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T T Hansen - One of the best experts on this subject based on the ideXlab platform.
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chemical abundances in the ultra faint dwarf galaxies grus i and triangulum ii Neutron Capture elements as a defining feature of the faintest dwarfs
The Astrophysical Journal, 2019Co-Authors: Alexander P Ji, Joshua D Simon, Anna Frebel, Kim A Venn, T T HansenAbstract:We present high-resolution of spectroscopy of four stars in two candidate ultra-faint dwarf galaxies (UFDs) Grus I (Gru I) and Triangulum II (Tri II). Neither object currently has a clearly determined velocity dispersion, placing them in an ambiguous region of parameter space between dwarf galaxies and globular clusters. No significant metallicity difference is found for the two Gru I stars, but both stars are deficient in Neutron-Capture elements. We verify previous results that Tri II displays significant spreads in metallicity and [$\alpha$/Fe]. Neutron-Capture elements are not detected in our Tri II data, but we place upper limits at the lower envelope of Galactic halo stars, consistent with previous very low detections. Stars with similarly low Neutron-Capture element abundances are common in UFDs, but rare in other environments. This signature of low Neutron-Capture element abundances traces chemical enrichment in the least massive star-forming dark matter halos, and further shows that the dominant sources of Neutron-Capture elements in metal-poor stars are rare. In contrast, all known globular clusters have similar ratios of Neutron-Capture elements to those of halo stars, suggesting that globular clusters form as part of relatively massive galaxies rather than in their own dark matter halos. The low Neutron-Capture element abundances may be the strongest evidence that Gru I and Tri II are (or once were) galaxies rather than globular clusters, and we expect future observations of these systems to robustly find non-zero velocity dispersions or signs of tidal disruption. However, the nucleosynthetic origin of this low Neutron-Capture element floor remains unknown.
Akira Matsumura - One of the best experts on this subject based on the ideXlab platform.
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boron Neutron Capture therapy for newly diagnosed glioblastoma
Radiotherapy and Oncology, 2009Co-Authors: Tetsuya Yamamoto, Hiroaki Kumada, Yasushi Shibata, Kei Nakai, Teruyoshi Kageji, Kiyoshi Endo, Masahide Matsuda, Akira MatsumuraAbstract:Abstract Purpose The efficacy, safety, and dose distribution of Neutron Capture therapy (NCT) were evaluated in 15 patients with newly diagnosed glioblastoma. Methods and materials Seven patients received intraoperative NCT (protocol-1) and eight patients received external beam NCT (protocol-2). Sulfhydryl borane (5g/body) was administered intravenously. Additionally, p -dihydroxyboryl-phenylalanine (250mg/kg) was given in protocol-2. The external beam NCT was combined with fractionated photon irradiation. Results Four of 15 patients were alive at analysis for a mean follow-up time from diagnosis of 23.0M. Twelve of the 15 patients were followed up for more than one year, and 10 (83.3%) of the 12 patients maintained their Karnofsky Performance Status (KPS; 90 in eight patients and 100 in two patients) at 12 months. The median overall survival and the time to tumor progression (TTP) for all patients were 25.7 and 11.9M, respectively. There was no difference in TTP between the protocol-1 (12.0M) and protocol-2 (11.9M). The 1- and 2-year survival rates were 80.0% and 53.3%, respectively. Three protocol-1 patients and one protocol-2 patient suffered transient orbital swelling accompanied by double vision (Grade 2); one of the three protocol-1 patients suffered post-epileptic brain swelling (Grade 4) requiring surgical intervention. Conclusion It is suggested that NCT is effective for survival of newly diagnosed glioblastoma with acceptable adverse effects. Because of the limitation of the present NCT pilot study without the contemporary control arm, it is unconvincing whether the Neutron Capture reaction led to distinct survival benefits, and further optimized studies on less invasive external beam NCT in large series of patients are warranted.
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boron Neutron Capture therapy for glioblastoma
Cancer Letters, 2008Co-Authors: Tetsuya Yamamoto, Kei Nakai, Akira MatsumuraAbstract:Abstract Boron Neutron Capture therapy (BNCT) theoretically allows the preferential destruction of tumor cells while sparing the normal tissue, even if the cells have microscopically spread to the surrounding normal brain. The tumor cell-selective irradiation used in this method is dependent on the nuclear reaction between the stable isotope of boron ( 10 B) and thermal Neutrons, which release α and 7 Li particles within a limited path length (−9 μm) through the boron Neutron Capture reaction, 10 B(n, α) 7 Li. Recent clinical studies of BNCT have focused on high-grade glioma and cutaneous melanoma; however, cerebral metastasis of melanoma, anaplastic meningioma, head and neck tumor, and lung and liver metastasis have been investigated as potential candidates for BNCT. To date, more than 350 high-grade gliomas have been treated in BNCT facilities worldwide. Current clinical BNCT trials for glioblastoma (GBM) have used the epithermal beam at a medically optimized research reactor, and p -dihydroxyboryl-phenylalanine (BPA) and/or sulfhydryl borane Na 2 B 12 H 11 SH (BSH) as the boron delivery agent(s). The results from these rather small phase I/II trials for GBM appear to be encouraging, but prospective randomized clinical trials will be needed to confirm the efficacy of this theoretically promising modality. Improved tumor-targeting boron compounds and optimized administration methods, improved boron drug delivery systems, development of a hospital-based Neutron source, and/or other combination modalities will enhance the therapeutic effectiveness of BNCT in the future.
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Characterization of Neutron Beams for Boron Neutron Capture Therapy: In-Air Radiobiological Dosimetry
Radiation Research, 2003Co-Authors: Tetsuya Yamamoto, Akira Matsumura, Kazuyoshi Yamamoto, Hiroaki Kumada, Naohiko Hori, Y. Torii, Yasushi Shibata, Tadao NoseAbstract:Abstract Yamamoto, T., Matsumura, A., Yamamoto, K., Kumada, H., Hori, N., Torii, Y., Shibata, Y. and Nose, T. Characterization of Neutron Beams for Boron Neutron Capture Therapy: In-Air Radiobiological Dosimetry. Radiat. Res. 160, 70–76 (2003). The survival curves and the RBE for the dose components generated in boron Neutron Capture therapy (BNCT) were determined separately in Neutron beams at Japan Research Reactor No. 4. The surviving fractions of V79 Chinese hamster cells with or without 10B were obtained using an epithermal Neutron beam (ENB), a mixed thermal-epithermal Neutron beam (TNB-1), and a thermal (TNB-2) Neutron beam; these beams were used or are planned for use in BNCT clinical trials. The cell killing effect of the Neutron beam in the presence or absence of 10B was highly dependent on the Neutron beam used and depended on the epithermal and fast-Neutron content of the beam. The RBEs of the boron Capture reaction for ENB, TNB-1 and TNB-2 were 4.07 ± 0.22, 2.98 ± 0.16 and 1.42 ± 0.07, respec...
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a new boronated porphyrin sta bx909 for Neutron Capture therapy an in vitro survival assay and in vivo tissue uptake study
Cancer Letters, 1999Co-Authors: Akira Matsumura, Yasushi Shibata, Kei Nakai, Takashi Yamamoto, Fumiyo Yoshida, Tomonori Isobe, Yoshinori Hayakawa, Minako Kiriya, Nobuhiro Shimojo, Koji OnoAbstract:A new boronated porphyrin compound (STA-BX909) was developed as a possible agent for boron Neutron Capture therapy. The boron concentration was measured by an in vivo rat experimental brain tumor model and an in vitro cell culture study. This agent was compared to sodium borocaptate (BSH) which has been used in clinical trials of boron Neutron Capture therapy. In the 9L rat brain tumor model, STA-BX909 achieved a higher boron tumor/blood ratio 24 h after injection in comparison to BSH. A boron concentration study in cultured glioma cell lines (U-251, U-87, 9L) demonstrated an increased boron concentration as a function of exposure time to STA-BX909, while the boron concentration remained stable with increasing exposure time to BSH. Use of a colony forming assay with thermal Neutron irradiation revealed more cytotoxicity with STA-BX909 than BSH when the same concentration of 10B was administered. We concluded that STA-BX909 may be an effective drug for use in boron Neutron Capture therapy and that it merits further investigation.
Jeffrey A Coderre - One of the best experts on this subject based on the ideXlab platform.
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the radiobiological principles of boron Neutron Capture therapy a critical review
Applied Radiation and Isotopes, 2011Co-Authors: J. W. Hopewell, G M Morris, Amanda E Schwint, Jeffrey A CoderreAbstract:The radiobiology of the dose components in a BNCT exposure is examined. The effect of exposure time in determining the biological effectiveness of γ-rays, due to the repair of sublethal damage, has been largely overlooked in the application of BNCT. Recoil protons from fast Neutrons vary in their relative biological effectiveness (RBE) as a function of energy and tissue endpoint. Thus the energy spectrum of a beam will influence the RBE of this dose component. Protons from the Neutron Capture reaction in nitrogen have not been studied but in practice protons from nitrogen Capture have been combined with the recoil proton contribution into a total proton dose. The relative biological effectiveness of the products of the Neutron Capture reaction in boron is derived from two factors, the RBE of the short range particles and the bio-distribution of boron, referred to collectively as the compound biological effectiveness factor. Caution is needed in the application of these factors for different normal tissues and tumors.
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functional and histological changes in rat lung after boron Neutron Capture therapy
Radiation Research, 2008Co-Authors: Jingli Liu Kiger, J. W. Hopewell, Kent J. Riley, O.k. Harling, P J Binns, W S Kiger, Hemant Patel, Paul M Busse, Jeffrey A CoderreAbstract:Abstract Kiger, J. L., Kiger, W. S., III, Riley, K. J., Binns, P. J., Patel, H., Hopewell, J. W., Harling, O. K., Busse, P. M. and Coderre, J. A. Functional and Histological Changes in Rat Lung after Boron Neutron Capture Therapy. Radiat. Res. 170, 60–69 (2008). The motivation for this work was an unexpected occurrence of lung side effects in two human subjects undergoing cranial boron Neutron Capture therapy (BNCT). The objectives were to determine experimentally the biological weighting factors in rat lung for the high-LET dose components for a retrospective assessment of the dose to human lung during cranial BNCT. Lung damage after whole-thorax irradiation was assessed by serial measurement of breathing rate and evaluation of terminal lung histology. A positive response was defined as a breathing rate 20% above the control group mean and categorized as occurring either early ( 110 days). The ED50 values derived from probit analyses of the early breathing rate dose–response data for ...
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boron Neutron Capture therapy cellular targeting of high linear energy transfer radiation
Technology in Cancer Research & Treatment, 2003Co-Authors: Jeffrey A Coderre, Kent J. Riley, O.k. Harling, J Turcotte, P J Binns, W S KigerAbstract:Boron Neutron Capture therapy (BNCT) is based on the preferential targeting of tumor cells with10 B and subsequent activation with thermal Neutrons to produce a highly localized radiation. In theor...
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performance of silicon microdosimetry detectors in boron Neutron Capture therapy
Radiation Research, 1999Co-Authors: P. D. Bradley, Anatoly B. Rosenfeld, Jeffrey A Coderre, Barry Allen, Jacek CapalaAbstract:Reverse-biased silicon p-n junction arrays using Silicon-On-Insulator technology have been proposed as microdosimeters. The performance of such detectors in boron Neutron Capture therapy (BNCT) is discussed. This work provides the first reported measurements using boron-coated silicon diode arrays as microdosimeters in BNCT. Results are in good agreement with measurements with gas proportional counters. Various boron-coating options are investigated along with device orientation effects. Finally, a 235 U coating is tested to simulate the behavior of the device in a heavy-ion therapy beam.
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the radiation biology of boron Neutron Capture therapy
Radiation Research, 1999Co-Authors: Jeffrey A Coderre, G M MorrisAbstract:Boron Neutron Capture therapy (BNCT) is a targeted radiation therapy that significantly increases the therapeutic ratio relative to conventional radiotherapeutic modalities. BNCT is a binary approach: A boron-10 (10B)-labeled compound is administered that delivers high concentrations of 10B to the target tumor relative to surrounding normal tissues. This is followed by irradiation with thermal Neutrons or epithermal Neutrons which become thermalized at depth in tissues. The short range (5-9 microm) of the alpha and 7Li particles released from the 10B(n,alpha)7Li Neutron Capture reaction make the microdistribution of 10B of critical importance in therapy. The radiation field in tissues during BNCT consists of a mixture of components with differing LET characteristics. Studies have been carried out in both normal and neoplastic tissues to characterize the relative biological effectiveness of each radiation component. The distribution patterns and radiobiological characteristics of the two 10B delivery agents in current clinical use, the amino acid p-boronophenylalanine (BPA) and the sulfhydryl borane (BSH), have been evaluated in a range of normal tissues and tumor types. Considered overall, BSH-mediated BNCT elicits proportionately less damage to normal tissue than does BNCT mediated with BPA. However, BPA exhibits superior in vivo tumor targeting and has proven much more effective in the treatment of brain tumors in rats. In terms of fractionation effects, boron Neutron Capture irradiation modalities are comparable with other high-LET radiation modalities such as fast-Neutron therapy. There was no appreciable advantage in increasing the number of daily fractions of thermal Neutrons beyond two with regard to sparing of normal tissue in the rat spinal cord model. The experimental studies described in this review constitute the radiobiological basis for the new BNCT clinical trials for glioblastoma at Brookhaven National Laboratory, at the Massachusetts Institute of Technology, and at the High Flux Reactor, Petten, The Netherlands. The radiobiology of experimental and clinical BNCT is discussed in detail.
Melanie Hampel - One of the best experts on this subject based on the ideXlab platform.
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the intermediate Neutron Capture process and carbon enhanced metal poor stars
The Astrophysical Journal, 2016Co-Authors: Maria Lugaro, Melanie Hampel, Richard J Stancliffe, Bradley S MeyerAbstract:Carbon-enhanced metal-poor (CEMP) stars in the Galactic Halo display enrichments in heavy elements associated with either the s (slow) or the r (rapid) Neutron-Capture process (e.g., barium and europium respectively), and in some cases they display evidence of both. The abundance patterns of these CEMP-s/r stars, which show both Ba and Eu enrichment, are particularly puzzling since the s and the r processes require Neutron densities that are more than ten orders of magnitude apart, and hence are thought to occur in very different stellar sites with very different physical conditions. We investigate whether the abundance patterns of CEMP-s/r stars can arise from the nucleosynthesis of the intermediate Neutron-Capture process (the i process), which is characterised by Neutron densities between those of the s and the r processes. Using nuclear network calculations, we study Neutron Capture nucleosynthesis at different constant Neutron densities n ranging from $10^7$ to $10^{15}$ cm$^{-3}$. With respect to the classical s process resulting from Neutron densities on the lowest side of this range, Neutron densities on the highest side result in abundance patterns that show an increased production of heavy s-process and r-process elements but similar abundances of the light s-process elements. Such high values of n may occur in the thermal pulses of asymptotic giant branch (AGB) stars due to proton ingestion episodes. Comparison to the surface abundances of 20 CEMP-s/r stars show that our modelled i-process abundances successfully reproduce observed abundance patterns that could not be previously explained by s-process nucleosynthesis. Because the i-process models fit the abundances of CEMP-s/r stars so well, we propose that this class should be renamed as CEMP-i.
Alexander P Ji - One of the best experts on this subject based on the ideXlab platform.
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chemical abundances in the ultra faint dwarf galaxies grus i and triangulum ii Neutron Capture elements as a defining feature of the faintest dwarfs
The Astrophysical Journal, 2019Co-Authors: Alexander P Ji, Joshua D Simon, Anna Frebel, Kim A Venn, T T HansenAbstract:We present high-resolution of spectroscopy of four stars in two candidate ultra-faint dwarf galaxies (UFDs) Grus I (Gru I) and Triangulum II (Tri II). Neither object currently has a clearly determined velocity dispersion, placing them in an ambiguous region of parameter space between dwarf galaxies and globular clusters. No significant metallicity difference is found for the two Gru I stars, but both stars are deficient in Neutron-Capture elements. We verify previous results that Tri II displays significant spreads in metallicity and [$\alpha$/Fe]. Neutron-Capture elements are not detected in our Tri II data, but we place upper limits at the lower envelope of Galactic halo stars, consistent with previous very low detections. Stars with similarly low Neutron-Capture element abundances are common in UFDs, but rare in other environments. This signature of low Neutron-Capture element abundances traces chemical enrichment in the least massive star-forming dark matter halos, and further shows that the dominant sources of Neutron-Capture elements in metal-poor stars are rare. In contrast, all known globular clusters have similar ratios of Neutron-Capture elements to those of halo stars, suggesting that globular clusters form as part of relatively massive galaxies rather than in their own dark matter halos. The low Neutron-Capture element abundances may be the strongest evidence that Gru I and Tri II are (or once were) galaxies rather than globular clusters, and we expect future observations of these systems to robustly find non-zero velocity dispersions or signs of tidal disruption. However, the nucleosynthetic origin of this low Neutron-Capture element floor remains unknown.
