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At least 145 records · Page 8Linked to original sources
PubMed2004

Fast neutron beams for boron neutron capture therapy?

In view of Boron Neutron Capture Enhanced Fast Neutron Therapy (BNCEFNT) of brain tumours, the spatial distributions of thermal flux and fast neutron plus photon dose were measured in a hydrogenous cylinder phantom under conditions varying with respect to neutron energy, field size, and irradiation technique. The behaviour of the ratio thermal fluence per unit total dose leads to the conclusion that an appreciable dose contribution from the BNC reaction can be expected only with low energies and large fields. Beams from small apertures (< 6 x 6 cm2) produce only marginal BNC dose contributions, and might gain therapeutic relevance only in combination with a very effective tumour-seeking Boron-10 carrier.

Boron Neutron Capture Therapy↗
PubMed1982

Effect of collimator and depth in a phantom on the neutron spectrum from a 238Pu,Be neutron source.

A study has been made of some factors influencing the fast neutron spectrum emerging from the aperture of a collimated 238Pu,Be source, and influencing the spectrum at a depth in a water phantom, using a miniature liquid scintillator fast neutron spectrometer. The greatest changes in the spectrum emerging from the aperture were produced by changes in the length of the collimator and the field size of the collimator. No difference between the source spectrum above 1.5 MeV of 370 GBq (10 Ci) and 740 GBq (20 Ci) 238Pu,Be sources and a 37 GBq (1 Ci) 241Am,Be source was observed. Graphite was found to be a slightly more efficient reflector than steel or lead, and much better than wax. The mean energy and the proportion of the total neutron fluence with an energy between 1.5 MeV and 3.5 MeV reached a minimum and a maximum value respectively with increase in depth in the phantom. With further increase in depth, the two parameters increased and decreased respectively. The depth at which these minimum and maximum values occurred increased with field size. The overall changes through 15 cm depth in the mean energy and in the low energy fluence proportion were small (less than or equal to +/- 5%). No significant changes were detected in the spectral shape after the neutron beam traversed an air cavity or a bovine tibia in the phantom.

Beryllium↗
PubMed1993

Design of a californium-based epithermal neutron beam for neutron capture therapy.

The potential of the spontaneously fissioning isotope, 252Cf, to provide epithermal neutrons for use in boron neutron capture therapy (BNCT) has been investigated using Monte Carlo simulation. The Monte Carlo code MCNP was used to design an assembly composed of a 26 cm long, 11 cm radius cylindrical D2O moderator followed by a 64 cm long Al filter. Lithium filters are placed between the moderator and the filter and between the Al and the patient. A reflector surrounding the moderator/filter assembly is required in order to maintain adequate therapy flux at the patient position. An ellipsoidal phantom composed of skull- and brain-equivalent material was used to determine the dosimetric effect of this beam. It was found that both advantage depths and advantage ratios compare very favourably with reactor and accelerator epithermal neutron sources. The dose rate obtainable, on the other hand, is 4.1 RBE cGy min-1, based on a very large (1.0 g) source of 252Cf. This dose rate is two to five times lower than those provided by existing reactor beams and can be viewed as a drawback of using 252Cf as a neutron source. Radioisotope sources, however, do offer the advantage of in-hospital installation.

Californium↗
PubMed2005

Filter, collimator and moderating material to achieve boron neutron capture enhanced fast neutron therapy.

The combination of fast neutron therapy and boron neutron capture therapy is currently being studied as a possible treatment for some radio-resistant brain tumours. In an attempt to design a boron-enhanced fast neutron therapy beam for the Fermilab Fast Neutron Therapy Facility, the use of moderating material surrounding the patient's head has been investigated. Graphite, polyethylene, water and heavy water were studied as moderating materials, using MCNP. The use of tungsten, iron, lead and bismuth as materials for a small filter and collimator near the patient's head was investigated. Calculations showed that a filter and collimator made of tungsten with a graphite moderator was capable of producing a dose enhancement of 17.3 +/- 0.6% for a 100 microg g(-1) loading of 10B for a 5.6 cm diameter beam while delivering 1.5 Gy in 7 min.

Boron Neutron Capture Therapy↗
PubMed1999

Design for an accelerator-based orthogonal epithermal neutron beam for boron neutron capture therapy.

This paper is concerned with the proposed Birmingham accelerator-based epithermal neutron beam for boron neutron capture therapy (BNCT). In particular, the option of producing a therapy beam at an orthogonal direction to the incoming protons is considered. Monte Carlo radiation transport simulations, both with and without a head phantom, have shown that an orthogonal beam geometry is not only acceptable but is indeed beneficial, in terms of a lower mean neutron energy and an enhanced therapeutic ratio for the same useful neutron fluence in the therapy beam. Typical treatment times for various beam options have been calculated, and range from 20 to 48 min with a 5 mA beam of 2.8 MeV protons, if the maximum photon-equivalent dose delivered to healthy tissue is to be 12.6 Gy Eq. The effects of proton beam diameter upon the therapy beam parameters have also been considered.

Boron Neutron Capture Therapy↗
PubMed2005

Modified boron neutron capture therapy for malignant gliomas performed using epithermal neutron and two boron compounds with different accumulation mechanisms: an efficacy study based on findings on neuroimages.

OBJECT: To improve the effectiveness of boron neutron capture therapy (BNCT) for malignant gliomas, the authors used epithermal rather than thermal neutrons for deep penetration and two boron compounds-sodium borocaptate (BSH) and boronophenylalanine (BPA)-with different accumulation mechanisms to increase the boron level in tumors while compensating for each other's faults. METHODS: Thirteen patients, 10 of whom harbored a glioblastoma multiforme (GBM), one a gliosarcoma, one an anaplastic astrocytoma, and one an anaplastic oligoastrocytoma, were treated using this modified BNCT between January 2002 and December 2003. Postoperatively, neuroimaging revealed that only one patient with a GBM had no lesion enhancement postoperatively. The patients underwent 18F-BPA positron emission tomography, if available, to assess the accumulation and distribution of BPA before neutron radiotherapy. The neutron fluence rate was estimated using the Simulation Environments for Radiotherapy Applications dose-planning system before irradiation. The patients' volume assessments were performed using magnetic resonance (MR) imaging or computerized tomography (CT) scanning. Improvements in the disease as seen on neuroimages were assessed between 2 and 7 days after irradiation to determine the initial effects of BNCT; its maximal effects were also analyzed on serial neuroimages. The mean tumor volume before BNCT was 42.3 cm3. Regardless of the pre-BNCT tumor volume, in every patient harboring an assessable lesion, improvements on MR or CT images were recognized both at the initial assessment (range of volume reduction rate 17.4-71%, mean rate 46.4%) and at follow-up assessments (range of volume reduction rates 30.3-87.6%, mean rate 58.5%). More than 50% of the contrast-enhanced lesions disappeared in eight of the 12 patients during the follow-up period. CONCLUSIONS: This modified BNCT produced a good improvement in malignant gliomas, as seen on neuroimages.

Adult↗
PubMed1992

Dosimetry of 252Cf sources for neutron radiotherapy with and without augmentation by boron neutron capture therapy.

Interstitial and intracavity 252Cf sources have been used to treat a number of tumor types with encouraging results. In particular these tumors include a variety of cervical, head-and-neck, and oral-cavity cancers and possible malignant gliomas. As a neutron source, 252Cf offers certain theoretical advantages over photon therapy (i.e., in treating tumors with significant hypoxic or necrotic components). With the recent availability of 10B-labeled tumor-seeking compounds, the usefulness of 252Cf may be further improved by augmenting the 252Cf dose to the tumor with an additional dose due to the fission (following thermal neutron capture) of 10B located in the tumor itself. While the high mean neutron energy permits 252Cf to deliver a high-LET, low-OER dose to the tumor on a macroscopic scale, thermalization of neutrons followed by 10B capture may augment this dose at the cellular level if adequate loading of tumor cells with 10B is possible. This paper presents results of a Monte Carlo simulation study investigating the dosimetric characteristics of linear 252Cf sources both with and without the quantitative increase in tumor dose possible with the addition of 10B. Results are displayed in the form of "along and away" tables and dose profiles in a water phantom. Comparisons of Monte Carlo results with experimental and analytical dosimetry data available in the literature are also presented.

Boron Neutron Capture Therapy↗
PubMed1989

The production by 72 MeV protons of keV neutrons for 10B neutron capture therapy.

Fast neutrons, produced in a spallation process by 72 MeV protons hitting heavy nuclei, can be moderated down to keV energies, suitable for 10B capture therapy. Measurements of neutron flux from copper and lead targets, after moderation by water and hydrocarbons, have been performed, together with measurements of the fast neutron and gamma-backgrounds. The comparisons with Monte Carlo calculations show good agreement. As neutron fluences up to 10(12) to 10(13)n/cm2 can be produced within a few hours in about 0.5 m target distance the technique seems to be suitable for clinical experiments.

Boron↗
PubMed1990

Investigation of neutron beams for the realization of boron neutron capture therapy.

Results of the initial theoretical and experimental work performed at the Institute of Nuclear Technics of the Budapest Technical University (BTU NTI) regarding the design of a pure thermal neutron field for neutron capture therapy experiments are reported. Calculations show that a thermal neutron flux of approximately 10(9) neutrons cm-2s-1 will be generated using a filter made of graphite and bismuth.

Boron Compounds↗
PubMed1983

Neutron and neutron-boost irradiation of soft tissue sarcomas: a 4.5 year analysis of 139 patients.

A 4.5 year analysis of neutron and neutron-boost therapy is presented for 139 patients with soft tissue sarcomas. The actuarial survival rate of all patients is 64.3%, the disease-free survival rate is 61.6%. Significant differences in local control rates were found as a function of tumour stage (100% for T1, 72% for T2 and 46% for T3; p: 0.018) and as a function of the presence (50.5%) or absence of clinical evidence of tumour at the time of irradiation (76%; p: 0.002). The corresponding actuarial survival rates are 90.1% for T1 tumours, 78.5% for T2 tumours and 51.2% for T3 tumours, and on the other hand, 50.5% for patients with gross tumour and 76% for patients with no clinical evidence of tumour. A rather high morbidity rate (31/111, i.e. 28%) was observed after full neutron treatment. In order to reduce this complication rate, a combination of photons and a neutron boost was adopted. On 28 patients treated up to now, only two severe complications were observed. The effectiveness of this treatment regimen is presently being evaluated in a prospective European Organization for Research on Treatment of Cancer (EORTC) trial.

Adolescent↗
PubMed1996

A measurement of the fast-neutron sensitivity of a Geiger-Müller detector in the pulsed neutron beam from a superconducting cyclotron.

The kU value of a commercially available miniature energy compensated Geiger-Müller (GM) detector has been determined using the modified lead attenuation method of Hough. The measurements were made in a d(48.5)-Be neutron beam produced by the superconducting cyclotron based neutron therapy facility at Harper Hospital. The unique problems associated with making measurements in a 2 ms duration pulsed beam with a 20% duty cycle are discussed. The beam monitoring system, which allows the beam pulse shape at low beam intensities to be measured, is described. By gating the GM output with a discriminator pulse derived from the beam pulse shape, the gamma-ray count rates and dead-time corrections within the 2 ms pulse and between pulses can be measured separately. The kU value of (0.0245 +/- 0.0015) determined for this GM detector is consistent with the values measured by other workers with identical and similar detectors in neutron beams with comparable, but not identical, neutron spectra.

Biophysical Phenomena↗
PubMed2000

Calculation of the neutron W value for neutron dosimetry below the MeV energy region.

The effective neutron W value for tissue-equivalent gas in the energy region from 5 keV to 5.7 MeV has been calculated using W values for recoil particles (protons, alpha particles, oxygen, carbon and nitrogen ions), which are produced by incident neutrons. The W value is assumed to be an energy-fluence-average over the W values of the recoil particles. The energy fluence spectra for the recoil particles are calculated by using a continuous slowing down approximation (CSDA). For the W values of recoil particles in the low-energy region, the recently evaluated data by Siebert et al and Taylor et al were used. Results are presented which show that the effective neutron W value depends strongly on energy in the low-energy region. This result indicates that neutron dose measurements using ionization chambers need a considerable correction of the W value in the low-energy region.

Carbon↗
PubMed2004

Study of the ratio of non-neutron to neutron dose components of cosmic radiation at typical commercial flight altitudes.

CIEMAT, in close co-operation with Iberia Airlines, carried out an extensive programme of in-flight measurements, covering both hemispheres, during the years 2001 and 2002. Although the instrumentation onboard included different active devices, the results presented here were obtained from a polyethylene/tungsten-moderated rem meter (SWENDI2; Eberline) and an ionisation chamber (RSS-131; Reuter-Stokes) used for measuring the ambient dose equivalent due to the neutron and the non-neutron components of cosmic radiation, respectively. This paper presents a study of each of the dose components mentioned as a function of the vertical cut-off rigidity and the flight altitude. The ratio between the two components is also presented to determine the variations in cosmic radiation composition as a function of the aforementioned parameters. The experimental results have also been compared with those predicted by the code EPCARD3.2 for the non-neutron and the neutron components of the ambient dose equivalent.

Aircraft↗
PubMed2004

Measurement of neutron fluence spectra up to 150 MeV using a stacked scintillator neutron spectrometer.

A stacked scintillator neutron spectrometer (S3N) consisting of three slabs of liquid organic scintillator is described. A pulsed beam providing a broad spectrum of neutron energies is used to determine the detection efficiency of the spectrometer as a function of incident neutron energy and to measure the pulse height response matrix of the system. Neutron spectra can then be determined for beams with any kind of time structure by unfolding pulse height spectra measured by the S3N. Examples of fluence spectrum measurements in the energy range 20-150 MeV are presented.

Calibration↗
PubMed1986

Neutron dosimetry in the containment of a pressurized water reactor using a neutron-sensitive beta/gamma dosimetry system.

In this study the Panasonic UD-802 dosimeter was evaluated as a potential neutron dosimeter for use in the containment of a pressurized water reactor by comparing the results from the UD-802 with remmeter readings. The Panasonic UD-802 dosimeter is used routinely as a beta and gamma dosimeter but due to the natural Li and B in the thermoluminescent materials, it is also sensitive to neutrons. Since a dosimeter's response to neutrons is energy-dependent, proper calibration of the UD-802 in the environment for which it is to be used was an important consideration of the study. To calibrate the system, UD-802 dosimeters were mounted on polyethylene phantoms and irradiated to reference doses at selected locations in containment. The reference doses were determined based on remmeter dose-rate measurements and stay times. The thermoluminescent response of the dosimeters and the reference measurements were used to obtain a response ratio at each location. The average response ratio (unit of dosimeter response per millirem) was 3.7 and all response ratios were within +/-30% of this mean value. Specific characteristics of the UD-802 were also investigated, that is, the effects that dosimeter distance from the phantom and a person's movement through containment have on response. The dosimeter distance from the phantom was found to have a minimal effect on response, but the system was found to be dependent upon the angle of the phantom relative to the reactor core, necessitating a correction in the calibration factor. The overall conclusion of this study was that the Panasonic UD-802 dosimeter can be used for neutron dosimetry in containment of a pressurized water reactor.

Neutrons↗
PubMed2004

2003 review of neutron and non-neutron nuclear data.

This paper reviews the scientific literature for new measurements of both non-neutron and neutron nuclear data. Some of the highlights of this review are the following items. There was a withdrawal of a previous claim for discovery of element 118. There have been new measurements of some isotopic abundance values that have led to changes for many elements. There was a new set of recommended standards for calibration of gamma-ray energies published for many nuclides. There have been new half-life measurements reported for very short lived isotopes, for many long-lived nuclides, and for half-lives of double beta (betabeta) decay measurements for quasi-stable nuclides. There was also a new reassessment reported of spontaneous fission (sf) half-lives for ground state nuclides, which distinguished between the half-lives from sf decay and from cluster decay and from the new cluster-fission decay process. This review reports on various nuclear interactions such as charged particle cross sections (n,p) and (n,alpha) measurements for thermal neutrons incident on light nuclides. New thermal (n,gamma) cross sections and neutron resonance integrals that have been measured or re-evaluated are also presented.

Elements↗
PubMed2005

A comparison of the COG and MCNP codes in computational neutron capture therapy modeling, Part I: boron neutron capture therapy models.

The goal of this study was to evaluate the COG Monte Carlo radiation transport code, developed and tested by Lawrence Livermore National Laboratory, for neutron capture therapy related modeling. A boron neutron capture therapy model was analyzed comparing COG calculational results to results from the widely used MCNP4B (Monte Carlo N-Particle) transport code. The approach for computing neutron fluence rate and each dose component relevant in boron neutron capture therapy is described, and calculated values are shown in detail. The differences between the COG and MCNP predictions are qualified and quantified. The differences are generally small and suggest that the COG code can be applied for BNCT research related problems.

Body Burden↗
PubMedDate not supplied

The use of neutron and gamma ray spectral measurements and calculations to obtain dosimetric information for DT neutrons.

Neutron and gamma ray energy spectra were measured using an NE-213 scintillator at depths of 7.2, 15.2, and 22.2 cm in a tissue-equivalent phantom which was uniformly irradiated on one face by deuterium-tritium (DT) neutrons. Coupled neutron-gamma ray multigroup discrete ordinates calculations were performed using semi-infinite slab geometry. These calculations were used to supplement the measured spectra below 1 MeV. Similar calculations were performed to study the perturbation in the phantom due to the detector. The measured and calculated spectra were used to determine the kerma distributions for neutrons and gamma rays at each location. The gamma radiation was determined to contribute more than 10% of the total dose at each depth. The calculated kerma also reveals that a knowledge of the gamma ray spectra below 1 MeV is desirable.

Gamma Rays↗