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At least 1,009 records · Page 56Linked to original sources
PubMed2001

Disintegration rate measurement of a 192Ir solution.

The disintegration rate of 192Ir has been measured using the 4pibeta-gamma coincidence technique. This radionuclide decays by electron capture (EC) and beta-emission. Since the EC contribution is low (4.5%), it has been corrected using decay scheme data taken from the literature. This measurement has been performed in collaboration with the Laboratório Nacional de Metrologia das Radiações Ionizantes (IRDDM), in Rio de Janeiro. The results, which were obtained independently and employed different techniques, are compared with the Systéme International Reference (SIR) maintained at the Bureau International des Poids et Mesures.

Beta Particles↗
PubMed2001

Development of a personal dosimetry system based on optically stimulated luminescence of alpha-Al2O3:C for mixed radiation fields.

To develop a personal optically stimulated luminescence (OSL) dosimetry system for mixed radiation fields using alpha-Al2O3:C, a discriminating badge filter system was designed by taking advantage of its optically stimulable properties and energy dependencies. This was done by designing a multi-element badge system for powder layered alpha-Al2O3:C material and an optical reader system based on high-intensity blue light-emitting diode (LED). The design of the multielement OSL dosimeter badge system developed allows the measurement of a personal dose equivalent value Hp(d) in mixed radiation fields of beta and gamma. Dosimetric properties of the personal OSL dosimeter badge system investigated here were the dose response, energy response and multi-readability. Based on the computational simulations and experiments of the proposed dosimeter design, it was demonstrated that a multi-element dosimeter system with an OSL technology based on alpha-Al2O3:C is suitable to obtain personal dose equivalent information in mixed radiation fields.

Aluminum Oxide↗
PubMed2001

TL response study of the CaSO4:Dy pellets with graphite for dosimetry in beta radiation and low-energy photons fields.

The CaSO4:Dy is a good thermoluminescent dosimeter because of its high sensitivity and low cost. With graphite in the pellets it is possible to reduce the energy dependence. The sensitivity and energy dependence of the different thicknesses of CaSO4:Dy pellets was studied with different amounts of graphite. The results have shown the optimal quantity of the graphite and the appropriate thickness of the pellets that can be used in dosimetry of beta field, photons or both simultaneously.

Beta Particles↗
PubMedDate not supplied

Activity characterization of pure-beta-emitting brachytherapy sources.

A generalized approach for characterizing the activity content of sealed beta-emitting sources has been developed, and was employed to establish National Institute of Standards and Technology based activity standardizations for three different types of intravascular brachytherapy sources. Initial ionization current measurements on the sources prior to destructive assays led to the establishment of calibration factors that can be used for subsequent non-destructive measurements of similar sources. Activity characterizations are needed to unequivocally relate theoretic absorbed-dose modeling results to dosimetric measurements, as well as to establish production and quality controls by the source manufacturers, and to satisfy the requirements of various governmental regulatory authorities.

Angioplasty, Balloon, Coronary↗
PubMed2002

Radionuclide production for therapeutic radiopharmaceuticals.

A fundamental task within the framework of a project searching for new radiopharmaceuticals for systemic therapy was the evaluation of the capabilities of the Portuguese Research Reactor (RPI) for the production of several important radionuclides. The feasibility of producing 64Cu, 77As, 153Sm, 165Dy, 166Ho, 170Tm, 177Lu, 186Re, 199Au and 111Ag in useful quantities was evaluated for the present RPI operation schedule (12 h cycles) and for continuous operation. The main evaluation criteria are expressed in terms of specific activity for continuous irradiation and/or 12 h cycle and the use of natural or enriched targets if necessary. Selected samples were irradiated and a comparison between measured activities and values calculated according to the irradiation schedule and using the same software was performed.

Beta Particles↗
PubMed1997

Beta-ray photography of lyophilized animal sections.

A new photographic method that images the density distribution of lyophilized animal sections approximately 50 microns in thickness is described. The new method involves sandwiching the animal section between a radiation sensor and a 147Pm planar radiation source. Either conventional photographic film or an imaging plate for radioluminography can be used as the sensor. The method described herein will find promising applications in whole body autoradiography as well as in the study of osteoporosis in experimental animals.

Animals↗
PubMed1998

Beta-decay half-lives and level ordering of 102m,gRh.

Beta-decay half-lives of the ground state and an isomer of 102Rh have been determined 207.3(17) d and 3,742(10) y, respectively, by gamma-ray decay curves following each beta-decay. It has been found that a state (2-) which has a shorter half-life (207.3 d) is the ground state from the result that the half-life of the 41.9 keV isomeric gamma-transition was equal to 3.742 y. It has also been confirmed that the 41.9 keV transition is certainly an isomeric transition with X-gamma coincidence measurement.

Beta Particles↗
PubMed2000

Radiochemical analysis of 41Ca and 45Ca.

The radioactive isotopes of calcium, 41Ca (t1/2 = 1.03 x 10(5) yr) and 45Ca (t1/2 = 163 d), are produced by neutron capture in the stable isotopes 40Ca and 44Ca, respectively. These radionuclides are present in the environment due to the reactions between the galactic cosmic rays and the earth's surface, and in nuclear power plants by the activation of the structural components of nuclear reactor vessels. The aim of this paper is to propose a radiochemical separation method of 41Ca and 45Ca from the other beta gamma emitters present in radioactive materials, based on selective precipitation reactions. The activities were measured by liquid scintillation counting (LSC). The obtained decontamination factors are satisfactory for each radioactive component of the initial sample in that their activities in the final product were lower than the minimum detectable activity (MDA) due to the effectiveness of the radiochemical procedure. The sensitivity of the method allows the radiological characterization of 41Ca and 45Ca content in radioactive materials.

Beta Particles↗
PubMed1995

Sens-A-Ray characteristics with variations in beam quality.

This study examined the relationship between x-ray beam quality and image characteristics with the use of the Sens-A-Ray (Regam Medical Systems, Sundsvall, Sweden). To evaluate the x-ray response, properties of the image sensor, dark current and statistical noise, sensitivity, and contrast resolution were measured. Tube voltage, tube current, and exposure time were varied. Exposures were determined with the use of an ionization chamber. Pixel values beneath a lead strip were used to calculate dark current effects. Contrast was measured with pixel values from the images of a step-wedge. Dark current noise increased in proportion to exposure time. Although the sensitivity at each tube voltage was linear and proportional to the exposure, the gradient was inversely proportional to increased tube voltage. After subtraction of the dark current and statistical noise, the gradient of the sensitivity at low tube voltage remained steeper than at high tube voltages. Hence, sensitivity decreased with increased tube voltage. Sensitivity gradients at each different tube current were similar. Irrespective of exposure, contrast resolution between adjoining step-wedge steps > or = 9 mm were too small to distinguish at 50 kVp. The gray levels for each step below 12 mm in thickness were distinguishable with 90 kVp. Increased dark current noise consequent to long exposure times narrowed the available gray scale range. Lower tube voltage resulted in higher sensitivity with larger gradients than higher tube voltages.

Analog-Digital Conversion↗
PubMed2003

[Brachytherapy for coronary restenosis: state of art in 2003].

Based on therapeutic approach for benign diseases, vascular brachytherapy decreases smooth vascular muscle cells proliferation and multiplication which lead to the formation of the neo-intima. The radioactive positive action affects arterial recoil due to post angioplasty vessel injury. Randomised studies has shown good angiographic results up to 6 months of follow-up, with 50% in-stent restenosis rate decrease and on the analysed segment as well. Decrease on Mace and TLR show statistically significance. Results don't correlate with emitter and bêta emitters had been introduced in France recently. Vascular brachytherapy is actually indicated for in-stent restenosis, there is no evidence to perform this treatment for de novo lesion. Geographic miss, source centering, late thrombosis and pullback procedure may interfere with treatment quality. IVUS allows best target volume determination to a higher quality level. Internationals guidelines such as Eva-Gec-Estro recommendations could increase treatment safety and enable development of an optimal technique.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Clinical trials of vascular brachytherapy for in-stent restenosis: update.

Vascular brachytherapy has become the therapeutic strategy of choice for in-stent restenosis. Clinical trials evaluating the effectiveness and safety of this technology have enrolled nearly 4000 patients using both gamma and beta emitters. At present, ongoing controversies include optimal dosimetry, whether beta emitters are as effective as gamma and whether centering delivery systems perform better than non-centering systems. Complications of brachytherapy such as edge effect, late thrombosis and late restenosis have received increasing attention. This review provides an update of the current status of clinical trials utilizing vascular brachytherapy to prevent the recurrence of in-stent restenosis.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Shielding effects of metallic encapsulations and radiographic contrast agents for catheter-based intravascular brachytherapy.

PURPOSE/OBJECTIVE: Both photon- and beta-emitting radionuclides for intravascular brachytherapy (IVB) are under active investigation for prevention of restenosis following conventional angioplasty with or without stents. High atomic number materials are usually present in the coronary vessels undergoing treatment in the form of metallic encapsulations, stents, calcified plaque, or radiographic contrast agent. The high atomic number materials are likely to interfere with the photons and betas and, thus, change the dosimetry in the treatment volume. The purpose of this study is to investigate the shielding effects caused by the presence of high atomic number materials in IVB. MATERIALS AND METHODS: Dose rates at various distances in water, with and without the presence of various high atomic number materials, were calculated using Monte Carlo simulation techniques for photon and electron transport in extended media. The high atomic number materials investigated included titanium, stainless steel, calcified plaque, Hypaque, and Omnipaque. A wide range of monoenergetic photon and electron sources and several photon- and beta-emitting radionuclides, which have been under consideration for IVB, were used. The energy of the monoenergetic photon sources was in the range from 10 keV to 1 MeV, and that of the monoenergetic electron sources in the range from 0.5 to 2 MeV. Photon-emitting radionuclides (192)Ir, (125)I, and (103)Pd and beta-emitting radionuclides (90)Y, (32)P, and (188)Re were also considered. RESULTS: It was found that the high atomic number materials interfere considerably with the transport of photons of relatively low energies (below 40 keV) and all electron sources. When the energy of photon exceeds 100 keV, the interference becomes minimum for the high atomic number materials that are likely to be present in clinical situations. The shielding correction factors (SCFs) for dose rate at 2 mm from center were essentially 1.00 for photon energies above 100 keV; as the energy decreased below 100 keV, the SCF became smaller reaching a value of almost 0 for the lowest energy studied, 10 keV. For the photon source of (192)Ir, the SCF was essentially 1.00; while for the photon sources of (125)I and (103)Pd, shielding corrections were considerably lower than 1.00 depending on the type and thickness of the high atomic number material. For the beta emitting sources, the shielding effect can be expressed as a loss in effective penetration depth. This loss depends both on the material and its thickness. For titanium and stainless steel, the loss of range was about two and four times the thickness of the metal. CONCLUSIONS: The effects of high atomic number materials, such as metallic stents, calcified plaque, and contrast agents are minimal for high energy photon emitters, such as (192)Ir. The effects are pronounced for beta emitters and low energy photon emitters, and must be included in dosimetry planning.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Dosimetry of source stepping for intravascular brachytherapy.

PURPOSE: Both beta and gamma sources of fixed length are currently used in the catheter-based intravascular brachytherapy (IVBT). Source stepping is often used to treat a lesion longer than the effective treatment length of the source. A major challenge for the stepping procedure is to attain a perfect dosimetric match (uniform dose) at the source junction. This work presents a quantitative and systematic dosimetric analysis for source stepping during an IVBT procedure. MATERIALS AND METHODS: The three most commonly used beta and gamma sources (192Ir by BEST, 90Sr by NOVOSTE and 32P by Guidant) were studied using the EGSnrc Monte Carlo code. Dose distributions were calculated for a perfect end-to-end match and for a range of end-to-end gaps and overlaps between consecutive steps. RESULTS: It is found that a perfect end-to-end match during source stepping yields uniform dose distribution in the region of source junction. The doses in the case of a mismatch (in the presence of an end-to-end gap or overlap) were found to be significantly different from those with the perfect end-to-end match. The dose deviation depends on the size of the gap or overlap, radial distance and type of source. The dose deviation decreases with radial distance for a given gap/overlap. For example, for a gap/overlap of 2 mm, dose decreases/increases of 30%, 55% and 60% were found at the radial distance of 2 mm from source for 192Ir, 90Sr and 32P, respectively. These dose deviations are reduced by approximately 10% when the radial distance increases from 2 to 3 mm. The dose deviations for gaps or overlaps in the range of 0-5 mm are presented. CONCLUSIONS: During an IVBT procedure involving source stepping, a perfect end-to-end match is always desired. Significant underdosing or overdosing can occur in the case of a source mismatch. A considerable caution should be exercised to ensure that sources are properly matched.

Beta Particles↗
PubMedDate not supplied

Excimer laser coronary angioplasty and intracoronary radiation for in-stent restenosis: six-month angiographic and clinical outcomes.

BACKGROUND: The purpose of this study was to evaluate 6-month clinical and angiographic outcomes in patients treated with excimer laser coronary angioplasty (ELCA) and intracoronary radiation (ICR) for in-stent restenosis (ISR). METHODS: A consecutive series of 175 patients with ISR treated with ELCA+ICR (gamma and beta emitters) were compared to 33 patients with ISR treated with ELCA alone. Baseline characteristics were similar between groups. ELCA+ICR and ELCA-alone patients had similar lesion lengths (25.0+/-12.0 vs. 24.0+/-16.8 mm, P=NS) in predominantly saphenous vein grafts (SVG, 38% vs. 42%, P=NS). RESULTS: Procedural success was high (ELCA+ICR, 97.0% vs. ELCA alone, 98.5%, P=NS), with no perforations or acute vessel closures. ELCA+ICR therapy reduced target vessel revascularization (TVR; 27% vs. 64%, P<.0001) and major adverse cardiac events [MACE: death, myocardial infarction (MI), or TVR; 30% vs. 64%, P<.0001] compared to ELCA alone. Late loss was 0.66+/-0.90 mm in ELCA+ICR patients and 0.85+/-0.60 mm in ELCA-alone patients (P=NS). Angiographic binary restenosis (>50%) was significantly reduced with adjunctive ICR (28% vs. 54%, P=.014). CONCLUSION: Radiation therapy with ELCA significantly reduces angiographic binary restenosis at 6 months in patients with diffuse ISR, driven predominantly by reduced percutaneous TVR.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Topical application of beta-radiation to reduce intimal hyperplasia after carotid artery balloon injury in rabbit. A possible application for brachytherapy in vascular surgery.

PURPOSE: Endovascular brachytherapy for the prevention of intimal hyperplasia (IH) and restenosis after balloon/stent angioplasty has proven effective both in animal preparations and clinical trials. A variety of beta-emitting isotopes and catheter-based devices have been developed for the delivery of low-dose radiation in clinical coronary and peripheral trials. No platform, however, has yet been developed for brachytherapy in concert with vascular surgical operations. The purpose of this study was to evaluate the vascular histopathologic response following balloon injury to rabbit carotid arteries with and without topically applied low-dose beta-radiation. METHODS: The beta-emitting isotope strontium-90 (Sr-90) was conjugated onto the matrix of polypropylene (PLYP) mesh. Rabbit carotid arteries were balloon-injured with a #2 embolectomy catheter. Six carotid arteries were wrapped with nonradioactive PLYP mesh (controls) and Sr-90 ( approximately 90 microCi) PLYP mesh in order to deliver low-dose radiation to the vessel wall from the external (adventitial) surface. Tissue was harvested at 6 weeks and processed for histologic examination. RESULTS: There was consistent blockade of fibrocellular neointima formation with virtually no neointima present in all treated segments, compared to moderate neointima formation in controls. Medial thinning and smooth muscle cell (SMC) necrosis were also associated with topical brachytherapy. CONCLUSION: beta-Radiation applied by an externally wrapped PLYP mesh labeled with Sr-90 markedly suppressed neointima formation in an animal vascular surgical injury model. Further studies, however, are necessary to determine a suitable isotope and dosage for clinical application.

Administration, Topical↗
PubMedDate not supplied

Monte Carlo calculations of dose distribution for intramural delivery of radioisotopes using a direct injection balloon catheter.

PURPOSE: A unique method of delivering radiation dose to the coronary vessel wall to prevent restenosis is by direct injection of radioactive compounds into the vessel wall using a specially designed angioplasty balloon catheter. The radiation dose distribution resulting from such intramural delivery was investigated using Monte Carlo simulations. MATERIALS AND METHODS: The radioisotope source distribution was modeled for two configurations within the vessel wall: (1) uniform to a depth of 0.5 mm and (2) confined to discrete pools surrounding the delivery injection ports. Monte Carlo MCNP4B computer simulations were utilized to estimate the associated radiation dose distribution for the following radioisotopes: 188Re, 186Re, 32P, 153Sm, 111In, 123I, and 99mTc. RESULTS: For the uniform case where the radioisotopes are distributed uniformly to the depth of 0.5 mm into the vessel wall, an essentially constant radiation dose is delivered within the source distribution. Outside of the source volume, the dose falls off at a rate depending on the emission properties of the particular radioisotope. The nonuniform case involving discrete pools of activity showed the dose distribution being confined largely to the regions surrounding the delivery ports with significant regions between these ports receiving very little dose. CONCLUSIONS: Direct injection of selected radioisotopes into the arterial wall appears to represent a potentially effective method for delivering radiation dose for the prevention of restenosis. Sufficiently high doses may be obtained from relatively low activity and the dose falls off rapidly outside of the target area for certain radioisotopes.

Adult↗