F Estève

Unité Inserm U1077, Caen, Lower Normandy, France

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Publications (58)139.46 Total impact

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    ABSTRACT: Exercise training has been shown to improve cardiometabolic health in obese adolescents.
    Pediatric Obesity 08/2014; · 2.28 Impact Factor
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    ABSTRACT: This study investigated the changes in cerebral near-infrared spectroscopy (NIRS) signals, cerebrovascular and ventilatory responses to hypoxia and CO2 during altitude exposure. At sea level (SL), after 24 hours and 5 days at 4,350 m, 11 healthy subjects were exposed to normoxia, isocapnic hypoxia, hypercapnia, and hypocapnia. The following parameters were measured: prefrontal tissue oxygenation index (TOI), oxy- (HbO2), deoxy- and total hemoglobin (HbTot) concentrations with NIRS, blood velocity in the middle cerebral artery (MCAv) with transcranial Doppler and ventilation. Smaller prefrontal deoxygenation and larger ΔHbTot in response to hypoxia were observed at altitude compared with SL (day 5: ΔHbO2-0.6±1.1 versus -1.8±1.3 μmol/cmper mm Hg and ΔHbTot 1.4±1.3 versus 0.7±1.1 μmol/cm per mm Hg). The hypoxic MCAv and ventilatory responses were enhanced at altitude. Prefrontal oxygenation increased less in response to hypercapnia at altitude compared with SL (day 5: ΔTOI 0.3±0.2 versus 0.5±0.3% mm Hg). The hypercapnic MCAv and ventilatory responses were decreased and increased, respectively, at altitude. Hemodynamic responses to hypocapnia did not change at altitude. Short-term altitude exposure improves cerebral oxygenation in response to hypoxia but decreases it during hypercapnia. Although these changes may be relevant for conditions such as exercise or sleep at altitude, they were not associated with symptoms of acute mountain sickness.Journal of Cerebral Blood Flow & Metabolism advance online publication, 25 September 2013; doi:10.1038/jcbfm.2013.167.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 09/2013; · 5.46 Impact Factor
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    ABSTRACT: Changes in cerebral perfusion and CO(2) cerebrovascular reactivity during and immediately after a sojourn at high altitude remain unclear but may be critical for acclimatization. The aim of the present study was to assess the effects of 6days at 4,350m on cerebral perfusion and cerebrovascular reactivity (CVR) to CO(2) by arterial spin labeling (ASL) magnetic resonance imaging at sea level and to compare it with transcranial Doppler (TCD) results at altitude. Eleven healthy male subjects, non-acclimatized to altitude, stayed for 6days at 4,350m (Observatoire Vallot, massif du Mont-Blanc). Prior to the stay and within 6h after returning to sea level, subjects were investigated using pseudo-continuous ASL at 3T during a block-design inhalation paradigm to measure basal cerebral blood flow (CBF) and CO(2) CVR. End-tidal CO(2) (PetCO(2)), respiratory rate, heart rate and oxygen saturation were recorded during the exam. Subjects were also examined using TCD prior to and on day 5 of the stay at altitude to measure blood velocity in the middle cerebral artery (MCAv) and CO(2) CVR. CO(2) CVR was expressed as percent change in ASL CBF or TCD MCAv per mmHg change in PetCO(2). PetCO(2) was significantly decreased during and after altitude. Significant increases in TCD MCAv compared to before altitude measurements were observed on day 5 at altitude (+20.5±15.5 %). Interestingly, ASL CBF remained increased in the MCA and anterior vascular territories (+22.0±24.1 % and 20.5±20.3 %, respectively) after altitude under normoxic conditions. TCD CVR tended to decrease on day 5 at 4,350m (-12.3±54.5 % in the MCA) while the ASL CVR was significantly decreased after altitude (-29.5±19.8 % in the MCA). No correlation was observed between cerebral hemodynamic changes and symptoms of acute mountain sickness at high altitude. In conclusion, prolonged exposure to high altitude significantly increases blood flow during the altitude stay and within 6h after returning to sea level. Decreased CO(2) CVR after prolonged altitude exposure was also observed using ASL. Changes in cerebral hemodynamics with altitude exposure probably involve other mechanisms than the vasodilatory effect of hypoxia only, since it persists under normoxia several hours following the descent.
    NeuroImage 02/2013; · 6.25 Impact Factor
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    ABSTRACT: The aim of this study was to examine ventilatory responses to training in obese adolescents. We assessed body composition, pulmonary function and ventilatory responses (among which expiratory flow limitation and operational lung volumes) during progressive cycling exercise in 16 obese adolescents (OB) before and after 12 weeks of exercise training and in 16 normal-weight volunteers. As expected, obese adolescents' resting expiratory reserve volume was lower and inversely correlated with thoraco-abdominal fat mass (r=-0.74, p<0.0001). OB presented lower end expiratory (EELV) and end inspiratory lung volumes (EILV) at rest and during submaximal exercise, and modest expiratory flow limitation. After training, OB increased maximal aerobic performance (+19%) and maximal inspiratory pressure (93.7±31.4 vs 81.9±28.2cmH(2)O, +14%) despite lack of decrease in trunk fat and body weight. Furthermore, EELV and EILV were greater during submaximal exercise (+11% and +9% in EELV and EILV, respectively), expiratory flow limitation delayed but was not accompanied by increased V(T). However, submaximal exertional symptoms (dyspnea and leg discomfort) were significantly decreased (-71.3% and -70.7%, respectively). Our results suggest that exercise training can improve pulmonary function at rest (static inspiratory muscle strength) and exercise (greater operating lung volumes and delayed expiratory flow limitation) but these modifications did not entirely account for improved dyspnea and exercise performance in obese adolescents.
    Respiratory Physiology & Neurobiology 08/2012; 184(1):73-9. · 2.05 Impact Factor
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    ABSTRACT: Monochromatic x-ray minibeam radiotherapy is a new radiosurgery approach based on arrays of submillimetric interlaced planar x-ray beams. The aim of this study was to characterize the dose distributions obtained with this new modality when being used for preclinical trials. Monte Carlo simulations were performed in water phantoms. Percentage depth-dose curves and dose profiles were computed for single incidences and interleaved incidences of 80 keV planar x-ray minibeam (0.6 × 5 mm) arrays. Peak to valley dose ratios were also computed at various depths for an increasing number of minibeams. 3D experimental polymer gel (nPAG) dosimetry measurements were performed using MRI devices designed for small animal imaging. These very high spatial resolution (50 µm) dose maps were compared to the simulations. Preclinical minibeams dose distributions were fully characterized. Experimental dosimetry correlated well with Monte Carlo calculations (Student t-tests: p > 0.1). F98 tumor-bearing rats were also irradiated with interleaved minibeams (80 keV, prescribed dose: 25 Gy). This associated preclinical trial serves as a proof of principle of the technique. The mean survival time of irradiated glioma-bearing rats increased significantly, when compared to the untreated animals (59.6 ± 2.8 days versus 28.25 ± 0.75 days, p < 0.001).
    Physics in Medicine and Biology 06/2011; 56(14):4465-80. · 2.70 Impact Factor
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    ABSTRACT: An adequate dosimetry protocol for synchrotron radiation and the specific features of the ID17 Biomedical Beamline at the European Synchrotron Radiation Facility are essential for the preparation of the forthcoming clinical trials in the synchrotron stereotactic radiation therapy (SSRT). The main aim of this work is the definition of a suitable protocol based on standards of dose absorbed to water. It must allow measuring the absolute dose with an uncertainty within the recommended limits for patient treatment of 2%-5%. Absolute dosimetry is performed with a thimble ionization chamber (PTW semiflex 31002) whose center is positioned at 2 g cm(-2) equivalent depth in water. Since the available synchrotron beam at the ESRF Biomedical Beamline has a maximum height of 3 mm, a scanning method was employed to mimic a uniform exposition of the ionization chamber. The scanning method has been shown to be equivalent to a broad beam irradiation. Different correction factors have been assessed by using Monte Carlo simulations. The absolute dose absorbed to water at 80 keV was measured in reference conditions with a 2% global uncertainty, within the recommended limits. The dose rate was determined to be in the range between 14 and 18 Gy/min, that is to say, a factor two to three times higher than the 6 Gy/min achievable in RapidArc or VMAT machines. The dose absorbed to water was also measured in a RW3 solid water phantom. This phantom is suitable for quality assurance purposes since less than 2% average difference with respect to the water phantom measurements was found. In addition, output factors were assessed for different field sizes. A dosimetry protocol adequate for the specific features of the SSRT technique has been developed. This protocol allows measuring the absolute dose absorbed to water with an accuracy of 2%. It is therefore satisfactory for patient treatment.
    Medical Physics 03/2011; 38(3):1709-17. · 2.91 Impact Factor
  • Medical Physics 01/2011; 99. · 2.91 Impact Factor
  • Cancer Radiotherapie - CANCER RADIOTHER. 01/2011; 15(2):161-164.
  • Medical Physics 01/2011; 38(6):3564-. · 2.91 Impact Factor
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    Journal of Neuro- …. 01/2011;
  • Medical Physics 01/2011; 38(6):3534-. · 2.91 Impact Factor
  • Cancer/Radiothérapie 12/2010; 15(2):161-4; author reply 164-7. · 1.48 Impact Factor
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    ABSTRACT: Radiation therapy is commonly used in the treatment of cancer. The normal tissue tolerance can be a limit to deliver enough dose to the tumor to be curative. The synchrotron beam presents some interesting physical properties, which could decrease this limitation. Synchrotron beam is a medium energy X-ray nearly parallel beam with high intensity. Three methods are under preclinical investigations: the microbeam, the minibeam and the stereotactic radiotherapy. The first two use a geometric irradiation effect called spatial fractioning. The last one use highly conformational irradiation geometry combined with a dose enhancement due to the presence of high-Z element in the target. Synchrotron radiotherapy preclinical experiments have shown some curative effect on rodent glioma models. Following these encouraging results a phase I/II clinical trial of iodinated enhanced stereotactic synchrotron radiotherapy is currently being prepared at the European Synchrotron Radiation Facility.
    La Revue de Médecine Interne 08/2010; 31(8):586-9. · 0.90 Impact Factor
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    ABSTRACT: Synchrotron radiation (SR) therapy is a promising alternative to treat brain tumors, whose management is limited due to the high morbidity of the surrounding healthy tissues. Several approaches are being explored by using SR at the European Synchrotron Radiation Facility (ESRF), where three techniques are under development Synchrotron Stereotactic Radiation Therapy (SSRT), Microbeam Radiation Therapy (MRT) and Minibeam Radiation Therapy (MBRT).
    AIP Conference Proceedings. 07/2010; 1266(1):101-106.
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    ABSTRACT: For several years the ID17 Biomedical beamline at the ESRF has developed synchrotron radiation therapy preclinical programmes to treat aggressive brain tumours. Two techniques have been developed at the ESRF:
    AIP Conference Proceedings. 06/2010; 1234(1):161-164.
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    ABSTRACT: Synchrotron stereotactic radiotherapy (SSRT) is a treatment that involves the targeting of high-Z elements into tumors followed by stereotactic irradiation with monochromatic x-rays from a synchrotron source, tuned at an optimal energy. The irradiation geometry, as well as the secondary particles generated at a higher yield by the medium energy x-rays on the high-Z atoms (characteristic x-rays, photoelectrons, and Auger electrons), produces a localized dose enhancement in the tumor. Iodine-enhanced SSRT with systemic injections of iodinated contrast agents has been successfully developed in the past six years in the team, and is currently being transferred to clinical trials. The purpose of this work is to study the impact on the SSRT treatment of the contrast agent type, the beam quality, the irradiation geometry, and the beam weighting for defining an optimized SSRT treatment plan. Theoretical dosimetry was performed using the MCNPX particle transport code. The simulated geometry was an idealized phantom representing a human head. A virtual target was positioned in the central part of the phantom or off-centered by 4 cm. The authors investigated the dosimetric characteristics of SSRT for various contrast agents: Iodine, gadolinium, and gold; and for different beam qualities: Monochromatic x-ray beams from a synchrotron source (30-120 keV), polychromatic x-ray beams from an x-ray tube (80, 120, and 180 kVp), and a 6 MV x-ray beam from a linear accelerator. Three irradiation geometries were studied: One arc or three noncoplanar arcs dynamic arc therapy, and an irradiation with a finite number of beams. The resulting dose enhancements, beam profiles, and histograms dose volumes were compared for iodine-enhanced SSRT. An attempt to optimize the irradiation scheme by weighing the finite x-ray beams was performed. Finally, the optimization was studied on patient specific 3D CT data after contrast agent infusion. It was demonstrated in this study that an 80 keV beam energy was a good compromise for treating human brain tumors with iodine-enhanced SSRT, resulting in a still high dose enhancement factor (about 2) and a superior bone sparing in comparison with lower energy x-rays. This beam could easily be produced at the European Synchrotron Radiation Facility medical beamline. Moreover, there was a significant diminution of dose delivered to the bone when using monochromatic x-rays rather than polychromatic x-rays from a conventional tube. The data showed that iodine SSRT exhibits a superior sparing of brain healthy tissue in comparison to high energy treatment. The beam weighting optimization significantly improved the treatment plans for off-centered tumors, when compared to nonweighted irradiations. This study demonstrated the feasibility of realistic clinical plans for low energy monochromatic x-rays contrast-enhanced radiotherapy, suitable for the first clinical trials on brain metastasis with a homogeneous iodine uptake.
    Medical Physics 06/2010; 37(6):2445-56. · 2.91 Impact Factor
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    ABSTRACT: Radiation therapy is commonly used in the treatment of cancer. The normal tissue tolerance can be a limit to deliver enough dose to the tumor to be curative. The synchrotron beam presents some interesting physical properties, which could decrease this limitation. Synchrotron beam is a medium energy X-ray nearly parallel beam with high intensity. Three methods are under preclinical investigations: the microbeam, the minibeam and the stereotactic radiotherapy. The first two use a geometric irradiation effect called spatial fractioning. The last one use highly conformational irradiation geometry combined with a dose enhancement due to the presence of high-Z element in the target. Synchrotron radiotherapy preclinical experiments have shown some curative effect on rodent glioma models. Following these encouraging results a phase I/II clinical trial of iodinated enhanced stereotactic synchrotron radiotherapy is currently being prepared at the European Synchrotron Radiation Facility.
    Revue De Medecine Interne - REV MED INTERNE. 01/2010; 31(8):586-589.
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    ABSTRACT: A hybrid approach, combining deterministic and Monte Carlo (MC) calculations, is proposed to compute the distribution of dose deposited during stereotactic synchrotron radiation therapy treatment. The proposed approach divides the computation into two parts: (i) the dose deposited by primary radiation (coming directly from the incident x-ray beam) is calculated in a deterministic way using ray casting techniques and energy-absorption coefficient tables and (ii) the dose deposited by secondary radiation (Rayleigh and Compton scattering, fluorescence) is computed using a hybrid algorithm combining MC and deterministic calculations. In the MC part, a small number of particle histories are simulated. Every time a scattering or fluorescence event takes place, a splitting mechanism is applied, so that multiple secondary photons are generated with a reduced weight. The secondary events are further processed in a deterministic way, using ray casting techniques. The whole simulation, carried out within the framework of the Monte Carlo code Geant4, is shown to converge towards the same results as the full MC simulation. The speed of convergence is found to depend notably on the splitting multiplicity, which can easily be optimized. To assess the performance of the proposed algorithm, we compare it to state-of-the-art MC simulations, accelerated by the track length estimator technique (TLE), considering a clinically realistic test case. It is found that the hybrid approach is significantly faster than the MC/TLE method. The gain in speed in a test case was about 25 for a constant precision. Therefore, this method appears to be suitable for treatment planning applications.
    Physics in Medicine and Biology 09/2009; 54(15):4671-85. · 2.70 Impact Factor
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    ABSTRACT: Synchrotron radiation is an innovative tool for the treatment of brain tumors. In the stereotactic synchrotron radiation therapy (SSRT) technique a radiation dose enhancement specific to the tumor is obtained. The tumor is loaded with a high atomic number (Z) element and it is irradiated in stereotactic conditions from several entrance angles. The aim of this work was to assess dosimetric properties of the SSRT for preparing clinical trials at the European Synchrotron Radiation Facility (ESRF). To estimate the possible risks, the doses received by the tumor and healthy tissues in the future clinical conditions have been calculated by using Monte Carlo simulations (PENELOPE code). The dose enhancement factors have been determined for different iodine concentrations in the tumor, several tumor positions, tumor sizes, and different beam sizes. A scheme for the dose escalation in the various phases of the clinical trials has been proposed. The biological equivalent doses and the normalized total doses received by the skull have been calculated in order to assure that the tolerance values are not reached.
    Medical Physics 04/2009; 36(3):725-33. · 2.91 Impact Factor
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    ABSTRACT: The radiotherapy clinical trials projects, both aiming at treating aggressive brain tumors, require several major modifications and new constructions at the ESRF ID17 Biomedical beamline. The application of the Stereotactic Synchrotron Radiation Therapy (SSRT) technique mainly necessitates an upgrade of the existing patient positioning system, which was formerly used for the angiography program. It will allow for accurate positioning, translation and rotation of the patient during the treatment. For the Microbeam Radiation Therapy (MRT) clinical trials project, a new white beam hutch will be constructed to accommodate a dedicated patient positioning system. Consequently, the existing control hutches and the related installations will also be completely refurbished. Furthermore, the foreseen installation of a second X-ray source, which will allow doubling the currently available photon flux at high energies, requires a redesign of most optical components to handle the increased power and power densities. Starting from the current ID17 Biomedical beamline layout, the paper will present an update of the different modification/construction projects, including the general organization and planning.
    European journal of radiology 10/2008; 68(3 Suppl):S147-50. · 2.65 Impact Factor

Publication Stats

587 Citations
139.46 Total Impact Points

Institutions

  • 1997–2013
    • Unité Inserm U1077
      Caen, Lower Normandy, France
  • 2012
    • University of Grenoble
      Grenoble, Rhône-Alpes, France
  • 2010–2011
    • University Joseph Fourier - Grenoble 1
      Grenoble, Rhône-Alpes, France
  • 2000–2011
    • European Synchrotron Radiation Facility
      • Division of Experiments
      Grenoble, Rhône-Alpes, France
  • 2008
    • French Institute of Health and Medical Research
      Lutetia Parisorum, Île-de-France, France
  • 1998–2002
    • Centre Hospitalier Universitaire de Grenoble
      Grenoble, Rhône-Alpes, France
  • 1999
    • Psi Chi
      Chattanooga, Tennessee, United States