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PubMedDate not supplied

The first international intercomparison of EPR-dosimetry with teeth: first results.

Intercomparison of EPR-dosimetric techniques using tooth enamel had been performed in order to check whether the results produced by different laboratories are consistent and accurate. Participants were supposed to evaluate doses applied to pulverized enamel samples, using routine techniques from their laboratories. The intercomparison has demonstrated a great variety of methods used for dose reconstruction. Peculiarities of experimental approaches are discussed systematically in terms of procedure for recording the EPR-spectra, determination of the amplitude of the radiation induced signal, determination of the dose, and error propagation.

Dental Enamel↗

PubMed2001

Analysis of chromosome aberrations by FISH and Giemsa assays in lymphocytes of cancer patients undergoing whole-body irradiation: comparison of in vivo and in vitro irradiation.

PURPOSE: To study the cytogenetic effects of fractionated radiotherapy in peripheral blood lymphocytes of five cancer patients. In vitro experiments were performed in parallel using the same dose range and a comparison was made of the induced frequencies of stable and unstable chromosome aberrations. The object was to clarify the use of an in vitro calibration curve for immediate and retrospective dosimetry in cases of radiation accidents. MATERIALS AND METHODS: Patients were exposed to 60Co gamma-rays at a single dose of 11.5 cGy each day up to a total dose of 57.5 cGy, given in 5 days. For measurement of chromosome aberrations, blood was collected from patients before irradiation and after each exposure. Blood taken before treatment was used as a control and for in vitro irradiation experiments in the dose range 8-50 cGy. Chromosome aberration frequency (stable as well as unstable) was determined using fluorescence in situ hybridization (FISH) assay with specific DNA libraries for chromosomes 1, 4 and 8 and a pancentromertic probe for the whole genome. Giemsa-stained preparations were used to score unstable aberrations following in vivo and in vitro exposure. RESULTS: A linear dose-response curve was determined for both dicentrics and translocations. The in vivo frequency of translocations was higher than for dicentrics. Dose-response curves generated for translocations following in vivo and in vitro irradiation yielded similar frequencies. In contrast, for dicentrics, in vitro irradiation yielded a higher frequency when compared with data generated following in vivo exposure. CONCLUSIONS: For dose reconstruction purposes, translocations frequency seems to be a more adequate end-point than the scoring of dicentrics. The established in vitro calibration curve for dicentrics may underestimate absorbed radiation dose in cases of protracted exposure.

Adult↗

PubMed1996

Modeling dose distributions from portal dose images using the convolution/superposition method.

Post-treatment dose verification refers to the process of reconstructing delivered dose distributions internal to a patient from information obtained during the treatment. The exit dose is commonly used to describe the dose beyond the exit surface of the patient from a megavoltage photon beam. Portal imaging provides a method of determining the dose in a plane distal to a patient from a megavoltage therapeutic beam. This exit dose enables reconstruction of the dose distribution from external beam radiation throughout the patient utilizing the convolution/superposition method and an extended phantom. An iterative convolution/superposition algorithm has been created to reconstruct dose distributions in patients from exit dose measurements during a radiotherapy treatment. The method is based on an extended phantom that includes the patient CT representation and an electronic portal imaging device (EPID). The convolution/superposition method computes the dose throughout the extended phantom, which allows the portal dose image to be predicted in the EPID. The process is then reversed to take the portal dose measurement and infer what the dose distribution must have been to produce the measured portal dose. The dose distribution is modeled without knowledge of the incident intensity distribution, and includes the effects of scatter in the computation. The iterative method begins by assuming that the primary energy fluence (PEF) at the portal image plane is equal to the portal dose image, the PEF is then back-projected through the extended phantom and convolved with the dose deposition kernel to determine a new prediction of the portal dose image. The image of the ratio of the computed PEF to the computed portal dose is then multiplied by the measured portal dose image to produce a better representation of the PEF. Successive iterations of this process then converge to the exiting PEF image that would produce the measured portal dose image. Once convergence is established, the dose distribution is determined by back-projecting the PEF and convolving with the dose deposition kernel. The method is accurate, provided the patient representation during treatment is known. The method was used on three phantoms with a photon energy of 6 MV to verify convergence and accuracy of the algorithm. The reconstructed dose volumes agree to within 3% of the forward computation dose volumes. Furthermore, this technique assumes no prior knowledge of the incident fluence and therefore may better represent the dose actually delivered.

Algorithms↗

PubMed1998

FISH-based analysis of stable translocations in a Techa River population.

PURPOSE: Measurements of symmetrical translocations by fluorescence in situ hybridization (FISH) were performed for retrospective biodosimetry in a Techa River population exposed to external (gamma-rays) and internal (90Sr, 137Cs) irradiation. MATERIALS AND METHODS: Chromosome analyses were carried out on peripheral lymphocytes from 73 radiation-exposed residents from settlements along the Techa River (Southern Urals, Russia) located 7-148 km downstream from the site of release of liquid radioactive waste from the plutonium production facility Mayak. Thirty-nine unexposed persons from non-contaminated areas were used as controls. Whole-chromosome painting probes for chromosomes 1, 4 and 12 were used simultaneously with a pancentromeric probe. RESULTS: A significantly elevated mean translocation frequency compared with controls was found for the total study group and for either of two subgroups of inhabitants residing in villages of the upper regions of the Techa River (7-60 km) during 1950 to 1951, or in villages of the lower regions (78-148 km) until the time of blood sampling. Within the first subgroup, subjects born between 1937 and 1949 showed higher translocation frequencies than those born between 1914 and 1936. Collective biodosimetry estimates for the various groups were between 0.24 and 0.54 Gy. Individual dose estimates for seven subjects with at least five translocations ranged between 0.77 and 1.80 Gy and compared well with doses reconstructed on the basis of 90Sr whole-body counts (WBC) and electronic paramagnetic resonance (EPR) measurements. Individual translocation frequencies from 40 subjects with existing WBC data and calculated cumulative red bone marrow doses below 0.6 Gy fall within the 95% prediction limits of the calibration curve. CONCLUSIONS: FISH-based translocation measurements can provide useful information for a retrospective biodosimetric interpretation. However, with the analysed number of cells, individual estimates required for a reliable evaluation of this highly variable exposure situation can be obtained only for a minority of subjects. In addition, influence of a temporal decline on the yield of stable translocations cannot be fully excluded.

Body Burden↗

PubMed1999

Simple model for the reconstruction of radionuclide concentrations and radiation exposures along the Techa River.

The Techa River (Southern Urals, Russia) was contaminated in 1949-1956 by liquid radioactive wastes from the Mayak complex, the first Russian facility for the production of plutonium. The measurements of environmental contamination were started in 1951. A simple model describing radionuclide transport along the free-flowing river and the accumulation of radionuclides by bottom sediments is presented. This model successfully correlates the rates of radionuclide releases as reconstructed by the Mayak experts, hydrological data, and available environmental monitoring data for the early period of contamination (1949-1951). The model was developed to reconstruct doses for people who lived in the riverside communities during the period of the releases and who were chronically exposed to external and internal irradiation. The model fills the data gaps and permits reconstruction of external gamma-exposure rates in air on the river bank and radionuclide concentrations in river water used for drinking and other household needs in 1949-1951.

Body Burden↗

PubMed2002

Tomographic motion detection and correction directly in sinogram space.

Patient motion, especially respiratory motion, results in various artefacts such as blurring and streaks in tomographic images. The interplay of the movement of the beam aperture and variations of organ anatomy during delivery can create 'hot' and 'cold' spots throughout the field in intensity-modulated radiation therapy (IMRT). Detection and correction of patient motion is extremely important in tomographic imaging and IMRT. Tomographic projection data (sinogram) encode not only the patient anatomy information, but also the intra-scanning motion information. In this paper, we developed an algorithm to detect and correct the in-plane respiratory motion directly in sinogram space. The respiratory motion is modelled as time-varying scaling along the x and y directions. Its effects on the sinogram are discussed. Based on the traces of some nodal points in the sinogram, the intra-scanning motion is determined. The motion correction is also implemented in sinogram space. The motion-corrected sinogram is used for reconstruction by the filtered back-projection (FBP) method. Computer simulations validate the motion detection and correction algorithm. The reconstructed images from the motion-corrected sinogram eliminate the majority of the artefacts. The method could be applied to projection data used in CT and ECT, as well as in tomotherapy delivery modification and dose reconstruction.

Computer Simulation↗

PubMed1997

Integrated retrospective radiation dose assessment.

Radiation dose reconstruction is used to estimate exposure to radiation that has occurred externally, e.g., from an atomic bomb, or internally, e.g., from radionuclide ingestion. This commentary reviews techniques for biological dosimetry that have been developed to estimate radiation doses from internal exposures, but which can also be used to estimate external exposures. The author argues for increased development and use of these biological tools.

Biomarkers↗

PubMed2006

Dose estimation of a soft X-ray exposure incident.

A dose reconstruction was carried out on a case in which a worker was exposed to soft x rays using time motion studies, an ionization chamber for low energy photon measurements, and CdZnTe (CZT) spectrometry. The worker estimated his dose to be over 600 mSv. However, the doses to the skin and testes were evaluated to be 14 and 0.44 mSv, respectively, with an effective dose of 0.099 mSv.

Body Burden↗

PubMed2005

ESR spectrometry: a future-oriented tool for dosimetry and dating.

ESR spectroscopy is currently taking root as a key technology in dosimetry, dating and imaging. In dosimetry, it competes with cytometry in the fields of biological dosimetry and retrospective dosimetry, leads in high-level reference and routine dosimetry, is high-ranking among the methods to identify radiation preserved foods, represents a method of choice to date geological, archaeological and paleontological materials back millions of years, and has demonstrated capacity for imaging. Further scientific and technological progress as predicted in the recent past (Appl. Radiat. Isot. 52 (2000) 1023) is reviewed here. Additionally, the review is expanded to include international reports and recommendations on ESR dosimetry and dose reconstruction, under way at the American Society for Testing and Materials (ASTM), the International Organisation of Standards (ISO), the International Atomic Energy Agency (IAEA) and the International Commission on Radiation Units and Measurements (ICRU). Emphasis is placed on interpretation of tooth enamel doses in terms of organ and effective doses, using CT-based virtual humans. The future of EPR spectroscopy for in situ dose measurements is noted, depicting a non-destructive in vivo dosimetry applicable directly to individuals, but also to hominid and animal fossils for direct dating.

Body Burden↗

PubMed2006

Importing measured field fluences into the treatment planning system to validate a breathing synchronized DMLC-IMRT irradiation technique.

BACKGROUND AND PURPOSE: Recalculating dose distributions using measured IMRT fluence fields imported into the treatment planning system (TPS) to evaluate the technical feasibility of a prototype developed for breathing synchronized irradiation. PATIENTS AND METHODS: DMLC-IMRT fluence patterns acquired on radiographic film, generated by the linac in non-gated and gated mode, have been imported into the TPS. The effect of dose blurring and possible interplay between organ motion and leaf motion, and the efficacy of a breathing synchronized irradiation technique (an adapted version of a commercially available image-guidance system: NOVALIS BODY/ExacTrac4.0, BrainLAB AG) have been evaluated using radiographic film mounted to a simple phantom simulating a breathing pattern of 16 cycles per minute and covering a distance of 4 cm to obtain the resulting fluence maps. Two situations have been investigated to illustrate this principle: (a) a tumor located close to the diaphragm to assess the influence of organ motion on the dose to the target volume as well as to the gastro-intestinal tract that presents a high risk at intersecting with the beam during the breathing cycle. (b) A mediastinal lesion requiring complicated fluence patterns. RESULTS: Importing measured fluence maps yielded highly disturbed reconstructed dose distributions in case of the non-gated delivery with the phantom in motion (both orthogonal and parallel to the leaf direction), whereas the measurements from the static (film fixed in space) and the gated delivery showed good agreement with the original theoretical dose distribution. These findings have been confirmed by the dose-volume histograms, corresponding tumor control probabilities, conformity index and dose heterogeneity values. The normal tissue complication probabilities investigated in this study seem to be affected to a lesser degree, which concurs with the observation that the motion effects result in a dose spread in the direction of motion. The applied breathing synchronization technique introduced an increased treatment time with a factor 3-4. CONCLUSIONS: The use of measured fluence fields, delivered by the linac in non-gated and gated mode, as imported fluence maps for the treatment planning system is an interesting quality assurance tool and revealed the dramatic impact of dose blurring and interplay between DMLC-IMRT dose delivery and organ motion, as well as the potential of breathing synchronization to resolve this issue. The possible advantage of breathing synchronized irradiation is compromised with an increased treatment time.

Artifacts↗

PubMed2002

A perspective on public concerns about exposure to fallout from the production and testing of nuclear weapons.

Exposures of the American public occurred nationwide from the testing of nuclear weapons in the United States, the Pacific, and the former Soviet Union. After decades of diminished public awareness on the subject of health risks resulting from exposure to fallout, the release of the National Cancer Institute's 1997 report on nationwide exposure to 131I from the Nevada Test Site (NTS) has led to renewed interest. Public requests for information are focused on individual and family health problems, the right to credible and full disclosure of information, and the need for medical care and assistance for exposure-related health problems. Public concerns have been raised regarding: (a) the lack of information on the potential health risks from exposure to all biologically significant radionuclides in fallout; (b) the lack of independent oversight that includes public participation; (c) governmental portrayal of exposures averaged over very large segments of the population without identification of much larger values for individuals or population subgroups likely to be at highest risk; and (d) a governmental response to known or suspected human exposures that consumes large periods of time and devotes considerable funding to various research-related activities before serious consideration is given to addressing health care responsibilities to exposed individuals. To some extent, these complaints and concerns are rooted in the legacy of government secrecy surrounding the development and testing of nuclear weapons, public distrust of government sources of information about radiation exposures and health risks, and the imposition of past exposures without informed consent. Members of the public participating in the oversight of dose reconstruction projects and epidemiologic studies are requesting information on the total impact from all relevant sources of exposure at each site that might contribute significantly to an individual's risk, including exposure to local releases and to NTS and global fallout. Information is being requested on individual doses and risks from these cumulative exposures, with estimates of uncertainty, including estimates of the absorbed organ dose (as opposed to the effective dose), the risk of disease incidence as opposed to the risk of a cancer fatality, and the chance that a person's diagnosed disease was caused by past exposure (i.e., the probability of causation). This paper attempts to address some of these concerns. We conclude by noting that many individuals exposed in childhood during the 1950's to 131I in fallout from nuclear weapons production and testing would qualify for compensation and medical care if the present rules for the adjudication of claims for atomic veterans and radiation workers at DOE sites were to be extended to the public.

Disclosure↗

PubMed1996

Estimating internal dose due to ingestion of radionuclides from Nevada Test Site fallout.

The U.S. Department of Energy initiated the Radiation Exposure Review Project to provide a critical reexamination of radiation doses to people resulting from testing nuclear devices at the Nevada Test Site. One part of this effort focused on the dose resulting from the ingestion of contaminated food. The PATHWAY radionuclide transport model was developed to provide estimates of food concentrations for 20 radionuclides for each of 86 test events and 15 agricultural scenarios. These results were then used as input to the Human Ingestion model to provide dose estimates for individuals and populations in 9 western states. The model considered the life-style and age of the people, and accounted for the transport of milk between locations. Estimates of uncertainty were provided for all doses using Monte Carlo simulation techniques. Propagation of uncertainty between the PATHWAY model and the Human Ingestion model required the development of special strategies to ensure that the inherent correlations between concentrations of the radionuclides in foods were handled properly. In addition, the size of the input data base (60 megabytes), the number of cases to consider (over 30,000), and the number of Monte Carlo simulations (over 6 million) required the development of efficient and reliable methods of data access and storage while running simulations concurrently on up to 14 UNIX workstations. The problems encountered in this effort are likely to be typical of any dose reconstruction involving geographically heterogeneous environmental conditions. This paper documents the methods used to disaggregate the system to achieve computation efficiency, the methods used to propagate uncertainty through the model system, and the techniques used to manage data in a distributed computing environment. The radionuclide- and age-specific dose factors used in the analysis are also provided.

Environmental Exposure↗

PubMed1997

Early dose assessment following severe radiation accidents.

Early treatment of victims of high level acute whole-body x-ray or gamma exposure has been shown to improve their likelihood of survival. However, in such cases, both the magnitude of the exposure and the dosimetry profile(s) of the victim(s) are often not known in detail for days to weeks. A simple dose-prediction algorithm based on lymphocyte kinetics as documented in prior radiation accidents is presented here. This algorithm provides an estimate of dose within the first 8 h following an acute whole-body exposure. Early lymphocyte depletion kinetics after a severe radiation accident follow a single exponential, L(t) = L(o)e(-k(D¿t), where k(D) is a rate constant, dependent primarily on the average dose, D. Within the first 8 h post-accident, K(D) may be calculated utilizing serial lymphocyte counts. Data from the REAC/TS Radiation Accident Registry were used to develop a dose-prediction algorithm from 43 gamma exposure cases where both lymphocyte kinetics and dose reconstruction were felt to be reasonably reliable. The inverse relationship D(K) may be modeled by a simple two parameter curve of the form D = a/(1 + b/K) in the range 0 < or = D < or = 15 Gy, with fitting parameters (mean +/- SD): a = 13.6 +/- 1.7 Gy, and b = 1.0 +/- 0.20 d(-1). Dose estimated in this manner is intended to serve only as a first approximation to guide initial medical management.

Algorithms↗

PubMed1997

Health impacts of large releases of radionuclides. Cytogenetic effects as quantitative indicators of radiation exposure.

Scoring of dicentrics in metaphase preparations of human T lymphocytes is the method of choice for estimating individual whole-body doses of radiation exposure. A quantification of partial-body exposures or non-uniform distribution of the dose is more complicated but it can be achieved by using specific mathematical approaches. For retrospective biodosimetry, conventional scoring of dicentrics is less precise because these unstable aberrations are eliminated with time post-exposure. Symmetrical translocations are not selected against during mitotic division in the haematopoietic cell reproductive centres, so the frequencies of these stable aberrations are generally assumed to remain constant even for decades. They can now be analysed precisely by fluorescence in situ hybridization using whole chromosome-specific DNA probes (chromosome painting) with an alpha-satellite DNA probe for centromere detection. Based on in vitro calibration curves established with single or multicolour paints covering 4-22% of the total human genomic DNA content, scoring of translocations has been applied for dose reconstruction in smaller groups of atomic bomb survivors and victims of the Chernobyl and Goiania radiation accidents. However, prior to routine use, the method requires further validation. Such work includes the precise evaluation of the unexpectedly high frequency of complex exchanges (> or = 3 breaks in > or = 2 chromosomes) found both at > 2 Gy doses of low linear energy transfer (LET) radiation and generally for high LET alpha-particles. Data on the long-term stability of translocations and the appearance of clonal abberrations, as well as improved measurements of the linear coefficient of standard calibration curves, are also required.

Centromere↗

PubMed1978

Radiation necrosis of the brain: correlation between computed tomography, pathology, and dose distribution.

Delayed necrosis of the brain following exposure to high doses of radiation is a recognized hazard. It is important to predict the nature of these postradiation changes, since surgical removal of radiation necrosis may reverse neurological deterioration of patients so affected. The present report stresses the importance of correlating the findings on computed tomography (CT) scans and zones of high radiation dose on dose reconstruction plans in order to differentiate between delayed radiation necrosis and tumors of the brain. This differentiation is not possible using the criteria of CT alone.

Adult↗

PubMed2002

Investigations of thermoluminescence dosimetry in the Techa river flood plain: analysis of the new results.

The Techa river region was highly contaminated due to radioactive releases from a nuclear production facility in the period from 1949 to 1956. The inhabitants of the upper Techa river settlements received significant doses of external radiation. The majority of the houses in the upper Techa river villages were demolished after the evacuation of the population in 1956. Only three buildings (red-brick construction) in the former village of Metlino can still be used for thermoluminescence (TL) investigations in an external dose reconstruction study. The radiation source configuration changed in 1956 after an artificial reservoir was created next to Metlinsky pond. Preliminary TL studies showed good properties of the bricks that were sampled from the buildings. This paper presents an analysis of new results of TL investigations obtained on the samples collected from different walls of the buildings. The highest dose values in the range 1-4 Gy were found in bricks collected from the walls of building exposed to the artificial reservoir (Reservoir-10) and values of 1-1.5 Gy were found next to the Metlinsky pond shoreline. The measurements of the radiation source geometry were carried out simultaneously with the dose rates, radionuclide concentration in water and bottom sediments near the wall facing the old river bed. The measurements allow a validation of models used in the current Techa River Dosimetry System (TRDS-2000) to estimate external doses of the former inhabitants of the upper Techa riverside. In particular, the results can be applied for a more correct description of the source geometry in the settlement.

Fresh Water↗

PubMed1998

A non-parametric method of reconstructing single-dose survival curves from multi-fraction experiments.

PURPOSE: A method of estimating the single-dose curve from designed multifraction experiments is described and applied to three datasets. MATERIALS AND METHODS: The method, which is non-parametric and based on standard statistical regression techniques, can be used for functional endpoints which are either continuous or binary. The datasets are concerned with wound healing on mice, myelopathy in guinea pigs and spermatogenesis in mice. The results are compared with the results from fitting the linear quadratic model. The statistical methods of Bootstrapping and residual plots are illustrated. RESULTS: The method is based in part on an assumed statistical model, however, exact knowledge of the correct statistical model is not necessary to obtain an estimate of the shape of the single-dose survival curve. We find no good evidence from the reconstructed single-dose survival curve of an "induced repair" phenomena at low doses for the wound healing and spermatogenesis experiments. For the myelopathy experiment the data are consistent with the LQ model with a low alpha-beta ratio down to doses of at least 1.5 Gy per fraction. CONCLUSIONS: A robust statistical method of estimating the shape of the single-dose survival curve is demonstrated using standard statistical software on three datasets.

Animals↗

PubMed1996

Radiation dose distributions in three dimensions from tomographic optical density scanning of polymer gels: I. Development of an optical scanner.

A new method of dosimetry of ionizing radiations has been developed that makes use of tissue-equivalent polymer gels which are capable of recording three-dimensional dose distributions. The dosimetric data stored within the gels are measured using optical tomographic densitometry. The dose-response mechanism relies on the production of light scattering microparticles which result from the polymerization of acrylic comonomers dispersed in the gel. The attenuation of a collimated light beam caused by scattering in the irradiated optically turbid medium is directly related to the radiation dose over the range 0-10 Gy. An optical scanner has been developed which incorporates an He-Ne laser, photodiode detectors, and a rotating gel platform. Using mirrors mounted on a translating stage, the laser beam scans across the gel between each incremental rotation of the platform. Using the set of optical density projections obtained, a cross sectional image of the radiation field is then reconstructed. Doses in the range 0-10 Gy can be measured to better than 5% accuracy with a spatial resolution approximately 2 mm using the current prototype scanner. This method can be used for the determination of three-dimensional dose distributions in irradiated gels, including measurements of the complex distributions produced by multi-leaf collimators, dynamic wedge and stereotactic treatments, and for quality assurance procedures.

Algorithms↗