Intracavitary in vivo dosimetry based on multichannel fiber-coupled Radioluminescence and Optically Stimulated Luminescence of Al2_2O3_3 :C

International audienceFiber Optic Dosimetric Catheters (FODCs) composed of chains of alumina crystals are investigated by the CEA LIST within the French ANR-INTRADOSE Project in the purpose of intracavitary in vivo dosimetry (IVD) during Brachytherapy (BT) with iridium sources and Intensity-Modulated Radiation Therapy (IMRT) with linear accelerators. A dedicated process involving PMMA fibers, casted altogether forming hexagonal bundle, is demonstrated. Optically Stimulated Luminescence (OSL) signals are recorded on-line after irradiation and absorbed doses are compared to planned dose distribution. Real-time dose measurements may also be performed by recording the RadioLuminescence (RL), spontaneously emitted by the crystals during irradiation. In this case, a correction method is implemented to correct for stem effect influence (Cerenkov and scintillation generated within the fibers). For BT, the dual-fiber subtraction method is used (using a reference fiber) whereas the time discrimination method is used for IMRT. The experimental dose distribution leads to an underestimation of the source-sensor distance presumably due to energy dependence of the alumina crystal at low photon energy. At the time being, Monte-Carlo modeling of the FODC is performed with the aim to estimate this energy dependence and finally correct for it. Finally, metrological and preclinical validations are still running at Centre Léon Bérard (Lyon, France) in the purpose of checking the compliance of the FODC prototypes with treatment specifications and medical constraints

PIXSIC, a wireless radiosensitive intracerebral probe to monitor PET radiotracers in anaesthetized and awake rat

Présentation oraleAim. In neuroscience, PET functional imaging and behavioural assays in rodents are complementary approaches, despite the fact that they are rarely associated simultaneously because general anaesthesia inherent to PET precludes behavioural studies. To address this methodological limit, we have developed a radiosensitive pixelated intracerebral probe, PIXSIC, that provides access to the combination of simultaneous observations of molecular and behavioural parameters on rodents. Material and Methods. PIXSIC proposes a novel strategy for in vivo recording of the local time-activity curves of PET radiopharmaceuticals. It relies on a sub-millimetre pixelated probe of Si (17 mm long hosting 10 pixels with dimension 200 µm x 500 µm) implanted into the brain region of interest by stereotaxic surgery. Positrons are detected by reverse-biased, high-resistivity silicon diodes. The system Aims at time-resolved high sensitivity measurements in a volume of a few mm3. The pixelated detection scheme adds "imaging" features as it allows recording of the time-activity curves in different brain regions along the probe position. PIXSIC has a compact and autonomous design based on a radiofrequency data exchange link that allows for full freedom in the animals motion and behavioural activity while limiting stress during acquisition. Results and Conclusion. The first biological validations were performed on anaesthetized rats implanted with two probes, one in the region of interest (hippocampus or striatum, according to the radiotracer) and the other one in a control region (cerebellum). We used [11C]-raclopride for dopamine D2 receptors and [18F]-MPPF for serotonin 5HT1A receptors. According to our previous studies with the Beta-Microprobe (J Nucl Med 2002, 43(2):227-33; Eur J Nucl Med 2002 29(9) 1237-47), the radioactive signals measured with the PIXSIC pixels are reproducible and well-correlated with the distributions of the targeted receptors. The simultaneous measurement of implanted rats in a small animal PET camera confirmed the similarity between PIXSIC and microPET time-activity curves. Moreover, the binding curves highlighted the possibility for PIXSIC to distinguish different tracer kinetics within the structure of interest (cortex/striatum or cortex/hippocampus) in accordance to the stereotaxic location of the pixels. In addition, PIXSIC allowed us to perform the first kinetic measurements of [11C]-raclopride and [18F]-MPPF on awake and freely moving rats. In conclusion, PIXSIC constitutes an unprecedented instrumental methodology for connecting PET molecular imaging and behavioral measurements with freely-moving rodents

Rat interleukin-1 beta binding sites in rat hypothalamus and pituitary gland.

International audienceIn this study, radiolabeled recombinant rat interleukin-1 beta (r125I-IL-1 beta) was used to localize and characterize IL-1 beta binding in rat hypothalamus and pituitary gland by quantitative autoradiography. The ability of this ligand to bind to type I IL-1 receptor was first tested on murine lymphoma cells (EL-4). In the rat-tissue sections, high densities of specific r125I-IL-1 beta binding sites were localized in the anterior as well as the posterior pituitary and in the choroid plexus. A fine labeling was observed in meninges and third ventricle walls while no binding was detected in the hypothalamic nuclei. Saturation experiments, in the anterior and posterior pituitary, revealed one specific binding site with an affinity constant (Kd) of 0.5 nM. Competition experiments were achieved using either rat IL-1 beta (rIL-1 beta) or human IL-1s (hIL-1 alpha, hIL-1 beta and IL-1 receptor antagonist: hIL-1a). Affinity constants (Ki) were drastically different according to the ligand used, while Ki values were found similar in anterior and posterior pituitary. Competition with rIL-1 beta revealed one binding affinity (Ki of 0.1 nM range). In contrast, competition with hIL-1 beta revealed two binding affinities: a high (Ki: 0.1 pM range) and a low one (Ki: 1 nM range). Competition with hIL-1ra was obtained for high concentrations only (Ki: 10-100 nM range), whereas human IL-1 alpha (hIL-1 alpha) was unable to compete at 1-100 nM.(ABSTRACT TRUNCATED AT 250 WORDS

SESAME: A software tool for the numerical dosimetric reconstruction of radiological accidents involving external sources and its application to the accident in Chile in December 2005

Estimating the dose distribution in a victim's body is a relevant indicator in assessing biological damage from exposure in the event of a radiological accident caused by an external source. This dose distribution can be assessed by physical dosimetric reconstruction methods. Physical dosimetric reconstruction can be achieved using experimental or numerical techniques. This article presents the laboratory-developed SESAME-Simulation of External Source Accident with MEdical images-tool specific to dosimetric reconstruction of radiological accidents through numerical simulations which combine voxel geometry and the radiation-material interaction MCNP(X) Monte Carlo computer code. The experimental validation of the tool using a photon field and its application to a radiological accident in Chile in December 2005 are also described. © 2009 Health Physics Society

General guidelines for the assessment of internal dose from monitoring data (project IDEAS) [Guide pratique pour estimer la dose interne à partir des résultats de mesure de surveillance (projet IDEAS)]

In recent major international intercomparison exercises on intake and internal dose assessments from monitoring data, the results calculated by different participants varied significantly. This was mainly due to the broad variety of methods and assumptions applied in the assessment procedure. Based on these experiences the need for harmonisation of the procedures has been formulated within an EU research project under the 5th Framework Programme. The aim of the project, IDEAS, is to develop general guidelines for standardising assessments of intakes and internal doses. The IDEAS project started in October 2001 and will end in March 2005. Eight institutions from seven European countries are participating. Inputs from internal dosimetry professionals from across Europe are also being used to ensure a broad consensus in the outcome of the project. The IDEAS project is closely related to some goals of the work of committee 2 of the ICRP and since 2003 there has been close cooperation between the two groups. To ensure that the guidelines are applicable to a wide range of practical situations, the first step has been to compile a database of well-documented cases of internal contamination. In parallel, an improved version of an existing software package has been developed and distributed to the partners for further use. A large number of cases from the database have been evaluated independently by partners in the project using the same software and the results have been reviewed. Based on these evaluations, guidelines are being drafted and will be discussed with dosimetry professionals from around the world by means of a virtual workshop on the Internet early in 2004. The guidelines will be revised and refined on the basis of the experiences and discussions of this virtual workshop and the outcome of an intercomparison exercise organised as part of the project. This will be open to all internal dosimetry professionals. © 2005 EDP Sciences