Determination of radium-226 in aqueous solutions by alpha-spectrometry.

The new European legislation imposes a lower threshold for radioactivity in drinking water. This requires the development of more sensitive and reliable analytical methods. This work presents an improved alpha-spectrometric technique to determine the radium-226 activity in aqueous solution relying on the radium adsorption onto a thin manganese oxide layer followed by alpha-measurement. The preparation of the MnO2 deposit has been optimized as well as the radium adsorption conditions. Detection threshold and limit of 5 and 10 mBq x L(-1), respectively, with a 10% (95% confidence) uncertainty are currently reached. This paper reports on the overall technique and on its application to assess the radium-226 activity in 28 French mineral waters. In addition, the gross alpha- and beta-activities have been evaluated using proportional counting while the uranium concentrations were derived from ICPMS.

Natural radioactivity in phosphates, phosphogypsum and natural waters in Morocco.

The contents of natural radionuclides (uranium, actinium and thorium series) were measured in sedimentary phosphate rock samples using high-resolution gamma spectrometry. Data obtained for uranium content (ppm) were compared with the results obtained by a method based on the measurements using solid-state nuclear track detectors (SSNTD) in the same samples. The potential leaching of radionuclides from sedimentary phosphate rock during the industrial production of the phosphoric acid was studied. The process of leaching of the radioisotopes from phosphogypsum was discussed. A method for the direct alpha counting of 226Ra thin source, elaborated by the deposition of Ra from aqueous solutions on manganese oxides film deposited on polyvinyl support, have been developed and applied for the determination of 226Ra in natural water samples. The results show that only the water sample from the mine area reveals the presence of 226Ra at a level of about 0.2 Bq l-1.

Gamma radiation effects on potassium pertechnetate in carbonate media.

Gamma radiation effects on the stability of the oxidation state of radioelements and diffusion within the framework of nuclear waste repositories are often neglected, although it may influence physicochemical processes and thus transfer to biosphere and geosphere. This knowledge is essential to model transport phenomena. This study reports on effects of gamma irradiation on technetium in carbonate media, which is representative of natural systems. Depending on media compositions, the gamma irradiation on pertechnetate leads to formation of Tc(IV) only in the absence of carbonate. CO3*- radicals are able to re-oxidise technetium intermediate oxidation states to the +7 state.

Validation of 213Bi-alpha radioimmunotherapy for multiple myeloma.

The efficacy of radioimmunotherapy (RIT) with beta emitters has been clinically demonstrated in the treatment of refractory forms of lymphoma. Alpha-emitting radionuclides with a short half-life are also good potential candidates for RIT directed at tumor targets easily accessible to radioimmunoconjugate molecules and small enough to benefit from the short range of alpha particles (<100 microm). The purpose of this study was to demonstrate the feasibility of ex vivo purging of multiple myeloma-invaded bone marrow. Tumor cells were targeted by a specific monoclonal antibody (B-B4) coupled to 213Bi by a chelating agent (pentaacetic triamine diethylene p-aminobenzyl acid). The efficacy of alpha-RIT was assessed in vitro by analysis of thymidine incorporation, cell mortality, apoptosis of myeloma cells, and the study of nonspecific irradiation of hematopoietic cell lines not recognized by B-B4-pentaacetic triamine diethylene p-aminobenzyl acid immunoconjugate. High dose-dependent cell mortality of myeloma cells was found with radiolabeled B-B4, and this mortality was total at 30 kBq/10(5) cells. Cells were found in apoptotic state at rates of up to 40% for a dose of 7.4 kBq/10(5) cells. Nonspecific mortality was low compared with specific mortality (up to 1%).

Uptake and metabolism of boronophenylalanine in human uveal melanoma cells in culture Relevance to boron neutron capture therapy of cancer cells.

The transport of boronophenylalanine (BPA) and its metabolic fate have been studied in a human uveal melanoma cell line isolated from a primary enucleated tumor. The boronated compound was rapidly incorporated into the cells reaching a peak of incorporation in two hours. This was followed by a trough between 10 and 24 hours and by an increase thereafter. The analogy with the amino acids phenylalanine (Phe) and tyrosine (Tyr) was studied in competition experiments incubating cultures of cell line MK-T, isolated in this laboratory, with [(3)H]-Phe and [(125)I]-Tyr, in the presence or absence of various concentrations of BPA, between 0 and 5 min. The presence of BPA severely reduced the uptake of both amino acids. The kinetics of the transport of [(3)H]-Phe and [(3)H]-Tyr in the presence of BPA, measured after 10 sec of incubation, showed that the boronated compound exerted a competitive inhibition on both transport systems. The intracellular metabolism of BPA was followed by measuring boron concentration (measured with Ionization Coupled Mass Spectrometry) in subcellular fractions and after membrane extraction by the detergent Triton X-100. The results showed that BPA remained in the supernatant and was not metabolized into macromolecules. These results and the relative absence of melanine in these cells, as observed by electron microscopy, suggest that BPA may be actively transported into melanoma cells but not metabolized. The results may have a relevance in studies on Boron Neutron Capture Therapy.

[Therapy by neutron capture of ocular melanoma: dosimetry and microdosimetry]. / Thérapie par capture de neutrons des mélanomes oculaires: approches dosimétrique et microdosimétrique.

Neutron capture therapy (NCT) aims at destroying cancerous cells with the alpha and 7Li particles produced by the neutron capture reaction on 10B. This note reports on the study of the boron distribution in tissues on an animal model (nude mice) xenografted with a human ocular melanoma after an i.p.injection of 2g/kg of 10B-BPA and in cells cultured in the presence of 530 mumol/l of 10B-BPA. A concentration of 64 ppm of 10B in the active part of the tumour with a ratio of concentrations versus the skin of 3.7 are observed. Investigations on cells reveal the presence of boron in the cytoplasm. The biological, dosimetric and microdosimetric consequences of these findings are discussed.

[Radiotherapy of ocular melanoma: physical and radiobiological bases, current techniques and future prospects]. / Radiothérapie des mélanomes oculaires: bases physiques et radiobiologiques, techniques actuelles et perspectives d'avenir.

Primitive ocular melanoma is a rare tumor in adults. Although this tumor is radio-resistant and located in a very radiosensitive organ, a conservative approach using radiotherapy is feasible for small or medium size melanomas. The physical and radiobiological basis of the techniques presently used, brachytherapy and protontherapy, are presented together with the complications inherent to each treatment. Future prospects discussed concern the association of hyperthermia with conventional irradiation and Boron Neutron Capture Therapy (BNCT). The relevance of each technique with reference to the size and location of the tumor is discussed.

[Morphological characterization of cell lines of human uveal melanoma]. / Caractérisation morphologique de lignées cellulaires de mélanome uvéal humain.

Several cell lines have been derived from an ocular melanoma obtained from an enucleated patient. Three cell types are observed during the time in culture of all the cell lines under study. Two of them have epithelial and spindle shape respectively. A third cell type, having a spheroidal shape, is formed from spindle cells and may be transformed into epithelial cells upon re-seeding. Further experiments showed that the same cell may change of shape following the cycle: spheroidal-->epithelial-->fusiform-->spheroidal. Scanning microscopy shows the coexistence of the three cell shapes in the same culture and the presence of several filaments and processes protruding at the surface of the cells. Transmission electron microscopy shows that the cell lines, in general, contain melanosomes empty or fairly pigmented and several filaments and microtubules. The presence of melanin may be stimulated by seeding of melanoma cells over a "feeder layer" of fibroblasts.

Distribution of lithium in the rat brain after a single administration known to elicit aversive effects.

In order to get insight into the brain areas involved in the initial unpleasant effects resulting from the administration of lithium (Li+), its distribution was mapped in the rat brain using the 6Li(n,alpha)3H nuclear reaction after a single injection of 6Li2SO4 at doses and latencies corresponding to the elicitation of such unpleasant effects. An improved method for visualization and measurement of local Li+ concentrations was used consisting in diffracting light along the tracks left by alpha particles in a dielectric detector. The distribution of Li+ was found less homogeneous than when Li+ was administered chronically. Periaqueductal and periventricular structures were the brain areas containing the highest concentrations of Li+.

[Lethal effect of boron neutron capture reaction on human uveal melanoma cells in culture incubated with borophenylalanine]. / Effet létal de la réaction de capture neutronique du bore sur des cellules de mélanome uvéal humain en culture incubées avec la boro-phénylalanine.

Cell cultures obtained from human uveal tumours have been used as experimental model to study the lethal effect consecutive to the neutron capture reaction on boron incorporated into cells as borophenylalanine. An irradiation with a neutron fluence of 6 x 10(9) n cm-2 reduced the number of viable cells by about 30%.