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PubMed1993

51Cr-release assay adapted to a 96-well format sample reading.

The application of the Matrix 96, a direct beta counter, to monitor cell-mediated lympholysis assays (CML) was investigated. Until now, the gamma rays emitted from 51Cr, released in the supernatant of the sample following lysis of targets by effector cells, were read in gamma counters using individual tubes for each sample. The Matrix 96 has been designed to count 96 wells simultaneously for assays performed in 96-well microplates. Aliquots of supernatants were spotted on a 96-well disposable metal spotting plate and dried prior to reading in the Matrix 96. A tight correlation was observed between the counts obtained in the Matrix 96 and a gamma counter, which indicates that the detection of electron capture beta particles emitted from 51Cr was as accurate as reading gamma rays from the same isotope. Both methods confirmed the minimal level of cytotoxicity mediated by unstimulated lymphocytes and the high levels of nonspecific cytolytic activity mediated by lymphokine-activated killer (LAK) cells against several tumor cell lines.

Beta Particles↗
PubMed1990

A single TLD dose algorithm to satisfy federal standards and typical field conditions.

Modern whole-body dosimeters are often required to accurately measure the absorbed dose in a wide range of radiation fields. While programs are commonly developed around the fields tested as part of the National Voluntary Accreditation Program (NVLAP), the actual fields of application may be significantly different. Dose algorithms designed to meet the NVLAP standard, which emphasizes photons and high-energy beta radiation, may not be capable of the beta-energy discrimination necessary for accurate assessment of absorbed dose in the work environment. To address this problem, some processors use one algorithm for NVLAP testing and one or more different algorithms for the work environments. After several years of experience with a multiple algorithm approach, the Dosimetry Services Group of Yankee Atomic Electric Company (YAEC) developed a one-algorithm system for use with a four-element TLD badge using Li2B4O7 and CaSO4 phosphors. The design of the dosimeter allows the measurement of the effective energies of both photon and beta components of the radiation field, resulting in excellent mixed-field capability. The algorithm was successfully tested in all of the NVLAP photon and beta fields, as well as several non-NVLAP fields representative of the work environment. The work environment fields, including low- and medium-energy beta radiation and mixed fields of low-energy photons and beta particles, are often more demanding than the NVLAP fields. This paper discusses the development of the algorithm as well as some results of the system testing including: mixed-field irradiations, angular response, and a unique test to demonstrate the stability of the algorithm. An analysis of the uncertainty of the reported doses under various irradiation conditions is also presented.

Algorithms↗
PubMed1988

Calculations for beta dosimetry using Monte Carlo code (OREC) for electron transport in water.

A Monte Carlo computer code (OREC) for calculating the detailed transport and energy deposition for primary electrons and all of their secondaries in liquid water has been investigated for use in beta-ray dosimetry. Some modifications have been made in the original code for its application to tissue and tissue-equivalent materials. The code gives reasonably good agreement with beta spectral data and depth-dose curves measured in tissue-equivalent plastics for several calibrated beta sources. The calculations permit a direct evaluation of the skin dose equivalent, i.e., the dose equivalent, Hs (0.07), at a depth of 0.070 mm in tissue. Calculations are presented for monoenergetic electrons, showing the distributions in the maximum depth of penetration and in the total pathlength traveled. Direct comparisons are made between depth-dose curves calculated for 99Tc and 147Pm plaque sources and measurements made with extrapolation chambers. The energy spectrum of beta particles emerging from a thick 99Tc plaque source also is calculated, and the angular distribution is found to be almost independent of the energy. The pulse-height spectrum in a tissue-equivalent plastic scintillator calculated for this source shows good agreement with the measured spectrum. The calculations also provide the Hs(0.07) dose equivalent for the 99Tc source, which is found to be consistent with that inferred independently from the spectral measurements. A calculated curve for converting spectrometer measurements to Hs(0.07) dose equivalent is in good agreement with a semi-empirical curve that was developed independently. It appears that calculations made with the electron transport code for water can provide useful information for beta dosimetry.

Beta Particles↗
PubMed1994

Magnetically enhanced radionuclide therapy.

UNLABELLED: Radiopharmaceutical therapy is an increasingly common treatment for cancer. This therapy involves the injection of radiolabeled tumor-specific agents into the patient with subsequent preferential accumulation in the tumor sites. Particulate radiation (usually beta particles) emitted by the radioisotope kill or damage the tumor cells. The effectiveness of radiopharmaceutical therapy, however, is limited by the size of the tumor treated. Energetic particles can easily exist small tumors before they are able to deposit their energy and inflict significant damage. METHODS: We propose the use of a static magnetic field to be applied after the radiopharmaceutical has localized in the tumors, constraining these particles to helical paths. This application would result in substantially confining the emitted particles within the tumor's boundaries, thus increasing radiation dose to the tumor. RESULTS: Computer simulations of radionuclide treatments using 131I, 186Re and 90Y show that a magnetic field of 10 Tesla can increase the radiation dose achieved by conventional radionuclide therapy by up to 71%. In addition, total radiation dose to surrounding normal tissues is substantially reduced. CONCLUSION: Magnetically enhanced radionuclide therapy (MERiT) therefore shows promise as an effective treatment of cancer and warrants further study.

Beta Particles↗
PubMed1996

A new method for quantitative determination of tritium-labeled nucleoside kinase products adsorbed on DEAE-cellulose.

The counts of tritiated compounds--adsorbed to paper disks, paper chromatograms, electrophoretograms or TLC plates--can be strongly affected by extended self-absorption of tritium beta-particles on the matrix, due to their low energy. Therefore fully quantitative results can be obtained only by elution of the substances or decomposition of the matrix and subsequent counting in homogeneous solution. In this study we describe a new method for fast and proper decomposition of cellulose matrices by cellulase digestion prior to scintillation counting. This new approach yields up to 98% recovery. For method validation recombinant herpes simplex type 1 thymidine kinase was characterised kinetically. The Km of 0.2 microM remained the same as expected but Vmax was considerably higher yielding 1050 pmol/microgram/min.

Adsorption↗
PubMed1998

A new high resolution radioimager for the quantitative analysis of radiolabelled molecules in tissue section.

We present a high-speed, high-resolution imager of beta particles. It is devoted to be used in autoradiography experiments such as receptor binding or in situ hybridization experiments, either instead of, or in complement with autoradiographic film and emulsions. It allows the user to locate and perform quantitative analyses of (3H, 14C, 35S, 33P, 32P, 125I) labelled molecules with a 15 microm spatial resolution on a 0.9 x 1.3 cm2 sensitive area. Combining recent techniques (specific scintillator thin sheets and intensified charge-coupled device (CCD)) this imager offers a wide dynamic range and real-time acquisition.

Animals↗
PubMedDate not supplied

EGS4 Monte Carlo determination of the beta dose kernel in water.

The EGS4 Monte Carlo code has been used to simulate the emission and energy deposition in H2O about point sources of monoenergetic electrons and radionuclides of potential use in radioimmunotherapy. The radiations studied were 0.05, 0.1, 0.5, 1.0, 2.0, and 3.0 MeV monoenergetic electrons and 32P, 67Cu, 90Y, 105Rh, 131I, 153Sm, 186Re, and 188Re beta particles and conversion and Auger electrons. Ten batches of 10,000 electrons (or 10,000 radionuclide decays) each were started isotropically at a point in an infinite homogeneous H2O phantom. The parameter-reduced electron-step transport algorithm (PRESTA) version of the EGS4 Monte Carlo code was used to follow these and their progeny, scoring the energy deposited in thin spherical shells. The scaled dose kernels are calculated and compared to kernels available in the literature. These previously published kernels either completely ignore secondary electrons or are based on a Monte Carlo code which improperly sampled the Landau energy straggling distribution.

Beta Particles↗
PubMed2004

Performance of different thermoluminescence dosimeters in 90SR+90Y radiation fields.

The dosimetry of beta radiation is a difficult process especially because of the low penetration of beta particles in matter. The dosemeter utilised for this kind of procedure needs to approximate an ideal point-like detector: it should be as thin as possible, and its area should be small. The thermoluminescence dosemeters (TLDs) meet with these requirement properties. The aim of this work was to study the dosimetric characteristics of different TLDs to verify the possibility of their use for the calibration of 90Sr+90Y plane applicators. The response reproducibility, calibration curves, TL response as a function of the source-detector distance, the transmission factors and the linearity of the sample response were obtained for several types of dosimetric pellets.

Beta Particles↗
PubMed1998

Calculating lens dose and surface dose rates from 90Sr ophthalmic applicators using Monte Carlo modeling.

Using a 90Sr applicator for brachytherapy for the reduction of recurrence rates after pterygium excisions has been an effective therapeutic procedure. Accurate knowledge of the dose being applied to the affected area on the sclera has been lacking, and for decades inaccurate estimates for lens dose have thus been made. Small errors in the assumptions which are required to make these estimates lead to dose rates changing exponentially because of the attenuation of beta particles. Monte Carlo simulations have been used to evaluate the assumptions that are now being used for the calculation of the surface dose rate and the corresponding determination of lens dose. For an ideal 90Sr applicator, results from this study indicate dose rates to the most radiosensitive areas of the lens ranging from 8.8 to 15.5 cGy/s. This range is based on different eye dimensions that ultimately corresponds to a range in distance between the applicator surface and the germinative epithelium of the lens of 2-3 mm. Furthermore, the conventional 200 cGy threshold for whole lens cataractogenesis is questioned for predicting complications from scleral brachytherapy. The dose to the germinative epithelium should be used for studying radiocataractogenesis.

Beta Particles↗
PubMed1998

177Lu-EDTMP: a potential therapeutic bone agent.

Lutetium-177 (177Lu) has both beta particle emissions for a therapeutic effect and gamma emissions for imaging. This study was undertaken to synthesize and evaluate 177Lu-EDTMP (ethylenediaminetetramethylene phosphonic acid) as a therapeutic radiopharmaceutical for the palliation of pain from bone metastases. Chelation of 177Lu to EDTMP was obtained by heating for 30 min in boiling water at pH 8.8, resulting in a radiochemical yield of over 99%. The compound was stable for 20 days without any appreciable dissociation. Biodistribution studies in normal rats indicated selective bone accumulation, showing faster blood clearance, higher bone uptake and higher bone-to-soft tissue ratios than 99Tcm-MDP. In conclusion, 177Lu-EDTMP has favourable biological and physical characteristics for the palliative treatment of painful bone metastases.

Animals↗
PubMed1998

Direct beta measurements to determine in vivo whole-body activities of 90Sr in residents of the southern Urals: description of a new method.

For 44 individuals living in areas of the Southern Urals with historical 90Sr contamination, whole-body activities of this radionuclide were investigated using a new mobile detection system. Beta-particles from 90Sr/90Y decay were measured in vivo via two proportional counters mounted in front of the forehead and above the head, respectively. In order to correct for absorption by the skin, scalp thickness was measured using ultrasonic techniques. Corrections are given with respect to self-absorption by the bone matrix and absorption by hair. A procedure is described to extrapolate from measured 90Sr activity of the skull bone to total 90Sr skeleton burden. As a result, 90Sr whole-body activities of up to 50 kBq were recorded in the selected cohort. For the same individuals, 90Sr was measured via the detection of bremsstrahlung using an established whole-body counting device. The overall results of both systems agree within 15%, but differences exceeding a factor of 2 were observed in some cases.

Absorption↗
PubMed1985

New estimates of asymmetric decomposition of racemic mixtures by natural beta-radiation sources.

The Vester-Ulbricht hypothesis suggests that the chirality of biological molecules originates from the beta-radiolysis of prebiotic racemic mixtures. Despite the inconclusiveness of past investigations, recent calculations have shown that beta particles, because of their helicity, radiolyse L- and D-enantiomers at slightly different rates, the asymmetry, AR, being predicted to be 10(-11) (new experimental tests, give /AR/ < 2 x 10(-9)). Before this, the size of the radiolysis-induced chiral polarization, eta R (eta triple bond (nL - nD)/(nL + nD) where nL and nD are the numbers of L and D molecules present), was estimated for different values of AR; according to Keszthelyi et al., if /AR/ approximately 10(-11), /eta R/ can never exceed the chiral polarization, /eta F/, produced by statistical fluctuations, thus invalidating the V-U hypothesis. Here we re-examine the major assumptions on which these calculations were based and find that several overly restrictive conditions were imposed, which, when relaxed, allow the condition /eta R/ > /eta F/, in accordance with the V-U hypothesis.

Amino Acids↗
PubMed2002

Characterisation of the thermally stimulated conductivity and thermoluminescence of natural topaz.

Thermally stimulated conductivity (TSC) and thermoluminescence (TL) measurements were conducted to investigate the mechanisms of charge transfer and luminescence emission in natural samples of Brazilian topaz irradiated with beta particles from a 90Sr/90Y source or with a 1.75 MeV Van de Graaff electron beam. The luminescence and conductivity were simultaneously monitored during the heating of the samples, allowing direct comparison of the TL and TSC peaks. The results show that the three main TL peaks are accompanied by corresponding TSC peaks, usually shifted to higher temperatures. Comparison of the relative TL/TSC intensities of peaks 2 and 3 indicates that the process of thermal quenching of the luminescence is probably active, which is also supported by TL/TSC measurements at different heating rates. Results on the dose response of TL/TSC peaks also reveal an interesting feature: the TL intensity shows a monotonic increase with dose in the range of study (50 Gy-3 kGy) comprising a linear-supralinear-saturation characteristic, while the TSC peaks exhibit an increase from 50 Gy to 1 kGy, followed by a small decrease for doses greater than 1 kGy. This result is interpreted in terms of a model involving multiple traps and one recombination centre.

Aluminum Silicates↗
PubMed2005

Response of Harshaw neutron thermoluminescence dosemeters in terms of the revised ICRP/ICRU recommendations.

To monitor workers for external neutron radiation dose, the Y-12 National Security Complex utilises the thermoluminescence dosemeters (TLDs) manufactured by Harshaw. At Y-12, the majority of external dose to workers is due to low-energy photon and/or beta particles emitted from uranium and its progeny. However, some neutron dose is expected since neutrons are produced from (alpha,n) reactions in various compounds found at the plant, including UF4 and UF6. Neutron sources, such as 252Cf, are also used throughout the complex. The Harshaw neutron dosemeter consists of two gamma-sensitive elements (7Li) and two neutron-sensitive elements enriched in 6Li with various shielding/filter materials placed around each of them. In this work, the energy response of the dosemeter to neutrons has been calculated using the Monte Carlo transport code MCNP Version 4-C and, these results are compared with the measured response of the dosemeter to unmoderated and D2O-moderated 252Cf neutrons. The response of the dosemeter has also been determined in terms of the personal absorbed dose and personal dose equivalent as a function of neutron energy based on the recommendations of the ICRP Publication 60 and ICRU Report 49. The energy response of the dosemeter characteristics can be used to generate spectral conversion coefficients for routine neutron absorbed dose and dose equivalent calculations.

Beta Particles↗
PubMed2001

The toxicity of insoluble cerium-144 inhaled by beagle dogs: non-neoplastic effects.

The biological effects of inhaled beta-particle-emitting radionuclides are not well known. The non-neoplastic diseases induced by an inhaled, relatively insoluble form of cerium-144 ((144)Ce) were studied in beagle dogs exposed to graded activity levels of (144)Ce in fused aluminosilicate particles by a single, brief inhalation exposure and observed for their life span. The initial lung burdens (ILBs) achieved ranged from 0.000093-7.6 MBq (144)Ce/kg body weight. The (144)Ce was retained in the lung with an effective half-life of about 190 days. Significant (144)Ce was translocated to the tracheobronchial lymph nodes, and the concentration exceeded that of the lung at about 400 days after inhalation exposure. Significant radiation doses were delivered to the lung and tracheobronchial lymph nodes and to the heart adjacent to the tracheobronchial lymph nodes. Radiation pneumonitis was the predominant non-neoplastic disease. The dose response for radiation pneumonitis indicated that an ILB of 1.4 MBq/kg would cause death from radiation pneumonitis in 50% of the exposed dogs. This ILB resulted in a pulmonary dose to death of about 350 Gy. The tracheobronchial lymph nodes developed lesions in dogs with ILBs lower than those causing radiation pneumonitis. The overall results of this study, however, showed that (144)Ce, inhaled in an insoluble form, did not cause any unique or inexplicable biological effects in dogs or cause effects at unusually low doses that might call current radiation protection guidelines into question.

Administration, Inhalation↗
PubMed2001

Monte Carlo dose calculations of beta-emitting sources for intravascular brachytherapy: a comparison between EGS4, EGSnrc, and MCNP.

The dose parameters for the beta-particle emitting 90Sr/90Y source for intravascular brachytherapy (IVBT) have been calculated by different investigators. At a distant distance from the source, noticeable differences are seen in these parameters calculated using different Monte Carlo codes. The purpose of this work is to quantify as well as to understand these differences. We have compared a series of calculations using an EGS4, an EGSnrc, and the MCNP Monte Carlo codes. Data calculated and compared include the depth dose curve for a broad parallel beam of electrons, and radial dose distributions for point electron sources (monoenergetic or polyenergetic) and for a real 90Sr/90Y source. For the 90Sr/90Y source, the doses at the reference position (2 mm radial distance) calculated by the three code agree within 2%. However, the differences between the dose calculated by the three codes can be over 20% in the radial distance range interested in IVBT. The difference increases with radial distance from source, and reaches 30% at the tail of dose curve. These differences may be partially attributed to the different multiple scattering theories and Monte Carlo models for electron transport adopted in these three codes. Doses calculated by the EGSnrc code are more accurate than those by the EGS4. The two calculations agree within 5% for radial distance <6 mm.

Beta Particles↗
PubMed2001

Dosimetry of beta-ray ophthalmic applicators: comparison of different measurement methods.

An international intercomparison of the dosimetry of three beta particle emitting ophthalmic applicators was performed, which involved measurements with radiochromic film, thermoluminescence dosimeters (TLDs), alanine pellets, plastic scintillators, extrapolation ionization chambers, a small fixed-volume ionization chambers, a diode detector and a diamond detector. The sources studied were planar applicators of 90Sr-90Y and 106Ru-106Rh, and a concave applicator of 106Ru-106Rh. Comparisons were made of absolute dosimetry determined at 1 mm from the source surface in water or water-equivalent plastic, and relative dosimetry along and perpendicular to the source axes. The results of the intercomparison indicate that the various methods yield consistent absolute dosimetry results at the level of 10%-14% (one standard deviation) depending on the source. For relative dosimetry along the source axis at depths of 5 mm or less, the agreement was 3%-9% (one standard deviation) depending on the source and the depth. Crucial to the proper interpretation of the measurement results is an accurate knowledge of the detector geometry, i.e., sensitive volume and amount of insensitive covering material. From the results of these measurements, functions which describe the relative dose rate along and perpendicular to the source axes are suggested.

Alanine↗
PubMed2001

Free radical-initiated and gap junction-mediated bystander effect due to nonuniform distribution of incorporated radioactivity in a three-dimensional tissue culture model.

To investigate the biological effects of nonuniform distribution of radioactivity in mammalian cells, we have developed a novel three-dimensional tissue culture model. Chinese hamster V79 cells were labeled with tritiated thymidine and mixed with unlabeled cells, and multicellular clusters (approximately 1.6 mm in diameter) were formed by gentle centrifugation. The short-range beta particles emitted by (3)H impart only self-irradiation of labeled cells without significant cross-irradiation of unlabeled bystander cells. The clusters were assembled in the absence or presence of 10% dimethyl sulfoxide (DMSO) and/or 100 microM lindane. DMSO is a hydroxyl radical scavenger, whereas lindane is an inhibitor of gap junctional intercellular communication. The clusters were maintained at 10.5 degrees C for 72 h to allow (3)H decays to accumulate and then dismantled, and the cells were plated for colony formation. When 100% of the cells were labeled, the surviving fraction was exponentially dependent on the mean level of radioactivity per labeled cell. A two-component exponential response was observed when either 50 or 10% of the cells were labeled. Though both DMSO and lindane significantly protected the unlabeled or bystander cells when 50 or 10% of the cells were labeled, the effect of lindane was greater than that of DMSO. In both cases, the combined treatment (DMSO + lindane) elicited maximum protection of the bystander cells. These results suggest that the bystander effects caused by nonuniform distributions of radioactivity are affected by the fraction of cells that are labeled. Furthermore, at least a part of these bystander effects are initiated by free radicals and are likely to be mediated by gap junctional intercellular communication.

Animals↗