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At least 109 records · Page 6Linked to original sources
PubMed2002

In-phantom two-dimensional thermal neutron distribution for intraoperative boron neutron capture therapy of brain tumours.

The aim of this study was to determine the in-phantom thermal neutron distribution derived from neutron beams for intraoperative boron neutron capture therapy (IOBNCT). Gold activation wires arranged in a cylindrical water phantom with (void-in-phantom) or without (standard phantom) a cylinder styrene form placed inside were irradiated by using the epithermal beam (ENB) and the mixed thermal-epithermal beam (TNB-1) at the Japan Research Reactor No 4. With ENB, we observed a flattened distribution of thermal neutron flux and a significantly enhanced thermal flux delivery at a depth compared with the results of using TNB-1. The thermal neutron distribution derived from both the ENB and TNB-1 was significantly improved in the void-in-phantom, and a double high dose area was formed lateral to the void. The flattened distribution in the circumference of the void was observed with the combination of ENB and the void-in-phantom. The measurement data suggest that the ENB may provide a clinical advantage in the form of an enhanced and flattened dose delivery to the marginal tissue of a post-operative cavity in which a residual and/or microscopically infiltrating tumour often occurs. The combination of the epithermal neutron beam and IOBNCT will improve the clinical results of BNCT for brain tumours.

Boron Neutron Capture Therapy↗
PubMed2004

A parameter study to determine the optimal source neutron energy in boron neutron capture therapy of brain tumours.

The values of the parameters used in boron neutron capture therapy (BNCT) to calculate a given dose to human tissue vary with patients due to different physical, biological and/or medical circumstances. Parameters include the tissue dimensions, the 10B concentration and the relative biological effectiveness (RBE) factors for the different dose components associated with BNCT. Because there is still no worldwide agreement on RBE values, more often than not, average values for these parameters are used. It turns out that the RBE-problem can be circumvented by taking into account all imaginable parameter values. Approaching this quest from another angle: the outcome will also provide the parameters (and values) which influence the optimal source neutron energy. For brain tumours it turns out that the 10B concentration, the RBE factors for 10B as well as fast neutrons, together with the dose limit set for healthy tissue, affect the optimal BNCT source neutron energy. By using source neutrons of a few keV together with neutrons of a few eV, it ensures that, under all imaginable circumstances, a maximum of alpha (and lithium) particles can be delivered in the tumour.

Algorithms↗
PubMedDate not supplied

Increased neutron penetration in partially deuterated water: application to neutron capture therapy.

Theoretically, partial deuteration of body water should allow significantly increased neutron penetration in tissue. To evaluate the possible usefulness of partially deuterated water in neutron capture therapy (NCT), neutron flux density distributions were measured in a 23 x 16.5 cm (length x diameter) cylinder for incident thermal and epithermal neutron beams, at 20 and 40 at. % deuteration of water. Relative to neutron flux densities in nondeuterated water, flux densities increased significantly with increasing depth and increasing levels of deuteration. For example, at a depth of 6 cm, flux density was increased approximately 20% to 50% for 20 to 40 at. % deuteration. In a clinical situation, this would increase tumor dose by approximately 30%. Further benefits include the reduced hydrogen neutron capture and the chemical radioprotective effects of partial deuteration for photon radiation.

Body Water↗
PubMed2000

Development and construction of a neutron beam line for accelerator-based boron neutron capture synovectomy.

A potential application of the 10B(n, alpha)7Li nuclear reaction for the treatment of rheumatoid arthritis, termed Boron Neutron Capture Synovectomy (BNCS), is under investigation. In an arthritic joint, the synovial lining becomes inflamed and is a source of great pain and discomfort for the afflicted patient. The goal of BNCS is to ablate the synovium, thereby eliminating the symptoms of the arthritis. A BNCS treatment would consist of an intra-articular injection of boron followed by neutron irradiation of the joint. Monte Carlo radiation transport calculations have been used to develop an accelerator-based epithermal neutron beam line for BNCS treatments. The model includes a moderator/reflector assembly, neutron producing target, target cooling system, and arthritic joint phantom. Single and parallel opposed beam irradiations have been modeled for the human knee, human finger, and rabbit knee joints. Additional reflectors, placed to the side and back of the joint, have been added to the model and have been shown to improve treatment times and skin doses by about a factor of 2. Several neutron-producing charged particle reactions have been examined for BNCS, including the 9Be(p,n) reaction at proton energies of 4 and 3.7 MeV, the 9Be(d,n) reaction at deuteron energies of 1.5 and 2.6 MeV, and the 7Li(p,n) reaction at a proton energy of 2.5 MeV. For an accelerator beam current of 1 mA and synovial boron uptake of 1000 ppm, the time to deliver a therapy dose of 10,000 RBEcGy ranges from 3 to 48 min, depending on the treated joint and the neutron producing charged particle reaction. The whole-body effective dose that a human would incur during a knee treatment has been estimated to be 3.6 rem or 0.75 rem, for 1000 ppm or 19,000 ppm synovial boron uptake, respectively, although the shielding configuration has not yet been optimized. The Monte Carlo design process culminated in the construction, installation, and testing of a dedicated BNCS beam line on the high-current tandem electrostatic accelerator at the Laboratory for Accelerator Beam Applications at the Massachusetts Institute of Technology.

Animals↗
PubMed1984

Radiotherapy of soft tissue sarcomas with neutrons or a neutron boost.

A cooperative trial of neutron therapy for soft tissue sarcomas was started in 1978. 112 unselected and not previously irradiated patients (62% T3 tumours, 35% recurrent tumours) were treated up to June 1982 with neutrons alone. An analysis of these cases with a mean follow-up period of 22 months (range 12 to 45 months) is given in this report. Very preliminary results are presented for 60 patients treated with a neutron boost only. These showed a substantially lower complication rate. The major results of this phase II trial are: The survival rate of 3.5 years was strongly dependent on the stage of the tumour; for 8 patients with T1 tumours it was 100%, for 35 patients with T2 tumours, 77%, and for 69 patients with T3 tumours, 45%. The survival rate at 3.5 years was strongly dependent on surgery before the beginning of radiotherapy; for 54 patients after surgery without clinical evidence of residual tumour it was 73%, for 58 patients with inoperable primary or recurrent tumour, 47%. The survival rate of 31 patients with recurrence after neutron therapy was only 36%. The overall rate of serious complications was 28.6% after neutron therapy, but only 5% after neutron boost therapy (mean follow-up period: 12 months, range 5 to 48 months).

Follow-Up Studies↗
PubMed1990

Long term results of neutron- and neutron-boost irradiation of soft tissue sarcomas.

The five-year follow-up results of 221 patients treated with neutrons or a neutron-boost at the West German Tumour Centre, Essen, are presented. 94 patients with gross tumour were treated with neutrons alone. 127 patients without gross tumour left behind post surgery were irradiated using a "mixed beam" schedule. The disease-free survival rate at five years is 62.6% for T1-, 71.5% for T2- and 28.7% for T3-tumours (p = 0.016). Significant differences were also found for various grades, i.e. 73.3% for G1-, 47.7% for G2- (p = 0.035) and 22.4% for G3-tumours (p = 0.024). Patients without microscopic tumour residue fared best with a survival rate of 86.6%, followed by patients with microscopic tumour (65.5%; p = 0.042) and patients with gross tumour (25.5%; p = 0.003) left behind. A functional limb was preserved in 86% of the patients with extremity lesions. The local control rate of patients with gross tumour was 76.5% compared with 53% in previous photon series. This finding underlines the potential biological advantage of neutrons in these tumours. Serious side effects ranged from 28% in the patients treated with neutrons for large volumes to 7% in patients treated with a neutron boost.

Evaluation Studies as Topic↗
PubMedDate not supplied

[Relative biological effectiveness of gamma-neutron irradiation with neutron energy of 0.9 MeV].

Relative biological effectiveness (RBE) of gamma-neutron radiation with neutron energy of 0.9 MeV was estimated with a reference to rat death. It was shown that RBE of gamma-neutron radiation (the share of neutrons was 67% as related to dose) at LD33/30 and LD100/30 was 2, and RBE of 0.9 MeV neutrons, in experiments with mixed radiation, was 3.1 and 2.86 at LD33/30 and LD100/30, respectively. The value of a maximum dose at which death was not registered during 30 days, was 1 Gy with gamma-neutron radiation and 4 Gy with X-radiation.

Animals↗
PubMed1995

Monte Carlo simulation of the biological effects of boron neutron capture irradiation with d(14)+Be neutrons in vitro.

It was shown that radiation effects in tumor cells treated with fast neutrons may be increased by the neutron capture reaction 10B(n, alpha)7Li. The classic approach for macroscopic dosimetry in fast-neutron therapy cannot be applied to the dose in boron neutron capture therapy (BNCT). The effectiveness of BNCT in killing tumor cells depends on the number of 10B atoms delivered to the tumor, the subcellular distribution of 10B and the thermal neutron fluence at the site of the tumor. Monte Carlo calculations of the energy depositions of short-range particles with high LET coming from 10B disintegrations were performed and compared to the observed biological effects. The simulation allows us to study the influence of the localization of intracellular 10B in the nucleus, cytoplasma, plasma membrane or extracellular space. The biological response function which describes the probability of the lethal effect produced by a single particle track through the cell nucleus was found by comparing the calculated microscopic dose distribution spectra for single events with the survival observed experimentally. Calculations for a human melanoma cell population treated as a monolayer in the presence or absence of boron with d(14)+Be neutrons will be demonstrated. Two different boron compounds enriched in 10B were investigated in this study: boric acid (H3 10BO3) and p-dihydroxyboryl phenylalanine (BPA). The study shows that a high fraction of BPA enters the cytoplasm while boric acid was found only in the extracellular space. The computer simulations indicate that BPA yields a higher potential effectiveness for inactivation of melanoma cells than boric acid.

Boron Neutron Capture Therapy↗
PubMed1978

Neutron uniformity studies related to clinical total body in vivo neutron activation analysis.

Methods of assessing the uniformity of thermal and fast neutron fluence in relation to total body in vivo neutron activation analysis are described. Results are presented for 14 MeV neutrons emitted by sealed tube generators housed in a massive concrete shield, representing a substantial source of neutrons degraded in energy. Optimisation of conditions for patient irradiations is discussed and it is shown that acceptable uniformity of fluence can be achieved with little or no premoderation of the incident neutrons.

Activation Analysis↗
PubMed2000

Neutron radii in nuclei and the neutron equation of state.

The root-mean-square radius for neutrons in nuclei is investigated in the Skyrme Hartree-Fock model. The main source of theoretical variation comes from the exchange part of the density-dependent interaction which can be related to a basic property of the neutron equation of state. A precise measurement of the neutron radius in 208Pb would place an important new constraint on the equation of state for neutron matter. The Friedman-Pandharipande neutron equation of state would lead to a very precise value of 0.16+/-0.02 fm for the difference between the neutron and the proton root-mean-square radius in 208Pb.

Journal Article↗
PubMed2001

Neutron star structure and the neutron radius of 208Pb.

We study relationships between the neutron-rich skin of a heavy nucleus and the properties of neutron-star crusts. Relativistic effective field theories with a thicker neutron skin in 208Pb have a larger electron fraction and a lower liquid-to-solid transition density for neutron-rich matter. These properties are determined by the density dependence of the symmetry energy which we vary by adding nonlinear couplings between isoscalar and isovector mesons. An accurate measurement of the neutron radius in 208Pb-via parity violating electron scattering-may have important implications for the structure of the crust of neutron stars.

Journal Article↗
PubMed1990

Preclinical studies with the Faure high energy neutron facility: response of pig skin to fractionated doses of fast neutrons (66 MeVp----Be).

The early and late responses of pig skin to fractionated doses of both unfiltered and filtered (i.e. hardened) neutrons using the Faure neutron therapy facility (66 MeVp----Be) were determined and compared with those following fractionated doses with 60Co gamma-rays. Dose-effect curves for the quantal responses of moist desquamation (early epithelial response) and dermal necrosis (late response) were fitted by probit analysis and ED50 values obtained. For a neutron fractionation scheme comprised of 12 fractions in 26 days, and using an unfiltered beam, the ED50 values for moist desquamation and dermal necrosis were 18.67 +/- 2.22 and 22.25 +/- 0.48 Gy, respectively, whereas in the case of the filtered beam, the corresponding ED50 values were 24.78 +/- 1.44 and 23.30 +/- 0.47 Gy. In order to provide a comparison, the values for 24 fractions of 60Co gamma-rays given in 39 days (a clinical protocol used in the Groote Schuur Hospital) were 74.02 +/- 2.92 and 66.72 +/- 1.93 Gy for moist desquamation and dermal necrosis, respectively. For the unfiltered beam, values for the comparative biological effectiveness (CBE) were 3.96 and 3.00 for the early and late skin response, respectively. The corresponding CBE values were for the filtered beam 2.99 and 2.86. These results for the Faure neutron therapy facility can be extrapolated to the human situation with a high degree of confidence, so that the neutron dose which would yield acceptable skin damage in patients may be determined using the data presented here.

Animals↗
PubMed1991

Effects of target shape and neutron scattering on element sensitivities for neutron-capture prompt gamma-ray activation analysis.

Results are presented for a study of the effects of neutron scattering by hydrogen on element sensitivities for in-beam neutron capture prompt gamma-ray activation analysis. In a scattering matrix, sensitivities vary as a function of both the scattering density, i.e., the number of scatters per unit volume and the magnitude of scattering cross sections, and the target geometry, i.e., the target shape and orientation with respect to the neutron beam. Element sensitivities (counts.s-1.mg-1) increased linearly with H density (g.mL-1) for H, B, Na, Cl, K, Mn, Br, Ag, Cd, I, Sm, and Gd, measured for liquids packaged in Teflon bags. Nine of the 12 elements studied had 1.69 +/- 0.18% sensitivity enhancement per percent increase in H density. Samarium sensitivity was enhanced by only 0.54 +/- 0.07%/% H, which may indicate that neutron scattering by H causes a shift in the energy distribution of the neutrons. Manganese sensitivity was enhanced by 2.44 +/- 0.26%/% H. The enhancement of the sensitivity for H itself varied with matrix composition. For several series of disk-shaped, solid, hydrogenous targets, element sensitivities increased with decreasing target thickness until, at some limiting thickness, this trend was reversed. Consistent with theory, sensitivities measured for spherical hydrogenous targets showed no enhancement.

Chlorine↗
PubMed1995

An expression for the RBE of neutrons as a function of neutron energy.

The goal of this paper is to develop a relationship between a neutron RBE and neutron energy, En, which can be used to design neutron sources for BNCT. In an earlier calculation of a neutron RBE as a function of En, we approximated the contribution to a total neutron RBE, RBEt (En), arising from 14N(n,p)14C reactions. In this paper, we recalculate RBEt (En), accounting more exactly for the contribution to RBEt (En) from 14N(n,p)14C reactions.

Animals↗
PubMed1998

Designing accelerator-based epithermal neutron beams for boron neutron capture therapy.

The 7Li(p,n)7Be reaction has been investigated as an accelerator-driven neutron source for proton energies between 2.1 and 2.6 MeV. Epithermal neutron beams shaped by three moderator materials, Al/AlF3, 7LiF, and D2O, have been analyzed and their usefulness for boron neutron capture therapy (BNCT) treatments evaluated. Radiation transport through the moderator assembly has been simulated with the Monte Carlo N-particle code (MCNP). Fluence and dose distributions in a head phantom were calculated using BNCT treatment planning software. Depth-dose distributions and treatment times were studied as a function of proton beam energy and moderator thickness. It was found that an accelerator-based neutron source with Al/AlF3 or 7LiF as moderator material can produce depth-dose distributions superior to those calculated for a previously published neutron beam design for the Brookhaven Medical Research Reactor, achieving up to approximately 50% higher doses near the midline of the brain. For a single beam treatment, a proton beam current of 20 mA, and a 7LiF moderator, the treatment time was estimated to be about 40 min. The tumor dose deposited at a depth of 8 cm was calculated to be about 21 Gy-Eq.

Aluminum↗
PubMed2002

Direct effect in DNA radiolysis. Boron neutron capture enhancement of radiolysis in a medical fast-neutron beam.

SècheThis paper is devoted to the study of the molecular basis of the boron neutron capture enhancement of fast-neutron radiotherapy. Plasmid DNA was irradiated with a medical fast-neutron beam in the presence of either (10)B or (11)B. The number of induced SSBs and DSBs was much higher in samples containing (10)B compared to (11)B. The additional breaks are attributed to the nuclear reaction (10)B(n, alpha)(7)Li induced by the capture by (10)B of thermal neutrons produced in the medium by scattering and slowing down of neutrons. Irradiation in the presence of DMSO (OH radical scavenger) allows the number of nonscavengeable breaks to be determined. The ratio DSB/SSB is within the range of those observed with heavy ions, in good agreement with the hypothesis that the additional breaks are due to alpha particles and recoil lithium nuclei. The simulation of the energy deposition along the paths of the alpha and (7)Li particles allows the calculation of core and penumbra track volumes. Further, the number of plasmids encountered by the core and the penumbra was evaluated. Their number was compared to the nonscavengeable additional breaks. Since the two sets of values are of the same order of magnitude, we conclude that the nonscavengeable additional SSBs and DSBs could be due to direct effects.

Alpha Particles↗
PubMed1994

Enhancement of fast neutron beams with boron neutron capture therapy. A mechanism for achieving a selective, concomitant tumor boost.

Both fast neutron radiotherapy and boron neutron capture therapy (BNCT) have been utilized to treat malignant disease. Herein we discuss the potential of combining these treatments to enhance the effectiveness of fast neutron therapy through a concomitant BNCT boost. Using a fast neutron beam generated from a 50 MeV proton on beryllium reaction, we have determined that 0.1% of the beam per microgram of boron-10 per gram of tissue (microgram/g) can be deposited via BNCT. Our mathematical modeling predicts that BNCT enhancement of our beam will lead to an additional 1-2 logs of tumor cell kill for boron-10 concentrations of 30-50 micrograms/g. We have validated this via V-79 cell line in vitro measurements. A Poisson model estimation of how this additional cell kill will influence local tumor control, predicts that BNCT enhancement of fast neutron radiation will lead to a clinically significant improvement in outcome.

Animals↗
PubMed1996

In vivo neutron activation analysis of sodium and chlorine in tumor tissue after fast neutron therapy.

In 12 patients with recurrences and metastases of different primaries (head and neck cancer, breast cancer, malignant melanoma, and osteosarcoma) who were treated with reactor fission neutrons the photon emission of irradiated tissue was measured after each radiotherapy fraction. Spectral analyses of the decay rates resulted in data for the exchange of sodium (Na) and chlorine (Cl) between the irradiated tissue and the body. About 60% of Na and Cl exchanged rapidly with a turnover half-life of 13 +/- 2 min. New defined mass exchange rates for Na and Cl amount to an average of 0.8 mval/min/kg of soft tissue. At the beginning of radiotherapy the turnover of the electrolytes in tissues with large tumor volumes was about twice that in tissues with small tumor volumes. Depending on the dose, neutron therapy led in all cases to variation in the metabolism. A maximum of Cl exchange and a minimum of Na exchange occurred after 10 Gy of neutrons (group of six previously untreated patients) or after 85 Gy (photon equivalent dose) of combined photon-neutron therapy. A significant increase in non-exchangeable fraction of Na from about 40 to 80% was observed in three tumors after a neutron dose of 10 Gy administered in five fractions correlated with a rapid reduction of tissue within 4 weeks after end of therapy. These results demonstrate for the first time the local response of the electrolyte metabolism to radiotherapy.

Chlorides↗