Search results for "RADIATION"

A Graph-Based Method for PET Image Segmentation in Radiotherapy Planning: A Pilot Study

2013

Target volume delineation of Positron Emission Tomography (PET) images in radiation treatment planning is challenging because of the low spatial resolution and high noise level in PET data. The aim of this work is the devel- opment of an accurate and fast method for semi-automatic segmentation of me- tabolic regions on PET images. For this purpose, an algorithm for the biological tumor volume delineation based on random walks on graphs has been used. Va- lidation was first performed on phantoms containing spheres and irregular in- serts of different and known volumes, then tumors from a patient with head and neck cancer were segmented to discuss the clinical applicability of this algo- rith…

Studies in thermal and dynamical duality

2011

Argon plasma coagulation in the treatment of post-radiotherapy rectal bleeding

2012

Introduction: Chronic radiation proctitis is often associated to radiotherapy for treatment of pelvic cancer. The most common side effect of this pathological condition is rectal bleeding but despite the great number of clinical approaches and techniques that have been employed no consensus for the management of it is available. Although prospective randomized trials about hemorrhagic radiation proctitis are still lacking, endoscopic approach delivering an Argon Plasma Coagulation (APC) seems to be a successful and available option. Patients and Methods: Sixteen patients suffering from post-radiotherapy rectal bleeding were followed. In the nine cases presenting a rectum ulcerative colitis …

DOES STILL EXIST A CORRELATION BETWEEN X-RAYS OCCUPATIONAL EXPOSURE AND BENIGN NODULAR THYROID DISEASE?

2019

Objective: The prevalence of benign nodular thyroid disease in the general population is high, as shown by various studies, and the diagnosis is eased by the improved diagnostic capacity of the instruments used. The aim of the present study is the evaluation of occupational exposure to ionizing radiation as a possible significant risk factor in the determinism of this pathology. Method: A cross-sectional observational study in “A category” X-ray exposed workers (doctors, nurses, technicians) of the University Hospital of Palermo, compared with a sample of the general population, was carried out from June 2016 to June 2017. We evaluated data obtained from the Personal Health Records, includi…

AE Aurigae: First detection of non-thermal X-ray emission from a bow shock produced by a runaway star

2012

Runaway stars produce shocks when passing through interstellar medium at supersonic velocities. Bow shocks have been detected in the mid-infrared for several high-mass runaway stars and in radio waves for one star. Theoretical models predict the production of high-energy photons by non-thermal radiative processes in a number sufficiently large to be detected in X-rays. To date, no stellar bow shock has been detected at such energies. We present the first detection of X-ray emission from a bow shock produced by a runaway star. The star is AE Aur, which was likely expelled from its birthplace due to the encounter of two massive binary systems and now is passing through the dense nebula IC 405…

Modeling particle acceleration and non-thermal emission in supernova remnants

2021

According to the most popular model for the origin of cosmic rays (CRs), supernova remnants (SNRs) are the site where CRs are accelerated. Observations across the electromagnetic spectrum support this picture through the detection of non-thermal emission that is compatible with being synchrotron or inverse Compton radiation from high energy electrons, or pion decay due to proton-proton interactions. These observations of growing quantity and quality promise to unveil many aspects of CRs acceleration and require more and more accurate tools for their interpretation. Here, we show how multi-dimensional MHD models of SNRs, including the effects on shock dynamics due to back-reaction of acceler…

Assessment of Fatigue Effects Induced by Fast Beam Transients in the IFMIF-DONES Li Target

2020

One of the crucial steps toward the commercial exploitation of fusion energy is the availability of a high-intensity neutron source able to test and qualify structural materials to be used in future fusion power reactors. The International Fusion Materials Irradiation Facility-DEMO Oriented NEutron Source (IFMIF-DONES) facility, which is currently being designed within the framework of the EUROfusion Consortium, represents the European effort to develop such a neutron source. It employs a liquid lithium target struck by an accelerated deuteron (D+) beam to produce fusion-like neutrons used to irradiate materials samples. So far, a detailed investigation of the thermomechanical behavior of t…

Modeling nonthermal emission from stellar bow shocks

2016

Context. Runaway O- and early B-type stars passing through the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high-energy photons by nonthermal radiative processes, but their efficiency is still debated. Aims: We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. Methods: We applied our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations fa…

Crushing of interstellar gas clouds in supernova remnants II. X-ray emission

2006

AIMS. We study and discuss the time-dependent X-ray emission predicted by hydrodynamic modeling of the interaction of a SNR shock wave with an interstellar gas cloud. The scope includes: 1) to study the correspondence between modeled and X-ray emitting structures, 2) to explore two different physical regimes in which either thermal conduction or radiative cooling plays a dominant role, and 3) to investigate the effects of the physical processes at work on the emission of the shocked cloud in the two different regimes. METHODS. We use a detailed hydrodynamic model, including thermal conduction and radiation, and explore two cases characterized by different Mach numbers of the primary shock: …

Shock oscillation model for quasi-periodic oscillations in stellar mass and supermassive black holes

2007

We numerically examine centrifugally supported shock waves in 2D rotating accretion flows around a stellar-mass (10M_sun) and a supermassive (10^6M_sun) black holes over a wide range of input accretion rates of 10^7 >\dot M/\dot M_E>10^{-4}. The resultant 2D-shocks are unstable with time and the luminosities show quasi-periodic oscillations (QPOs) with modulations of a factor of 2-3 andwith periods of a tenth seconds to several hours, depending on the black hole masses. The shock oscillation model may explain the intermediate frequency QPOs with 1-10 Hz observed in the stellar-mass black hole candidates and also suggest the existence of QPOs with the period of hours in AGNs. When the accret…