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Showing papers in "Health Physics in 2003"


Journal ArticleDOI
TL;DR: This renowned work is derived from the authors' acclaimed national review course (“Physics of Medical Imaging") at the University of California-Davis for radiology residents and addresses topics common to all forms of diagnostic imaging, including image quality and medical informatics.
Abstract: This renowned work is derived from the authors' acclaimed national review course (“Physics of Medical Imaging\") at the University of California-Davis for radiology residents. Coverage includes the production, characteristics and interactions of ionizing radiation used in medical imaging and the imaging modalities in which they are used, including radiography, mammography, fluoroscopy, computed tomography and nuclear medicine. Special attention is paid to optimizing patient dose in each of these modalities. Sections of the book address topics common to all forms of diagnostic imaging, including image quality and medical informatics as well as the non-ionizing medical imaging modalities of MRI and ultrasound.

563 citations


Journal ArticleDOI
TL;DR: Temporal trends indicate that worldwide population exposure from medical radiation is increasing, and patients treated with radium appear to have an elevated risk of bone sarcomas and possibly cancers of the breast, liver, kidney, thyroid, and bladder.
Abstract: About 15% of the ionizing radiation exposure to the general public comes from artificial sources, and almost all of this exposure is due to medical radiation, largely from diagnostic procedures. Of the approximately 3 mSv annual global per caput effective dose estimated for the year 2000, 2.4 mSv is from natural background and 0.4 mSv from diagnostic medical exams. Diagnostic and therapeutic radiation was used in patients as early as 1896. Since then, continual improvements in diagnostic imaging and radiotherapy as well as the aging of our population have led to greater use of medical radiation. Temporal trends indicate that worldwide population exposure from medical radiation is increasing. In the United States, there has been a steady rise in the use of diagnostic radiologic procedures, especially x rays. Radiotherapy also has increased so that today about 40% of cancer patients receive some treatment with radiation. Epidemiologic data on medically irradiated populations are an important complement to the atomic-bomb survivors' studies. Significant improvement in cancer treatment over the last few decades has resulted in longer survival and a growing number of radiation-related second cancers. Following high-dose radiotherapy for malignant diseases, elevated risks of a variety of radiation-related second cancers have been observed. Risks have been particularly high following treatment for childhood cancer. Radiation treatment for benign disease was relatively common from the 1940's to the 1960's. While these treatments generally were effective, some resulted in enhanced cancer risks. As more was learned about radiation-associated cancer risks and new treatments became available, the use of radiotherapy for benign disease has declined. At moderate doses, such as those used to treat benign diseases, radiation-related cancers occur in or near the radiation field. Cancers of the thyroid, salivary gland, central nervous system, skin, and breast as well as leukemia have been associated with radiotherapy for tinea capitis, enlarged tonsils or thymus gland, other benign conditions of the head and neck, or benign breast diseases. Because doses from diagnostic examinations typically are low, they are difficult to study using epidemiologic methods, unless multiple examinations are performed. An excess risk of breast cancer has been reported among women with tuberculosis who had multiple chest fluoroscopies as well as among scoliosis patients who had frequent diagnostic x rays during late childhood and adolescence. Dental and medical diagnostic x rays performed many years ago, when doses were presumed to be high, also have been linked to increased cancer risks. The carcinogenic effects of diagnostic and therapeutic radionuclides are less well characterized. High risks of liver cancer and leukemia have been demonstrated following thorotrast injections, and patients treated with radium appear to have an elevated risk of bone sarcomas and possibly cancers of the breast, liver, kidney, thyroid, and bladder.

357 citations


Journal ArticleDOI
TL;DR: A simple, unified method for internal dose calculations is described, which brings together and simplifies concepts used in nuclear medicine and occupational internal dose systems previously described, and dose factors for bone and marrow have been updated with recently suggested corrections.
Abstract: Internal dose assessment depends on the use of mathematical formulas for dose calculation and models of the human body and its organs. A simple, unified method for internal dose calculations is described, which brings together and simplifies concepts used in nuclear medicine and occupational internal dose systems previously described. Using the best current decay data and phantoms for internal dose calculations, dose factors for internal dose assessment are provided. Decay data for over 800 radionuclides from the data service at Brookhaven National Laboratory were combined with absorbed fraction data from a number of currently available mathematical whole body and organ models to provide the dose factors. This represents the first published update on nuclear medicine dose factors since MIRD Pamphlet No. 11 in 1975; in this paper, dose factors for many more nuclides are given (816 vs. 117 in MIRD 11), including some alpha emitters. New models are also employed, and dose factors for bone and marrow have been updated with recently suggested corrections. The good agreement of the new dose factors with previously published values for several of the models gives good confidence in their accuracy. This article gives an overview of the technical basis for these dose factors and some example tables of data, but the bulk of the data files will be distributed electronically. The use of an "electronic publishing" approach permits the publication of this kind of voluminous information in mainstream journals while facilitating rapid access and use without the need to purchase often expensive and bulky paper documents.

305 citations


Journal ArticleDOI
Eric J. Hall1
TL;DR: Bystander studies imply that the target for the biological effects of radiation is larger than the cell and this could make a simple linear extrapolation of radiation risks from high to low doses of questionable validity.
Abstract: The bystander effect refers to the induction of biological effects in cells that are not directly traversed by a charged particle. The data available concerning the bystander effect fall into two quite separate categories, and it is not certain that the two groups of experiments are addressing the same phenomenon. First, there are experiments involving the transfer of medium from irradiated cells, which results in a biological effect in unirradiated cells. Second, there is the use of sophisticated single particle microbeams, which allow specific cells to be irradiated and biological effects studied in their neighbors; in this case communication is by gap junction. Medium transfer experiments have shown a bystander effect for cell lethality, chromosomal aberrations and cell cycle delay. The type of cell, epithelial vs. fibroblast, appears to be important. Experiments suggest that the effect is due to a molecule secreted by irradiated cells, which is capable of transferring damage to distant cells. Use of a single microbeam has allowed the demonstration of a bystander effect for chromosomal aberrations, cell lethality, mutation, and oncogenic transformation. When cells are in close contact, allowing gap junction communication, the bystander effect is a much larger magnitude than the phenomenon demonstrated in medium transfer experiments. A bystander effect has been demonstrated for both high- and low-LET radiations but it is usually larger for densely ionizing radiation such as alpha particles. Experiments have not yet been devised to demonstrate a comparable bystander effect on a three-dimensional normal tissue. Bystander studies imply that the target for the biological effects of radiation is larger than the cell and this could make a simple linear extrapolation of radiation risks from high to low doses of questionable validity.

215 citations



Journal ArticleDOI
TL;DR: An analysis of the dose response relationship for the probability of acute lethality from prompt or short-term exposure to ionizing radiation is presented to provide recommendations concerning estimates of casualties expected from radiation accidents, the use of nuclear weapons, or possible terrorist activities.
Abstract: A review and analysis of the dose response relationship for the probability of acute lethality from prompt or short-term exposure to ionizing radiation is presented. The purpose of this analysis is to provide recommendations concerning estimates of casualties expected from radiation accidents, the use of nuclear weapons, or possible terrorist activities. Previous work on acute ionizing radiation-induced lethality risk together with a collection of dose response relationships are analyzed and presented based on historical case data and expert opinion that have evolved from whole-body radiation therapy experience, radiation exposure accidents, nuclear weapon detonations, and animal experimentation. The nature of the data reviewed ranges from direct individual events to those offered according to collective expert opinion and consensus published as journal articles and in various technical documents and reports. The dose response relationships are expressed as two-parameter (median exposure level and slope) probability distribution models as a function of radiation exposure in terms of a free-in-air dose. Twelve different dose response relationships are presented and discussed, including the impact of some medical care.

145 citations


Journal ArticleDOI
TL;DR: Preliminary findings, if sustained by ongoing dose-response analyses, provide reassurance that cancer treatments including radiotherapy do not carry much if any risk for inherited genetic disease in offspring conceived after exposure.
Abstract: —Radiation-induced heritable diseases have not been demonstrated in humans and estimates of genetic risks for protection purposes are based on mouse experiments. The most comprehensive epidemiologic study is of the Japanese atomic bomb survivors and their children, which found little evidenc

127 citations


Journal ArticleDOI
TL;DR: There appears to be a low dose threshold effect with low LET, beyond which no additional genomic instability is induced, and data concerning dose rate effects of high and low LET radiation and their capacity to induce genomic instability assayed by chromosomal aberrations, delayed lethal mutations, micronuclei and apoptosis are reviewed.
Abstract: Genomic instability is a term used to describe a phenomenon that results in the accumulation of multiple changes required to convert a stable genome of a normal cell to an unstable genome characteristic of a tumor. There has been considerable recent debate concerning the importance of genomic instability in human cancer and its temporal occurrence in the carcinogenic process. Radiation is capable of inducing genomic instability in mammalian cells and instability is thought to be the driving force responsible for radiation carcinogenesis. Genomic instability is characterized by a large collection of diverse endpoints that include large-scale chromosomal rearrangements and aberrations, amplification of genetic material, aneuploidy, micronucleus formation, microsatellite instability, and gene mutation. The capacity of radiation to induce genomic instability depends to a large extent on radiation quality or linear energy transfer (LET) and dose. There appears to be a low dose threshold effect with low LET, beyond which no additional genomic instability is induced. Low doses of both high and low LET radiation are capable of inducing this phenomenon. This report reviews data concerning dose rate effects of high and low LET radiation and their capacity to induce genomic instability assayed by chromosomal aberrations, delayed lethal mutations, micronuclei and apoptosis.

113 citations


Journal ArticleDOI
TL;DR: Findings of the Life Span Study (LSS) cohort of atomic-bomb survivors are a primary source for quantitative risk estimates that underlie radiation protection, with some indication that attained-age-specific rates are higher for those exposed at younger ages.
Abstract: Findings of the Life Span Study (LSS) cohort of atomic-bomb survivors are a primary source for quantitative risk estimates that underlie radiation protection. Because of the size and length of follow-up, the LSS provides considerable information on both the nature of the dose response and on how radiation-associated excess risks vary with age, age at exposure, sex, and other factors. Our current analyses extend the mortality follow-up by 7 y (through 1997) and add 8 y (through 1995) to the incidence follow-up. During the follow-up periods there have been a total of about 9,300 solid cancer deaths and almost 12,200 incident cases. As outlined in this presentation, while discussing issues related to the shape of the dose response and low dose risks in some detail, the new reports consider temporal patterns in greater detail than has been done previously. As we have reported, the LSS solid cancer dose response is well described by simple linear dose response over the 0 to 2 Sv range (with some leveling off at higher estimated doses). This remains the case with the extended follow-up. Although LSS is often referred to as a high dose study, about 75% of the 50,000 cohort members with doses in excess of 5 mSv have dose estimates in a range of direct interest for radiation protection (0-200 mSv). Analyses of data limited to this low dose range provide direct evidence of a significant solid cancer dose response with a risk per unit dose that is consistent with that seen for the full dose range. Previous LSS reports have focused on descriptions of the solid cancer excess risks in which the excess relative risk varies with age at exposure and sex. In addition to the age at exposure effects, our current analyses suggest excess relative risks also vary with age (at death or diagnosis). Excess relative risks are higher for those exposed earlier in life, with attained age-specific risks changing by about 20% per decade, but tend to decrease with increasing attained age, roughly in proportion to (l/attained-age) 1.5 , for any age at exposure. Despite the decreasing relative risk, excess rates have increased rapidly throughout the study period with some indication, especially for the incidence data, that attained-age-specific rates are higher for those exposed at younger ages. Simple comparisons of site-specific excess risks are used to illustrate how the interpretation of age-at-exposure effects on excess relative risks or excess rates is complicated by changes in baseline rates with birth cohort or time period.

79 citations


Journal ArticleDOI
TL;DR: In this article, the authors quantified and evaluated both patient and staff doses by direct thermoluminescent dosimetry during various clinical CT fluoroscopy guided procedures, and the maximum recorded patient entrance skin dose stayed well below the deterministic threshold level of 2 Gy.
Abstract: As CT scanners are more routinely used as a guidance tool for various types of interventional radiological procedures, concern has grown for high patient and staff doses. CT fluoroscopy provides the physician immediate feedback and can be a valuable tool to dynamically assist various types of percutaneous interventions. However, the fixed position of the scanning plane in combination with high exposure factors may lead to high cumulative patient skin doses that can reach deterministic threshold limits. The staff is also exposed to a considerable amount of scatter radiation while standing next to the patient during the procedures. Although some studies have been published dealing with this subject, data of patient skin doses determined by direct in vivo dosimetry remains scarce. The purpose of this study is to quantify and to evaluate both patient and staff doses by direct thermoluminescent dosimetry during various clinical CT fluoroscopy guided procedures. Patient doses were quantified by determining the entrance skin dose with direct thermoluminescent dosimetry and by estimating the effective dose (E). Staff doses were quantified by determining the entrance skin dose at the level of the eyes, thyroid, and both the hands with direct thermoluminescent dosimetry. For a group of 82 consecutive patients, the following median values were determined (data per procedure): patient E (19.7 mSv), patient entrance skin dose (374 mSv), staff entrance skin dose at eye level (0.21 mSv), thyroid (0.24 mSv), at the left hand (0.18 mSv), and at the right hand (0.76 mSv). The maximum recorded patient entrance skin dose stayed well below the deterministic threshold level of 2 Gy. Poor correlation between both patient/staff doses and integrated procedure mAs emphasizes the need for in vivo measurements. CT fluoroscopy doses are markedly higher than classic CT-scan doses and are comparable to doses from other interventional radiological procedures. They consequently require adequate radiation protection management. An important potential for dose reduction exists by limiting the fluoroscopic screening time and by reducing the tube current (mA) to a level sufficient to provide adequate image quality.

74 citations



Journal ArticleDOI
TL;DR: The results indicate that the negative trend previously reported for lung cancer can be largely accounted for by a negative correlation between smoking and radon levels across counties, and the observed ecological correlation provides no substantial evidence for a protective effect of low level radon exposure.
Abstract: Cohen has reported a negative correlation between lung cancer mortality and average radon levels by county. In this paper, the correlation of U.S. county mortality rates for various types of cancers during the period 1970-1994 with Cohen's radon measurements is examined. In general, quantitatively similar, strongly negative correlations are found for cancers strongly linked to cigarette smoking, weaker negative correlations are found for cancers moderately increased by smoking, whereas no such correlation is found for cancers not linked to smoking. The results indicate that the negative trend previously reported for lung cancer can be largely accounted for by a negative correlation between smoking and radon levels across counties. Hence, the observed ecological correlation provides no substantial evidence for a protective effect of low level radon exposure.

Journal ArticleDOI
TL;DR: It is demonstrated that radiation expression profiles are a good predictor of p53 function in cell lines, and such profiles also indicate a major role for p53-regulated genes in the in vivo radiation response.
Abstract: Advances in high throughput analysis of mRNA expression have made it possible to establish gene expression profiles for different cells, tissues, diseases and exposure states For instance, recent studies have demonstrated the utility of such an approach to classify sub-types of cancers with more detail than was previously possible In addition, gene expression studies of ionizing radiation exposure both in vitro and in vivo are affording insight into the molecular mechanisms of mammalian radiation response We have demonstrated that radiation expression profiles are a good predictor of p53 function in cell lines, and such profiles also indicate a major role for p53-regulated genes in the in vivo radiation response Gene expression can be a sensitive indicator of radiation response as we have shown linear dose-responses for induction of several genes down to doses as low as 2 cGy As profiles are established from radiation studies, it is hoped that they may be useful for identifying individuals with specific exposures or predisposition to negative outcome of exposure Although this technology holds great promise, some obstacles remain to be overcome before it can be successfully applied to population studies



Journal ArticleDOI
TL;DR: The weight of evidence suggests that lesions that are precursors to cancer, and certain types of cancer as well, may increase in frequency linearly with the dose in the low-dose domain, and no alternative dose-response model is more plausible than the linear-nonthreshold model.
Abstract: To reassess the use of the linear-nonthreshold dose-response model in the light of advancing knowledge, the National Council on Radiation Protection and Measurements formed Scientific Committee 1-6 and charged it to evaluate the evidence for and against the linear-nonthreshold dose-response hypothesis without reference to any associated policy ramifications. To accomplish this task, the Committee reviewed the relevant theoretical, experimental, and epidemiological data on those effects of ionizing radiation that are generally postulated to be stochastic in nature (i.e., genetic and carcinogenic effects). From its review of the data, the Committee concluded that the weight of evidence suggests that lesions that are precursors to cancer (i.e., mutations and chromosome aberrations), and certain types of cancer as well, may increase in frequency linearly with the dose in the low-dose domain. On this basis, the Committee concluded that no alternative dose-response model is more plausible than the linear-nonthreshold model although other dose-response relationships cannot be excluded, especially in view of growing evidence that the dose-response relationship may be modified by adaptive responses, bystander effects, and other variables.

Journal ArticleDOI
TL;DR: A cohort of 2,224 children given x-ray treatment and 1,380 given only topical medications for ringworm of the scalp during 1940–1959 have been followed up for a median of 39 y to characterize the risk of tumors from radiation exposure to the head and neck.
Abstract: The objective of the study is to characterize the risk of tumors from radiation exposure to the head and neck A cohort of 2,224 children given x-ray treatment and 1,380 given only topical medications for ringworm of the scalp (tinea capitis) during 1940-1959 have been followed up for a median of 39 y to determine tumor incidence Follow-ups were by mail/telephone questionnaire, with 84-88% of the original cohort followed and with medical verification of diseases of interest Sixteen intracranial tumors [7 brain cancers, 4 meningiomas, and 5 acoustic neuromas (vestibular schwannomas)] occurred in the x-irradiated group following an average brain dose of about 14 Gy, compared to 1 acoustic neuroma in the control group The standardized incidence ratio (SIR) for brain cancer was 30 [95% confidence interval (CI): 13, 59] Even though the dose to the thyroid gland was only about 60 mGy, 2 thyroid cancers were found in the irradiated group vs none among controls, and 11 vs 1 thyroid adenomas were found in the respective groups Following an average dose of about 4 Gy to cranial marrow, 8 cases of leukemia (SIR = 32, CI: 15, 61) were observed in the irradiated group and 1 in the control group There was also a suggestive excess of blood dyscrasias There was no difference between the groups in the frequency of other cancers of the head and neck (excluding nonmelanoma skin cancer) or in total mortality

Journal ArticleDOI
TL;DR: Investigations of components of the daily diet showed that the high 137Cs contamination levels found in soils of zone II do not affect in any way low 137Cs concentrations of all important agricultural products harvested and consumed by villagers.
Abstract: The paper gives averages of 137 Cs deposition densities in soils from three areas in Northern Ukraine measured 12 to 15 y following the Chernobyl accident: in an area near Narodici (75 km west of the Chernobyl nuclear power plant in the so-called zone II) heavily contaminated by the Chernobyl fall-out and in areas around Korosten and Zhitomir showing contamination levels to be much lower. The three areas exhibited very different 137 Cs deposition densities of 2.2 MBq m -2 , 400 kBq m -2 , and 5 kBq m -2 , respectively. During a 1-y observation, measurements of the 137 Cs transfer in the food chain to humans and 137 Cs whole body contents dependent on the 137 Cs daily intake were carried out under realistic conditions of the rural inhabitants who lived in settlements within zone II. Detailed investigations of components of the daily diet showed that the high 137 Cs contamination levels found in soils of zone II do not affect in any way low 137 Cs concentrations of all important agricultural products harvested and consumed by villagers. With regard to consumption habits of the population of zone II, mushrooms and wild berries were found to contribute more than 95% of the 137 Cs daily intake to the 137 Cs whole body content of about 12 kBq (with maximum values up to 760 kBq) measured in a group of inhabitants of zone II during a period from July 1998 to July 1999. The median of the annual dose of these inhabitants from external and internal exposures was 1.2 mSv y -1 with a geometric standard deviation of 2.6. Excluding extreme habits, the geometric mean of the total exposure was 1.0 mSv y -1 with a geometric standard deviation of 1.3.

Journal ArticleDOI
TL;DR: Thyroid cancer incidence in the Bryansk region, the most contaminated area of Russia after the Chernobyl accident, is analyzed for the residents aged 15–69 y at the time of the accident and sex and age standardized incidence rates are presented and compared to the whole Russian population rates.
Abstract: Thyroid cancer incidence in the Bryansk region, the most contaminated area of Russia after the Chernobyl accident, is analyzed for the residents aged 15-69 y at the time of the accident (about 1 million persons according to the 1989 census) for the period from 1986 to 1998. Sex and age standardized incidence rates are presented and compared to the whole Russian population rates (SIR analysis). Also, a geographical correlation analysis is performed for incidence rates and mean thyroid doses at the district level, which provides a basis for preliminary estimation of radiation associated risks for the period 1991-1998 (to allow for a potential five year latent period). Thyroid doses were estimated based on the State official document "Methodology for reconstruction of dose from iodine radioisotopes in residents of the Russian Federation exposed to radioactive contamination as a result of the Chernobyl accident in 1986" (2000). Altogether, 1,051 thyroid cancer cases were detected in the Bryansk oncological dispensary from 1986 to 1998 and 769 from 1991 to 1998. Histological confirmation was available for 87% and 95% of these cases, respectively. Standardized incidence ratios (SIR) were 1.27 (95% CI = 0.92, 1.73) for the period 1986-1990 and 1.45 (95% CI = 1.20, 1.73) for the period 1991-1998 for males and 1.94 (95% CI = 1.70, 2.20) and 1.96 (95% CI = 1.82, 2.1) for females. The excess relative risk per 1 Gy (using external control) estimate for the period 1991-1998 was -0.4 (95% CI = -3.5, 2.7), -1.3 (95% CI = -2.8, 0.1) for males and females, respectively, and -0.6 (95% CI = -2.1, 0.8) for both sexes. Using internal controls, the excess relative risk (ERR(1Gy)) per unit dose of 1 Gy was found to be 0.7 with 95% CI (-2.3, 5.2) for males, -0.9 with 95% CI (-2.4, 0.8) for females and 0.0 with 95% CI (-1.4, 1.7) for males and females together. These results are discussed in the light of the quality of information available on thyroid cancer cases and screening campaigns carried out after the Chernobyl accident.

Journal ArticleDOI
TL;DR: Results from the genetic data are still preliminary and must be interpreted with caution especially because of the relatively small number of genotyped cases, but ionizing radiation from x rays as well as polymorphisms in DNA repair genes are plausible risk factors for childhood leukemia and should be studied more.
Abstract: A model for childhood leukemia proposes that characteristic chromosomal translocations can arise in utero and that for most cases a second hit occurring postnatally will be necessary. Possible causal mechanisms for leukemias are environmental factors such as ionizing radiation from x rays and inherited susceptibility from polymorphisms in DNA repair genes. We performed a case-control study of childhood acute lymphoblastic leukemia measuring reported postnatal x rays in 7111 cases aged 0-14 y and in as many population-based controls matched on age and sex. In addition we performed a case-only study in 207 cases to evaluate the interaction between x ray exposure and polymorphisms in DNA repair genes. There was an increase in risk of leukemia with number of x rays: the adjusted odds ratio for two or more x rays vs. none was 1.48 (95% confidence interval: 1.11-1.97). That risk was slightly higher among girls (odds ratio = 1.67). A polymorphism in the APE gene (ex 5) involved in the base excision repair system was suggestive of an increased risk among boys and a reduced risk among girls. HMLH1 (ex 8), a mismatch repair gene, was associated with reduction of risk among girls. Results from the genetic data are still preliminary and must he interpreted with caution especially because of the relatively small number of genotyped cases. However, ionizing radiation from x rays as well as polymorphisms in DNA repair genes are plausible risk factors for childhood leukemia and should be studied more.

Journal ArticleDOI
TL;DR: Measurements demonstrated that the model TN-502RDI dosimeter has a nearly isotropic response at diagnostic x-ray energies with variations of less than 3% deviation from the mean response for radiation incident from most directions.
Abstract: MOSFET dosimeters are seeing increased use for various dosimetry applications. Previously available commercial MOSFET dosimeters demonstrate significant anisotropies in the response when irradiated from certain directions at diagnostic x-ray energies. The angular response of a more recently introduced MOSFET dosimeter that claims an isotropic response to incident radiation is characterized. Measurements of the Thomson-Nielsen model TN-502RDI dosimeter were made for rotations of 360 degrees in 15 degrees increments about both the axial and normal-to-axial axes. These measurements demonstrated that the model TN-502RDI dosimeter has a nearly isotropic response at diagnostic x-ray energies with variations of less than 3% deviation from the mean response for radiation incident from most directions. Only two specific orientations showed significant deviation from the overall isotropic response. These correspond to the exposure scenarios where radiation is incident directly along the axis where the wire leads attach to the MOSFET device and the distal tip, the 90 degrees and 270 degrees orientations for normal-to-axial rotations, respectively. The largest deviations from an isotropic response occur when the dosimeter is irradiated free-in-air. Irradiations performed at the center of a tissue equivalent cylinder resulted in smaller deviations in angular response. The improved angular response of the TN-502RDI allows greater freedom in placement and use of MOSFET dosimeters in diagnostic radiology applications.

Journal ArticleDOI
TL;DR: A quantitative mechanistic model of bystander effects was extended to include protracted exposure, with inverse dose-rate effects attributed to replenishment, during exposure, of a subpopulation of cells which are hypersensitive to bystander signals, and concludes that current domestic radon risk estimates are unlikely to be underestimates as a result of bystanderser effects.
Abstract: Radon risks derive from exposure of bronchio-epithelial cells to alpha particles. Alpha-particle exposure can result in bystander effects when irradiated cells emit signals resulting in damage to nearby unirradiated bystander cells. Bystander effects can cause downwardly-curving dose-response relations and inverse dose-rate effects. We have extended a quantitative mechanistic model of bystander effects to include protracted exposure, with inverse dose-rate effects attributed to replenishment, during exposure, of a subpopulation of cells which are hypersensitive to bystander signals. In this approach, bystander effects and the inverse dose-rate effect are manifestations of the same basic phenomenon. The model was fitted to dose- and dose-rate dependent radon-exposed miner data; the results suggest that one directly-hit target cell can send bystander signals to about 50 neighboring cells and that, in the case of domestic radon exposures, the risk could be dominated by bystander effects. The analysis concludes that a naive linear extrapolation of radon miner data to low doses, without accounting for dose rate/bystander effects, would result in an underestimation of domestic radon risks by about a factor of ∼4. However, recent domestic radon risk estimates (BEIR VI) have already applied a phenomenological correction factor of ∼4 for inverse dose-rate effects, and have thus already implicitly taken into account corrections which we here suggest are due to bystander effects. Thus current domestic radon risk estimates are unlikely to be underestimates as a result of bystander effects.

Journal ArticleDOI
TL;DR: The study of natural gamma radioactivity was made to determine the concentrations of natural radionuclides in soil to calculate the dose to the population from outdoor exposure to terrestrial gamma rays.
Abstract: The study of natural gamma radioactivity was made to determine the concentrations of natural radionuclides in soil. Twenty soil samples collected in the cities of Zacatecas and Guadalupe and their suburban areas in the Mexican state of Zacatecas were analyzed by gamma-ray spectrometry to determine the activity concentrations of 226 Ra, 232 Th, and 40 K. Gamma-spectrometry measurements were made using a hyperpure germanium detector surrounded with shielding material to reduce the background counting rate. The GammaVision-32 MCA emulation software was used for gamma-ray spectrum analysis and the TRUMP card of 2k as a MCA emulator. Conversion factors were used to calculate the dose to the population from outdoor exposure to terrestrial gamma rays. The measured activity concentration of 226 Ra varies from 11 to 38 Bq kg -1 , the activity concentration of 232 Th varies from 8 to 38 Bq kg -1 . The activity concentration of 40 K is in the range 309-1,049 Bq kg -1 . The overall population mean outdoor terrestrial gamma dose rate is 44.94 nGy h -1 .

Journal ArticleDOI
TL;DR: The results imply that by using home stored compact disks long-term retrospective 222Rn measurements could be made with an uncertainty that could be potentially better than 10% and appears to cover practically the whole range of indoors 222 Rn concentrations.
Abstract: The radon absorption ability and the track etch properties of the polycarbonate material of commercial compact disks make them very useful as sensitive retrospective 222Rn detectors. The basic idea is to remove, after exposure, a surface layer that is thicker than the range of the alpha particles of the 222Rn and 220Rn progenies and to count the electrochemically etched tracks at the corresponding depths (>80 microm). The effects on the response due to differences in pressure, temperature, and humidity have been studied experimentally. The effect of the growing of 210Po after long-term exposures was also estimated. The effect of all listed factors except the temperature is either absent or restricted to maximum--about 10% for the very extreme cases. The variation of the response at 83 microm depth over the temperature interval 15-25 degrees C is +/-12% around the 20 degrees C value. The dependence of the calibration factor on the etched depth beneath the surface was studied at 4 different temperatures within the range expected indoors. The results show that the depth dependence is exponential with the parameters of the exponent also being dependent on the temperature. In practice, using the track density obtained in two or more depths beneath the compact disk's front surface, an a posteriori temperature correction could be made. By this correction it is possible to substantially reduce the bias in the results due to the unknown temperature during exposure. The results imply that by using home stored compact disks long-term retrospective 222Rn measurements could be made with an uncertainty that could be potentially better than 10%. The useful range of the method starts at about 3 Bq m(-3) (for 10 y exposure time) and appears to cover practically the whole range of indoors 222Rn concentrations.

Journal ArticleDOI
TL;DR: The present body of evidence does not appear to support external doses greater than 0.5 Gy; however, research is continuing to try and resolve the difference in dose estimates from the different methods.
Abstract: The presently available evidence about the magnitude of doses received by members of the public living in villages in the vicinity of Semipalatinsk nuclear test in Kazakhstan, particularly with respect to external radiation, while preliminary, is conflicting. The village of Dolon, in particular, has been identified for many years as the most highly exposed location in the vicinity of the test site. Previous publications cited external doses of more than 2 Gy to residents of Dolon while an expert group assembled by the WHO in 1997 estimated that external doses were likely to have been less than 0.5 Gy. In 2001, a larger expert group workshop was held in Helsinki jointly by the WHO, the National Cancer Institute of the United States, and the Radiation and Nuclear Safety Authority of Finland, with the expressed purpose to acquire data to evaluate the state of knowledge concerning doses received in Kazakhstan. This paper summarizes evidence presented at that workshop. External dose estimates from calculations based on sparse physical measurements and bio-dosimetric estimates based on chromosome abnormalities and electron paramagnetic resonance from a relatively small sample of teeth do not agree well. The physical dose estimates are generally higher than the biodosimetric estimates (1 Gy or more compared to 0.5 Gy or less). When viewed in its entirety, the present body of evidence does not appear to support external doses greater than 0.5 Gy; however, research is continuing to try and resolve the difference in dose estimates from the different methods. Thyroid doses from internal irradiation, which can only be estimated via calculation, are expected to have been several times greater than the doses from external irradiation, especially where received by small children.

Journal ArticleDOI
TL;DR: In this article, the authors used Monte Carlo techniques to calculate the leakage neutron spectra and its transmission through high-density concretes and found that neutrons can be estimated most reasonably and conservatively by using the linear tenth value layer of normal concrete if specific values of the tenth-value layer of the high density concrete are not known.
Abstract: Optimum shielding of the radiation from particle accelerators requires knowledge of the attenuation characteristics of the shielding material. The most common material for shielding this radiation is concrete, which can be made using various materials of different densities as aggregates. These different concrete mixes can have very different attenuation characteristics. Information about the attenuation of leakage photons and neutrons in ordinary and heavy concrete is, however, very limited. To increase our knowledge and understanding of the radiation attenuation in concrete of various compositions, we have performed measurements of the transmission of leakage radiation, photons and neutrons, from a Varian Clinac 2100C medical linear accelerator operating at maximum electron energies of 6 and 18 MeV. We have also calculated, using Monte Carlo techniques, the leakage neutron spectra and its transmission through concrete. The results of these measurements and calculations extend the information currently available for designing shielding for medical electron accelerators. Photon transmission characteristics depend more on the manufacturer of the concrete than on the atomic composition. A possible cause for this effect is a non-uniform distribution of the high-density aggregate, typically iron, in the concrete matrix. Errors in estimated transmission of photons can exceed a factor of three, depending on barrier thickness, if attenuation in high-density concrete is simply scaled from that of normal density concrete. We found that neutron transmission through the high-density concretes can be estimated most reasonably and conservatively by using the linear tenth-value layer of normal concrete if specific values of the tenth-value layer of the high-density concrete are not known. The reason for this is that the neutron transmission depends primarily on the hydrogen content of the concrete, which does not significantly depend on concrete density. Errors of factors of two to more than ten, depending on barrier thickness, in the estimated transmission of neutrons through high-density concrete can be made if the attenuation is scaled by density from normal concrete.

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TL;DR: The U.S. Department of Energy’s Low Dose Radiation Research Program is a 10 y activity currently funded at $21 million per year, and research to date suggests the need for some major paradigm shifts.
Abstract: The U.S. Department of Energy's Low Dose Radiation Research Program is a 10 y activity currently funded at $21 million per year. It focuses on biological responses to low doses (<0.1 Gy) of low-LET ionizing radiation. The overall goal of this program is to provide a sound scientific basis for the radiation protection standards. The program supports basic research that combines modern genomic, molecular, and cellular techniques with recent advances in scientific instrumentation. These combinations make it possible to detect responses and test paradigms associated with the mechanisms of low dose radiation action not previously measurable or testable. Research to date is briefly reviewed and suggests the need for some major paradigm shifts. Exposure of the extracellular matrix can modify both the pattern of gene expression and the phenotype of the cells which result in cell transformation without direct mutation. Low dose radiation exposure results in a range of dose-response relationships for changes in the number, types, and patterns of gene expression. Such studies suggest an increased role for gene expression relative to single mutations for radiation induced cancer. Low dose research using microbeams demonstrated that cells do not require a direct hit to result in significant biological alterations. These bystander effects demonstrate that non-hit cells respond with changes in gene expression, DNA repair, chromosome aberrations, mutations, and cell killing. Research to link genomic instability with cancer is also being conducted and will be discussed. Detection of radiosensitivity genes as markers of genetic susceptibility in individuals and populations can be used in epidemiological studies to determine how molecular changes may impact risk. It is not possible to determine how this research will influence current radiation standards. However, the Low Dose Research Program will help ensure that radiation standards are set using the best scientific data available, and that they are adequate and appropriate for the protection of workers and the public.


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TL;DR: The intervention against radon in homes, therefore, seems justifiable, and the estimated cost per life is large, mainly due to uncertainty in the risk of lung cancer from radon.
Abstract: —Background: Radon is a radioactive gas that may leak into buildings from the ground. Radon exposure is a risk factor for lung cancer. An intervention against radon exposure in homes may consist of locating homes with high radon exposure (above 200 Bq m−3) and improving these, and protecting

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TL;DR: The measured temperature increases during the exposures agree with the model within the variability of the data, and thresholds for thermal damage to the cornea can be predicted for a range of exposure conditions.
Abstract: —Recent data on damage to the primate cornea from exposure to millimeter wave radiation are interpreted in terms of a simple thermal model. The measured temperature increases during the exposures (duration 1–5 s, 35 or 94 GHz, 2–7 W cm−2) agree with the model within the variability of the da