EXAFS study of rubidium-doped single-wall carbon nanotube bundles

International audienceThe local structure around the rubidium ions inserted in single-wall carbon nanotube bundles (Rb-doped SWCNT) is studied by Rb K-edge extended x-ray-absorption fine structure (EXAFS). The dependence of the local order around the rubidium ions is investigated as a function of the time of doping (i.e., as a function of the stoichiometry of the sample). The first coordination shell of the rubidium ions, related to the distance between rubidium and the first nearest-neighboring carbon atoms, has a clear time doping dependence. Comparison between ab initio simulations of the EXAFS spectra and experimental data questions the interstitial site (between three tubes) as the preferential insertion site in SWCNT bundles. The results indicate that the rubidium ions are mainly located inside the tubes and around the bundles. The results are in good agreement with combined x-ray and neutron diffraction experiments performed on the same samples

Lattice Displacements Above Tc in the Layered Manganite La1.2Sr1.8Mn2O7

Neutron diffraction data presented in this paper demonstrates the relevance of lattice displacement above TC, in our understanding of the evolution of the crystal structure with temperature in the layered CMR manganite La1.2Sr1.8Mn2O7. The anomalous temperature behavior of thermal diffuse scattering (TDS) in La1.2Sr1.8Mn2O7 strongly suggests that it arises from lattice displacements and correlates directly with anomalies in the displacement parameters of the O- and Mn-atoms and Mn-O bond lengths. From our measurements, the insulator - metal transition can be described as a transition from a high temperature state with disordered Mn-O bond lengths to a low temperature state with a more uniform distribution on Mn-O bonds. These observations are in agreement with polaronic charge transport above TC in the perovskite manganites; as electron hopping is responsible for bond disorder above TC, below the transition where eg carries are delocalized, any lattice displacements are uniformly averaged.Comment: 5 pages, 3 figures, submitted to Phys. Rev.

Fractionated Stereotactic Radiation Therapy for Pituitary Adenomas: An alternative escalating protocol of hypofractionated stereotactic radiotherapy delivering 35Gy in 5 fractions

PURPOSE: Evaluate efficacy and toxicity of hypofractionated stereotactic radiotherapy (HSRT) for patients treated for pituitary adenoma (PA) with an alternative HSRT escalating protocol delivering 35Gy in 5 fractions. MATERIAL AND METHODS: From June 2007 to March 2017, 29 patients with pituitary adenoma were treated in Antoine Lacassagne Cancer Centre with an alternative HSRT protocol. Prescribed dose was 35Gy in 5 fractions of 7Gy. Radiographic responses were assessed by annual MRI. Hormone blood samples were evaluated each year after HSRT. RESULTS: A total of 29 patients aged between 23 and 86 years (median 54 years) were included. Twelve patients received HSRT for recurrent cases and 12 received postoperative adjuvant HSRT, 5 patients did not have surgery. After a median follow-up period of 47 months local control rate was 96%. One patient presented an out-field tumor regrowth 73 months after HSRT. The majority of PA were endocrine-active (18 patients, 62%). After HSRT, 8 patients (44%) presented complete response on initial secretion, 4 patients (23%) presented partial response on initial secretion. Four patients (14%) presented grade 2 or more acute radiation toxicities. One grade 4 visual disorder was observed for one patient. CONCLUSIONS: HSRT delivering 35Gy in 5 fractions represents a feasible treatment and shows promising results to reduce hormonal overproduction and to improve local control in PA

Chemotherapy and diffuse low-grade gliomas: a survey within the European Low-Grade Glioma Network.

Diffuse low-grade gliomas (DLGGs) are rare and incurable tumors. Whereas maximal safe, functional-based surgical resection is the first-line treatment, the timing and choice of further treatments (chemotherapy, radiation therapy, or combined treatments) remain controversial. An online survey on the management of DLGG patients was sent to 28 expert centers from the European Low-Grade Glioma Network (ELGGN) in May 2015. It contained 40 specific questions addressing the modalities of use of chemotherapy in these patients. The survey demonstrated a significant heterogeneity in practice regarding the initial management of DLGG patients and the use of chemotherapy. Interestingly, radiation therapy combined with the procarbazine, CCNU (lomustine), and vincristine regimen has not imposed itself as the gold-standard treatment after surgery, despite the results of the Radiation Therapy Oncology Group 9802 study. Temozolomide is largely used as first-line treatment after surgical resection for high-risk DLGG patients, or at progression. The heterogeneity in the management of patients with DLGG demonstrates that many questions regarding the postoperative strategy and the use of chemotherapy remain unanswered. Our survey reveals a high recruitment potential within the ELGGN for retrospective or prospective studies to generate new data regarding these issues

Imaging practice in low-grade gliomas among European specialized centers and proposal for a minimum core of imaging

Objective: Imaging studies in diffuse low-grade gliomas (DLGG) vary across centers. In order to establish a minimal core of imaging necessary for further investigations and clinical trials in the field of DLGG, we aimed to establish the status quo within specialized European centers. Methods: An online survey composed of 46 items was sent out to members of the European Low-Grade Glioma Network, the European Association of Neurosurgical Societies, the German Society of Neurosurgery and the Austrian Society of Neurosurgery. Results: A total of 128 fully completed surveys were received and analyzed. Most centers (n=96, 75%) were academic and half of the centers (n=64, 50%) adhered to a dedicated treatment program for DLGG. There were national differences regarding the sequences enclosed in MRI imaging and use of PET, however most included T1 (without and with contrast, 100%), T2 (100%) and TIRM or FLAIR (20, 98%). DWI is performed by 80% of centers and 61% of centers regularly performed PWI.ConclusionA minimal core of imaging composed of T1 (w/wo contrast), T2, TIRM/FLAIR, PWI and DWI could be identified. All morphologic images should be obtained in a slice thickness of 3mm. No common standard could be obtained regarding advanced MRI protocols and PET. Importance of the study: We believe that our study makes a significant contribution to the literature because we were able to determine similarities in numerous aspects of LGG imaging. Using the proposed minimal core of imaging in clinical routine will facilitate future cooperative studies

Tractography dissection variability: What happens when 42 groups dissect 14 white matter bundles on the same dataset?

White matter bundle segmentation using diffusion MRI fiber tractography has become the method of choice to identify white matter fiber pathways in vivo in human brains. However, like other analyses of complex data, there is considerable variability in segmentation protocols and techniques. This can result in different reconstructions of the same intended white matter pathways, which directly affects tractography results, quantification, and interpretation. In this study, we aim to evaluate and quantify the variability that arises from different protocols for bundle segmentation. Through an open call to users of fiber tractography, including anatomists, clinicians, and algorithm developers, 42 independent teams were given processed sets of human whole-brain streamlines and asked to segment 14 white matter fascicles on six subjects. In total, we received 57 different bundle segmentation protocols, which enabled detailed volume-based and streamline-based analyses of agreement and disagreement among protocols for each fiber pathway. Results show that even when given the exact same sets of underlying streamlines, the variability across protocols for bundle segmentation is greater than all other sources of variability in the virtual dissection process, including variability within protocols and variability across subjects. In order to foster the use of tractography bundle dissection in routine clinical settings, and as a fundamental analytical tool, future endeavors must aim to resolve and reduce this heterogeneity. Although external validation is needed to verify the anatomical accuracy of bundle dissections, reducing heterogeneity is a step towards reproducible research and may be achieved through the use of standard nomenclature and definitions of white matter bundles and well-chosen constraints and decisions in the dissection process

Imaging practice in low-grade gliomas among European specialized centers and proposal for a minimum core of imaging.

OBJECTIVE: Imaging studies in diffuse low-grade gliomas (DLGG) vary across centers. In order to establish a minimal core of imaging necessary for further investigations and clinical trials in the field of DLGG, we aimed to establish the status quo within specialized European centers. METHODS: An online survey composed of 46 items was sent out to members of the European Low-Grade Glioma Network, the European Association of Neurosurgical Societies, the German Society of Neurosurgery and the Austrian Society of Neurosurgery. RESULTS: A total of 128 fully completed surveys were received and analyzed. Most centers (n = 96, 75%) were academic and half of the centers (n = 64, 50%) adhered to a dedicated treatment program for DLGG. There were national differences regarding the sequences enclosed in MRI imaging and use of PET, however most included T1 (without and with contrast, 100%), T2 (100%) and TIRM or FLAIR (20, 98%). DWI is performed by 80% of centers and 61% of centers regularly performed PWI. CONCLUSION: A minimal core of imaging composed of T1 (w/wo contrast), T2, TIRM/FLAIR, PWI and DWI could be identified. All morphologic images should be obtained in a slice thickness of ≤ 3 mm. No common standard could be obtained regarding advanced MRI protocols and PET. IMPORTANCE OF THE STUDY: We believe that our study makes a significant contribution to the literature because we were able to determine similarities in numerous aspects of LGG imaging. Using the proposed "minimal core of imaging" in clinical routine will facilitate future cooperative studies

Œdème papillaire secondaire à un schwannome vestibulaire : un cas atypique sans hypertension intracrânienne

International audienceIn most cases, vestibular schwannomas with papilledema are associated with intracranial hypertension secondary to hydrocephalus (obstructive or communicating). We describe the atypical case of a 39-years-old man who presented with bilateral papilledema revealing a vestibular schwannoma, but without hydrocephalus and with normal intracranial pressure. Ophtalmologic signs were completely resolved after tumor removal. The pathophysiological mechanism generally described to explain bilateral papilledema in such cases is tumor-induced hyperproteinorachia. However, in the absence of hydrocephalus or intracranial hypertension, this case raises the question of the mechanisms involved in the visual impairment related to vestibular schwannoma.Les schwannomes vestibulaires avec œdème papillaire sont en général associés à une hypertension intracrânienne secondaire à une hydrocéphalie (communicante ou obstructive). Nous décrivons ici le cas atypique d’un homme de 39 ans ayant présenté un œdème papillaire révélateur d’un schwannome vestibulaire, mais sans hydrocéphalie et avec une pression intracrânienne normale. L’exérèse tumorale a permis une régression complète des signes ophtalmologiques. En l’absence d’obstruction ventriculaire, le mécanisme physiopathologique généralement décrit pour expliquer l’atteinte visuelle est l’hydrocéphalie secondaire à une hyperprotéinorachie. Cependant, en l’absence d’hydrocéphalie ou d’hypertension intracrânienne, ce cas soulève la question des mécanismes impliqués dans l’atteinte visuelle secondaire à la présence d’un schwannome vestibulair

Orbital exenteration and conjunctival melanoma: a 14-year study at the Jules Gonin Eye Hospital.

To report our 14-year experience with orbital exenteration and assess risk factors for poor prognosis by focusing on conjunctival melanoma. A retrospective study was conducted in our tertiary care centre (Jules Gonin Eye Hospital, Lausanne, Switzerland) between 2003 and 2017. Inclusion criteria were patients aged ≥18 years with a follow-up >12 months, without metastatic spread at the time of surgery. Data recorded were age, gender, tumour histology, surgical technique, postoperative complications, surgical margin status, local recurrence, postoperative radiation beam therapy and metastatic status. Twenty-five patients with a mean age of 63.2 years (38-92) were included. Conjunctival melanoma was the most frequently identified tumour (n = 14, 56%) followed by conjunctival squamous cell carcinoma (n = 4, 16%), sebaceous carcinoma (n = 3, 12%), choroidal melanoma (n = 2, 8%) and basal cell carcinoma (n = 2, 8%). Eighteen tumours (72%) originated from the conjunctival tissue. Clear surgical margins were achieved in 21 (84%) patients. Fourteen (56%) patients experienced distant metastases and died from metastatic spread after a mean follow-up of 52.3 months (6-120). The 1-, 3- and 5-year overall survival (OS) was 96%, 72% and 60%, respectively. In the univariate analysis, positive surgical margins, local recurrence and metachronous metastases were associated with a decreased OS (p = 0.002, p = 0.005 and p = 0.007, respectively). In the multivariate analysis, positive surgical margins and metachronous metastases were also associated with a decreased OS (p = 0.02 and p = 0.042, respectively). Conjunctival melanoma was not associated with a poorer prognosis (p = 0.280). Free surgical margins are needed to increase OS. To achieve clearer surgical margins, neoadjuvant targeted therapies/immunotherapies may be considered