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PubMed2004

Estimation of thyroid radiation doses for the hanford thyroid disease study: results and implications for statistical power of the epidemiological analyses.

Residents of eastern Washington, northeastern Oregon, and western Idaho were exposed to I released into the atmosphere from operations at the Hanford Nuclear Site from 1944 through 1972, especially in the late 1940's and early 1950's. This paper describes the estimated doses to the thyroid glands of the 3,440 evaluable participants in the Hanford Thyroid Disease Study, which investigated whether thyroid morbidity was increased in people exposed to radioactive iodine from Hanford during 1944-1957. The participants were born during 1940-1946 to mothers living in Benton, Franklin, Walla Walla, Adams, Okanogan, Ferry, or Stevens Counties in Washington State. Whenever possible someone with direct knowledge of the participant's early life (preferably the participant's mother) was interviewed about the participant's individual dose-determining characteristics (residence history, sources and quantities of food, milk, and milk products consumed, production and processing techniques for home-grown food and milk products). Default information was used if no interview respondent was available. Thyroid doses were estimated using the computer program Calculation of Individual Doses from Environmental Radionuclides (CIDER) developed by the Hanford Environmental Dose Reconstruction Project. CIDER provided 100 sets of doses to represent uncertainty of the estimates. These sets were not generated independently for each participant, but reflected the effects of uncertainties in characteristics shared by participants. Estimated doses (medians of each participant's 100 realizations) ranged from 0.0029 mGy to 2823 mGy, with mean and median of 174 and 97 mGy, respectively. The distribution of estimated doses provided the Hanford Thyroid Disease Study with sufficient statistical power to test for dose-response relationships between thyroid outcomes and exposure to Hanford's I.

Adolescent↗

PubMed1998

Issues in the reconstruction of environmental doses on the basis of thermoluminescence measurements in the Techa riverside.

The potential of thermoluminescence measurements of bricks from the contaminated area of the Techa river valley, Southern Urals, Russia, for reconstructing external exposures of affected population groups has been studied. Thermoluminescence dating of background samples was used to evaluate the age of old buildings available on the river banks. The anthropogenic gamma dose accrued in exposed samples is determined by subtracting the natural radiation background dose for the corresponding age from the accumulated dose measured by thermoluminescence. For a site in the upper Techa river region, where the levels of external exposures were extremely high, the depth-dose distribution in bricks and the dependence of accidental dose on the height of the sampling position were determined. For the same site, Monte Carlo simulations of radiation transport were performed for different source configurations corresponding to the situation before and after the construction of a reservoir on the river and evacuation of the population in 1956. A comparison of the results provides an understanding of the features of the measured depth-dose distributions and height dependencies in terms of the source configurations and shows that bricks from the higher sampling positions are likely to have accrued a larger fraction of anthropogenic dose from the time before the construction of the reservoir. The applicability of the thermoluminescent dosimetry method to environmental dose reconstruction in the middle Techa region, where the external exposure was relatively low, was also investigated.

Alpha Particles↗

PubMedDate not supplied

An approach to the assessment of overall uncertainty of determination of dose using an ESR technique.

An approach to the assessment of overall uncertainty of dose reconstruction by means of an ESR with additive dose technique is proposed. This approach takes account of uncertainties caused by different sources giving a quantitative measure of uncertainty of the determined dose. Dose is determined as an interval assessment rather than a deterministic value, allowing for the analytical estimation of both the mean value and the 95% confidence intervals. The effects of the number of additional irradiations and the value of dose increment on the uncertainty of dose determination are analyzed.

Dental Enamel↗

PubMed1998

Comparison of dose-response curves for chromosomal aberrations established by chromosome painting and conventional analysis.

PURPOSE: To establish 60Co gamma-ray dose-response curves for dicentrics and translocations visualized by chromosome painting and for dicentrics analysed after conventional solid staining. MATERIALS AND METHODS: Analysis of chromosomal aberrations was performed on peripheral blood lymphocytes obtained from 48 h old cultures of irradiated whole blood. Dicentrics were scored from Giemsa-stained preparations, and bi-coloured dicentrics and translocations after FISH painting of chromosomes 1, 2 and 4. RESULTS: Equal frequencies of complete dicentrics and translocations, where both members of the exchanges were seen, were observed in the chromosome painting analysis at all doses, resulting in similar calibration curves. Due to differences in scoring criteria, dicentrics scored in conventionally Giemsa-stained slides agreed better with data for total than for complete exchanges. Donor differences for translocations at the control level and at low doses were seen and large uncertainty surrounds the linear component of the dose-response for total translocations. CONCLUSIONS: Dose reconstruction of past exposures in cases of low doses is very dependent on the linear coefficient of the curve. Results indicate that total translocations would give less reliable dose estimates and therefore complete translocations are preferred.

Adult↗

PubMed2004

Comparison of retrospective luminescence dosimetry with computational modeling in two highly contaminated settlements downwind of the Chernobyl NPP.

The cumulative absorbed dose in bricks collected from six buildings in two heavily contaminated settlements (137Cs > 2,000 kBq m(-2)) located downwind of the Chernobyl Nuclear Power Plant was determined using luminescence techniques by six laboratories. The settlements, Vesnianoje in Ukraine and Zaborie in Russia, are located in, respectively, proximal and distal locations relative to the Chernobyl Nuclear Power Plant. The luminescence determinations of cumulative dose in brick, after subtraction of the natural background dose, were translated to absorbed dose in air at a Reference Location using conversion factors derived from Monte Carlo simulations of photon transport. The simulations employed source distributions inferred from contemporary soil contamination data and also took into account heterogeneity of fallout deposition. This translation enables the luminescence determinations to be compared directly with values of cumulative absorbed dose obtained by computational modeling and also other dose reconstruction methods. For each sampled location the cumulative dose was calculated using three deterministic models, two of which are based on the attenuation of dose-rate with migration of radionuclides in soil and the third on historic instrumental gamma dose-rate data. The results of the comparison of the two methods indicate overall agreement within margins of +/-25%. The methodology developed is generally applicable and adaptable to areas contaminated by much lower levels of radioactive fallout in which brick buildings are found.

Computer Simulation↗

PubMed2006

Clinical implementation of adaptive helical tomotherapy: a unique approach to image-guided intensity modulated radiotherapy.

Image-guided IMRT is a revolutionary concept whose clinical implementation is rapidly evolving. Methods of executing beam intensity modulation have included individually designed compensators, static multi-leaf collimators (MLC), dynamic MLC, and sequential (serial) tomotherapy. We have developed helical tomotherapy as an innovative solution to overcome some of the limitations of other IMRT systems. The unique physical design of helical tomotherapy allows the realization of the concepts of adaptive radiotherapy and conformal avoidance. In principle, these advances should improve normal tissue sparing and permit dose reconstruction and verification, thereby allowing significant biologically effective dose escalation. Recent radiobiological findings can be translated into altered fractionation schemes that aim to improve the local control and long-term survival. This strategy is being tested at the University of Wisconsin using helical tomotherapy with its highly precise delivery and verification system along with meticulous and practical forms of immobilization. Innovative techniques such optical guidance, respiratory gating, and ultrasound assessments are being designed and tailored for helical tomotherapy use. The intrinsic capability of helical tomotherapy for megavoltage CT (MVCT) imaging for IMRT image-guidance is being optimized. The unique features of helical tomotherapy might allow implementation of image-guided IMRT that was previously impossible or impractical. Here we review the technological, physical, and radiobiological rationale for the ongoing and upcoming clinical trials that will use image-guided IMRT in the form of helical tomotherapy; and we describe our plans for testing our hypotheses in a rigorous prospective fashion.

Humans↗

PubMed1996

Reconstruction of radioactive contamination in the Columbia River.

As part of the Hanford Environmental Dose Reconstruction Project, an unsteady flow hydraulic model, modified to include radionuclide decay, was used to simulate the transport of radionuclides released to the Columbia River from Hanford. The model was applied to the river from Priest Rapids Dam to the vicinity of Portland, Oregon, for the period from January 1950 through January 1971. Model output consisted of monthly-average water concentrations for 24Na, 32P, 65Zn, 76As, and 239Np. Model validation was accomplished by comparing computed water depths and 51Cr concentrations to measured field data. This paper discusses the modeling approach and compares the results to historical river monitoring data collected during the peak years of operation.

Arsenic↗

PubMed2002

A reconsideration of the external dose assessment for the Techa river population.

A new methodology is employed to infer the time course of the external dose rate that affected the Techa riverside population. This was accomplished using information on the radionuclide composition of released radioactive waste and from earlier and current data on the degree of the river floodplain contamination with (137)Cs. The new approach is proposed for use in the dose reconstruction. Compared to current assumptions it indicates a considerably higher dose contribution due to short-lived fission products from the predominant peak of contamination in 1951. Relative to the present Techa river dosimetry system (TRDS-2000) this information may increase the external dose estimates several fold and correspondingly reduce the solid cancer risk estimate.

Cesium Radioisotopes↗

PubMed1999

Childhood exposure due to the Chernobyl accident and thyroid cancer risk in contaminated areas of Belarus and Russia.

The thyroid dose due to 131I releases during the Chernobyl accident was reconstructed for children and adolescents in two cities and 2122 settlements in Belarus, and in one city and 607 settlements in the Bryansk district of the Russian Federation. In this area, which covers the two high contamination spots in the two countries following the accident, data on thyroid cancer incidence during the period 1991-1995 were analysed in the light of possible increased thyroid surveillance. Two methods of risk analysis were applied: Poisson regression with results for the single settlements and Monte Carlo (MC) calculations for results in larger areas or sub-populations. Best estimates of both methods agreed well. Poisson regression estimates of 95% confidence intervals (CIs) were considerably smaller than the MC results, which allow for extra-Poisson uncertainties due to reconstructed doses and the background thyroid cancer incidence. The excess absolute risk per unit thyroid dose (EARPD) for the birth cohort 1971-1985 by the MC analysis was 2.1 (95% CI 1.0-4.5) cases per 10(4) person-year Gy. The point estimate is lower by a factor of two than that observed in a pooled study of thyroid cancer risk after external exposures. The excess relative risk per unit thyroid dose was 23 (95% CI 8.6-82) Gy(-1). No significant differences between countries or cities and rural areas were found. In the lowest dose group of the settlements with an average thyroid dose of 0.05 Gy the risk was statistically significantly elevated. Dependencies of risks on age-at-exposure and on gender are consistent with findings after external exposures.

Child↗

PubMed1996

Atmospheric dispersion and deposition of 131I released from the Hanford Site.

Approximately 2.6 x 10(4) TBq (700,000 Ci) of 131I were released to the air from reactor fuel processing plants on the Hanford Site in southcentral Washington State from December 1944 through December 1949. The Hanford Environmental Dose Reconstruction Project developed a suite of codes to estimate the doses that might have resulted from these releases. The Regional Atmospheric Transport Code for Hanford Emission Tracking (RATCHET) computer code is part of this suite. The RATCHET code implements a Lagrangian-trajectory, Gaussian-puff dispersion model that uses hourly meteorological and release rate data to estimate daily time-integrated air concentrations and surface contamination for use in dose estimates. In this model, iodine is treated as a mixture of three species (inorganic gases, organic gases, and particles). Model deposition parameters are functions of the mixture and meteorological conditions. A resistance model is used to calculate dry deposition velocities. Equilibrium between concentrations in the precipitation and the air near the ground is assumed in calculating wet deposition of gases, and irreversible washout of the particles is assumed. RATCHET explicitly treats the uncertainties in model parameters and meteorological conditions. Uncertainties in 131I release rates and partitioning among the nominal species are treated by varying model input. The results of 100 model runs for December 1944 through December 1949 indicate that monthly average air concentrations and deposition have uncertainties ranging from a factor of two near the center of the time-integrated plume to more than an order of magnitude near the edge. These results indicate that approximately 10% of the 131I released to the atmosphere decayed during transit in the study area, approximately 56% was deposited within the study area, and the remaining 34% was transported out of the study area while still in the air.

Air Pollutants, Radioactive↗

PubMed1996

The myth of the second prophylactic antibiotic dose in aortoiliac reconstructions.

OBJECTIVES: To determine whether a prophylactic second dose of antibiotics is justified when severe blood loss and/or prolonged operation time occurs during aortoiliac reconstructions. METHODS: We measured the cefuroxime concentration in venous blood serum and subcutaneous fat tissue of 30 patients who underwent elective aortoiliac reconstruction after a single intravenous dose of 1500 mg cefuroxime. RESULTS: The mean blood loss was 1912 ml (range 200-7000). The mean operation time was 212 min (range 70-330). The cefuroxime concentration in blood serum 30 min after the gift varied from 53.7-561.6 mg/l and during closure of the abdominal incision from 13.2-90.0 mg/l. Taking the minimum inhibitory concentration for Staphylococcus species as 1.0 mg/l, we found an adequate prophylactic serum cefuroxime concentration in all patients. There was a statistically significant correlation between serum cefuroxime concentration and blood loss (p = 0.01) and operation time (p = 0.0001). CONCLUSIONS: Although serum concentration of cefuroxime is greatly influenced by blood loss and operation time, a second dose of cefuroxime in aortoiliac reconstructions is not necessary if the operation is completed within 5.5 h and if perioperative blood loss does not exceed 7000 ml.

Adipose Tissue↗

PubMed2002

Studies of cancer risk among Chernobyl liquidators: materials and methods.

The current paper presents the methods and design of two case-control studies among Chernobyl liquidators-one of leukaemia and non-Hodgkin lymphoma, the other of thyroid cancer risk-carried out in Belarus, Estonia, Latvia, Lithuania and Russia. The specific objective of these studies is to estimate the radiation induced risk of these diseases among liquidators of the Chernobyl accident, and, in particular, to study the effect of exposure protraction and radiation type on the risk of radiation induced cancer in the low-to-medium- (0-500 mSv) radiation dose range. The study population consists of the approximately 10000 Baltic, 40000 Belarus and 51 000 Russian liquidators who worked in the 30 km zone in 1986-1987, and who were registered in the Chernobyl registry of these countries. The studies included cases diagnosed in 1993-1998 for all countries but Belarus, where the study period was extended until 2000. Four controls were selected in each country from the national cohort for each case, matched on age, gender and region of residence. Information on study subjects was obtained through face-to-face interview using a standardised questionnaire with questions on demographic factors, time, place and conditions of work as a liquidator and potential risk and confounding factors for the tumours of interest. Overall, 136 cases and 595 controls after receiving their consent were included in the studies. A method of analytical dose reconstruction has been developed, validated and applied to the estimation of doses and related uncertainties for all the subjects in the study. Dose-response analyses are underway and results are likely to have important implications to assess the adequacy of existing protection standards, which are based on risk estimates derived from analyses of the mortality of atomic bomb survivors and other high dose studies.

Baltic States↗

PubMed2005

A feasibility study for image guided radiotherapy using low dose, high speed, cone beam X-ray volumetric imaging.

BACKGROUND AND PURPOSE: Image Guidance of patient set-up for radiotherapy can be achieved by acquiring X-ray volumetric images (XVI) with Elekta Synergy and registering these to the planning CT scan. This enables full 3D registration of structures from similar 3D imaging modalities and offers superior image quality, rotational set-up information and a large field of view. This study uses the head section of the Rando phantom to demonstrate a new paradigm of faster, lower dose XVI that still allows registration to high precision. MATERIALS AND METHODS: One high exposure XVI scan and one low exposure XVI scan were performed with a Rando Head Phantom. The second scan was used to simulate ultra low dose, fast acquisition, full and half scans by discarding a large number of projections before reconstruction. Dose measurements were performed using Thermo Luminescent Dosimeters (TLD) and an ion chamber. The reconstructed XVI scans were automatically registered with a helical CT scan of the Rando Head using the volumetric, grey-level, cross-correlation algorithm implemented in the Syntegra software package (Philips Medical Systems). Reproducibility of the registration process was investigated. RESULTS: In both XVI scans the body surface, bone-tissue and tissue air interfaces were clearly visible. Although the subjective image quality of the low dose cone beam scan was reduced, registration of both cone beam scans with the planning CT scan agreed within 0.1 mm and 0.1 degrees . Dose to the patient was reduced from 28mGy to less than 1mGy and the equivalent scan speed reduced to one minute or less. CONCLUSIONS: Automatic 3D registration of high speed, ultra low dose XVI scans with the planning CT scan can be used for precision 3D patient set-up verification/image guidance on a daily basis with out loss of accuracy when compared to higher dose XVI scans.

Dose Fractionation, Radiation↗

PubMed2000

Calibration of a tomotherapeutic MVCT system.

Megavoltage CT provides the ability to image the patient before, during or after a radiotherapy treatment. This allows one to verify not only the placement of a patient's external boundary, but also the locations of internal anatomy. In addition, the reconstructed MVCT values are potentially useful for treatment planning inhomogeneity corrections and dose reconstruction. To this end, dosimetric calibration of the University of Wisconsin Tomotherapy Benchtop MVCT system was investigated. It was found that MVCT values correlate extremely well with electron density and that unlike kilovoltage CT, this correlation is well maintained for higher atomic number materials. Improvements of the order of 1% in the dosimetric calculations of high atomic number materials should be possible by deriving input images from MVCT as opposed to kVCT, and calibrating in terms of electron density, as opposed to physical density.

Calibration↗

PubMed2004

In phantom Dosimetric response of tooth enamel to neutrons.

Electron Paramagnetic Resonance dosimetry based on tooth enamel has one important application in dose reconstruction of nuclear plant workers, where the contribution of neutrons to individual dose is often important. Evaluation of tooth enamel response to neutrons is thus an important goal. A few experimental data at thermal and fast neutron energies are available. A first evaluation of the tooth enamel relative response to 60Co in monoenergetic neutron flux of 2.8 and of 14 MeV, published elsewhere, has provided results apparently non-consistent with the results obtained at lower and higher energies. A comparison of those results in the 2.8 and 14 MeV beams with those available in the literature for other beams is reported and possible reasons for incongruities are discussed. Dose conversion factors of enamel to the water and air are also calculated and reported.

Algorithms↗

PubMed2005

Radiation risk estimates after radiotherapy: application of the organ equivalent dose concept to plateau dose-response relationships.

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional (3D) dose distributions for each individual patient. The dose distributions can be converted into organ equivalent doses to describe radiation-induced cancer after radiotherapy (OED(rad-ther)) in the irradiated organs. The OED(rad-ther) concept assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer risk. In this work, this concept is applied to dose-response relationships, which are leveling off at high dose. The organ-dependent operational parameter of this dose-response relationship was estimated by analyzing secondary cancer incidence data of patients with Hodgkin's disease. The dose distributions of a typical radiotherapy treatment plan for treating Hodgkin's disease was reconstructed. Dose distributions were calculated in individual organs from which cancer incidence data were available. The model parameter was obtained by comparing dose and cancer incidence rates for the individual organs.

Body Burden↗

PubMed2003

Chromosomal biodosimetry by unfolding a mixed Poisson distribution: a generalized model.

PURPOSE: The current chromosomal biodosimetry system is practically limited to the estimation of equivalent whole-body dose in the low or moderate dose range. To circumvent this problem, a new dosimetry system was developed which was effective over a wide dose range and dose gradient. MATERIALS AND METHODS: In order to establish a quantitative formalism of a comprehensive dose-response kinetics, chromosome aberration frequencies were studied in human peripheral blood lymphocytes irradiated in vitro with gamma-rays in a dose range of 0.01-50Gy. Using the dose-yield relationship thus established, a new model of biodosimetry was developed which involved unfolding the chromosome aberration distribution into a mixed Poisson distribution and thence into a dose-distribution profile. The model was then tested with chromosome aberration data in lymphocytes irradiated in vitro, simulated partial body irradiation, accidental radiation exposure, therapeutic local irradiation and protracted exposure by internal deposit of Thorotrast. RESULTS: The dose-yield relations over a wide dose range fit satisfactorily a multiparametric dose-response curve, which included the first approximation kinetics of linear-quadratic dose-response and its distortion by mutual interference among multiple breaks on a chromosome arm. The unfolding strategy using these dose-response kinetics was successfully applied to the various types of radiation exposures; the reconstructed dose profile showing a sharp unimodal peak for moderate or high doses of gamma-rays in vitro irradiation, broadening for high-linear energy transfer radiation, discrimination of doses in the mixed culture of irradiated and unirradiated blood, and reasonable dose distribution for the in vivo exposures. CONCLUSION: A novel biodosimetry system was developed. The system is innovative in that it provides information not only on the macroscopic dose inhomogeneity, but also on the microscopic spectrum of doses stemming from the variability of energy transfer by charged particles as well as the multiple ionization events to which the target cell nucleus is exposed.

Chromosome Aberrations↗

PubMed1996

Reconstruction of radionuclide releases from the Hanford Site, 1944-1972.

Historic releases of key radionuclides were estimated as a first step in determining the radiation doses that resulted from Hanford Site operations. The Hanford Site was built in southcentral Washington State during World War II to provide plutonium for the U.S. nuclear weapons program. As part of the Hanford Environmental Dose Reconstruction (HEDR) Project, releases to the Columbia River of 24Na, 32P, 46Sc, 51Cr, 56Mn, 65Zn, 72Ga, 76As, 90Y, 131I, 239Np, and nonvolatile gross beta activity from operation of eight Hanford single-pass production reactors were estimated. Releases of 90Sr, 103Ru, 106Ru, 131I, 144Ce, and 239Pu to the atmosphere from operation of chemical separation facilities were also estimated. These radionuclides and the atmospheric and Columbia River pathways were selected for study because scoping studies showed them to be the largest contributors to dose from Hanford operations. The highest doses resulted from releases to the atmosphere of 131I from chemical separations plants in the pre-1950 period. Prior to 1950, the technology for limiting iodine releases had not been developed. Hence, a very detailed reconstruction of the hourly 131I release history was achieved for 1944-1949 using Monte Carlo methods. Atmospheric releases of the other radionuclides were estimated on a monthly basis for 1944-1972 using deterministic calculations. Monthly releases to the Columbia River for 1944-1971 were based on Monte Carlo methods.

Air Pollutants, Radioactive↗