425 research outputs found

    Laser-driven ion acceleration: State of the art and emerging mechanisms

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    AbstractIon acceleration driven by high intensity laser pulses is attracting an impressive and steadily increasing research effort. Experiments over the past 10–15 years have demonstrated, over a wide range of laser and target parameters, the generation of multi-MeV proton and ion beams with unique properties, which have stimulated interest in a number of innovative applications. While most of this work has been based on sheath acceleration processes, where space-charge fields are established by relativistic electrons at surfaces of the irradiated target, a number of novel mechanisms has been the focus of recent theoretical and experimental activities. This paper will provide a brief review of the state of the art in the field of laser-driven ion acceleration, with particular attention to recent developments

    The evolution of a slow electrostatic shock into a plasma shock mediated by electrostatic turbulence

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    The collision of two plasma clouds at a speed that exceeds the ion acoustic speed can result in the formation of shocks. This phenomenon is observed not only in astrophysical scenarios such as the propagation of supernova remnant (SNR) blast shells into the interstellar medium, but also in laboratory-based laser-plasma experiments. These experiments and supporting simulations are thus seen as an attractive platform for the small-scale reproduction and study of astrophysical shocks in the laboratory. We model two plasma clouds, which consist of electrons and ions, with a 2D PIC simulation. The ion temperatures of both clouds differ by a factor of 10. Both clouds collide at a speed, which is realistic for laboratory studies and for SNR shocks in their late evolution phase like that of RCW86. A magnetic field, which is orthogonal to the simulation plane, has a strength that is comparable to that at SNR shocks. A forward shock forms between the overlap layer of both plasma clouds and the cloud with the cooler ions. A large-amplitude ion acoustic wave is observed between the overlap layer and the cloud with the hotter ions. It does not steepen into a reverse shock, because its speed is below the ion acoustic speed. A gradient of the magnetic field amplitude builds up close to the forward shock as it compresses the magnetic field. This gradient gives rise to an electron drift that is fast enough to trigger an instability. Electrostatic ion acoustic wave turbulence develops ahead of the shock. It widens its transition layer and thermalizes the ions, but the forward shock remains intact.Comment: Accepted for publication in the New Journal of Physic

    Role of multiparametric magnetic resonance imaging for the selection of patients with very low risk prostate cancer and suitable for active surveillance: a prospective study

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    Obiettivi. L’introduzione della risonanza magnetica multiparametrica (RMmp) in un protocollo di sorveglianza attiva (SA) potrebbe ridurre il rischio di erronea identificazione della classe di rischio. Obiettivo di questo studio è di ottenere nei pazienti arruolati in SA e sottoposti a RMmp entro 12 settimane, un tasso di riclassificazione tardiva di malattia inferiore al 10%. Materiali e Metodi. Studio prospettico, randomizzato, multicentrico che include tutti pazienti affetti da neoplasia prostatica a rischio basso o molto basso che soddisfano i requisiti per essere candidati a SA secondo l’attuale protocollo PRIAS, arruolati da Maggio 2015 a Novembre 2017. I pazienti sono stati randomizzati in due gruppi: Gruppo 1, pazienti sottoposti a sorveglianza attiva secondo i vigenti ed emendati criteri PRIAS; Gruppo 2, pazienti sottoposti a sorveglianza attiva con i medesimi criteri PRIAS, ma con l’introduzione di una RMmp a 8-12 settimane dalla conferma istologica. Risultati Sono stati arruolati 65 pazienti, di cui 31 (47.7%) sono stati randomizzati nel Gruppo 1 e i restanti 34 (52.3%) nel Gruppo 2. Complessivamente, 32 su 34 pazienti (94%) del Gruppo 2 hanno eseguito la RMmp; in 10 (31.3%) pazienti la RMmp è risultata positiva per una lesione sospetta con PI-RADS ≥ 3. Tra i 10 pazienti con RMmp positiva e sottoposti a biopsia confermatoria con tecnica “fusion”, 8 (80%) sono stati riclassificati ad una malattia più aggressiva. A 12 mesi dall’inserimento in SA, 2 (6.6%) pazienti nel Gruppo 2 sono stati riclassificati, inferiori ai 6 (19.4%) pazienti riclassificati nel Gruppo 1 (p=0.02). Conclusioni. L’introduzione di una RMmp a 12 settimane dalla diagnosi offre un indiscusso valore aggiunto per il paziente dopo inserimento in un percorso di SA, in quanto consente una più precoce riclassificazione delle malattie non indolenti, e di ridurre il tasso di riclassificazione tardiva ad un valore decisamente inferiore al 10%.OBJECTIVES. Utilization of multiparametric magnetic resonance imaging (mpMRI) could reduce the risk of understaging and undergrading of Prostate Cancer (PCa) in men undergoing active surveillance (AS). Primary objective of this study is to obtain a reclassification rate at 12 months after PCa diagnosis <10% in a cohort of patients diagnosed with indolent PCa scheduled for AS. MATERIAL AND METHODS. This is a prospective, multi-institutional randomized open-label study including all patients with very-low and low risk prostate cancer suitable for AS according to the PRIAS criteria enrolled from May 2015 to November 2017. Patients were randomized in two groups: Group 1, patients undergoing AS according to PRIAS; Group 2: patients receiving mpMRI at 8-12 weeks from the initial diagnosis, and then undergoing AS according to PRIAS. RESULTS. Overall, 65 patients were enrolled; of them, 31 (47.7%) were randomized in Group 1 and 34 (52.3%) in Group 2. Median (IQR) age was 65 (61-69) years, median (IQR) PSA 5.8 (4.7-7.2) ng/ml. No statistically significant differences were found in the two Groups in terms of clinico-demographic characteristics. Globally, 32 out of 34 patients (94%) in Group 2underwent mpMRI; in 10 (31.3%) it showed positive findings with PIRADS ≥ 3. Among these patients, managed with ultrasound-MRI fusion prostate biopsy, 8 (80%) were reclassified with a more aggressive disease. At 12 months, only 2 (6.6%) patients in Group 2 were reclassified, compared to 6 (19.4%) patients in Group 1 (p=0.02). CONCLUSIONS. The utilization of mpMRI within 12 weeks from the initial diagnosis of indolent PCa offers a valuable advantage for an earlier reclassification of patients scheduled for AS. Remarkably, the reclassification rate was much more inferior than 10%. An earlier reclassification of aggressive diseases could allow a more appropriate and correct teratment of such patients, potentially improving the oncological outcomes

    Flying through congested airspaces: imaging of chronic rhinosinusitis

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    The complex regional anatomy of the nose and paranasal sinuses makes the interpretation of imaging studies of these structures intimidating to many radiologists. This paper aims to provide a key to interpretation by presenting a simplified approach to the functional anatomy of the paranasal sinuses and their most common (and most relevant) variants. This knowledge is basic for the full understanding of chronic rhinosinusitis and its computed tomography (CT) patterns. As fungal infections may be observed in the setting of chronic rhinosinusitis, these are also discussed. Chronic sinus inflammation produces bone changes, clearly depicted on CT images. Finally, clues to suspecting neoplastic lesions underlying inflammatory sinus conditions are provided

    Biomarkers in Genitourinary Cancers, Volume I

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    project LA/P/0140/2020 of the Associate Laboratory Institute for Health and Bioeconomy - i4HB.Genitourinary cancers are known as significant causes of mortality worldwide. This heterogeneous group includes, among others, the most common cancer in men, prostate cancer, the most common form of kidney cancer, renal cell carcinoma (RCC), and the 10th most common cancer, bladder cancer. These entities present biological diversity with various histological subtypes and a poor prognosis when metastatic. There has been considerable progress in treating patients with genitourinary cancers due to the improved understanding of their pathological mechanisms and the identification of meaningful biomarkers. The treatment progress has led to a fundamental paradigm shift in treatments. For example, our current understanding of the immunogenicity of these tumours has improved tremendously. Thanks to that, today, immunotherapy is a reliable strategy to improve the outcomes of patients with metastatic urothelial carcinoma, renal cell carcinoma, and prostate cancer. However, there is still a critical need to enrich our understanding of additional molecular mechanisms. Along with the mechanisms, there is an urgent requirement to identify novel biomarkers to progress the diagnosis and prognosis of genitourinary cancers and their treatment. Biomarkers have become a significant focus of research, primarily on how they can help predict response to systemic therapy, identify treatment resistance, and avoid toxicities. Biomarkers that reveal the mutated tumour suppressor genes, the altered signalling pathways and the aberrantly expressed molecules help select potentially responsive patients to a given therapy. In this way, biomarkers improve outcomes and reduce costs related to ineffective treatments, and, most importantly, they significantly upsurge patients’ quality of life. This Research Topic named Biomarkers in Genitourinary Cancers includes an interesting and up to date palette of publications from prominent research and clinical groups focused on identifying significant and emerging prognostic and predictive biomarkers. These biomarkers encompass non-coding RNA, serum proteins, gene expression, and glycans, among other entities identified in patients’ cohorts, samples and in the increasing number of public databases.publishersversionpublishe

    Ion dynamics and coherent structure formation following laser pulse self-channeling

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    The propagation of a superintense laser pulse in an underdense, inhomogeneous plasma has been studied numerically by two-dimensional particle-in-cell simulations on a time scale extending up to several picoseconds. The effects of the ion dynamics following the charge-displacement self-channeling of the laser pulse have been addressed. Radial ion acceleration leads to the ``breaking'' of the plasma channel walls, causing an inversion of the radial space-charge field and the filamentation of the laser pulse. At later times a number of long-lived, quasi-periodic field structures are observed and their dynamics is characterized with high resolution. Inside the plasma channel, a pattern of electric and magnetic fields resembling both soliton- and vortex-like structures is observed.Comment: 10 pages, 5 figures (visit http://www.df.unipi.it/~macchi to download a high-resolution version), to appear in Plasma Physics and Controlled Fusion (Dec. 2007), special issue containing invited papers from the 34th EPS Conference on Plasma Physics (Warsaw, July 2007

    Radiation Pressure Acceleration by Ultraintense Laser Pulses

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    The future applications of the short-duration, multi-MeV ion beams produced in the interaction of high-intensity laser pulses with solid targets will require improvements in the conversion efficiency, peak ion energy, beam monochromaticity, and collimation. Regimes based on Radiation Pressure Acceleration (RPA) might be the dominant ones at ultrahigh intensities and be most suitable for specific applications. This regime may be reached already with present-day intensities using circularly polarized (CP) pulses thanks to the suppression of fast electron generation, so that RPA dominates over sheath acceleration at any intensity. We present a brief review of previous work on RPA with CP pulses and a few recent results. Parametric studies in one dimension were performed to identify the optimal thickness of foil targets for RPA and to study the effect of a short-scalelength preplasma. Three-dimensional simulations showed the importance of ``flat-top'' radial intensity profiles to minimise the rarefaction of thin targets and to address the issue of angular momentum conservation and absorption.Comment: 11 pages, 8 figures, accepted for publication to the special issue "EPS 2008" of PPC

    Stereotactic Radiotherapy for Brain Metastases: Imaging Tools and Dosimetric Predictive Factors for Radionecrosis

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    Radionecrosis (RN) is the most important side effect after stereotactic radiotherapy (SRT) for brain metastases, with a reported incidence ranging from 3% to 24%. To date, there are no unanimously accepted criteria for iconographic diagnosis of RN, as well as no definitive dose-constraints correlated with the onset of this late effect. We reviewed the current literature and gave an overview report on imaging options for the diagnosis of RN and on dosimetric parameters correlated with the onset of RN. We performed a PubMed literature search according to the preferred reporting items and meta-analysis (PRISMA) guidelines, and identified articles published within the last ten years, up to 31 December 2019. When analyzing data on diagnostic tools, perfusion magnetic resonance imaging (MRI) seems to be very useful allowing evaluation of the blood flow in the lesion using the relative cerebral blood volume (rCBV) and blood vessel integrity using relative peak weight (rPH). It is necessary to combine morphological with functional imaging in order to match information about lesion morphology, metabolism and blood-flow. Eventually, serial imaging follow-up is needed. Regarding dosimetric parameters, in radiosurgery (SRS) V12 < 8 cm3 and V10 < 10.5 cm3 of normal brain are the most reliable prognostic factors, whereas in hypo-fractionated stereotactic radiotherapy (HSRT) V18 and V21 are considered the main predictive independent risk factors of RN

    Complications After Systematic, Random, and Image-guided Prostate Biopsy

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    Prostate biopsy (PB) represents the gold standard method to confirm the presence of cancer. In addition to traditional random or systematic approaches, a magnetic resonance imaging (MRI)-guided technique has been introduced recently. OBJECTIVE: To perform a systematic review of complications after transrectal ultrasound (TRUS)-guided, transperineal, and MRI-guided PB. EVIDENCE ACQUISITION: We performed a systematic literature search of Web of Science, Embase, and Scopus databases up to October 2015, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Complications and mortality following random, systematic, and image-guided PBs were reviewed. Eighty-five references were included. EVIDENCE SYNTHESIS: The most frequent complication after PB was minor and self-limiting bleeding (hematuria and hematospermia), regardless of the biopsy approach. Occurrence of rectal bleeding was comparable for traditional TRUS-guided and image-guided PBs. Almost 25% of patients experienced lower urinary tract symptoms, but only a few had urinary retention, with higher rates after a transperineal approach. Temporary erectile dysfunction was not negligible, with a return to baseline after 1-6 mo. The incidence of infective complications is increasing, with higher rates among men with medical comorbidities and older age. Transperineal and in-bore MRI-targeted biopsy may reduce the risk of severe infectious complications. Mortality after PB is uncommon, regardless of biopsy technique. CONCLUSIONS: Complications after PB are frequent but often self-limiting. The incidence of hospitalization due to severe infections is continuously increasing. The patient's general health status, risk factors, and likelihood of antimicrobial resistance should be carefully appraised before scheduling a PB. PATIENT SUMMARY: We reviewed the variety and incidence of complications after prostate biopsy. Even if frequent, complications seldom represent a problem for the patient. The most troublesome complications are infections. To minimize this risk, the patient's medical condition should be carefully evaluated before biopsy
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