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At least 199 records · Page 11Linked to original sources

PubMed2006

Computer-aided detection of solid lung nodules in lossy compressed multidetector computed tomography chest exams.

RATIONALE AND OBJECTIVES: To assess the effect of three-dimensional (3D) lossy image compression of multidetector computed tomography chest scans on computer-aided detection (CAD) of solid lung nodules greater than 4 mm in size. MATERIALS AND METHODS: A total of 120 cases, acquired with 1.25-mm collimation, were collected from 5 different sites, of which 66/120 were low-dose cases. Two chest radiologists established that 37 cases had no actionable lung nodules; the remaining 83 cases contained 169 nodules (range 3.8-35.0 mm, mean 5.8 mm +/- 3.0 [SD]). All cases were compressed using the 3D Set Partitioning in Hierarchical Trees algorithm to 24:1, 48:1, and 96:1 levels. A study of the effect of compression on computer-aided detection (CAD) sensitivity was performed at operating points of 2.5 false marks (FM), 5 FM, and 10 FM per case using McNemar's test. Logistic regression models were used to evaluate the impact on CAD sensitivity by compression level on nodule and image characteristics. RESULTS: Compared with no compression, there was no significant degradation in CAD sensitivity found at any of the studied compression levels and operating points. However, between compression levels, there was marginal association with sensitivity. Specifically, 24:1 level was significantly better than 96:1 at all operating points, and occasionally better than no compression at 10 FM/case. Based on multivariate analysis, nodule location was found to be a significant predictor (P = .01) with a lower sensitivity associated with juxtapleural nodules. Nodule size, dose, reconstruction filter, and contrast medium were not significant predictors. CONCLUSION: CAD detection performance of solid lung nodules did not suffer until 48:1 compression.

Algorithms↗

PubMed2006

New developments in exposure assessment: the impact on the practice of health risk assessment and epidemiological studies.

The field of exposure assessment has matured significantly over the past 10-15 years. Dozens of studies have measured the concentrations of numerous chemicals in many media to which humans are exposed. Others have catalogued the various exposure pathways and identified typical values which can be used in the exposure calculations for the general population such as amount of water or soil ingested per day or the percent of a chemical than can pass through the skin. In addition, studies of the duration of exposure for many tasks (e.g. showering, jogging, working in the office) have been conducted which allow for more general descriptions of the likely range of exposures. All of this information, as well as the development of new and better models (e.g. air dispersion or groundwater models), allow for better estimates of exposure. In addition to identifying better exposure factors, and better mathematical models for predicting the aerial distribution of chemicals, the conduct of simulation studies and dose-reconstruction studies can offer extraordinary opportunities for filling in data gaps regarding historical exposures which are critical to improving the power of epidemiology studies. The use of probabilistic techniques such as Monte Carlo analysis and Bayesian statistics have revolutionized the practice of exposure assessment and has greatly enhanced the quality of the risk characterization. Lastly, the field of epidemiology is about to undergo a sea change with respect to the exposure component because each year better environmental and exposure models, statistical techniques and new biological monitoring techniques are being introduced. This paper reviews these techniques and discusses where additional research is likely to pay a significant dividend. Exposure assessment techniques are now available which can significantly improve the quality of epidemiology and health risk assessment studies and vastly improve their usefulness. As more quantitative exposure components can now be incorporated into these studies, they can be better used to identify safe levels of exposure using customary risk assessment methodologies. Examples are drawn from both environmental and occupational studies illustrating how these techniques have been used to better understand exposure to specific chemicals. Some thoughts are also presented on what lessons have been learned about conducting exposure assessment for health risk assessments and epidemiological studies.

Bayes Theorem↗

PubMed2006

Benefit of three-dimensional image-guided stereotactic localization in the hypofractionated treatment of lung cancer.

PURPOSE: The aim of this study was to investigate the benefit of image-guided stereotactic localization in the hypofractionated treatment for medically inoperable non-small-cell lung cancer. METHODS AND MATERIALS: A stereotactic body localizer (SBL) system was used for patient immobilization, reliable image registration among multiphase computed tomography (CT) scanning, and image-guided stereotactic localization. Three sets of CT scans were taken (free breathing, and breath holding at the end-tidal inspiration and expiration, respectively) to contrast target motion. Target delineation was performed on all 3 sets of images and the combination of the targets forms an internal target volume (ITV). In this retrospective study of treatment dose verification, we performed image fusion between the simulation CT scan and each pretreatment CT scan to obtain the same target and critical structure information. The same treatment plans were reloaded onto each pretreatment CT scan with their respective stereotactic coordinate system. The changes in dose distributions were assessed by dose-volume histograms of the planning target volume (PTV) and the critical structures before and after isocenter corrections which were prompted by image-guided stereotactic localization. We compared D95, D99, and V95 for the PTV and internal target volume, and V20 and V30 for the ipsilateral lung. RESULTS: Our retrospective study for 10 patients with 40 dose reconstructions showed that the average D95, D99, and V95 of the PTVs are 92.1%, 88.1%, and 95.8% of the planned values before isocenter corrections. With the corrections, all of these values are improved to 100% of the planned values. CONCLUSIONS: Three-dimensional image guidance is crucial for stereotactic radiotherapy of lung tumors.

Carcinoma, Non-Small-Cell Lung↗

PubMed2004

A comparative study of (239,240)Pu in soil near the former Rocky Flats Nuclear Weapons Facility, Golden, CO.

The Rocky Flats Nuclear Weapons Plant near Golden, CO released plutonium into the environment during almost 40 years of operation. Continuing concern over possible health impacts of these releases has been heightened by lack of public disclosure of the US Department of Energy (DOE) activities. A dose reconstruction study for the Rocky Flats facilities, begun in 1990, provided a unique opportunity for concerned citizens to design and implement field studies without participation of the DOE, its contractors, or other government agencies. The Citizens Environmental Sampling Committee was formed in late 1992 and conducted a field sampling program in 1994. Over 60 soil samples, including both surface and core samples, were collected from 28 locations where past human activities would have minimal influence on contaminant distributions in soil. Cesium-137 activity was used as a means to assess whether samples were collected in undisturbed locations. The distribution of plutonium (as (239,240)Pu) in soil was consistent with past sampling conducted by DOE, the Colorado Department of Public Health and Environment, and others. Elevated levels of (239,240)Pu were found immediately east of the Rocky Flats Plant, with concentrations falling rapidly with distance from the plant to levels consistent with background from fallout. Samples collected in areas south, west, and north of the plant were generally consistent with background from fallout. No biases in past sampling due to choice of sampling locations or sampling methodology were evident. The study shows that local citizens, when provided sufficient resources, can design and implement technical studies that directly address community concerns where trust in the regulated community and/or regulators is low.

Colorado↗

PubMed2005

Model testing using data on 137Cs from Chernobyl fallout in the Iput River catchment area of Russia.

Data collected for 10 years following the Chernobyl accident in 1986 have provided a unique opportunity to test the reliability of computer models for contamination of terrestrial and aquatic environments. The Iput River scenario was used by the Dose Reconstruction Working Group of the BIOMASS (Biosphere Modelling and Assessment Methods) programme. The test area was one of the most highly contaminated areas in Russia following the accident, with an average contamination density of 137Cs of 800,000 Bq m-2 and localized contamination up to 1,500,000 Bq m-2, and a variety of countermeasures that were implemented in the test area had to be considered in the modelling exercise. Difficulties encountered during the exercise included averaging of data to account for uneven contamination of the test area, simulating the downward migration and changes in bioavailability of 137Cs in soil, and modelling the effectiveness of countermeasures. The accuracy of model predictions is dependent at least in part on the experience and judgment of the participant in interpretation of input information, selection of parameter values, and treatment of uncertainties.

Cesium Radioisotopes↗

PubMed1999

Modelling radionuclide distribution and transport in the environment.

Mathematical models of radionuclide distribution and transport in the environment have been developed to assess the impact on people of routine and accidental releases of radioactivity from a variety of nuclear activities, including: weapons development, production, and testing; power production; and waste disposal. The models are used to estimate human exposures and doses in situations where measurements have not been made or would be impossible or impractical to make. Model results are used to assess whether nuclear facilities are operated in compliance with regulatory requirements, to determine the need for remediation of contaminated sites, to estimate the effects on human health of past releases, and to predict the potential effects of accidental releases or new facilities. This paper describes the various applications and types of models currently used to represent the distribution and transport of radionuclides in the terrestrial and aquatic environments, as well as integrated global models for selected radionuclides and special issues in the fields of solid radioactive waste disposal and dose reconstruction. Particular emphasis is placed on the issue of improving confidence in the model results, including the importance of uncertainty analysis and of model verification and validation.

Journal Article↗

PubMed2002

Radiation-induced health effects on atmospheric flight crew members: clues for a radiation-related risk analysis.

There are few human data on low-dose-rate-radiation exposure and the consequent acute and late effects. This fact makes it difficult to assess health risks due to radiation in the space environment, especially for long-term missions. Epidemiological data on civilian flight personnel cohorts can provide information on effects due to the low-dose and low-dose rate mixed high- and low-LET radiation environment in the earth's atmosphere. The physical characteristics of the radiation environment of the atmosphere make the results of the studies of commercial flight personnel relevant to the studies of activities in space. The cooperative international effort now in progress to investigate dose reconstructions will contribute to our understanding of radiation risks for space exploration.

Aerospace Medicine↗

PubMed2003

Image guidance for precise conformal radiotherapy.

PURPOSE: To review the state of the art in image-guided precision conformal radiotherapy and to describe how helical tomotherapy compares with the image-guided practices being developed for conventional radiotherapy. MATERIALS AND METHODS: Image guidance is beginning to be the fundamental basis for radiotherapy planning, delivery, and verification. Radiotherapy planning requires more precision in the extension and localization of disease. When greater precision is not possible, conformal avoidance methodology may be indicated whereby the margin of disease extension is generous, except where sensitive normal tissues exist. Radiotherapy delivery requires better precision in the definition of treatment volume, on a daily basis if necessary. Helical tomotherapy has been designed to use CT imaging technology to plan, deliver, and verify that the delivery has been carried out as planned. The image-guided processes of helical tomotherapy that enable this goal are described. RESULTS: Examples of the results of helical tomotherapy processes for image-guided intensity-modulated radiotherapy are presented. These processes include megavoltage CT acquisition, automated segmentation of CT images, dose reconstruction using the CT image set, deformable registration of CT images, and reoptimization. CONCLUSIONS: Image-guided precision conformal radiotherapy can be used as a tool to treat the tumor yet spare critical structures. Helical tomotherapy has been designed from the ground up as an integrated image-guided intensity-modulated radiotherapy system and allows new verification processes based on megavoltage CT images to be implemented.

Animals↗

PubMed2000

From dating to biophysics--20 years of progress in applied ESR spectroscopy.

ESR spectroscopy represents a tool for quantitative radiation analysis that was developed somehow simultaneously for dating purposes in Japan and in Germany for high-level standardization, in the mid-seventies. Meanwhile, ESR dosimetry has reached an established metrology level. Present research fields of ESR dosimetry consider post-accident dose reconstruction in the environment, and biophysical dosimetry using human tissues. The latter promises a re-definition of radiation risk for chronicle exposure to be derived from individuals of the early nuclear facilities in Russia, and hopefully United States in the future. An attempt is made to sketch development and potential future of the ESR technique.

Archaeology↗

PubMed2000

Decomposition study of the electron paramagnetic resonance spectrum of irradiated alanine.

Recent Electron Paramagnetic Resonance (EPR) studies on alanine powders as a function of irradiation dose and temperature on the one hand and single crystal Electron Nuclear DOuble Resonance (ENDOR) studies on the other hand, showed the presence of at least three radicals contributing to the total alanine EPR spectrum. The latter spectrum obtained after irradiation at room temperature (RT), is dominated by the well-known stable-alanine-radical (SAR) CH3C*HCOO-, also denoted R1. Appropriate heating of irradiated alanine causes the relative contribution of R1 to decrease, resulting in a spectrum mainly caused by the H-abstraction radical CH3C*(NH3)COO-, denoted R2. Although the EPR spectrum of these two radicals could be satisfactorily simulated, their influence on dose reconstruction has not been reported yet. Therefore, a detailed Maximum Likelihood Common Factor Analysis (MLCFA) study has been performed on EPR spectra from polycrystalline alanine samples, after irradiation and heat treatments. Conclusions concerning the number of contributing radicals and their influence on the RT irradiated alanine EPR spectrum will be made.

Alanine↗

PubMedDate not supplied

Maternal exposure to trichloroethylene in drinking water and birth-weight outcomes.

An ecological epidemiological study was conducted with data obtained from an environmental dose-reconstruction study and the Arizona Birth Information Tapes. Before 1981, a portion of the city of Tucson water-distribution system was contaminated with trichloroethylene (i.e., < 5 micrograms per liter of water to 107 micrograms per liter of water). Target and comparison populations were selected with a Geographic Information System. Logistical-regression analysis revealed an association between maternal exposure to trichloroethylene via drinking water and very-low-birth-weight babies (i.e., < 1,501 grams) (odds ratio = 3.3; 95% confidence interval = 0.5, 20.6; and Wald chi-square p value = 0.2). No association was found between maternal exposure to trichloroethylene via drinking water and low birth weight or full-term low-birth-weight infants (gestational period > 35 wk and < 46 wk).

Arizona↗

PubMed2003

Distribution of radiation-induced exchange aberrations in all human chromosomes.

PURPOSE: To investigate the DNA-proportional distribution of radiation-induced chromosome aberrations for all chromosomes of a male and a female human karyotype. MATERIALS AND METHODS: Metaphases were prepared from whole blood cultures obtained from two healthy donors and set up after irradiation with 3 Gy 220 kV X-rays. Single whole-chromosome FISH painting simultaneously with pancentromeric DNA painting were performed separately for each chromosome of the human karyotype. One thousand exclusively first-division metaphases were analysed per chromosome and donor. After statistical analysis, the data obtained were compared with theoretically expected values. RESULTS: All aberration types (translocations, dicentrics) showed deviations from a DNA-proportional distribution. For both donors, chromosomes 2 and 3 exhibited significantly less and chromosome 4 more symmetrical translocations than expected. Chromosomes 15 and 22 showed more symmetrical translocations than predicted for one of the two donors. Less dicentrics than expected became apparent for chromosomes 2, 3 and 18, while more dicentrics were seen for chromosomes 15, 16 and 17. Moreover, chromosomes 4, 14 and 22 showed a significant deviation from the theoretically expected 1:1 ratio of the yields of symmetrical translocations to the yields of dicentrics. CONCLUSION: The results from the whole-chromosome complement in two different donors confirmed published data from the analysis of single chromosomes that some human chromosomes were not involved in radiation-induced dicentrics and symmetrical translocations proportional to their DNA content. This must be taken into account if chromosome subsets for dose reconstruction are selected or if whole genomic frequencies have to be calculated from partial genome analysis.

Adult↗

PubMed1999

Dose calculations for external photon beams in radiotherapy.

Dose calculation methods for photon beams are reviewed in the context of radiation therapy treatment planning. Following introductory summaries on photon beam characteristics and clinical requirements on dose calculations, calculation methods are described in order of increasing explicitness of particle transport. The simplest are dose ratio factorizations limited to point dose estimates useful for checking other more general, but also more complex, approaches. Some methods incorporate detailed modelling of scatter dose through differentiation of measured data combined with various integration techniques. State-of-the-art methods based on point or pencil kernels, which are derived through Monte Carlo simulations, to characterize secondary particle transport are presented in some detail. Explicit particle transport methods, such as Monte Carlo, are briefly summarized. The extensive literature on beam characterization and handling of treatment head scatter is reviewed in the context of providing phase space data for kernel based and/or direct Monte Carlo dose calculations. Finally, a brief overview of inverse methods for optimization and dose reconstruction is provided.

Humans↗

PubMed2000

Megavoltage CT imaging as a by-product of multileaf collimator leakage.

In addition to their potential for the delivery of highly conformal radiation therapy treatments, tomotherapeutic treatments also feature increased potential for verification. For example, megavoltage CT allows one to use the megavoltage linac to generate tomographic images of the patient in the treatment position. This is typically done before or after radiation therapy treatments. However, it is also possible to collect MVCT images entirely during the treatment itself. This process utilizes the leakage radiation through the closed leaves of the Nomos MIMiC MLC, along with slight inefficiencies in treatment delivery, to generate MVCT images during treatment that require neither additional time nor dose. The image quality is limited, yet sufficient to see a patient's external boundary, density differences over 8% for 25.0 mm objects and resolutions of 3.0 mm for high-contrast objects. Such images can potentially be viewed during treatment, used to flag additional CT immediately after the treatment and provide a representation of the patient's exact position during treatment for use with dose reconstruction.

Humans↗

PubMed2006

Whole-body voxel phantoms of paediatric patients--UF Series B.

Following the previous development of the head and torso voxel phantoms of paediatric patients for use in medical radiation protection (UF Series A), a set of whole-body voxel phantoms of paediatric patients (9-month male, 4-year female, 8-year female, 11-year male and 14-year male) has been developed through the attachment of arms and legs from segmented CT images of a healthy Korean adult (UF Series B). Even though partial-body phantoms (head-torso) may be used in a variety of medical dose reconstruction studies where the extremities are out-of-field or receive only very low levels of scatter radiation, whole-body phantoms play important roles in general radiation protection and in nuclear medicine dosimetry. Inclusion of the arms and legs is critical for dosimetry studies of paediatric patients due to the presence of active bone marrow within the extremities of children. While the UF Series A phantoms preserved the body dimensions and organ masses as seen in the original patients who were scanned, comprehensive adjustments were made for the Series B phantoms to better match International Commission on Radiological Protection (ICRP) age-interpolated reference body masses, body heights, sitting heights and internal organ masses. The CT images of arms and legs of a Korean adult were digitally rescaled and attached to each phantom of the UF series. After completion, the resolutions of the phantoms for the 9-month, 4-year, 8-year, 11-year and 14-year were set at 0.86 mm x 0.86 mm x 3.0 mm, 0.90 mm x 0.90 mm x 5.0 mm, 1.16 mm x 1.16 mm x 6.0 mm, 0.94 mm x 0.94 mm x 6.00 mm and 1.18 mm x 1.18 mm x 6.72 mm, respectively.

Adolescent↗

PubMed2001

Iodine nutrition and the risk from radioactive iodine: a workshop report in the chernobyl long-term follow-up study.

The major fallout of radionuclides from the nuclear power station accident at Chernobyl on 26 April, 1986, occurred in regions of Ukraine and Belarus that are believed to be moderately deficient in dietary iodine. On 17 November, 2000, in conjunction with the Ukraine-Belarus-USA study of developing thyroid disease in a cohort of individuals exposed as children, a workshop was held to review what is known about iodine nutrition in the region, how this might influence the risk of thyroid tumor formation from radioiodine, and whether and how iodine nutrition should be monitored in this long-term project. This report is a summary of the workshop proceedings. Although no precise information about iodine intake in 1986 was found, the prevalence of mild goiter in the region's children suggested iodine deficiency and urinary iodine measurements begun in 1990 indicated that mild to moderate deficiency existed. Increased thyroid iodine uptake and increased thyroid size in 1986 resulting from iodine deficiency would have had counteracting influence on the thyroid radiation dose and knowledge of these parameters is required for dose reconstruction. More problematic is the possible role of iodine deficiency in the years following the accident. Theoretically, the resulting increase in thyroid cellular activity might increase the risk of tumorigenesis but experimental or clinical evidence supporting this hypothesis is meager or absent. Despite this limitation it was considered important to monitor iodine nutrition in the cohort subjects in relation to their place of residence and over time. Methods to accomplish this were discussed.

Goiter↗

PubMed1997

Lessons from Chernobyl: the event, the aftermath fallout: radioactive, political, social.

The accident at the Chernobyl nuclear power station on April 26, 1986, released about 300 MCi of radioactive substances, including about 40 MCi of 131I and 100 MCi of short-lived radioiodines. In the immediate surroundings there were 143 cases of acute radiation syndrome, 34 deaths, and hundreds of thousands of people displaced from their homes, many permanently. The social and psychologic stresses that followed have been enormous and long-lasting. This article focuses on the rising incidence of thyroid cancer in exposed children. Radiation-induced thyroid cancer following external radiation is well documented but there is little evidence in humans of thyroid cancer from internal radiation and the risk coefficient for radioiodine exposure is known. To achieve this, thyroid dose reconstruction and prospective follow-up of about 50,000 persons who were children in 1986 will be required. Thyroid cancer in children of southern Belarus began to increase in 1990 and there now are about 1,000 cases in Belarus and northern Ukraine. These aggressively growing tumors, almost all variants of papillary thyroid cancer, are typical for thyroid cancer in children not exposed to radiation, and a low mortality rate is to be expected. It also is expected, however, that malignant as well as benign thyroid neoplasms will continue to arise in these exposed children well into their adult life.

Adult↗

PubMed2003

The estimation of absorbed doses received by a victim of a Chinese radiation accident.

The aim of this work was to estimate absorbed doses received by a victim of the radiation accident with a 60Co source in Henan province, China. With a Monte Carlo stochastic simulation method, an estimation method for doses to the radiation accident victim was made. It utilised a mathematical model of adult man (MIRD) and a relative applied computer program was developed. By means of the simulated conditions of the accident, the absorbed doses to the victim's main organ and total body doses were estimated. The results estimated by our Monte Carlo method are close to those of experimental simulation measurement of the accident. With its convenience and rapidity, this method will be valuable for radiation dose reconstruction for victims in radiation accidents.

Adult↗