A 238Pu irradiator for exposure of cultured cells with alpha-radiation: Construction,calibration and dosimetry

An alpha-particle irradiator that can facilitate investigations of alpha-radiation effects on human cells in radiation protection, carcinogenesis and radioimmunotherapy was constructed. The irradiator was based on a 1.3 GBq ²³⁸Pu source, housed in a stainless steel tube flushed with helium. Radiation provided by ²³⁸Pu consists mainly of alpha-particles with energy of 5.5 MeV. The alpha-particle fluence and energy spectra were measured with a silicon semiconductor detector. Monte Carlo simulations were used to estimate the mean number of alpha-particles and the mean absorbed alpha-particle dose to cells for various irradiation times and distances between cells and source. There was a linear dependence between exposure time and alpha-particle fluence for exposure times above 1 s. The alpha-particle activity concentration varied with a factor 2.7 over the source area, while the variation in energy peak position was <4%. At the cell nucleus position and with a distance of 45 mm between the source and the mylar dish surface, the α-fluence was 4.6×10⁴ counts/(mm² s), the average incident α-particle energy was 2.5 MeV and the average linear energy transfer was 167 keV/μm. The average dose rate to the cells, with 5 μm diameter nucleus, was 1.2 Gy/s. The ²³⁸Pu α-particle irradiator is feasible for irradiation of cells and it can be used for studies of both direct effects and bystander effects of alpha-radiation.     

Telomeric sequences, radiation sensitivity and genomic instability.

PURPOSE: To review the basic features of telomeres with particular emphasis on their potential importance in radiation biology. Recent findings suggest that telomere length can influence radiation sensitivity in mouse and that several human radiosensitive disorders also show abnormalities in telomere dynamics. Numerous studies indicate that telomeric sequences may play a role in determining the stability of certain genomic regions both spontaneously and following irradiation. Furthermore, a number of transmissible genomic instability systems have been described in which it appears that telomere metabolism may be contributing to the delayed effects observed. Features of telomeres and telomere biology relevant to these topics are reviewed. CONCLUSIONS: The evidence that telomeres and the molecular pathways of telomere maintenance can play a role in determining the outcome of radiation exposure is now substantial. Thus, the field of telomere biology deserves continued attention from radiobiologists.     

The effect of growth architecture on the induction and decay of bleomycin and X-ray-induced bystander response and genomic instability in lung adenocarcinoma cells and blood lymphocytes

Abstract

Purpose: Cancer patients treated with radiomimetic drug bleomycin (BLM) have shown incidence of 7% second malignancy. Studies regarding BLM-induced genomic instability in bystander cells are scarce, and experiments with cells grown on three-dimensional (3D) cultures to mimic the in-vivo condition have never been attempted.

Materials and methods: A549 and NCI-H23 (human lung adenocarcinoma) cells were grown as 3D cultures using Cytomatrix^?, exposed to BLM or X-radiation and co-cultured with their respective unexposed cells. The DNA damage in direct and bystander cells were assessed by the induction of micronuclei (MN) or phosphorylated serine-15 residue in protein 53 (p53^ser-15), a reflection of DNA damage, and by up-regulation of protein 21 (p21Waf1). The persistence of DNA damage was measured using MN assay and fluorescence in situ hybridization (FISH) in cancer cells and human peripheral blood lymphocytes (PBL) respectively.

Results: BLM or X-irradiation induced DNA damage in both A549 and NCI-H23 cells and their respective bystander cells grown in 2D or 3D cultures. Further persistence of these damages in bystander PBL at delayed times indicated genomic instability in these cells.

Conclusion: BLM-induced genomic instability in the progeny of bystander cells and their significance in therapy-induced second malignancy may not be eliminated completely.     

Design and construction of a new chamber for measuring the thickness of alpha-particle sources

The thickness of charged-particle emitting sources can be determined by varying the incidence angle of particles using silicon semiconductor detectors. The differences in energy between the peaks for an alpha emission measured with different incident angles are due to the energy loss of alpha particles in the source. These shifts can thus be used to estimate the source thickness. A new detection chamber has been constructed for this purpose. Its advantage is the registration of the alpha particles emitted from a given source using up to three different detectors simultaneously. Monte Carlo simulation was used to help to determine the best measurement conditions and interpret the results.     

Radiation-induced biologic bystander effect elicited in vitro by targeted radiopharmaceuticals labeled with alpha-, beta-, and auger electron-emitting radionuclides.

Recent studies have shown that indirect effects of ionizing radiation may contribute significantly to the effectiveness of radiotherapy by sterilizing malignant cells that are not directly hit by the radiation. However, there have been few investigations of the importance of indirect effects in targeted radionuclide treatment. Our purpose was to compare the induction of bystander effects by external beam gamma-radiation with those resultant from exposure to 3 radiohaloanalogs of metaiodobenzylguanidine (MIBG): (131)I-MIBG (low-linear-energy-transfer [LET] beta-emitter), (123)I-MIBG (potentially high-LET Auger electron emitter), and meta-(211)At-astatobenzylguanidine ((211)At-MABG) (high-LET alpha-emitter). METHODS: Two human tumor cell lines-UVW (glioma) and EJ138 (transitional cell carcinoma of bladder)-were transfected with the noradrenaline transporter (NAT) gene to enable active uptake of MIBG. Medium from cells that accumulated the radiopharmaceuticals or were treated with external beam radiation was transferred to cells that had not been exposed to radioactivity, and clonogenic survival was determined in donor and recipient cultures. RESULTS: Over the dose range 0-9 Gy of external beam radiation of donor cells, 2 Gy caused 30%-40% clonogenic cell kill in recipient cultures. This potency was maintained but not increased by higher dosage. In contrast, no corresponding saturation of bystander cell kill was observed after treatment with a range of activity concentrations of (131)I-MIBG, which resulted in up to 97% death of donor cells. Cellular uptake of (123)I-MIBG and (211)At-MABG induced increasing recipient cell kill up to levels that resulted in direct kill of 35%-70% of clonogens. Thereafter, the administration of higher activity concentrations of these high-LET emitters was inversely related to the kill of recipient cells. Over the range of activity concentrations examined, neither direct nor indirect kill was observed in cultures of cells not expressing the NAT and, thus, incapable of active uptake of MIBG. CONCLUSION: Potent toxins are generated specifically by cells that concentrate radiohalogenated MIBG. These may be LET dependent and distinct from those elicited by conventional radiotherapy.     

Design and validation of a motion stage for in vitro MR experiments

A computer-controlled motion stage was designed to facilitate motion studies and simulations of cardiac magnetic resonance (MR) experiments. The stage was constructed to move a phantom of up to 6 kg at velocities up to 15 cm/sec along a two-dimensional trajectory within an MR scanner. The operation of the motion stage was validated and found to be accurate to within 0.08 cm in displacement and 1.5 cm/sec in velocity (root-mean-square error). No image degradation was observed.J. Magn. Reson. Imaging 1999;10:972-977.     

Improvement of a method for the sequential determination of Pb, Ra, and uranium isotopes by LSC and alpha-particle spectrometry

In a previous paper the authors proposed a sequential method for the determination of isotopes of uranium, thorium, radium, and lead from environmental samples using alpha-particle spectrometry and LSC techniques. Although the radiochemical yields were suitable when the assays were performed on synthetic samples, application to real environmental samples caused a major decrease in the radiochemical yield, especially for uranium in inorganic samples (soils). A modification of the procedure is described that overcomes this drawback.     

Detection limits for 90Sr, Pu, Am and Cm in soil and pasture vegetation shortly after a nuclear accident.

This work estimates the critical activity concentrations of 90Sr and the alpha-emitting isotopes of Pu, Am and Cm in soil and pasture vegetation that would be required to exceed the action levels for foodstuffs recommended by the IAEA. The results show that the common detection limits for environmental analysis of these nuclides may be increased by orders of magnitude if the aim of the analysis is to determine whether or not the action levels will be exceeded. This information is useful in the development of more simple and rapid analytical methods to be used shortly after a nuclear accident. In addition to activity concentrations, the critical deposition densities on soil and grazing areas are estimated. Critical limits are also derived for 137Cs and 131I.     

Investigation of neutron shielding properties depending on number of boron atoms for colemanite, ulexite and tincal ores by experiments and FLUKA Monte Carlo simulations

(241)Am-Be source and three samples including different amounts of boron atoms per unit volume called colemanite, ulexite and tincal were used in total macroscopic cross section experiments. Also FLUKA Monte Carlo code was used to simulate total macroscopic cross sections, absorbed doses and deposited energies by low energy neutron interactions. Besides half value layers of samples were calculated and compared to paraffin. As a result, ascending concentration of boron atoms can enhance neutron shielding property of samples.     

Monte Carlo simulations and radiation dosimetry measurements of 142Pr capillary tube-based radioactive implant (CTRI): a new structure for brachytherapy sources

Objective

Previously, a promising $ {\beta^- } $ -emitting praseodymium-142 glass seed was proposed for brachytherapy of prostate cancer. In accordance with the previous study, a ¹⁴²Pr capillary tube-based radioactive implant (CTRI) was suggested as a source with a new structure to enhance application of $ {\beta^- } $ -emitting radioisotopes such as ¹⁴²Pr in brachytherapy.

Methods

Praseodymium oxide powder was encapsulated in a glass capillary tube. Then, a thin and flexible fluorinated ethylene propylene Teflon^® layer sealed the capillary tube. The source was activated in the Tehran Research Reactor by the ¹⁴¹Pr(n,γ) ¹⁴²Pr reaction. Measurements of the dosimetric parameters were performed using GafChromic^® radiochromic film. In addition, the dose rate distribution of ¹⁴²Pr CTRI was calculated by modeling ¹⁴²Pr source in a water phantom using Monte Carlo N-Particle Transport (MCNP5) Code.

Results

The active source was unreactive and did not leak in water. In comparison with the earlier proposed ¹⁴²Pr seed, the suggested source showed similar desirable dosimetric characteristics. Moreover, the ¹⁴²Pr CTRI production procedure may be technically and economically more feasible. The mass of praseodymium in CTRI structure could be greater than that of the ¹⁴²Pr glass seed; therefore, the required irradiation time and the neutron flux could be reduced.

Conclusion

A ¹⁴²Pr CTRI was proposed for brachytherapy of prostate cancer. The dosimetric calculations by the experimental measurements and Monte Carlo simulation were performed to fulfill the requirements according to the American Association of Physicists in Medicine recommendations before the clinical use of new brachytherapy sources. The characteristics of the suggested source were compared with those of the previously proposed ¹⁴²Pr glass seed.     

Incorporating the effects of transcytolemmal water exchange in a reference region model for DCE-MRI analysis: theory, simulations, and experimental results.

Models have been developed for the analysis of dynamic contrast-enhanced MRI (DCE-MRI) data that do not require direct measurements of the arterial input function; such methods are referred to as reference region models. These models typically return estimates of the volume transfer constant (K(trans)) and the extravascular extracellular volume fraction (v(e)). To date such models have assumed a linear relationship between the measured R(1) ( identical with 1/T(1)) and the concentration of contrast agent, a transformation referred to as the fast exchange limit, but this assumption is not valid for all concentrations of an agent. A theory for DCE-MRI reference region models which accounts for water exchange is presented, evaluated in simulations, and applied in tumor-bearing mice. Using reasonable parameter values, simulations show that the assumption of fast exchange can underestimate K(trans) and v(e) by up to 82% and 46%, respectively. By analyzing a large region of interest and a single voxel the new model can return parameters within approximately +/-10% and +/-25%, respectively, of their true values. Analysis of experimental data shows that the new approach returns K(trans) and v(e) values that are up to 90% and 73%, respectively, greater than conventional fast exchange analyses.     

Direct and indirect parameters of free thyroxine. I. Method, quality control and in vitro experiments on storage of samples and effect of drugs

The clinical applicability of direct FT4 determinations by the radioimmunoassays ImmoPhase, GammaCoat, Liquisol, Amerlex and LisoPhase is tested in comparison to the FT4 index and the T4/TBG ratio. Part I of this study deals with technical aspects concerning quality control as well as with in-vitro experiments concerning storage of samples and interference of drugs. The precision of FT4-RIAs is satisfactory; inter-assay coefficients of variation are generally lower than 10% for medium hormone concentrations. Because of a change of the standard curve calibration by the manufacturer of the Liquisol kit, the inter-assay variability (17%) of this assay is unacceptably high. The comparison of working ranges shows that the sensitivity of all FT4 assays is sufficient. However, the upper limits of working ranges of the Liquisol and LisoPhase kits are too low. Storing the samples in form of serum yields lower values for any FT4 parameter than storing as whole blood. This unexpected observation is true for room temperature as well as for refrigeration at 4 degrees C. To be sure, the values of indirect FT4 parameters from serum and whole blood coincide somewhat better especially when the samples are stored in the refrigerator. Repeated thawing and refreezing does not influence the results of FT4-RIAs significantly. In vitro testing of drug interferences by addition of therapeutic doses of primidone, phenobarbital, phenytoin and acetylsalicylic acid yields significant effects only for the last quoted pharmaceutical. While the FT4 levels of the Liquisol and LisoPhase assays rise with the acetylsalicylic acid dose according to expectations, the values of the Amerlex and GammaCoat assays decrease. With regard to handling of the tests, there are no special technical problems for all FT4-RIAs tested.     

Performance of CdTe, HPGe and NaI(Tl) detectors for radioactivity measurements.

The characteristics and performances of the NIST High-Purity Germanium (HPGe), Sodium Iodide (NaI(Tl)) and Cadmium Telluride (CdTe) gamma-ray detectors were studied. The efficiencies, the minimum detectable activities and the energy resolutions of each were measured and compared. The data were analyzed using different software packages. The measurements were performed in a low background radiation environment using calibrated point sources. The CdTe detector showed a higher energy resolution than the NaI(Tl) detector but a lower efficiency than both the HPGe and NaI(Tl) detectors. This makes it a suitable detector only for relatively high activity measurements restricted to the 35 keV to 200 keV energy range.     

Correlation between detector array measurements and a computer algorithm for enhanced dynamic wedge profiles.

Verification of dosimetric data computed by a treatment planning system is necessary in the commissioning process for any clinical software, just as it is necessary for any annual quality assurance testing. Direct verification of the dosimetric data is achievable when calculating the enhanced dynamic wedge (EDW) off-axis ratio at each point of interest. As mathematical models for hand-calculating such factors are still evolving, measurement of these external beam arrangements has proven significantly more accurate. This research presents a correlation for measured and planned data, specific for 6- and 18-MV photon beams on a Varian 21EX linear accelerator, using the EDW mode. Field generation was created using the Varian Eclipse treatment planning system. On treatment field delivery, the Sun Nuclear MapCHECK diode array was used to plot each beam profile in 2 dimensions. Wedge angles of 10 degrees , 15 degrees , 20 degrees , 25 degrees , 30 degrees , 45 degrees and 60 degrees were studied here, under isocentric geometry, at a fixed water equivalent depth of 15 cm. Field size dependence was considered with each wedge and energy combination, where symmetric apertures of 5 x 5 cm(2), 10 x 10 cm(2), 15 x 15 cm(2) and 20 x 20 cm(2) were used. Accurate dosimetric results were found to be achievable when using this treatment planning system to within 2.8% maximum deviation, and to within 1% deviation averaged over all. The diode array also proved to be simple and ideally suited for EDW measurements.     

Development and characterisation of a head calibration phantom for in vivo measurements of actinides.

The investigation of actinides' internal contamination in human body makes use of a variety of techniques. In large scale screening the technique of "in vivo" evaluation of bone 241Am burden via the determination of the nuclide activity in the skull is often used. For this purpose, adequate calibration procedures and standard phantoms are needed. The present paper summarises the studies and technical procedures followed for the development of a calibration phantom based on a commercial Alderson angiographic head in which a set of 24 241Am point sources were embedded. A theoretical study was first carried out, at the ENEA Institute for Radiation Protection, using the MCNP4-B Monte Carlo code to determine the point source distribution that closely approximates a homogeneous bone contamination. The numerical models were also used to evaluate the resulting degree of approximation. The point sources were prepared at the ENEA National Metrology Institute for ionising radiation quantities and were traceable to the Italian national standard of radionuclide activity. The sources were prepared by quantitatively dispensing a liquid solution onto a plastic disc. The activity of each source was checked by gamma-ray spectrometry and the reproducibility of the activity values was determined. Each source was then placed in the optimum position in the skull, given by the Monte Carlo modelling, by a precision mechanical device. The phantom was finally used to calibrate a whole body counter operating at the ENEA Institute for Radiation Protection. The paper reports the main theoretical and experimental aspects of this work, and also discusses the results of the first calibrations.     

Study of an alpha track analysis and a fission track analysis for determining the hot particles contaminated with Pu and U isotopes.

A fission track analysis and alpha track analysis were developed to detect fissile particles such as uranium and plutonium isotopes as well as to identify particle-bound plutonium in contaminated soil or sediment. To record a reference point, a locator SEM grid electroplated with boron was used to obtain a recorded grid image on the Lexan or CR-39 detector. With the fission track technique, the track images of the grid coated with boron and the fissile nuclides on the CR-39 detector were clearly recorded so that the location of the fissile particles could be easily identified in the radio-contaminated soil matrix. With the alpha track technique, many of the hot particles in the BOMARC soil turned out to be contaminated with plutonium isotopes rather than uranium isotopes.