induced in biological tissues by hadronic therapeutic beams. Thanks to the correlation existing between beam-delivered dose profiles and beam-induced activity profiles, in vivo information about the effective ion paths can be extracted from the in-beam PET image. In-situ measurements, immediately after patient irradiation, are recommended in order to exploit the maximum statistics, by detecting the contribution provided by short lived isotopes. A compact, dedicated tomograph should then be developed for such an application, so as to be used in the treatment room. We have realized a small PET prototype in order to demonstrate the feasibility of such technique for the monitoring of proton therapy of ocular tumors at the CATANA facility (Catania, Italy). The DoPET (Dosimetry with a Positron Emission Tomograph) tomograph consists of two planar heads, with an active area of about 5 cm × 5 cm. Each head is made up of a squared position sensitive photomultiplier (Hamamatsu H8500) coupled to a matrix of the same size of LYSO scintillating crystals (2 mm × 2 mm × 18 mm pixel dimensions). Dedicated, compact electronic boards are used for the signal multiplexing, amplification and digitization. The distance between the pair can be set from 10 cm up to a maximum of about 20 cm. The validation of the prototype was performed using 62 MeV protons at the CATANA beam line and plastic phantoms. Different dose distributions have been delivered and a good correlation between the distal fall-off of the activity profiles and of the dose profiles was found, i.e., better than 2 mm along the beam direction
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