Biomedical subjects

S Agosteo

Publications and source records attributed to S Agosteo.

At least 19 recordsLinked to original sources

PubMed2006

A solid state microdosimeter based on a monolithic silicon telescope.

A monolithic silicon telescope, consisting of a DeltaE and an E stage-detector ( approximately 1.9 microm and 500 microm thick, respectively), was coupled to a polyethylene converter in order to investigate the feasibility of a solid state microdosimeter with respect to the field-funnelling effect. This work discusses the preliminary results of an analytical approach for the correction of a spectrum measured with this silicon-based microdosimeter for tissue-equivalence and geometrical effects. The device was irradiated with 2.7 MeV monoenergetic neutrons at the INFN-Laboratori Nazionali di Legnaro (Legnaro, Italy). The non tissue-equivalence of silicon was corrected by exploiting the signals generated in the E-stage. The correction for the sensitive volume geometry was optimised by taking into account the track length distribution of the recoil-protons generated in the converter. The derived dose distribution of the energy imparted per event was compared to the one measured with a cylindrical tissue-equivalent proportional counter (TEPC). The agreement is satisfactory.

Computer-Aided Design↗

PubMed2006

Pitfalls and modelling inconsistencies in computational radiation dosimetry: lessons learnt from the QUADOS intercomparison. Part I: Neutrons and uncertainties.

The QUADOS EU cost shared action conducted an intercomparison on the usage of numerical methods in radiation protection and dosimetry. The eight problems proposed were intended to test the usage of Monte Carlo and deterministic methods by assessing the accuracy with which the codes are applied and also the methods used to evaluate uncertainty in the answer gained through these methods. The overall objective was to spread good practice through the community and give users information on how to assess the uncertainties associated with their calculated results.

Bayes Theorem↗

PubMed2006

Pitfalls and modelling inconsistencies in computational radiation dosimetry: lessons learnt from the QUADOS intercomparison. Part II: Photons, electrons and protons.

'QUADOS', a concerted action of the European Commission, has promoted an intercomparison aimed at evaluating the use of computational codes for dosimetry in radiation protection and medical physics. This intercomparison was open to all users of radiation transport codes. Eight problems were selected for their relevance to the radiation dosimetry community, five of which involved photon and proton transport. This paper focuses on a discussion of lessons learned from the participation in solving the photon and charged particle problems. The lessons learned from the participation in solving the neutron problems are presented in a companion paper (in this issue).

Angioplasty↗

PubMed2005

A feasibility study of a solid-state microdosimeter.

A solid-state silicon detector is a challenging device for microdosimetry, mainly because it can provide sensitive zones of the order of a micrometer. Moreover, these detectors are characterized by a high spatial and a good energy resolution. However, they may present some limitations, such as: (i) the minimum detectable energy which is limited by the electronic noise; (ii) radiation hardness; (iii) the geometry of the sensitive volume; (iv) the field-funnelling effect; (v) the non-tissue-equivalence of silicon. This work discusses a feasibility study of a microdosimeter based on a monolithic silicon telescope, consisting of a DeltaE and an E stage-detector, about 1 and 500 microm thick, respectively. Charges are collected separately in the two stage-detectors. The use of the DeltaE stage coupled with a tissue-equivalent converter was investigated as a solid-state microdosimeter. Irradiations with monoenergetic neutrons were performed at the INFN-Laboratori Nazionali di Legnaro (Italy). The field-funnelling effect appears to be negligible from the comparison of the experimental data with the results of Monte Carlo simulations, performed with the FLUKA code. The preliminary results of an analytical approach for the correction for geometrical effects and tissue-equivalence are also presented.

Journal Article↗

PubMed2005

Radiation protection aspects of a 4 MW target.

The CERN Superconducting Proton Linac (SPL) is expected to provide a 2.2 GeV, 4 MW proton beam to feed facilities such as, for example, a neutrino factory or a neutrino superbeam. Material activation in such facilities is an important aspect that has to be taken into account at an early stage in designing it. In particular, the choice of the target has consequences on the induced radioactivity and dose rates in the target station and its surroundings. In the present work, the radiological aspects of a stationary target made up of tantalum pellets are compared with those of a free-surface jet of mercury. An estimation of the hadronic inelastic interactions and the production of residual nuclei in the target, the two concentric magnetic horns, the decay tunnel, the surrounding rock and a downstream dump were performed for both targets using the Monte Carlo code FLUKA. The aim was to assess the dose-equivalent rate that is to be expected during maintenance work and to evaluate the amount of residual radioactivity, which will have to be disposed of after the facility has ceased operation. The problem of after-heat in the tantalum target and the consequences of raising the proton beam energy from 2.2 to 4 GeV were also investigated.

Computer Simulation↗

PubMed2005

Performance of a neutron spectrometer based on a PIN diode.

The neutron spectrometer discussed in this work consists of a PIN diode coupled with a polyethylene converter. Neutrons are detected through the energy deposited by recoil-protons in silicon. The maximum detectable energy is -6 MeV and is imposed by the thickness of the fully depleted layer (300 microm for the present device). The minimum detectable energy which can be assessed with pulse-shape discrimination (PSD) is -0.9 MeV. PSD is performed with a crossover method and setting the diode in the 'reverse-injection' configuration (i.e. with the N+ layer adjacent to the converter). This configuration provides longer collection times for the electron-hole pairs generated by the recoil-protons. The limited interval of detectable energies restricts the application of this spectrometer to low-energy neutron fields, such as the ones which can be produced at facilities hosting low-energy ion accelerators. The capacity to reproduce continuous neutron spectra was investigated by optimising the electronic chain for pulse-shape discrimination. In particular, the spectrometer was irradiated with neutrons that were generated by striking a thick beryllium target with protons of several energies and the measured spectra were compared with data taken from the literature.

Equipment Design↗

PubMed2005

Beam dumps design and local radiation protection at TERA synchrotron.

The realisation of the National Center of Hadrontherapy was funded by the Italian Government in 2002. The Centre will be built in the area of Pavia (Italy). The synchrotron designed in the framework of this programme will accelerate protons and carbon ions up to 250 MeV and 400 MeV u(-1), respectively. Some of the main aspects which were taken into account in the design of the acceleration system are the patient's safety and the beam control. From this point of view an important role is played by the beam dumps in the synchrotron ring and upstream of the extraction system. In particular, an horizontal and a vertical beam dump will be installed in the synchrotron ring: the former will be used for lowering the beam intensity and the latter for beam abortion. The dump at the extraction will absorb the particles during the mounting and the falling ramps of the synchrotron magnetic cycle, thus extracting only the flat top of the ion spill. Beam dumps can produce intense fields of secondary radiation (neutrons, charged light-hadrons and photons) and high rates of induced activity, since they can absorb the beam completely. Usually they have to be shielded to protect the electronics during machine operation and to attenuate the radiation dose below the limits imposed by the law when the personnel access to the synchrotron hall. The part of the shielding design of the beam dumps concerning with the acceleration of protons was made using Monte Carlo simulations with the FLUKA code. Both induced activity and secondary radiation were taken into account. The shields against secondary radiation produced by carbon ions were designed, referring only to secondary neutrons, taking double-differential distributions from the literature as sources for the FLUKA simulations. The induced activity from carbon ions interactions was estimated analytically, using the data generated by the EPAX 2 code. The dose-equivalent rates from the induced radionuclides were calculated at 1 m from the shielded dumps, taking into account the contribution of activated components of the synchrotron ring.

Computer Simulation↗

PubMed2005

Secondary photon fields produced in accelerator-based sources for neutron generation.

Neutrons can be produced with low-energy ion accelerators for many applications, such as the characterisation of neutron detectors, the irradiation of biological samples and the study of the radiation damage in electronic devices. Moreover, accelerator-based neutron sources are under development for boron neutron capture therapy (BNCT). Thin targets are used for generating monoenergetic neutrons, while thick targets are usually employed for producing more intense neutron fields. The associated photon field produced by the target nuclei may have a strong influence on the application under study. For instance, these photons can play a fundamental role in the design of an accelerator-based neutron source for BNCT. This work focuses on the measurement of the photon field associated with neutrons that are produced by 4.0-6.8 MeV protons striking both a thin 7LiF target (for generating monoenergetic neutrons) and a thick beryllium target. In both cases, very intense photon fields are generated with energy distribution extending up to several MeV.

Beryllium↗

PubMed2005

QUADOS intercomparison: a summary of photon and charged particle problems.

QUADOS, a Concerted Action of the European Commission, has promoted an intercomparison aimed at evaluating the use of computational codes for dosimetry in radiation protection and medical physics. This intercomparison was open to all users of radiation transport codes. Eight problems were selected for their relevance to the radiation dosimetry community, five of which involved photon and proton transport. This paper focuses on the analysis of the photon and charged particle problems. The neutron problems were presented in a paper at the NEUDOS9 conference.

Algorithms↗

PubMed2004

Study of a method based on TLD detectors for in-phantom dosimetry in BNCT.

A method has been developed, based on thermoluminescent dosemeters (TLD), aimed at measuring the absorbed dose in tissue-equivalent phantoms exposed to thermal or epithermal neutrons, separating the contributions of various secondary radiation generated by neutrons. The proposed method takes advantage of the very low sensitivity of CaF2:Tm (TLD-300) to low energy neutrons and to the different responses to thermal neutrons of LiF:Mg,Ti dosemeters with different 6Li percentage (TLD-100, TLD-700, TLD-600). The comparison of the results with those obtained by means of gel dosemeters and activation foils has confirmed the reliability of the method. The experimental modalities allowing reliable results have been studied. The glow curves of TLD-300 after gamma or neutron irradiation have been compared; moreover, both internal irradiation effect and energy dependence have been investigated. For TLD-600, TLD-100 and TLD-700, the suitable fluence limits have been determined in order to avoid radiation damage and loss of linearity.

Body Burden↗

PubMed2004

The response of a bonner sphere spectrometer to charged hadrons.

Bonner sphere spectrometers (BSSs) are employed in neutron spectrometry and dosimetry since many years. Recent developments have seen the addition to a conventional BSS of one or more detectors (moderator plus thermal neutron counter) specifically designed to improve the overall response of the spectrometer to neutrons above 10 MeV. These additional detectors employ a shell of material with a high mass number (such as lead) within the polyethylene moderator, in order to slow down high-energy neutrons via (n,xn) reactions. A BSS can be used to measure neutron spectra both outside accelerator shielding and from an unshielded target. Measurements were recently performed at CERN of the neutron yield and spectral fluence at various angles from unshielded, semi-thick copper, silver and lead targets, bombarded by a mixed proton/pion beam with 40 GeV per c momentum. These experiments have provided evidence that under certain circumstances, the use of lead-enriched moderators may present a problem: these detectors were found to have a significant response to the charged hadron component accompanying the neutrons emitted from the target. Conventional polyethylene moderators show a similar behaviour but less pronounced. These secondary hadrons interact with the moderator and generate neutrons, which are in turn detected by the counter. To investigate this effect and determine a correction factor to be applied to the unfolding procedure, a series of Monte Carlo simulations were performed with the FLUKA code. These simulations aimed at determining the response of the BSS to charged hadrons under the specific experimental situation. Following these results, a complete response matrix of the extended BSS to charged pions and protons was calculated with FLUKA. An experimental verification was carried out with a 120 GeV per c hadron beam at the CERF facility at CERN.

Computer Simulation↗

PubMed2004

Intercomparison on the usage of computational codes in radiation dosimetry.

'QUADOS', a Concerted Action of the European Commission, has run an intercomparison aimed at evaluating the use of computational codes for dosimetry in radiation protection and medical physics. This intercomparison was open to all users of Monte Carlo, analytic and semi-analytic codes or deterministic methods. Its main aim was to provide a snapshot of the methods and codes currently in use. It also intended to furnish information on the methods used to assess the reliability of computational results and disseminate 'good practice' throughout the radiation dosimetry community. Eight problems were selected for their relevance to the radiation dosimetry community, three of which involve neutron transport. This paper focuses on the analysis of the neutron problems.

Algorithms↗

PubMed2004

A recoil-proton spectrometer based on a p-i-n diode implementing pulse-shape discrimination.

A recoil-proton spectrometer was created by coupling a p-i-n diode with a polyethylene converter. The maximum detectable energy, imposed by the thickness of the totally depleted layer, is approximately 6 MeV. The minimum detectable energy is limited by the contribution of secondary electrons generated by photons in the detector assembly. This limit is approximately 1.5 MeV at full-depletion voltage and was decreased using pulse-shape discrimination. The diode was set up in the 'reverse-injection' configuration (i.e. with the N+ layer adjacent to the converter). This configuration provides longer collection times for the electron-hole pairs generated by the recoil-protons. The pulse-shape discrimination was based on the zero-crossing time of bipolar signals from a (CR)2-(RC)2 filter. The detector was characterised using monoenergetic neutrons generated in the Van De Graaff CN accelerator at the INFN-Laboratori Nazionali di Legnaro. The energy limit for discrimination proved to be approximately 900 keV.

Body Burden↗

PubMed2002

High-energy neutron dosimetry with superheated drop detectors.

A systematic analysis of the response of dichlorodifluoromethane superheated drop detectors was performed in the 46-133 MeV energy range. Experiments with quasi-monoenergetic neutron beams were performed at the Université Catholique de Leuvain-la-Neuve, Belgium and the Svedberg Laboratory, Sweden, while tests in a broad field were performed at CERN. To determine the response of the detectors to the high-energy beams, the spectra of incident neutrons were folded over functions modelled after the cross sections for the production of heavy ions from the detector elements. The cross sections for fluorine and chlorine were produced in this work by means of the Monte Carlo high-energy transport code HADRON based on the cascade exciton model of nuclear interactions. The new response data permit the interpretation of measurements at high-energy accelerators and on high-altitude commercial flights, where a 30-50% under-response had been consistently recorded with respect to neutron dose equivalent. The introduction of a 1 cm lead shell around the detectors effectively compensates most of the response defect.

Chlorofluorocarbons, Methane↗

PubMed2002

A feasibility study of a single event spectrometer based on semiconductor devices.

The electronics employed around particle accelerators can be disturbed or damaged because of single event effects (SEE). The most likely effect is the single event upset (SEU) which may affect all memory devices. In the case of high energy accelerators, SEUs are mostly produced by secondary charged particles generated by neutron interactions. The measurement of the energy and the lineal energy distribution of these neutron-induced charged particles was proposed. As a first approach, a commercial p-i-n photodiode was employed. This device was irradiated with thermal and monoenergetic fast neutrons. Some effects limiting the use of such a detector as a SEE spectrometer were observed, giving guidelines for the design of an application specific integrated circuit (ASIC). The possibility of creating a solid state microdosemeter by coupling the ASIC with a tissue-equivalent radiator is discussed. Moreover, the p-i-n photodiode covered with a hydrogenated plastic radiator may be employed as a proton-recoil spectrometer.

Dose-Response Relationship, Radiation↗

PubMed2001

Radiation protection at medical accelerators.

This paper focuses on radiation protection at proton and light ion accelerators for radiotherapy. The National Centre of Hadrontherapy, which is planned to he built in Italy in the next five years, is considered as a reference facility for applying the various methodologies presented. The shielding design is firstly discussed, together with that of the access maze to the treatment rooms. Subsequently, the main aspects for the estimate of the air activation in the environment hosting the accelerator system are described. The estimate of the dose equivalent due to the activated air transferred to the neighbourhood population is also treated. Outlines are given of the radioactivity induced by the primary beam in the materials constituting the magnets and the patient's personal collimator.

Humans↗

PubMed1998

Secondary neutron and photon dose in proton therapy.

BACKGROUND AND PURPOSE: The dose due to secondary neutrons and photons in proton therapy was estimated with Monte Carlo simulations. Three existing facilities treating eye and deep-seated tumours were taken into account. The results of the calculations related to eye proton therapy were verified with measurements. MATERIALS AND METHODS: The simulations were performed with the FLUKA code. Neutron fluence was measured inside an Alderson phantom (type ART) with activation techniques. RESULTS: The maximum dose due to secondaries produced in a passive beam delivery system was estimated to be of the order of 10(-4) and 10(-2) Gy per therapy Gy for eye and deep tumour treatments, respectively. In the case of irradiations of deep-seated tumours carried out with an active system, the dose was of the order of 10(-3) Gy per therapy Gy. CONCLUSIONS: The dose due to secondaries depends on the geometry of the beam delivery system and on the energy of the primary beam and is lower in the healthy tissues distant from the target volume.

Eye Neoplasms↗

PubMed1998

Neutron measurements in the stray field produced by 158 GeV c(-1) per nucleon lead ion beams.

This paper discusses measurements carried out at CERN in the stray radiation field produced by 158 GeV c(-1) per nucleon 208Pb82+ ions. The purpose was to test and intercompare the response of several detectors, mainly neutron measuring devices, and to determine the neutron spectral fluence as well as the microdosimetric (absorbed dose and dose equivalent) distributions in different locations around the shielding. Both active instruments and passive dosimeters were employed, including different types of Andersson-Braun rem counters, a tissue equivalent proportional counter, a set of superheated drop detectors, a Bonner sphere system, and different types of ion chambers. Activation measurements with 12C plastic scintillators and with 32S pellets were also performed to assess the neutron yield of high energy lead ions interacting with a thin gold target. The results are compared with previous measurements and with measurements made during proton runs.

Environmental Exposure↗