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Biomedical subjects

L Simon

Publications and source records attributed to L Simon.

At least 19 recordsLinked to original sources
PubMed2006

[Comparative study and clinical implementation of two breathing-adapted radiotherapy techniques: dosimetric benefits for lung cancer treatment].

Breathing can lead to organ motions up to several centimeters. For radiotherapy of lung, these motions are generally taken into account by adding a specific margin around the target. Thus, treated volumes are often too large to allow for the high-dose values requested for local control. To manage respiratory motion, deep-inspiration breath-hold technique (DIBH) and gated radiotherapy are starting being used clinically. DIBH consists in asking the patient to perform breath-hold during the treatment and the image acquisition, DIBH level being measured by a spirometer. Gated radiotherapy consists in treating the patient at a certain phase of the free breathing. Linac is synchronized with the motion of a marker located on the patient chest. Planning images are obtained by a four-dimensional CT (4D-CT) using the same marker. We have assessed the value of these two methods. For lung treatment, compared to a standard treatment, toxicity reduction was mainly due to the lung total volume increase. It is therefore more significant for breath-hold approach. It is also due to the reduction of safety margins, which is similar for both methods. These two techniques, which have specific advantages and drawbacks, are used routinely at Curie Institute for a large proportion of lung patients, but also for some breast, liver or even Hodgkin disease treatments.

Adenocarcinoma↗
PubMed2006

Reduction of organ motion effects in IMRT and conformal 3D radiation delivery by using gating and tracking techniques.

Respiration-gated radiotherapy offers a significant potential for improvement in the irradiation of tumour sites affected by respiratory motion such as lung, breast and liver tumours. An increased conformality of irradiation fields leading to decreased complications rates of organs at risk (lung, heart) is expected. Four main strategies are used to reduce respiratory motion effects: integration of respiratory movements into treatment planning, breath-hold techniques, respiratory gating techniques, and tracking techniques. Measurements of respiratory movements can be performed either in a representative sample of the general population, or directly on the patient before irradiation. The measured amplitude could be applied to a geometrical margin or integrated into dosimetry. However, these strategies remain limited for very mobile tumours, in which this approach results in larger irradiated volumes. Reduction of breathing motion can be achieved by using either breath-hold techniques or respiration synchronized gating techniques. Breath-hold can be achieved with active techniques, in which a valve temporarily blocks airflow of the patient, or passive techniques, in which the patient voluntarily breath-holds. Synchronized gating techniques use external devices to predict the phase of the respiration cycle while the patient breaths freely. Another category is tumour tracking, which consists of two major aspects: real-time localization of, and real-time beam adaptation to, a constantly moving tumour. These techniques are presently being investigated in several medical centres worldwide. Although promising, the first results obtained in lung and liver cancer patients require confirmation. This paper describes the most frequently used gating and tracking techniques and the main published clinical reports.

Artifacts↗
PubMed2005

Evidence of hole-electron quasiparticle interference in ErSi2 semimetal by Fourier-transform scanning tunneling spectroscopy.

The semimetallic ErSi2 layer grown on Si(111) substrates provides an ideally confined 2D electron and hole gas that reflects in complex standing wave pattern at 77 K. The quasiparticles exist in a wide energy range from -800 to 300 meV without mixing with silicon bulk excitations. By comparing high resolution Fourier transform of dI/dV maps, with joint density of states calculations, we are able to determine the 2D band structure. We also clearly demonstrate that hole-hole and hole-electron quantum interferences dominate over electron-electron ones.

Journal Article↗
PubMed2005

Low dose (-)deprenyl is cytoprotective: it maintains mitochondrial membrane potential and eliminates oxygen radicals.

Hypoxia leads to a collapse in mitochondrial transmembrane potential (Deltapsi(M)), a fall in the ATP/ADP ratio, and finally cell death. Since (-)deprenyl directly modulates Deltapsi(M) and production of reactive oxygen species (ROS) by altering the respiratory function of mitochondria, we were interested in the dose-response relations of these effects. The changes in JC-1 red/green signal ratios {mitochondrial transmembrane potential}, and the changes in the cerium staining (intracellular ROS) in hypoxic and normoxic PC12 cell cultures were measured following 1 h of Argon hypoxia and 24 h of re-oxygenation in the absence and in the presence of various concentrations of (-)deprenyl. Deltapsi(M) shifted to lower values following hypoxia/re-oxygenation and all cells had decreased and uniform Deltapsi(M) levels. The amount of ROS increased. Following 24 h of treatment with various concentrations of (-)deprenyl during the re-oxygenation period, survival increased, the Deltapsi(M) shift caused by oxygen deprivation was reversed and the peroxy radical levels decreased except for at 10(-3) M.

Animals↗
PubMed2005

[Radiotherapy for breast cancer: respiratory and set-up uncertainties].

Adjuvant Radiotherapy has been shown to significantly reduce locoregional recurrence but this advantage is associated with increased cardiovascular and pulmonary morbidities. All uncertainties inherent to conformal radiation therapy must be identified in order to increase the precision of treatment; misestimation of these uncertainties increases the potential risk of geometrical misses with, as a consequence, underdosage of the tumor and/or overdosage of healthy tissues. Geometric uncertainties due to respiratory movements or set-up errors are well known. Two strategies have been proposed to limit their effect: quantification of these uncertainties, which are then taken into account in the final calculation of safety margins and/or reduction of respiratory and set-up uncertainties by an efficient immobilization or gating systems. Measured on portal films with two tangential fields, CLD (central lung distance), defined as the distance between the deep field edge and the interior chest wall at the central axis, seems to be the best predictor of set-up uncertainties. Using CLD, estimated mean set-up errors from the literature are 3.8 and 3.2 mm for the systematic and random errors respectively. These depend partly on the type of immobilization device and could be reduced by the use of portal imaging systems. Furthermore, breast is mobile during respiration with motion amplitude as high as 0.8 to 10 mm in the anteroposterior direction. Respiratory gating techniques, currently on evaluation, have the potential to reduce effect of these movements. Each radiotherapy department should perform its own assessments and determine the geometric uncertainties with respect of the equipment used and its particular treatment practices. This paper is a review of the main geometric uncertainties in breast treatment, due to respiration and set-up, and solutions proposed to limit their impact.

Breast Neoplasms↗
PubMed2005

Evolution of multilevel order in supramolecular assemblies.

The process of self-assembly at multiple length scales of bis-urea substituted toluene on a Au(111) surface was studied by low temperature scanning tunneling microscopy. Pattern formation is controlled by specific hydrogen bonds between these molecules but also by significantly weaker lateral coupling between the resulting supramolecular polymers and a quasiepitaxial interlocking with the substrate. The ordered assemblies exhibit a tunnel transparency. Our experiments indicate the necessity of multiple interactions of different strengths for obtaining ordered structures with hierarchical levels of organization.

Journal Article↗
PubMed2005

An analytical solution for percutaneous drug absorption: application and removal of the vehicle.

The methods of Laplace transform were used to solve a mathematical model developed for percutaneous drug absorption. This model includes application and removal of the vehicle from the skin. A system of two linear partial differential equations was solved for the application period. The concentration of the medicinal agent in the skin at the end of the application period was used as the initial condition to determine the distribution of the drug in the skin following instantaneous removal of the vehicle. The influences of the diffusion and partition coefficients, clearance factor and vehicle layer thickness on the amount of drug in the vehicle and the skin were discussed.

Administration, Cutaneous↗
PubMed2005

[Preparation and administration of cytotoxic drugs: prickly innovation].

The requirement for safe and optimal administration of cytotoxic drugs led us to test a new product manufactured by Codan. The transfer set (CONNECT SET) and the administration set (CYTO-AD-SET) were assessed successively by pharmacist assistance within a centralized unit for cytotoxic drug preparation and by the nursing staff in an ambulatory unit. Transfer sets can be handled in the centralized units without using needles, but with an increased sterilization load and production cost. Assessment of the administration sets demonstrated time saving for the nursing staff. These materials require significant expenditures, careful training, and a change in treatment routine, but provide important time savings for the nursing staff and considerable improvement in the safety of handling cytotoxic drugs.

Antineoplastic Agents↗
PubMed2005

Phase-space analysis of acoustics fields and its application to waveguide.

A description of two-dimensional acoustic fields by means of a joint "space-wave number" representation is discussed. A function defined in the phase-space domain (x,y,k(x),k(y)) is associated with a signal which is a function of spatial coordinates (x,y). This paper presents two methods to realize it. The first is to associate with each point (x,y) of the wave field a two-dimensional wave number spectrum (k(x),k(y)), called local spectrum. The second is to process by other coordinates the wave field along an arbitrary direction, introduced in quantum mechanics for the study of classical billiards, and provided by the Birkhoff variables (s,cos phi). Phase-space diagrams are given by quadratic phase-space distributions. Simulations are presented for wave fields in a 2D planar waveguide for a pedagogical point of view with Gaussian beam or point-source excitation, and nonuniform waveguides as a sudden area expansion chamber and an open billiard with a single incoming mode at the entrance of each of them. In these problems, local spectrum and Birkhoff analysis are used in order to identify the structures hidden in the field. The result is the contribution of different wave vectors which contribute to the field value at the analysis point or at a certain section of the boundary, and show complicated structure of the acoustic field like whispering gallery or diffracted waves.

Journal Article↗
PubMed2005

Vibrato of saxophones.

Several alto saxophone players' vibratos have been recorded. The signals are analyzed using time-frequency methods in order to estimate the frequency modulation (vibrato rate) and the amplitude modulation (vibrato extent) of each vibrato sample. Some parameters are derived from the results in order to separate the two ways of vibrato playing: vibrato "à la machoire" and vibrato "sur l'air." Moreover, time domain simulations of single-reed instrument vibratos are created. The model is controlled by two parameters: the mouth overpressure and a parameter characterizing the reed-mouthpiece system. Preliminary comments and comparisons between the simulated vibratos and recorded vibratos results are made.

Acoustics↗
PubMed2004

GATE: a simulation toolkit for PET and SPECT.

Monte Carlo simulation is an essential tool in emission tomography that can assist in the design of new medical imaging devices, the optimization of acquisition protocols and the development or assessment of image reconstruction algorithms and correction techniques. GATE, the Geant4 Application for Tomographic Emission, encapsulates the Geant4 libraries to achieve a modular, versatile, scripted simulation toolkit adapted to the field of nuclear medicine. In particular, GATE allows the description of time-dependent phenomena such as source or detector movement, and source decay kinetics. This feature makes it possible to simulate time curves under realistic acquisition conditions and to test dynamic reconstruction algorithms. This paper gives a detailed description of the design and development of GATE by the OpenGATE collaboration, whose continuing objective is to improve, document and validate GATE by simulating commercially available imaging systems for PET and SPECT. Large effort is also invested in the ability and the flexibility to model novel detection systems or systems still under design. A public release of GATE licensed under the GNU Lesser General Public License can be downloaded at http:/www-lphe.epfl.ch/GATE/. Two benchmarks developed for PET and SPECT to test the installation of GATE and to serve as a tutorial for the users are presented. Extensive validation of the GATE simulation platform has been started, comparing simulations and measurements on commercially available acquisition systems. References to those results are listed. The future prospects towards the gridification of GATE and its extension to other domains such as dosimetry are also discussed.

Computer Simulation↗
PubMed2004

Patient Preference for Placebo, Acetaminophen (paracetamol) or Celecoxib Efficacy Studies (PACES): two randomised, double blind, placebo controlled, crossover clinical trials in patients with knee or hip osteoarthritis.

BACKGROUND: Acetaminophen (paracetamol) is recommended as the initial pharmacological treatment for knee or hip osteoarthritis. However, survey and clinical trial data indicate greater efficacy for non-steroidal anti-inflammatory drugs and cyclo-oxygenase-2 specific inhibitors. DESIGN: Two randomised, double blind, placebo controlled, crossover multicentre clinical trials, Patient Preference for Placebo, Acetaminophen or Celecoxib Efficacy Studies (PACES). PATIENTS: Osteoarthritis of knee or hip. INTERVENTION: "Wash out" of treatment; randomisation; 6 weeks of celecoxib 200 mg/day, acetaminophen 1000 mg four times a day, or placebo; second "wash out;" crossover to 6 weeks of second treatment. MEASUREMENTS: Western Ontario McMaster Osteoarthritis Index (WOMAC), visual analogue pain scale, patient preference between two treatments. RESULTS: Celecoxib was more efficacious than acetaminophen in both periods in both studies; WOMAC and pain scale scores differed at p<0.05 in period II and both periods combined of PACES-a and in periods I and II and both periods combined in PACES-b, but not in period I of PACES-a. Acetaminophen was more efficacious than placebo, generally p<0.05 in PACES-b, and >0.05 in PACES-a. Patient preferences were 53% celecoxib v 24% acetaminophen in PACES-a (p<0.001) and 50% v 32% in PACES-b (p = 0.009); 37% acetaminophen v 28% placebo in PACES-a (p = 0.340) and 48% v 24% in PACES-b (p = 0.007). No clinically or statistically significant differences were seen in adverse events or tolerability among the three treatment groups. CONCLUSIONS: Greater efficacy was seen for celecoxib v acetaminophen v placebo, while adverse events and tolerability were similar. Variation in results and statistical significance in the two different trials are of interest.

Acetaminophen↗
PubMed2004

OMERACT-OARSI initiative: Osteoarthritis Research Society International set of responder criteria for osteoarthritis clinical trials revisited.

BACKGROUND: The OARSI Standing Committee for Clinical Trials Response Criteria Initiative had developed two sets of responder criteria to present the results of changes after treatment in three symptomatic domains (pain, function, and patient's global assessment) as a single variable for clinical trials (1). For each domain, a response was defined by both a relative and an absolute change, with different cut-offs with regard to the drug, the route of administration and the OA localization. OBJECTIVE: To propose a simplified set of responder criteria with a similar cut-off, whatever the drug, the route or the OA localization. METHODS: Data driven approach: (1) Two databases were considered: the "elaboration" database with which the formal OARSI sets of responder criteria were elaborated, and the "revisit" database. (2) Six different scenarios were evaluated: The two formal OARSI sets of criteria; Four proposed scenarios of simplified sets of criteria. Data from clinical randomized blinded placebo controlled trials were used to evaluate the performances of the two formal scenarios with two different databases ("elaboration" versus "revisit") and those of the four proposed simplified scenarios within the "revisit" database. The placebo effect, active effect, treatment effect, and the required sample arm size to obtain the placebo effect and the active treatment effect observed were the performances evaluated for each of the six scenarios. Experts' opinion approach: Results were discussed among the participants of the OMERACT VI meeting, who voted to select the definite OMERACT-OARSI set of criteria (one of the six evaluated scenarios). RESULTS: Data driven approach: Fourteen trials totaling 1886 OA patients and fifteen studies involving 8164 OA patients were evaluated in the "elaboration"and the "revisit" databases respectively. The variability of the performances observed in the "revisit" database when using the different simplified scenarios was similar to that observed between the two databases ("elaboration" versus "revisit") when using the formal scenarios. The treatment effect and the required sample arm size were similar for each set of criteria. Experts' opinion approach: According to the experts, these two previous performances were the most important of an optimal set of responder criteria. They chose the set of criteria considering both pain and function as evaluation domain and requiring an absolute change and a relative change from baseline to define a response, with similar cut-offs whatever the drug, the route of administration or the OA localization. CONCLUSION: This data driven and experts' opinion approach is the basis for proposing an optimal simplified set of responder criteria for OA clinical trials. Other studies, using other sets of OA patients, are required in order to further validate this proposed OMERACT-OARSI set of criteria.

Clinical Trials as Topic↗
PubMed2003

Box-modeling of bone and tooth phosphate oxygen isotope compositions as a function of environmental and physiological parameters.

A time-dependent box model is developed to calculate oxygen isotope compositions of bone phosphate as a function of environmental and physiological parameters. Input and output oxygen fluxes related to body water and bone reservoirs are scaled to the body mass. The oxygen fluxes are evaluated by stoichiometric scaling to the calcium accretion and resorption rates, assuming a pure hydroxylapatite composition for the bone and tooth mineral. The model shows how the diet composition, body mass, ambient relative humidity and temperature may control the oxygen isotope composition of bone phosphate. The model also computes how bones and teeth record short-term variations in relative humidity, air temperature and delta18O of drinking water, depending on body mass. The documented diversity of oxygen isotope fractionation equations for vertebrates is accounted for by our model when for each specimen the physiological and diet parameters are adjusted in the living range of environmental conditions.

Animals↗
PubMed2003

[Formulation and stability of hospital preparation of 3,4-diaminopyridine capsules].

Administration of 3,4-diamynopyridine (3,4-DAP) has been found to be effective in the symptomatic treatment of patients with Eaton-Lambert Myasthenic syndrome. A recent case of this syndrome in Val de Grâce Military hospital led us to manufacture 3,4-DAP capsules. In agreement with good manufactoring processes, we have performed mass uniformity and content tests. Six different formulations were tested, starch maize and magnesium stearate have been validated as excipients. The stability study showed that the conservation was good even under extreme conditions. Clinical and electromyographic improvement seen in this patient suggests this preparation may be of benefit.

4-Aminopyridine↗
PubMed2002

Preoperative coagulation tests in former preterm infants undergoing spinal anaesthesia.

BACKGROUND: Clinical history is insufficient to detect disorders of haemostasis in infants aged less than 1 year and laboratory coagulation testing is recommended in infants before perimedullar anaesthesia. METHODS: We designed a retrospective study to assess the preoperative coagulation tests [activated partial thromboplastin time (aPTT), prothrombin time, platelet count] performed in 141 former preterm infants who underwent spinal anaesthesia for elective inguinal hernia repair. All the infants had recovered from any significant medical event (necrotizing enterocolitis, intracranial haemorrhages, transfusions of blood products, sepsis, etc.) when they were scheduled for surgery. RESULTS: Mean values for aPTT were frequently abnormal (60.4%) in infants with a postconceptional age of less than 45 weeks. No complication related to the puncture or abnormal perioperative bleeding was detected. CONCLUSIONS: Other coagulation tests should be evaluated to assess the coagulation status in infants with a postconceptional age of less than 45 weeks.

Anesthesia, Spinal↗