Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 8 de 8
Filter
Add more filters










Database
Language
Publication year range
1.
Phys Med Biol ; 57(19): 6167-91, 2012 Oct 07.
Article in English | MEDLINE | ID: mdl-22971664

ABSTRACT

Neutron peripheral contamination in patients undergoing high-energy photon radiotherapy is considered as a risk factor for secondary cancer induction. Organ-specific neutron-equivalent dose estimation is therefore essential for a reasonable assessment of these associated risks. This work aimed to develop a method to estimate neutron-equivalent doses in multiple organs of radiotherapy patients. The method involved the convolution, at 16 reference points in an anthropomorphic phantom, of the normalized Monte Carlo neutron fluence energy spectra with the kerma and energy-dependent radiation weighting factor. This was then scaled with the total neutron fluence measured with passive detectors, at the same reference points, in order to obtain the equivalent doses in organs. The latter were correlated with the readings of a neutron digital detector located inside the treatment room during phantom irradiation. This digital detector, designed and developed by our group, integrates the thermal neutron fluence. The correlation model, applied to the digital detector readings during patient irradiation, enables the online estimation of neutron-equivalent doses in organs. The model takes into account the specific irradiation site, the field parameters (energy, field size, angle incidence, etc) and the installation (linac and bunker geometry). This method, which is suitable for routine clinical use, will help to systematically generate the dosimetric data essential for the improvement of current risk-estimation models.


Subject(s)
Neutrons/adverse effects , Online Systems , Organs at Risk/radiation effects , Radiation Dosage , Radiotherapy, Computer-Assisted/adverse effects , Radiotherapy, Computer-Assisted/instrumentation , Acceleration , Humans , Monte Carlo Method , Phantoms, Imaging , Proton Therapy/adverse effects , Proton Therapy/instrumentation , Radiotherapy Dosage
2.
Radiat Prot Dosimetry ; 126(1-4): 371-5, 2007.
Article in English | MEDLINE | ID: mdl-17575290

ABSTRACT

Positron emission tomography (PET) is a non-invasive medical imaging technique normally used for diagnostic purposes to determine the location and concentration of physiologically active compounds in a human body. An unshielded cyclotron is used for PET at the Clinica Universitaria de Navarra to produce short-lived positron emitting radionuclides ((15)O, (13)N, (11)C and (18)F) by bombarding appropriate target material with proton or deuteron beams with energies up to 18 and 9 MeV, respectively. Subsequent nuclear reactions may generate undesirable neutrons that should be evaluated and controlled. In this study, the neutron measurements performed with an active and a passive Bonner sphere systems at different locations outside and inside the cyclotron vault during operation have been presented. The neutron spectrum at each location was determined with an unfolding code developed by the authors.


Subject(s)
Neutrons , Positron-Emission Tomography/instrumentation , Radiation Monitoring/instrumentation , Radiation Protection/instrumentation , Spectrum Analysis/instrumentation , Equipment Design , Equipment Failure Analysis , Radiation Dosage , Radiation Monitoring/methods , Radiation Protection/methods , Reproducibility of Results , Sensitivity and Specificity , Spain
3.
Radiat Prot Dosimetry ; 126(1-4): 366-70, 2007.
Article in English | MEDLINE | ID: mdl-17513852

ABSTRACT

The Grup de Física de les Radiacions (GFR) of the Universitat Autònoma de Barcelona (UAB), in collaboration with the Institute for Radiological Protection and Nuclear Safety (IRSN), has developed a passive Bonner sphere system (UAB-BSS), with gold foils as thermal neutron detectors, for application in pulsed neutron fields or in mixed neutron-photon fields with high photon intensities. In such fields, active devices suffer from saturation and dead-time effects. The MCNPX Monte-Carlo code has been used to determine the response to neutrons of different energies of each polyethylene sphere belonging to the BSS. The passive UAB-BSS system was characterised with the ISO (252)Cf reference source at the IRSN facilities. The energy distribution of the reference source neutron fluence was folded with the response functions for comparison with the experimental data. A good agreement between the experimental and calculated count rates was found.


Subject(s)
Gold/chemistry , Gold/radiation effects , Models, Theoretical , Neutrons , Occupational Exposure/analysis , Radiation Monitoring/instrumentation , Radiation Protection/instrumentation , Computer Simulation , Equipment Design , Equipment Failure Analysis , Monte Carlo Method , Radiation Dosage , Radiation Monitoring/methods , Radiation Protection/methods , Reproducibility of Results , Sensitivity and Specificity
4.
Radiat Prot Dosimetry ; 126(1-4): 337-41, 2007.
Article in English | MEDLINE | ID: mdl-17513860

ABSTRACT

A passive Bonner sphere system (BSS), based on thermal neutron activation detectors, was developed to perform neutron spectrometry in pulsed and very intense (n-gamma) fields with predominant photon component, as those produced by high energy (>10 MV) medical linear electron accelerators. In this paper, a description of the new system is presented together with an experimental characterisation of a portable Sodium Iodide (NaI) detector and a fixed high-purity Germanium one, both used to measure the induced gamma-activity of the activated materials, respectively, in situ and in the laboratory. The choice of the activated materials is justified according to pre-established practical considerations and physical criteria. The response functions of the entire passive BSS were calculated using the MCNPX code. A preliminary experimental validation with a bare (252)Cf source is given as well.


Subject(s)
Neutrons , Photons , Radiation Monitoring/instrumentation , Radiation Protection/instrumentation , Spectrum Analysis/instrumentation , Transducers , Equipment Design , Equipment Failure Analysis , Radiation Dosage , Radiation Monitoring/methods , Radiation Protection/methods , Reproducibility of Results , Sensitivity and Specificity
5.
Radiat Prot Dosimetry ; 126(1-4): 361-5, 2007.
Article in English | MEDLINE | ID: mdl-17525060

ABSTRACT

The use of high-energy linear electron accelerators (LINACs) for medical cancer treatments is widespread on an international scale. The associated bremsstrahlung X rays may produce neutrons as a result of subsequent photonuclear reactions with the different materials constituting the accelerator head. The generated neutron field is highly variable and depends strongly on the beam energy, on the accelerator shielding, on the flattering filter as well as on the movable collimators (jaws) design and on the irradiation field geometry. An estimate of this photoneutron component is, thus, of practical interest to quantify the radiological risk for the working staff and patients. Due to high frequency electromagnetic fields, and also to the presence of abundant leaked and scattered photons in these installations, measurements of the corresponding neutron fields by active dosemeters are extremely difficult. A modified version of the Bonner sphere system, based on passive gold activation detectors, has been used to perform neutron measurements at two points in a Varian 2,100C LINAC facility. A home-made unfolding procedure (CDM) has been utilised to determine the neutron spectra present at the measurement points. Results indicate that the giant dipole resonance process is the most adequate model to explain neutron production in the LINAC and that a thermal component is present at the measurement points.


Subject(s)
Gold/chemistry , Gold/radiation effects , Neutrons , Occupational Exposure/analysis , Particle Accelerators/instrumentation , Radiation Monitoring/instrumentation , Radiation Protection/instrumentation , Equipment Design , Equipment Failure Analysis , Radiation Dosage , Radiation Monitoring/methods , Radiation Protection/methods , Reproducibility of Results , Sensitivity and Specificity , Spain
6.
Radiat Prot Dosimetry ; 126(1-4): 355-60, 2007.
Article in English | MEDLINE | ID: mdl-17525063

ABSTRACT

Neutron spectrometric measurements with an active Bonner Sphere System (BSS) allowed us to determine the reference dosimeter values in Ascó I and II and Cofrentes (PWR, BWR) Spanish nuclear power plants. Under a request from the Spanish National Nuclear Safety Council, the UAB group was in charge of characterising the neutron fields at several measurement points (a total of 10) inside the containment building of these nuclear installations using an active BSS and a home-made MITOM unfolding code. The measurement results in the three installations confirm the presence of low-energy neutron components in almost all selected points. This developed BSS can be considered as a reference system in neutron radiation protection when defining the corresponding protocols for a correct personal dosimetry in nuclear power plant installations.


Subject(s)
Neutrons , Nuclear Reactors , Occupational Exposure/analysis , Radiation Monitoring/instrumentation , Radiation Protection/instrumentation , Spectrum Analysis/instrumentation , Equipment Design , Equipment Failure Analysis , Radiation Dosage , Radiation Monitoring/methods , Radiation Protection/methods , Reproducibility of Results , Sensitivity and Specificity , Spain
7.
Radiat Prot Dosimetry ; 110(1-4): 701-4, 2004.
Article in English | MEDLINE | ID: mdl-15353734

ABSTRACT

Measurement of the personal dose equivalent rates for neutrons is a difficult task because available dosemeters do not provide the required energy response and sensitivity. Furthermore, the available wide calibration spectra recommended by the International Standard Organisation does not reproduce adequately the spectra encountered in practical situations of the nuclear industry. There is a real necessity to characterise the radiation field, in which workers can be exposed, and to calibrate personal dosemeters in order to determine the dose equivalent in these installations. For this reason, we measure the neutron spectrum with our Bonner sphere system and we fold this spectrum with energy-dependent fluence-to-dose conversion coefficients to obtain the reference dose equivalent rate. This reference value is then compared with the personal dosemeter reading to determine a field-specific correction factor. In this paper, we present the values of this field-specific correction factor for etched track and albedo thermoluminescence dosemeters at three measurement locations inside the containment building of the Vandellòs II nuclear power plant. We have found that assigning to each personal dosemeter the mean value of the field-specific correction factors of the three measurement locations, allows the evaluation of neutron personal dose equivalent rate with a relative uncertainty of approximately 25 and 15% for the PADC and albedo dosemeters, respectively.


Subject(s)
Neutrons , Occupational Exposure/analysis , Power Plants , Radiation Protection/instrumentation , Radioactive Hazard Release , Risk Assessment/methods , Thermoluminescent Dosimetry/instrumentation , Body Burden , Equipment Failure Analysis/instrumentation , Humans , Quality Assurance, Health Care/methods , Radiation Dosage , Radiation Protection/methods , Relative Biological Effectiveness , Reproducibility of Results , Risk Factors , Safety Management/methods , Sensitivity and Specificity , Thermoluminescent Dosimetry/methods
8.
Radiat Prot Dosimetry ; 102(4): 359-64, 2002.
Article in English | MEDLINE | ID: mdl-12474947

ABSTRACT

High indoor radon concentration means an increased risk of developing lung cancer. When high radon levels are present in a dwelling, the major source is normally the soil. Therefore, it is useful to know the radon concentration field in the soil underneath a building. A steady-state two-dimensional radon transport model has been used to calculate the effect of a reference building on the soil radon concentration, and the influence of soil parameters on radon entry through a single crack in the basement. Both advective and diffusive flows are considered. Away from the building, the well-known undisturbed soil radon concentration profile has been obtained, while under the house the radon level is increased. A variability analysis around the reference site has shown that the most relevant soil parameters on the radon flux at the top of the crack are, in this case, effective diffusion coefficient, soil gas-permeability and deep soil radon concentration.


Subject(s)
Air Pollutants, Radioactive , Air Pollution, Indoor , Radon , Soil Pollutants, Radioactive , Diffusion , Housing , Humans , Models, Theoretical , Radiation Monitoring , Soil
SELECTION OF CITATIONS
SEARCH DETAIL
...