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Biomedical subjects

M Silari

Publications and source records attributed to M Silari.

17 recordsLinked to original sources
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

Radiation issues in a radioactive ion decay ring.

In a beta-beam facility, a pure beam of electron neutrinos, or their antiparticles, are produced by the decay of fully stripped radioactive ions (6He and 18Ne) circulating in a storage ring. Since the beam is not extracted from the ring, all the particles will eventually be lost somewhere in the machine and thus activate the accelerator components and the surrounding concrete and rock. In particular, as nuclei change their charge in beta-decay, a large part of the particles will be lost in the arcs of the decay ring and mainly irradiate the magnets. The density of inelastic interactions of hadrons in the magnets, concrete and rock and the track-length distribution of secondary hadrons were calculated by means of the FLUKA Monte Carlo code. These values were used to estimate the induced radioactivity in the facility, the dose rates expected in the decay ring and the consequences for the environment.

Beta Particles↗
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↗
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↗
PubMed2001

Narrow beam dosimetry for high energy hadrons and electrons.

Organ doses and effective dose were calculated with the latest version of the Monte Carlo transport code FLUKA in the case of an anthropomorphic mathematical model exposed to monoenergetic narrow beams of protons, pions and electrons in the energy range 10-400 GeV. The target organs considered were right eye, thyroid, thymus, lung and breast. Simple scaling laws to the calculated values are given. The present data and formulae should prove useful for dosimetric estimations in the case of accidental exposures to high energy beams.

Breast↗
PubMed2001

Radiation protection at high energy proton accelerators.

The radiological problems associated with proton accelerators having maximum energies higher than a few GeV are discussed. Examples are given from accelerators where the authors have had practical experience for a number of years. The main focus will be on those problems which are unique to high energy proton accelerators, and which may not be necessarily associated with the proton beam operation itself.

Humans↗
PubMed2001

Special radiation protection aspects of medical accelerators.

Radiation protection aspects relevant to medical accelerators are discussed. An overview is first given of general safety requirements. Next, shielding and labyrinth design are discussed in some detail for the various types of accelerators, devoting more attention to hadron machines as they are far less conventional than electron linear accelerators. Some specific aspects related to patient protection are also addressed. Finally, induced radioactivity in accelerator components and shielding walls is briefly discussed. Three classes of machines are considered: (1) medical electron linacs for 'conventional' radiation therapy, (2) low energy cyclotrons for production of radionuclides mainly for medical diagnostics and (3) medium energy cyclotrons and synchrotrons for advanced radiation therapy with protons or light ion beams (hadron therapy).

Electrons↗
PubMed2001

A reference radiation facility for dosimetry at flight altitude and in space.

A reference facility for the intercomparison of active and passive detectors in high-energy neutron fields is available at CERN since 1993. A positive charged hadron beam (a mixture of protons and pions) with momentum of 120 GeV/c hits a copper target, 50 cm thick and 7 cm in diameter. The secondary particles produced in the interaction are filtered by a shielding of either 80 cm of concrete or 40 cm of iron. Behind the iron shielding, the resulting neutron spectrum has a maximum at about 1 MeV, with an additional high-energy component. Behind the concrete shielding, the neutron spectrum has a pronounced maximum at about 70 MeV and resembles the high-energy component of the radiation field created by cosmic rays at commercial flight altitudes. The facility is used for a variety of investigations with active and passive neutron dosimeters. Its use for measurements related to the space programme is discussed.

Altitude↗
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↗
PubMed1997

Proton beam dosimetry: a comparison between the Faraday cup and an ionization chamber.

From the theoretical point of view, the Faraday cup (FC) is an absolute instrument for fluence measurements of proton beams. As the FC is easily manufactured it can be considered an 'in-house' calibration system. Moreover, at the moment no national standards for proton dosimetry are available. Up to now the experimental tests of these instruments show that much study still has to be done to better understand their use in reference dosimetry. To investigate the possibility of using an FC as a secondary standard, an FC was jointly designed by the 'TERA Collaboration' and 'Centre Antoine-Lacassagne' (Nice, France) to evaluate the main parameters of the instrument. A comparison between two FCs of different designs--the 'TERA FC' and the 'Nice FC'--and an ionization chamber (IC) used for routine proton dosimetry was carried out. Results show that the two FCs agree to within 1.5-3.6%. While the differences between FC and IC are larger--6% for the 'TERA FC' and 8.2% for the 'Nice FC', the FC giving a lower dose evaluation--they follow the same trend shown by the calorimetric measurements. The data show that once the beam characteristics are defined, the fluence measurements are reproducible and show a good accuracy.

Biophysical Phenomena↗
PubMed1996

Physical specifications of clinical proton beams from a synchrotron.

Tumor treatment with charged particle beams is a quickly developing field aimed to translate the potential advantages offered by the superior physical dose distribution and relative biological effectiveness of heavy charged particles into a real improvement of tumor therapy. To this purpose the new proton and light-ion radiation therapy facilities must be designed according to strict clinical specifications to provide a reliable and effective tool against cancer. This paper provides the performance specifications of the accelerator and of the beam transport and delivery systems of the Italian Hadrontherapy Centre, which should be satisfied to meet the clinical specifications. A discussion is given on the requirements on energy range, energy variability, beam intensity, lateral penumbra, distal dose falloff, source-to-surface distance, time structure of the extracted beam, raster scanning system specifications, and beam abort time. Though the physical specifications are given for a particular accelerator, they can be used as a general guideline for the design of future biomedical particle accelerator facilities.

Biophysical Phenomena↗
PubMed1993

[The hadron therapy project].

The neologism "hadrontherapy" means radiotherapy with hadrons, which are the particles constituted by quarks, such as protons, neutrons and ions. The theoretical considerations about the clinical advantages this treatment modality can yield and the results obtained at the centers where it has already been used justify the proposal to project a center of this kind also in our Country. To this purpose, two of the authors of this paper (U. Amaldi, G. Tosi) founded the TERA Group formed by physicists, engineers and radiotherapists who work in close collaboration on a feasibility study for a hadrontherapy facility. The first aim of the Hadrontherapy Project is to design a center equipped with a synchrotron which, at the beginning, will accelerate negative hydrogen ions (H-) which will first produce 70-250 MeV proton beams and, then accelerate light ions (up to 16O) to 430 MeV/amu. This accelerator will serve four or five treatment rooms where patients can be irradiated simultaneously. Two rooms will be equipped with a fixed horizontal beam for the treatment of eye, head and neck tumors; the others will be equipped with rotating gantries to administer, in any clinical situation, really adequate treatment. Such a unit, when enough experience is fained, will allow at least 1000 patients to be treated yearly. The synchrotron injector will be designed so as to allow, parallel to the radiotherapy activities, other applications of medical and biological interest such as: the production of radioisotopes for diagnostic use (especially positron emitters), the analysis of trace elements through the PIXE technique and the production of thermal and epithermal neutrons for boron neutron capture therapy.

Biophysical Phenomena↗
PubMed1986

[Cyclotrons in medicine. A survey of commercial models and their biomedical applications].

At present in Italy there is a great interest in the use of cyclotrons for medical applications: according to a plan of CNR (National Research Council), accelerators of this kind are going to be installed in some hospitals. After the explanation of the cyclotron operation principles, an outline is given of the possible applications with particular care for the clinical ones. An up-to-date review of commercial models so far developed is reported and finally, after a short note concerning installation problems, some suggestions are given about criteria to be followed in the choice of a model, according to the foreseen scientific program.

Equipment and Supplies, Hospital↗
PubMedDate not supplied

Neutron measurements around medical electron accelerators by active and passive detection techniques.

Passive and active detection techniques have been employed in order to measure neutron fluence rates and corresponding exposure rates around medical electron accelerators operating at energies well above the neutron binding energies of the structural materials. In these conditions from the treatment head, in the direct photon flux and from the shielded region, a fast neutron flux emerges which is partly absorbed and partly scattered by the walls, eventually establishing a nearly uniform thermal and epithermal flux in the room. Both direct and scattered flux contribute to the dose to the patient. A smaller neutron dose rate can also be found outside the treatment room, where the therapy staff works. Passive detectors, of moderation type, have been employed in the treatment room and 3He active detectors in the external zones. For the treatment room the activation data were compared with results of Monte Carlo simulation of the neutron transport in the room. Technical features of the two measures are briefly presented and results obtained around three different types of accelerators are reported. At the higher beam energies, i.e., 25 MV, a neutron dose of 0.36 Sv was estimated in the treatment field in addition to a therapeutic x-ray dose of 50 Gy. At lower energies or out of the treatment field the neutron dose drops significantly. In the external zones the dose rates everywhere are below the recommended limits and normally very low, the highest values being recorded in positions very close to the access door of the treatment room.

Humans↗
PubMedDate not supplied

Biomedical applications of cyclotrons and review of commercially available models.

The growing use of cyclotrons in biomedicine, both for clinical and research purposes and in particular for the production of short-lived radionuclides which are extremely useful in nuclear medicine diagnosis, has reached a stage in which commercial companies are able to offer several models with different performances, in order to satisfy the demand of different users. Many of these commercially produced accelerators are installed all over the world and some of them have been operating for several years, demonstrating that this category of machine has reached a high degree of reliability. A brief description of the operating principle of the cyclotron is presented, together with an illustration of its possible applications in the medical field. A list of the models presently available on the market is given and the installation problems and the criteria to be followed in the choice of a model are discussed. Finally, likely future developments in the field are briefly discussed.

Fast Neutrons↗