Spatial Distribution Of Radioactivity Research Articles

Measurement and spatial distribution pattern of natural radioactivity in a uranium tailings pond in Northwest China

ABSTRACT Numbers of radioactive tailings were produced in the process of uranium mining and milling.In this study,radiation environment monitoring was carried out on a decommissioned uranium mining and milling tailings pond in northwest China, and the governance effect and operation status of the tailings pond was investigated. The soil radionuclide activity concentration and ambient dose equivalent rate (H*(10)) were measured, and soil surface radon exhalation rate was calculated. The results shown that in the tailings pond and its surrounding area, the average soil radionuclide activity concentration was respectively 238U: 42.64±11.17 Bq·kg-1, 226Ra: 45.47±13.56 Bq·kg-1, 232Th: 33.30±7.33 Bq·kg-1, 40K: 631.33±72.05 Bq·kg-1, the average H*(10) was 63.32±6.46 nSv·h-1, and the average radon exhalation rate was 40.46±11.29 mBq·m-2·s-1.Radionuclide activity concentration, H*(10) and radon exhalation rate were within the range of world natural background. Spatial distribution of radioactivity was analyzed by OK interpolation based on the investigated data. According to the measured results and spatial interpolation analysis,the decommissioning governance effect of the uranium tailings reservoir is good, the operation is normal, and there is no migration or diffusion situation of radionuclides in the pond has been found.

Targeting Micrometastases: The Effect of Heterogeneous Radionuclide Distribution on Tumor Control Probability.

The spatial distribution of radiopharmaceuticals that emit short-range high linear-energy-transfer electrons greatly affects absorbed dose and biological effectiveness. The purpose of this study was to investigate the effect of heterogeneous radionuclide distribution on tumor control probability (TCP) in a micrometastasis model. Methods: The cancer cell lines MDA-MB-468, SQ20B, and 231-H2N were grown as spheroids to represent micrometastases. The intracellular distribution of a representative radiopeptide (111In-labeled epidermal growth factor) and radioimmunotherapeutic (111In-labeled trastuzumab) was determined in cell internalization experiments. The intratumoral distribution was evaluated by microautoradiography of spheroids. γH2AX staining was performed on spheroid sections to correlate DNA damage with radionuclide distribution. Experimental surviving fractions were obtained using clonogenic assays. A random close-packed algorithm, which models the random packing behavior of cells and reflects variation in the radii of cells and nuclei, was used to simulate 3-dimensional spheroids. Calculated survival fractions were generated using an iterative modeling method based on Monte Carlo–determined absorbed dose with the PENELOPE code and were compared with experimental surviving fraction. Radiobiologic parameters deduced from experimental results and Monte Carlo simulations were used to predict the TCP for a 3-dimensional spheroid model. Results: Calculated survival fractions agreed well with experimental data, particularly when an increased value for relative biological effectiveness was applied to self-dose deposited by sources located in the nucleus and when radiobiologic parameters were adjusted to account for dose protraction. Only in MDA-MB-468 spheroids treated with 111In-epidermal growth factor was a TCP of more than 0.5 achieved, indicating that for this cell type the radiopeptide would be curative when targeting micrometastases. This ability is attributed to the relative radiosensitivity of MDA-MB-468 cells, high nuclear uptake of the radiopeptide, and uniform distribution of radioactivity throughout the spheroid. Conclusion: It is imperative to include biologic endpoints when evaluating the distribution of radionuclides in models emulating micrometastatic disease. The spatial distribution of radioactivity is a clear determinant of biological effect and TCP as demonstrated in this study.

Leaching of uranyl–silica complexes from the host metapelite rock favoring high radon activity of subsoil air: case of Castañar cave (Spain)

Castanar cave is a subterranean site with an outstanding natural environmental radioactivity. The maintaining of high radon activity of cave air and the detection of spatially anomalies of this gas in some cave emplacements, suggests that some natural geochemical processes are involved on the mobilization of radioactivity sources to cave environment, other than a simple exhalation of radon from the host-rock. The host rocks are interlaid dolostone–metapelite beds with radioactive nuclides of the three actinium, thorium and uranium decay series. In situ measurements on the spatial distribution of radioactivity, uranyl group’s luminescence and radon gas concentrations inside cave were main focus of this work to model lixiviation and deposition mechanisms of radioactive elements from the host rock to the karstic system. In addition, collected micro-samples were also analyzed by a multi-approach suite of analytical techniques: inductively coupled plasma mass spectrometry, environmental scanning electron microscopy with an attached X-ray energy dispersive system and spectral cathodoluminescence detector, thermoluminescence, Raman spectroscopy, X-ray diffraction, differential-thermal and thermogravimetry analysis, Alpha-spectrometry and Gamma-spectrometry techniques. The host metapelitic beds contain Zr(Hf)–Th(U)–Ti–P–REE phases such as zircon, xenotime-(Y), monazite-(Ce, La) and poly-metallic mineralization veins of hydrothermal origin. Carbonated host beds and speleothems show frequently chemical elements leaked from the upper host rock masses. The weathering leakage processes are favored by the existence of pyrite and limonite in the dolostone masses. The cave exhibits under UV lamps abundant hydrous silica–uranyl coatings covering carbonated speleothems with radionuclides of 238U natural decay series. The long-lived radio-nuclides of the radium radioactive decay chain are responsible of the continuous regeneration of radon gas inside cave. The experimental work was focused to identify origin and remobilization processes of radio-nuclides and their latte settlement into the cave environment associated to mineral phases of speleothems and cave deposits.

A systematic evaluation of the dose-rate constant determined by photon spectrometry for 21 different models of low-energy photon-emitting brachytherapy sources

The aim of this study was to perform a systematic comparison of the dose-rate constant (Λ) determined by the photon spectrometry technique (PST) with the consensus value (CONΛ) recommended by the American Association of Physicists in Medicine (AAPM) for 21 low-energy photon-emitting interstitial brachytherapy sources. A total of 63 interstitial brachytherapy sources (21 different models with 3 sources per model) containing either 125I (14 models), 103Pd (6 models) or 131Cs (1 model) were included in this study. A PST described by Chen and Nath (2007 Med. Phys. 34 1412–30) was used to determine the dose-rate constant (PSTΛ) for each source model. Source-dependent variations in PSTΛ were analyzed systematically against the spectral characteristics of the emitted photons and the consensus values recommended by the AAPM brachytherapy subcommittee. The values of PSTΛ for the encapsulated sources of 103Pd, 125I and 131Cs varied from 0.661 to 0.678 cGyh−1 U−1, 0.959 to 1.024 cGyh−1U−1 and 1.066 to 1.073 cGyh−1U−1, respectively. The relative variation in PSTΛ among the six 103Pd source models, caused by variations in photon attenuation and in spatial distributions of radioactivity among the source models, was less than 3%. Greater variations in PSTΛ were observed among the 14 125I source models; the maximum relative difference was over 6%. These variations were caused primarily by the presence of silver in some 125I source models and, to a lesser degree, by the variations in photon attenuation and in spatial distribution of radioactivity among the source models. The presence of silver generates additional fluorescent x-rays with lower photon energies which caused the PSTΛ value to vary from 0.959 to 1.019 cGyh−1U−1 depending on the amount of silver used by a given source model. For those 125I sources that contain no silver, their PSTΛ was less variable and had values within 1% of 1.024 cGyh−1U−1. For the 16 source models that currently have an AAPM recommended CONΛ value, the agreement between PSTΛ and CONΛ was less than 2% for 15 models and was 2.6% for 1 103Pd source model. Excellent agreement between PSTΛ and CONΛ was observed for all source models that currently have an AAPM recommended consensus dose-rate constant value. These results demonstrate that the PST is an accurate and robust technique for the determination of the dose-rate constant for low-energy brachytherapy sources.

Spatial distribution of 241Am, 137Cs, 238Pu, 239,240Pu and 241Pu over 17 year periods in the Ravenglass saltmarsh, Cumbria, UK

Ninety five surface scrape samples were collected at the Ravenglass saltmarsh and analysed for radionuclides by alpha spectrometry ( 238Pu and 239,240Pu), gamma spectrometry ( 241Am and 137Cs) and liquid scintillation counting ( 241Pu). Both 241Am and 137Cs activities are compared with those reported by Horrill [1983. Concentrations and spatial distribution of radioactivity in an ungrazed saltmarsh. In: Coughtrey, P.J. (Ed.), Ecological Aspects of Radionuclide Release. British Ecological Society Special Publication No. 3. Blackwell, Oxford, pp. 119–215.] Significant decreases in activities for both radionuclides were observed which is caused by the declining levels of discharges from the Sellafield nuclear reprocessing plant since the 1980s. It has been concluded that the spatial distribution of these radionuclides are controlled by the tidal currents and the clay contents in the sediments. There is evidence of surface erosion of the saltmarsh and redistribution of radionuclides in the saltmarsh using isotopic ratios of measured Pu.

18F]EF3 is not superior to [18F]FMISO for PET-based hypoxia evaluation as measured in a rat rhabdomyosarcoma tumour model

The aim of this investigation was to quantitatively compare the novel positron emission tomography (PET) hypoxia marker 2-(2-nitroimidazol-1-yl)-N-(3[(18)F],3,3-trifluoropropyl)acetamide ([(18)F]EF3) with the reference hypoxia tracer [(18)F]fluoromisonidazole ([(18)F]FMISO). [(18)F]EF3 or [(18)F]FMISO was injected every 2 days into two separate groups of rats bearing syngeneic rhabdomyosarcoma tumours. In vivo PET analysis was done by drawing regions of interest on the images of selected tissues. The resulting activity data were quantified by the percentage of injected radioactivity per gram tissue (%ID/g) and tumour to blood (T/B) ratio. The spatial distribution of radioactivity was defined by autoradiography on frozen tumour sections. The blood clearance of [(18)F]EF3 was faster than that of [(18)F]FMISO. The clearance of both tracers was slower in tumour tissue compared with other tissues. This results in increasing T/B ratios as a function of time post tracer injection (p.i.). The maximal [(18)F]EF3 tumour uptake, compared to the maximum [(18)F]FMISO uptake, was significantly lower at 2 h p.i. but reached similar levels at 4 h p.i. The tumour uptake for both tracers was independent of the tumour volume for all investigated time points. Both tracers showed heterogeneous intra-tumoural distribution. [(18)F]EF3 tumour uptake reached similar levels at 4 h p.i. compared with tumour retention observed after injection of [(18)F]FMISO at 2 h p.i. Although [(18)F]EF3 is a promising non-invasive tracer, it is not superior over [(18)F]FMISO for the visualisation of tumour hypoxia. No significant differences between [(18)F]EF3 and [(18)F]FMISO were observed with regard to the intra-tumoural distribution and the extra-tumoural tissue retention.

MO‐D‐AUD B‐02: Dose Rate Constants Determined by a Photon Spectrometry Technique for 20 Different Models of Low‐Energy Brachytherapy Sources

Purpose: To perform a systematic and independent determination of the dose rate constants (Λ) of available low‐energy interstitial brachytherapy sources using a recently developed photon spectrometry technique (PST). Method and Materials: A total of 60 low‐energy interstitial brachytherapy sources (20 different models with 3 sources per model) containing either (14 models), (5 models), or (one model) were included in this study. A recently developed photon spectrometry technique (Med. Phys. 34, 1412–1430, 2007) was used to determine the PSTΛ for each source. Source‐dependent variations in PSTΛ were analyzed systematically against the spectral characteristics of the emitted photons and the AAPM consensus values (CONΛ) when available. Results: The PSTΛ determined for the , , and sources had values of 0.661 to 0.678, 0.959 to 1.024, and 1.066 cGyh−1U−1, respectively. The variation in PSTΛ among the 5 source models was less than 3%; due mainly to the variations in spatial distribution of radioactivity. The variation in PSTΛ among the 14 source models was larger and the maximum difference was over 6%. These variations were caused primarily by the presence of silver in some source models and, to a lesser degree, by the variations in activity distribution. When silver was present, the PSTΛ exhibited strong dependence on the silver content with values varying from 0.959 to 1.019 cGyh−1U−1. When silver was absent, the PSTΛ was less variable and had values within 1% of 1.024 cGyh−1U−1. The PSTΛ was found within 2% (14 models) and 2.6% (one model) of CONΛ for 15 models current have such a value. Conclusion: Excellent agreement between PSTΛ and CONΛ was observed for all source models that currently have an AAPM consensus value. These results demonstrate that the PST is an accurate and robust technique for the determination of Λ for low‐energy brachytherapy sources.

Photon energy spectrum emitted by a novel polymer‐encapsulated source and its effect on the dose rate constant

Two independent groups have published intrinsic dosimetry parameters for the recently introduced OptiSeed103 interstitial brachytherapy source which contains 103Pd encapsulated by a novel polymer shell. The dose rate constant (Lambda) reported by the two groups, however, differed by more than 6% and there is currently no AAPM recommended consensus value for this source in clinical dosimetry. The aim of this work was to perform an independent determination of Lambda for the OptiSeed103 source using a recently developed photon spectrometry technique. Three OptiSeed103 sources (model 1032P) with known air-kerma strength were used in this study. The photon energy spectrum emitted along the radial direction on the source's bisector was measured in air using a high-resolution intrinsic germanium spectrometer designed and established for low-energy brachytherapy source spectrometry. The dose rate constant of each source was determined from its emitted energy spectrum and the spatial distribution of radioactivity in the source. Unlike other sources made with traditional titanium encapsulation, the photons emitted by the OptiSeed103 sources exhibited only slight spectral hardening, yielding a relative energy spectrum closer to that emitted by bare 103Pd. The dose rate constant determined by the photon spectrometry technique for water was 0.664 +/- 0.025 cGy h(-1) U(-1). This value agreed, within experimental uncertainties, with the Monte Carlo-calculated value (MCLambda) of 0.665 +/- 0.014 cGy h(-1) U(-1) and the TLD-measured value (with a Monte Carlo-calculated solid-phantom-to-water conversion factor) of 0.675 +/- 0.051 cGy h(-1) U(-1) reported by Wang and Hertel [Appl. Radiat. Isot. 63, 311-321 (2005)]. However, it differed by -6.7% from the McLambda of 0.712 +/- 0.043 cGy h(-1) U(-1) reported by Bernard and Vynckier [Phys. Med. Biol. 50, 1493-1504 (2005)]. The results obtained in this work provide additional information needed for establishing a consensus value for the dose rate constant for the OptiSeed103 source. It suggests that an eventual consensus value of Lambda for the OptiSeed103 source is likely to be closer to a value of 0.668 cGy h(-1) U(-1) rather than 0.693 cGy h(-1) U(-1) as initially recommended by the source manufacturer based on the two previously published results.

Optimization of wavelet processing of dynamic PET data

Several groups have reported that wavelet denoising can be used to increase the signal-to-noise (SNR) of dynamic PET studies (4D PET). But wavelet denoising can be applied in different ways and the process involves the arbitrary choice of strength parameters. Too much denoising results in a loss of resolution and biased concentration histories. The goal of this work is to study how to optimize wavelet denoising for neuroreceptor studies. Event by event Monte Carlo simulation was used to create an ensemble of 50 dynamic data sets. The simulation incorporates the geometry, electronic and detector characteristics of a commercial PET scanner (ECAT HR+) as well as the nuclear interactions necessary to describe the coincidence, random and scatter events. Temporal and spatial distribution of radioactivity was defined using a digital brain phantom and measured kinetic parameters. Sinograms for 70 minutes of data were computed to be similar to the noise level of 11C-raclopride in the human brain and then reconstructed using filtered back projection. 3D-wavelet denoising was applied to the ensemble of simulations. We studied denoising schemes that used either a fixed threshold for all wavelet coefficients or alternatives in which we varied thresholds for each sub-band. The wavelet transform of the mean of 50 fifty simulations was taken as the expected value. The RMS difference between the mean and noisy simulations was minimized by varying the thresholds. Noise was measured as the voxel-wise sample standard deviation for both conventional and denosied data sets. We also computed binding potential (BP) for the raw and processed data, with voxel-wise mean and standard deviation as end points. Bias was computed for both concentration and BP as the difference in means for the raw and denoised data set. Three-dimensional wavelet denosing with a single threshold yielded increased SNR, but only at the expense of significant bias. Optimization of sub-band thresholds yielded a 2x improvement in SNR for the 4D concentration data (See Fig. 1) and a 1.5x improvement for PB. More than 84% of voxels had bias less 3%. We conclude that optimized wavelet denoising can increase SNR in dynamic PET with low bias and minimal loss of resolution.

Method for 14C‐labeling maize field plots and assessment of label uniformity within plots

There is increasing interest in use of isotopic tracers to study nutrient liberation and transformation in plant tissues and soils. We developed a technique for pulse‐labeling plants in the field with 14C. Spatial distribution of radioactivity was measured in plots of maize (Zea mays L.) plants exposed to 14CO2. Two clear polyvinyl chambers measuring 1 m wide × 2 m long × 1 m high were used to 14C‐ label maize plants in conventional tillage and no‐tillage treatments. A closed loop in‐line with a pump allowed injection of 14CO2 and unlabeled CO2, and subsampling through an infrared gas analyzer. Cooling and mixing of the air within the chambers was achieved through the use of a free‐standing automobile radiator with fan placed in the center of each plot. The specific activities of leaf tips differed by an order of magnitude among maize plants within the plot. Tillage and time after labeling within the first 48 h had no significant effect on specific activity of maize plants. Plant activity significantly differed by row. The row closest to the inlet and along the edge of the chamber was significantly lower in several plots. Despite differences among leaf tip specific activities, total aboveground activity was uniform within the plot. Plant allometry and plant sampling immediately after labeling would help in correcting for within chamber variability in future field labeling studies.

α線測定用線源における放射性核種の平面分布の固体飛跡検出器によるオートラジオグラフィ

A technique of autoradiography using solid state track detectors is described by which spatial distribution of radioactivity in an alphacounting source can easily be visualized. As solid state track detectors, polymer of allyl diglycol carbonate was used. The advantage of the present technique was proved that alpha-emitters can be handled in the light place alone through the whole course of autoradiography, otherwise in the conventional autoradiography the alpha-emitters, which requires special carefulness from the point of radiation protection, must be handled in the dark place with difficulty. This technique was applied to rough examination of self-absorption of the plutonium source prepared by the following different methods; the source (A) was prepared by drying at room temperature, (B) by drying under an infrared lamp, (C) by drying in ammonia atmosphere after redissolving by the addition of a drop of distilled water which followed complete evaporation under an infrared lamp and (D) by drying under an infrared lamp after adding a drop of diluted neutral deter-gent. The difference in the spatial distributions of radioactivity could clearly be observed on the autoradiography. For example, the source (C) showed the most diffuse distribution, which suggested that the self-absorption of this source was the smallest. The present autoradiographic observation was in accordance with the result of the alpha-spectrometry with a silicon surface-barrier detector.

Radiation dose estimates for interstitialradiocolloid lymphoscintigraphy

The spatial distribution of radioactivity in the injection site, and its rate of clearance, have been measured in patients undergoing various types of interstitial radiocolloid lymphoscintigraphy using 99mTc-antimony sulfide colloid. The clearance of radioactivity from the injection site, and the expansion with time of the localized radioactivity vary considerably for different sites of injection. Maximum absorbed dose estimates of 45.6 rads to the center of the injection site (rectus sheath) and 21 rads to individual lymph nodes have been calculated for patients undergoing internal mammary lymphoscintigraphy with 450 mu Ci injected radioactivity. Absorbed dose estimates for finger web, toe web, and perianal injection sites are also presented.