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At least 37 records · Page 2Linked to original sources
PubMed1994

Low-dose, beta-particle emission from 'stent' wire results in complete, localized inhibition of smooth muscle cell proliferation.

BACKGROUND: Restenosis after catheter-based revascularization has been demonstrated to be primarily caused by medial and/or intimal smooth muscle cell (SMC) proliferation. The objective of this study was investigate the ability of local emission of beta-particles from a 32P-impregnated titanium "stent" wire source to inhibit vascular SMC and endothelial cell proliferation in cell culture and to determine the dose-response characteristics of this inhibition. METHODS AND RESULTS: A series of experiments were performed using 0.20-mm-diameter titanium wires that were impregnated with varying low concentrations of 32P (activity range, 0.002 to 0.06 microCi/cm wire, n = 47) or 31P (nonradioactive control, n = 28) in cultures of rat and human aortic SMCs and in cultured bovine aortic endothelial cells. The zone of complete cell growth inhibition (in millimeters from stent wire) was measured using light microscopy in the cultures exposed to the radioactive (32P) or control (31P) wires at 6 and 12 days after plating. In both rat and human SMC cultures there was a distinct 5.5- to 10.6-mm zone of complete SMC inhibition at wire activity levels > or = 0.006 microCi/cm. In contrast, there was no zone of inhibition surrounding the control (31P impregnated) wires (P < .001 versus 32P wires at all wire activities > or = 0.006 microCi/cm for human and rat SMCs). Proliferating bovine endothelial cells were more radioresistant than SMCs, with no zone of inhibition observed at wire activity levels up to 0.019 microCi/cm (P < .001 versus SMCs at 0.006 microCi/cm and 0.019 microCi/cm). CONCLUSIONS: We conclude that very low doses of beta-particle emission from a 32P-impregnated stent wire (activity levels as low as 0.006 microCi/cm of wire) completely inhibit the growth and migration of both rat and human SMCs within a range of 5.5 to 10.6 mm from the wire. Endothelial cells appear to be much more radioresistant than SMCs. These data suggest that an intra-arterial stent impregnated with a low concentration of 32P may have a salutary effect on the restenosis process. Whether this approach can be used successfully and safely to inhibit restenosis in vivo and in the clinical setting is under investigation.

Animals↗
PubMed1994

Extrapolation chamber measurements of 90Sr + 90Y beta-particle ophthalmic applicator dose rates.

Aspects of extrapolation chamber dose-rate measurements of 90Sr + 90Y beta-particle ophthalmic applicators are examined in this report, including the proper choice of collector electrode size, the gap width over which the measurement should be done, the effect of the entrance window materials, and the stopping-power ratio. Experiments, a simple analytic model for the effect of chamber geometry and nonzero gap width, and more detailed Monte Carlo simulations were used. The variation of the planar flux density as a function of angle for a thick 90Sr + 90Y source was measured and used as input for the model. From Monte Carlo simulation, the dose rate for tissue irradiation falls off by 8% between the surface and a depth of 7 mg/cm2. The derivative of chamber ionization as a function of gap width, needed for the dose-rate calibration, increases rapidly as the gap width decreases, typically by a factor of about 2 between gap widths of 1.5 and 0.15 mm. About half of this change is due to ionizing electrons leaving the collection volume at the larger gap widths as shown by the analytic model; the rest of the change is due to ionizing electrons which backscatter from the collector electrode and its backing as shown by Monte Carlo simulations. The backscattering effect increases the derived surface dose by a factor of 1.46. A satisfactory dose-rate extrapolation is obtained from gap widths of 0.1-0.25 mm, where the total ionization current is observed to be nearly linear in gap width.

Beta Particles↗
PubMed1994

Presence or absence of glycogen-beta particles in sinoatrial node cells.

The sinoatrial node is formed by specialized cells, the main ultrastructural differences of which, as compared with ordinary atrial myocardium, are a pale cytoplasm and sparse myofibrils. Moreover, nodal cells have been described to contain large amounts of glycogen particles in their pale cytosol; these glycogen inclusions are often used as the main criterion for identifying nodal cells. Nevertheless, the presence of glycogen cytosolic inclusions has been discussed by several authors. This paradox was solved by the description of some undesirable effects of uranyl acetate when used en bloc. To prove the presence of glycogen granules in nodal cells and the effects of uranyl acetate en bloc, we performed an ultrastructural study of the sinoatrial node in rats of different ages using different staining techniques. Our results do not reveal any beta-particles in nodal cells in tissues processed by either general or glycogen-specific methods. Uranyl acetate staining did not cause any change of appearance in the nodal or ordinary myocardium. From these results, one could conclude that, on the one hand, sinoatrial nodal cells do not show deposits of beta-particles of glycogen which can be detected with ultrastructural techniques, and, on the other hand, that uranyl acetate does not cause any morphological artifacts.

Aging↗
PubMed1996

The beta-particle-emitting radioisotope stent (isostent): animal studies and planned clinical trials.

Radiation delivered by intravascular stent is an appealing approach to prevent neointimal hyperplasia, since it nonselectively kills dividing cells. In particular, beta-particle-emitting radioisotope stents may prove to be an ideal means of local irradiation in that 95% of the dose is delivered within 4 mm of the stent edge and the dose drops off rapidly to < 1/1,000 of the original dose at 5 months postimplantation. In the in vitro smooth muscle cell model, one can observe a zone of growth inhibition around radioactive stent wires that averages about 6 mm at very-low-activity levels (0.006 microCi/cm of wire). In vivo studies in animal models, including porcine iliac and coronary arteries and rabbit iliac arteries, have shown the effectiveness of radioisotope stents in inhibiting neointimal proliferation. Proliferating endothelial cells appear to be relatively radioresistant. A computer model was employed to look at the radiation dose delivered as a function of distance from the stent. With very-low-activity stents, presumably, DNA of the smooth muscle cells is damaged as they migrate through the "electron fence" on the way to the neolumen, diminishing the population of myofibroblasts and reducing hyperplasia. Catheter-based radiation therapies may disable these cells before they migrate, although such an approach may not inhibit early recoil or late contraction. Based on the characteristics of beta emissions (i.e., rapid drop-off, minimal leaching), radioisotope stents containing phosphorus-32 appear to be safe. A randomized triple-blind clinical trial is planned to assess restenosis at 6 months in native coronary arteries treated with radioisotope stents.

Animals↗
PubMed1978

The response of E. coli Bs-1 to tritium-beta particles under aerated and anoxic conditions.

E. coli Bs-1 cells were exposed to acute doses of tritium-beta particles by suspension in tritiated water for known lengths of time. The resulting survival rate was compared with that obtained for external irradiation with 7 MeV electrons. The o.e.r. measured for tritium-beta s was not significantly different from the value of 2.15 measured for 7 MeV electrons. The r.b.e. of the tritium beta s relative to 7 MeV electrons was 1.21 in both air and nitrogen. These results were compared with existing data for low voltage electron irradiations and with track segment studies of the effect of varying LET on the radiosensitivity of E. coli Bs-1.

Dose-Response Relationship, Radiation↗
PubMed1989

Optical imaging of the spatial distribution of beta-particles emerging from surfaces.

The multiplication in gases of ionization electrons, by the effect of the electric fields between parallel electrodes, leads to the emission of light from the molecules excited in the avalanche process. The optical imaging of this light, with intensifiers, on charge-coupled devices permits the localization, in the gaseous volume, of the entrance points of the beta-particles emitted by radioactive compounds placed close to or at the cathode electrode. Thin slices of anatomical samples labeled with 3H show detailed structures 30 microns in size. Gels carrying 32P or 35S are imaged with accuracies of the order of 0.5 mm (full width at half maximum). In comparison with photographic emulsion, the gain in time for data taking is close to a factor of 100, with the advantage of linearity and wider dynamic range in the intensity measurement and a greatly improved signal-to-noise ratio.

Animals↗
PubMed1994

Absorbed fractions for electrons and beta particles in spheres of various sizes.

UNLABELLED: The use of electron-emitting radionuclides in tumor imaging and therapy has presented some new challenges to conventional radiation dosimetry. The fraction of electron energy absorbed in most source regions has usually been assumed to be unity. In small structures such as localized tumors or isolated regions containing moderate to high energy electron emitters, however, this may not always be the case. METHODS: Using an extension of Berger's scaled absorbed dose distributions for point sources to represent a spherical geometry, absorbed fractions of electron energy for sources uniformly distributed in spheres of various sizes have been calculated. RESULTS: Beta particle and monoenergetic electron energies studied range from 0.025 to 4.0 MeV and sphere masses range from 0.01 to 1000 g. S values have also been calculated for 90Y, 123I and 131I based on the results of the absorbed fraction calculations. CONCLUSION: These calculated absorbed fractions are valuable in estimating electron energy loss from small spherical structures and may be useful in estimating the radiation dose to these small volumes.

Beta Particles↗
PubMed1995

Magnetically enhanced protection of bone marrow from beta particles emitted by bone-seeking radionuclides: theory of application.

Utilization of radiopharmaceuticals that directly target radioactivity to tumors for treatment has a great deal of promise. Ideally, lethal doses of radiation could be delivered precisely to areas of disease, while, for the most part, sparing normal tissues. This potential, however, has not yet been fully realized. Current limitations of this approach are low tumor uptake of radiopharmaceuticals and dose-limiting radiotoxicity. In an effort to offset low uptake, radionuclides that emit high average-energy electrons have been proposed. Unfortunately, use of these radionuclides increases myelosuppression on a per decay basis. In order to allow for the utilization of high doses of this class of high-energy beta emitters, we propose the application of a strong static homogeneous magnetic field to constrain the beta particles. Monte Carlo computer simulations indicate that application of a 10 T magnetic field can decrease the total radiation dose from bone-avid tracers to marrow located in shafts of human long bones by 14%. More significantly, however, the penetration depth of high-energy electrons from the bone surface into the marrow can be reduced by up to 74.6%. Preservation of marrow in areas distal to the bone has previously been shown to facilitate relatively rapid recovery from pancytopenia produced by radiation damage to trabecular marrow (without marrow transplantation). Magnetically enhanced protection of bone marrow, therefore, may allow administered doses of high-energy beta-emitting radionuclides to be increased. By raising the limits on injected quantities of such highly ionizing radionuclides, amounts of the radiation dose absorbed by both soft and calcified tissue tumors will be increased, compared to conventional treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta Particles↗
PubMed1982

Estimates of absorbed energy in trabecular bone due to beta-particles or electrons.

A computer code, DAB-BE, has been written which can be used to calculate the absorbed energies of beta particles or electrons deposited inside human trabecular bone. The radiation source geometry can be either uniformly distributed in the whole bone or located at a fixed point inside the bone. Bremsstrahlung effects are not considered in these calculations. Results are presented and discussed for six monoenergetic sources of electrons distributed uniformly in a mathematical representation of the arm. In addition, a fixed point source configuration of 1.0 MeV monoenergetic electrons was studied.

Bone and Bones↗
PubMed1991

Localization and quantitation of tritiated compounds in tissue sections with a gaseous detector of beta particles: comparison with film autoradiography.

Quantitative analysis of tritium polymer standards and of brain sections labeled with tritiated vasopressin was carried out by using a gaseous detector of beta particles designed for this purpose. The gaseous detector showed major advantages compared with film autoradiography: the linearity and the large dynamic range of intensity measurements as well as the short time needed for data acquisition.

Animals↗
PubMed1983

A sensitive double isotope modification of the Farr assay using beta-particle emitters.

A sensitive modification of the ammonium sulfate precipitation assay for antibody affinity is described. The assay combines small reaction volumes and a 32P volume marker to determine the average relative affinity of small amounts of antibody to DNP hapten. The assay is relatively safe since two beta-particle emitters are utilized instead of two gamma-ray emitters. The assay has proven useful for the determination of small amounts of antibody such as might be found in secretions and column fractions.

Ammonium Sulfate↗
PubMed1991

SOFI: a bidimensional detector for fast direct on-line quantification of beta particles on blots.

We present a high-speed, high-resolution beta imager developed to replace autoradiographic films currently used in molecular biology experiments. It allows the user to locate and make quantitative analyses of 32P-labeled molecules on a 25.6 x 25.6-cm flat surface. Combining new techniques--scintillating optical fibers and multianode photomultipliers--this fast imager offers several advantages when compared with recent gas detectors and flexibility for further improvements. Several biological applications will be discussed.

Animals↗
PubMed1968

Rabbit skeletal muscle glycogen. A morphological and biochemical study of glycogen beta-particles isolated by the precipitation-centrifugation method.

Glycogen in its particulate beta-form is localized in the sarcoplasm close to the sarcoplasmic reticulum. Some particles are in close contact with the membranes, on the outer side of the vesicles. The mild technique of differential precipitation-centrifugation has been adapted to the preparation of glycogen from adult skeletal muscle. A preliminary low-speed centrifugation which eliminates the contractile protein structures and the cell debris is followed by a high-speed centrifugation which produces pellets containing glycogen mixed with smooth-walled vesicles, the glycogen-sarcovesicular fraction. The glycogen obtained after treatment of this fraction with deoxycholate and two washings contains 3% protein. A similar protein content contaminates glycogen banded in a linear sucrose gradient. The glycogen-sarcovesicular fraction and the purified glycogen have been examined, under the electron microscope, in sections of fixed and embedded material or with the negative staining technique. The glycogen beta-particles in negatively stained preparations have an average diameter of 39.4 mmicro. The largest particles present irregular outlines, suggesting the presence of conglomerated subunits, about 20 mmicro in diameter. These subunits seem to fall apart under the influence of concentrated potassium hydroxide. The mean sedimentation coefficients calculated for infinite dilution vary from 115 to 135S. The spectrophotometric analysis of the glycogen-iodine complex indicates the presence of long end-chains in the molecule.

Animals↗
PubMed1987

Experimental and computational techniques for beta-particle dosimetry.

This paper reports the experimental and the computational techniques that were specifically developed to provide dose response data for a new method of beta dosimetry, which is reported in an accompanying article (Sh87). The specific experimental techniques consist of setting up, calibrating and obtaining backscattering and resolution corrections for a plastic-scintillator-based beta spectrometer. The computation techniques involve (1) adapting a Monte Carlo electron transport computer code to use measured beta energy distributions as input data and (2) using the code to calculate the energy deposition of these distributions of electrons in a slab of material. The energy deposition of backscattered electrons incident on the slab is also taken into account. Codes, which were developed to calculate the energy deposited by photons in LiF, are used to derive a theoretical value for the TLD response calibration factor. This factor compares well to the experimentally derived result which was obtained by exposing TLDs to a calibrated 137Cs/137mBa photon source.

Algorithms↗
PubMed1998

Calibration and characterization of beta-particle sources for intravascular brachytherapy.

The calibration of a catheter-based system to be used for therapeutic radiation treatment to prevent restenosis following interventional coronary procedures is described. The primary dosimetry was performed ionometrically using an extrapolation chamber equipped with a 1-mm diameter collecting electrode to measure absorbed dose in tissue equivalent plastic at a depth of 2 mm. These results are compared with measurements with radiochromic dye film, which is also used to characterize sources for axial and trans-axial uniformity, and to determine dose distributions at various depths. A protocol for dose calculation based on that of AAPM TG43 is suggested for these sources, and examples of its use are given for the calculation of the enhancement effect on dose rate from a single seed source due to neighboring seeds. Monte Carlo calculations were also performed to validate the measured results.

Beta Particles↗