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At least 163 records · Page 9Linked to original sources
PubMed1996

An improved neutron collimator for brain tumor irradiations in clinical boron neutron capture therapy.

To improve beam penetration into a head allowing the treatment of deeper seated tumors, two neutron collimators were built sequentially and tested for use in the clinical boron neutron capture therapy (BNCT) program at the epithermal neutron irradiation facility of the Brookhaven Medical Research Reactor. The collimators were constructed from lithium-impregnated polyethylene, which comprises Li2CO3 powder (approximately 93% enriched isotopic 6Li) uniformly dispersed in polyethylene to a total 6Li content of 7.0 wt. %. The first collimator is 7.6 cm thick with a conical cavity 16 cm in diameter on the reactor core side tapering to 8 cm facing the patient's head. The second collimator is 15.2 cm thick with a conical cavity 20 cm in diameter tapering to 12 cm. A clinical trial of BNCT for patients with malignant brain tumors is underway using the first collimator. Results of phantom dosimetry and Monte Carlo computations indicate that the new 15.2 cm thick collimator will improve the neutron beam penetration. Thus, the second collimator was made and will be used in an upcoming clinical trial. In-air and in-phantom mixed-field dosimetric measurements were compared to Monte Carlo computations for both collimators. The deeper penetration is achieved but at a sacrifice in beam intensity. In this report, a performance comparison of both collimators regarding various fluence rate and absorbed dose distributions in a head model is presented and discussed.

Biophysical Phenomena↗
PubMed1975

A new method for determining the neutron response function of "neutron insensitive" dosimeters. Method and preliminary determinations.

Charged-particle bombardment of thick beryllium targets produces a neutron yield varying with angle, and an isotropic gamma component. Differences in detector response in such a field are due to neutrons alone. With accurate neutron spectral distributions and measurements of detector response, a computer code can be used to determine the neutron sensitivity of the detector as a function of energy.

Computers↗
PubMed2005

Genotoxicity of neutrons in Drosophila melanogaster. Somatic mutation and recombination induced by reactor neutrons.

This paper describes the observation of a direct relationship between the absorbed doses of neutrons and the frequencies of somatic mutation and recombination using the wing somatic mutation and recombination test (SMART) of Drosophila melanogaster. This test was used for evaluating the biological effects induced by neutrons from the Triga Mark III reactor of Mexico. Two different reactor power levels were used, 300 and 1000 kW, and two absorbed doses were tested for each power level: 1.6 and 3.2 Gy for 300 kW and 0.84 and 1.7 Gy for 1000 kW. A linear relationship was observed between the absorbed dose and the somatic mutation and recombination frequencies. Furthermore, these frequencies were dependent on larval age: In 96-h-old larvae, the frequencies were increased considerably but the sizes of the spots were smaller than in 72-h-old larvae. The analysis of the balancer-heterozygous progeny showed a linear absorbed dose- response relationship, although the responses were clearly lower than found in the marker-trans-heterozygous flies. Approximately 65% of the genotoxicity observed is due to recombinational events. The results of the study indicate that thermal and fast neutrons are both mutagenic and recombinagenic in the D. melanogaster wing SMART, and that the frequencies are dependent on neutron dose, reactor power, and the age of the treated larvae.

Animals↗
PubMed1977

Effect of roentgen, cyclotron neutron, or mixed neutron-photon fractionated irradiation of mice. LD50/4 day values.

Mice were whole-body-irradiated with 5 fractions of roentgen rays in 5 days, 5 fractions of cyclotron neutrons in 5 days, or with mixed neutron-photon fractionated radiation, in the sequence n-n-x-x-x or n-x-x-x-n. The LD50/4 day values were determined. Roentgen rays and neutrons interact in the additive manner in the mixed fractionation schemes: effective dose per fraction is as predicted from the roentgen ray-only and neutron-only experiments. This essentially agrees with HENDRY et coll. (1976). However, no trend was found towards a less-than -additive effect which was observed by those authors and has also been suggested in skin response to mixed schemes (NELSON et coll. 1975).

Animals↗
PubMed1990

[Investigation on thermal-neutron sensitivity of commercial BeO(Na) thermoluminescence dosimeter and development of thermal-neutron insensitive BeO(Na) phosphors encapsulated in quartz-capillary].

BeO(Na) TLD on the market, UD-170 L, gives thermoluminescence response equivalent to irradiation with 3.2 +/- 0.5 cGy of 60Co gamma-rays after irradiation with 10(10) thermal neutrons per cm2. Because of this neutron sensitivity, UD-170 L is not suitable for measurement of gamma-rays in gamma-neutron mixed radiation from a nuclear reactor of Kinki University when we use it for radiobiological research. To reduce this troublesome sensitivity, we replaced the glass capillary used for UD-170 L with a quartz capillary. Quartz tube encapsulated BeO(Na) showed a markedly reduced response to thermal neutrons.

Equipment Design↗
PubMed1992

Cytogenetic effect of 235U neutrons and d(50)+Be fast neutrons.

Induction of chromosome aberrations in G0 lymphocytes of peripheral human blood exposed to 235U and d(50)+Be neutron radiation was studied. Dose--effect relationships for different types of chromosome aberrations were analyzed. Linear dependence of the effect was established for the studied neutron radiation, except for the yield of dicentrics exposed to d(50)+Be neutrons. Accordingly to the yield of dicentrics, the relative biological efficiency (RBE) of 235U and d(50)+Be neutrons was 19.5 and 4.14, respectively.

Beryllium↗
PubMed1982

[Relative biological effectiveness (RBE) of d(50)-Be neutrons (Louvain-la-Neuve) and p(34)-Be neutrons (Orleans) for early intestinal tolerance in mice].

This paper compares the RBE of a neutron beam produced by 50 MeV deuterons on beryllium [d(50)-Be] at the cyclotron CYCLONE of Louvain-La-Neuve and of a neutron beam produced by 34 MeV protons on beryllium [p(34)-Be] of the Hôpital Régional d'Orléans. Early intestinal tolerance in mice was choosen as biological criterium; it is derived from LD50 determination after single and fractionated abdominal irradiation. For d(50)-Be neutrons, RBE was 1.8 +/- 0.2 (with respect to 60Co gamma-rays) for a single fraction. It increases up to 2.1 +/- 0.2 for an irradiation in 2 fractions (3.5 h interval) and reaches 2.5 +/- 0.3, 2.7 +/- 0.3 and 2.5 +/- 0.3 for irradiations in 10 fractions (7 and 3.5 h interval) and 20 fractions (3.5 h interval) respectively. RBE values observed for p(34)-Be neutrons (with respect to 60Co gamma-rays) are not significantly different. For a single fraction RBE = 1.7 +/- 0.2 and for 2 fractions (3.5 h interval) RBE = 2.0 +2- 0.2.

Animals↗
PubMed1988

A new monitoring system for the thermal neutron fluence rate and gamma dose rate in boron neutron capture therapy.

A new monitoring system for the thermal neutron fluence rate and gamma dose rate is described for boron neutron capture therapy (BNCT). A small pn junction Si diode was used as a new detector which was mechanically stronger and had better stability than a surface barrier detector. The pulse height of signals due to thermal neutrons was sufficiently high and was separated from signals due to gamma rays. The radiation damage to the detectors which results in a reduction of the pulse height was found to be quite small. By using the detectors, the thermal neutron fluence rate and gamma dose rate, not only in the head but also in the body, were measured simultaneously during therapy, and the new system has been efficiently used for BNCT of brain tumours.

Humans↗
PubMedDate not supplied

Clinical review of the Japanese experience with boron neutron capture therapy and a proposed strategy using epithermal neutron beams.

Our concept of boron neutron capture therapy (BNCT) is selective destruction of tumor cells using the heavy-charged particles yielded through 10B(n, alpha)7 Li reactions. To design a new protocol that employs epithermal neutron beams in the treatment of glioma patients, we examined the relationship between the radiation dose, histological tumor grade, and clinical outcome. Since 1968, 183 patients with different kinds of brain tumors were treated by BNCT; for this retrospective study, we selected 105 patients with glial tumors who were treated in Japan between 1978 and 1997. In the analysis of side effects due to radiation, we included all the 159 patients treated between 1977 and 2001. With respect to the radiation dose (i.e. physical dose of boron n-alpha reaction), the new protocol prescribes a minimum tumor volume dose of 15 Gy or, alternatively, a minimum target volume dose of 18 Gy. The maximum vascular dose should not exceed 15 Gy (physical dose of boron n-alpha reaction) and the total amount of gamma rays should remain below 10 Gy, including core gamma rays from the reactor and capture gamma in brain tissue. The outcomes for 10 patients who were treated by the new protocol using a new mode composed of thermal and epithermal neutrons are reported.

Adolescent↗
PubMed2004

A shielding design for an accelerator-based neutron source for boron neutron capture therapy.

Research in boron neutron capture therapy (BNCT) at The Ohio State University Nuclear Engineering Department has been primarily focused on delivering a high quality neutron field for use in BNCT using an accelerator-based neutron source (ABNS). An ABNS for BNCT is composed of a proton accelerator, a high-energy beam transport system, a (7)Li target, a target heat removal system (HRS), a moderator assembly, and a treatment room. The intent of this paper is to demonstrate the advantages of a shielded moderator assembly design, in terms of material requirements necessary to adequately protect radiation personnel located outside a treatment room for BNCT, over an unshielded moderator assembly design.

Boron Neutron Capture Therapy↗
PubMed2004

Radiation injury of boron neutron capture therapy using mixed epithermal- and thermal neutron beams in patients with malignant glioma.

The purpose of this study was to clarify the radiation injury in acute or delayed stage after boron neutron capture therapy (BNCT) using mixed epithermal- and thermal neutron beams in patients with malignant glioma. Eighteen patients with malignant glioma underwent mixed epithermal- and thermal neutron beam and sodium borocaptate between 1998 and 2004. The radiation dose (i.e. physical dose of boron n-alpha reaction) in the protocol used between 1998 and 2000 (Protocol A, n = 8) prescribed a maximum tumor volume dose of 15 Gy. In 2001, a new dose-escalated protocol was introduced (Protocol B, n = 4); it prescribes a minimum tumor volume dose of 18 Gy or, alternatively, a minimum target volume dose of 15 Gy. Since 2002, the radiation dose was reduced to 80-90% dose of Protocol B because of acute radiation injury. A new Protocol was applied to 6 glioblastoma patients (Protocol C, n = 6). The average values of the maximum vascular dose of brain surface in Protocol A, B and C were 11.4+/-4.2 Gy, 15.7+/-1.2 and 13.9+/-3.6 Gy, respectively. Acute radiation injury such as a generalized convulsion within 1 week after BNCT was recognized in three patients of Protocol B. Delayed radiation injury such as a neurological deterioration appeared 3-6 months after BNCT, and it was recognized in 1 patient in Protocol A, 5 patients in Protocol B. According to acute radiation injury, the maximum vascular dose was 15.8+/-1.3 Gy in positive and was 12.6+/-4.3 Gy in negative. There was no significant difference between them. According to the delayed radiation injury, the maximum vascular dose was 13.8+/-3.8 Gy in positive and was 13.6+/-4.9 Gy in negative. There was no significant difference between them. The dose escalation is limited because most patients in Protocol B suffered from acute radiation injury. We conclude that the maximum vascular dose does not exceed over 12 Gy to avoid the delayed radiation injury, especially, it should be limited under 10 Gy in the case that tumor exists in speech center.

Adult↗
PubMed2004

GE PETtrace cyclotron as a neutron source for boron neutron capture therapy.

This paper discusses the use of a General Electric PETtrace cyclotron as a neutron source for boron neutron capture therapy. In particular, the standard PETtrace (18)O target is considered. The resulting dose from the neutrons emitted from the target is evaluated using the Monte Carlo radiation transport code MCNP at different depths in a brain phantom. MCNP-simulated results are presented at 1, 2, 3, 4, 5, 6, 7, and 8 cm depth inside this brain phantom. Results showed that using a PETtrace cyclotron in the current configuration allows treating tumors at a depth of up to 4 cm with reasonable treatment times. Further increase of a beam current should significantly improve the treatment time and allow treating tumors at greater depths.

Boron Neutron Capture Therapy↗
PubMed2004

A conceptual design of a beam-shaping assembly for boron neutron capture therapy based on deuterium-tritium neutron generators.

A conceptual design of a beam-shaping assembly for boron neutron capture therapy using deuterium-tritium accelerator based neutrons source is developed. Calculations based on a simple geometry model for the radiation transport are initially performed to estimate the assembly materials and their linear dimensions. Afterward, the assembly geometry is produced, optimized and verified. In order to perform these calculations the general-purpose MCNP code is used. Irradiation time and therapeutic gain are utilized as beam assessment parameters. Metallic uranium and manganese are successfully tested for fast-to-epithermal neutron moderation. In the present beam-shaping assembly proposal, the therapeutic gain is improved by 23% and the accelerator current required for a fixed irradiation period is reduced by six times compared to previous proposals based on the same D-T reaction.

Boron Neutron Capture Therapy↗
PubMedDate not supplied

Neutron energy spectra and dose-distribution spectra of cyclotron-produced neutron beams.

Neutron energy spectra and spectra of dose deposition in tissue-equivalent material have been measured for neutron sources produced by 16-, 22-, 35-, and 45.5-MeV deuterons and 22.5-, 35-, 45-, and 65.5-MeV protons incident upon a thick beryllium target. Neutron spectra were measured using time-of-flight techniques and the dose distribution was measured using a 1/2 in. spherical "tissue-equivalent" proportional counter filled with "tissue-equivalent" gas.

Beryllium↗
PubMedDate not supplied

Neutron dose equivalent next to the target shield of a neutron therapy facility using an LET counter.

The use of a spherical tissue-equivalent proportional counter for measurements of the lineal energy (y) and derivations of the linear energy transfer (LET) for fast neutrons has the advantage of giving distributions of dose and dose equivalent as functions of either LET or y. A measurement next to the target shielding of the neutron therapy facility at the University of Chicago Hospitals and Clinics (UCHC) is described, and the data processing is outlined. The distributions are presented and compared to those from measurements in the neutron beam. The average quality factors are presented.

Energy Transfer↗
PubMed1997

Study of boron neutron capture therapy used neutron source with protons bombarding a thick 9Be target.

Neutron sources created by 4-, 3.5-, and 3-MeV protons striking a thick beryllium target were studied via the time-of-flight technique. Protons were accelerated by the Peking University 4.5 MV electrostatic accelerator. Two disk-shaped 9Be targets with thickness 1.5 and 3 mm were used in the measurements. The time-of-flight spectra were observed at zero degrees with respect to the incident proton beam. The analysis to these time-of-flight spectra is given. The time-of-flight spectra were converted to the energy spectra and compared to a neutron spectrum of 7Li(p, n)7 Be reaction with incident energy 2.5 MeV, which was also measured in this work. Restricted by the spectrometer itself, the threshold of the measurements is 400 keV. The results show that by using several MeV protons bombarding a thick beryllium target, reactions other than 9Be(p, n)9B produce significant contributions to the neutron yield with energy less than 1 MeV.

Beryllium↗
PubMed2001

Determination of radionuclides produced by neutrons in heavily exposed workers of the JCO criticality accident in Tokai-mura for estimating an individual's neutron fluence.

In the Tokai-mura criticality accident, three workers were heavily exposed. Biological materials, such as blood, urine, vomit and hair, were collected from the workers and analyzed for radioactivities, produced by the neutron irradiation. Activation products. such as 24Na, -K and 82Br, were found in these materials by gamma-ray spectrometry. The radionuclide of the highest activity observed in biological materials was 24Na, e.g. the concentrations of this nuclide in the blood samples from the three patients at the accident time were 169, 92 and 23 Bq/ml, respectively. The concentrations of stable sodium in the same samples were determined by ICP-AES to obtain specific activities of 24Na (concentration ratio between the produced 24Na and stable 23Na), which are essential for estimating the neutron fluences and radiation doses. The specific activities of 24Na obtained for the three patients through the blood analysis were 8.2 x 10(4),4.3 x 10(4) and 1.2 x 10(4) Bq24Na/g23Na. Based on these values, individual's neutron fluences were estimated to be 5.7 x 10(11), 3.0 x 10(-1) and 0.85 x 10(11) cm(-2), respectively.

Adult↗
PubMed1986

The value of neutron- and neutron-boost irradiation for the local control of advanced soft tissue sarcomas.

An analysis of neutron- and neutron-boost irradiation of 191 patients with soft tissue sarcomas is given. 101 patients had T3 (IVA) tumours. The actuarial disease free survival rate of all stages at 6.5 years is 59.8%. Patients with T1 and T2 tumours fared significantly better (73.5%) than patients with T3 tumours (31.3%, p = 0.016). Similar difference are seen according to grade, i.e. 75.1% for G1, 48.3% for G2 (p = 0.035) and 30.9% for G3 tumours (p = 0.024). Patients without microscopic tumour residue fared best (84%), followed by patients with microscopic tumour (72.3%) and patients with gross tumour (29.8%) left behind (p = 0.0003). A functional limb was preserved in 80.5% of patients with extremity lesions (95/118), 50 of them had T3-lesions. The highest local control rate of 76.5% was seen after neutron therapy of differentiated gross tumours. This finding underlines the biological advantage of densely ionizing radiation qualities in these tumours.

Combined Modality Therapy↗