Biomedical subjects

D G Hoel

Publications and source records attributed to D G Hoel.

At least 19 recordsLinked to original sources

PubMed2002

Breast dose variability in a bi-racial population undergoing screening mammography.

This study evaluated individual and population dose variability during screening mammography, among 570 white and black women in South Carolina, USA. Aspects of dosimetry that were considered include compressed breast thickness (CBT), number of films per screening session, and dose in previous or subsequent sessions. Breast dose was log-normally distributed in the population, with a geometric mean of 6.6 mGy per session. Doses were significantly higher for black women, for women with high CBT or who receive more than two views per breast, and for the mediolateral oblique, compared to the craniocaudal, view. No relationship was observed between age and dose. Total dose per breast varied by a factor of 20 across the study population, but the individual's dose varied little among repeat screening sessions, especially after adjusting for the number of films received per session. These results may inform assessments of the projected risks of inducing breast cancer from screening mammography.

Adult↗

PubMed2002

Mammography dose in relation to body mass index, race, and menopausal status.

Mammography dose increases with compressed breast thickness (CBT), but few studies have examined other correlates of dose. The purpose of this study was to evaluate the relation between factors such as race, age, body mass index (BMI), CBT, and menopausal status and mammography screening dose, measured for 509 women in a US population. A multiple linear regression model was developed for dose, based on consideration of these factors as well as examination characteristics. BMI and number of films during examination were positively related to dose. After adjusting for these factors, high CBT also leads to higher dose. Whites receive lower doses than black women but differences are slight after controlling for the effects of CBT and BMI, which were significantly higher among black women. Pre-menopausal women receive higher doses, after adjusting for all other factors, than post-menopausal women. Jointly, these factors account for approximately 75% to 80% of the variability in dose among this study population. Because rates of overweight are increasing in the US, average doses from mammography may be increasing as well.

Adult↗

PubMed2001

Health among commercial airline pilots.

BACKGROUND: The airline pilot works within a complex exposure environment that may present physiological challenges to long-term health. METHODS: This study investigated self-reported disease outcomes among a large group of active and retired commercial airline pilots in the United States and Canada. A survey methodology was used, including the collection of historical information. RESULTS: Of 10,678 surveys mailed, 6609 were returned (6533 men, 63 women). Given the limitations of survey methodology, increased disease rates among pilots were suggested for melanoma, motor neuron disease, and cataracts. However, rates for other diseases were in general lower than those for the U.S. population. CONCLUSIONS: Further study has been initiated to verify and follow reported cases, to expand the study to a larger group, and to collect more in-depth information on flight histories, occupational exposures, and lifestyle factors.

Adolescent↗

PubMed2000

Flight deck magnetic fields in commercial aircraft.

BACKGROUND: Airline pilots are exposed to magnetic fields generated by the aircraft's electrical system. The objectives of this study were (1) to directly measure flight deck magnetic fields in terms of personal exposure to the pilots when flying on different aircraft types over a 75-hour flight-duty month, and (2) to compare magnetic field exposures across flight deck types and job titles. METHODS: Measurements were taken using personal dosimeters carried by either the Captain or the First Officer on Boeing 737/200, Boeing 747/400, Boeing 767/300ER, and Airbus 320 aircraft. RESULTS: Approximately 1,008 block hours were recorded at a sampling frequency of 3 seconds. Total block time exposure to the pilots ranged from a harmonic geometric mean of 6.7 milliGauss (mG) for the Boeing 767/300ER to 12.7 mG for the Boeing 737/200. CONCLUSIONS: Measured flight deck magnetic field levels were substantially above the 0.8-1 mG level typically found in the home or office and suggest the need for further study to evaluate potential health effects of long-term exposure.

Aircraft↗

PubMed2000

Biologically-based risk estimation for radiation-induced chronic myeloid leukemia.

Radiation cancer risks are typically determined by the use of simple statistical descriptions of epidemiological data. It is important in risk assessment in general, however, to attempt to incorporate as much biological information into the risk models as possible. We illustrate this by presenting a biologically-based linear-quadratic-exponential (LQE) incidence rate model for radiation-induced chronic myeloid leukemia (CML). The model consists of a linear-quadratic dose-response for the induction of BCR-ABL, a waiting time distribution between BCR-ABL formation and detection of CML, and an exponential cell-killing term that multiplies both the background and induced incidence rates. Using data exclusive of the A-bomb survivor cohort, Bayesian priors are defined for each of the nine parameters in this LQE model. The priors are based on chromosomal translocations in lymphocytes, hematopoietic stem cell survival experiments, CML waiting times in women irradiated for benign disease, the background CML incidence rate in the U.S. population, and genomic DNA target sizes of BCR and ABL. Fixing three of the LQE model parameters to the means of their priors, maximum likelihood estimates of the remaining six parameters were obtained using A-bomb survivor incidence data for Hiroshima males. The likelihood estimates and the corresponding six prior distributions, both approximated as multivariate normal, were then used to form Bayesian posteriors for the six parameters not fixed. With these posteriors the LQE model yields Qgamma*=0.0042 Gy(-1) where Qgamma* is the upper 95% confidence bound of the lifetime CML risk per person-gray in the limit of low doses of gamma-rays. This value is slightly less than Qgamma*=0.0049 Gy(-1) obtained from likelihood estimates of the LQE parameters, and substantially less than Qgamma*=0.0158 Gy(-1) obtained for a simple statistical model linear in dose for kermas less than 4 Gy.

Algorithms↗

PubMed1999

Unexplained increases in cancer incidence in the United States from 1975 to 1994: possible sentinel health indicators?

To search for unexplained patterns in cancer incidence, we analyzed data from 1975 to 1994 that represent approximately 10% of the population of the United States. Our analysis focused on long-term time trends in incidence and on deviations from those trends attributable to birth cohorts or to calendar periods. On average, cancer incidence rose 0.8% annually in white women and 1.8% in white men. After removing several cancers related to smoking and increased screening, average annual increases fell to 0.1% in white women but persisted at 1.7% in white men. In particular, yearly increases in non-Hodgkin's lymphoma averaged 2.4% in white women and 4.7% in white men. Among men, incidence changes attributable to cohorts grew progressively larger from one cohort to the next. Cancer incidence patterns among black men and women were similar to those among whites despite smaller population sizes. Unexplained patterns of cancer incidence may signal changes in underlying risk factors and highlight the continuing need for research on cancer etiology and prevention.

Adult↗

PubMed1998

Cosmic radiation and magnetic field exposure to airline flight crews.

BACKGROUND: Flight crews are exposed to elevated levels of cosmic radiation and to magnetic fields generated by the aircraft's electrical system. The purpose of this study was to quantify these two occupational exposures. METHODS: Magnetic fields were measured during 37 flights (23 in the cockpit and 14 in the cabin) using an Emdex Lite personal dosimeter. All cockpit measurements were taken on the B737/200. Cabin measurements were taken in several aircraft types, including the B737, B757, DC9, and L1011. Cosmic radiation was computer estimated for 206 flights using the Federal Aviation Administration's program CARI-3C. RESULTS: Magnetic field levels in the cockpit had a mean value of approximately 17 milliGauss (mG), while cabin measurements were lower (mean values of approximately 3 or less in economy, 6 in first class, 8 in front serving areas). Cosmic radiation equivalent dose rates to bone marrow and skeletal tissue ranged from 0.3 to 5.7 microsieverts per hour. CONCLUSIONS: Elevated magnetic field levels in front serving areas and the cockpit suggest the need for further study to evaluate long-term exposure to flight crew members who work in these areas. Cosmic radiation levels are well below occupational limits for adults, but may require some pregnant flight crew members to adjust their flying time or routes.

Aerospace Medicine↗

PubMed1998

Is occupational organic solvent exposure a risk factor for scleroderma?

OBJECTIVE: The primary objective was to determine whether occupational exposure to organic solvents is related to an increased risk of systemic sclerosis (SSc; scleroderma). METHODS: Occupational histories were obtained from 178 SSc patients and 200 controls. Exposure scores were computed for each individual using job exposure matrices, which were validated by an industrial expert. RESULTS: Among men, those with SSc were more likely than controls to have a high cumulative intensity score (odds ratio [OR] 2.9, 95% confidence interval [95% CI] 1.1-7.6) and a high maximum intensity score (OR 2.9, 95% CI 1.2-7.1) for any solvent exposure. They were also more likely than controls to have a high maximum intensity score for trichloroethylene exposure (OR 3.3, 95% CI 1.0-10.3). Among men and women, significant solvent-disease associations were observed among SSc patients who tested positive for the anti-Scl-70 autoantibody; these trends were not observed among the men and women who tested negative for anti-Scl-70. CONCLUSION: These results provide evidence that occupational solvent exposure may be associated with an increased risk of SSc.

Adult↗

PubMed1998

Size distributions of misrejoining DNA fragments in irradiated cells.

When ionizing radiation strikes a cell it induces DNA double strand breaks (DSBs). Subsequently, some of the DSBs misrejoin and thus cause alterations in the size distribution of the DNA fragments. We derive a system of non-linear integro-differential equations describing the misrejoining interactions of five classes of DNA fragments, including rings and various types of linear fragments. The fragment classes are represented by density functions; the shape of a density function determines the probability that a fragment has a particular size and the amplitude (integral) equals the expected number of such fragments per cell. The equations are solved: analytically for exponentially distributed initial fragment sizes (corresponding to high doses) and numerically for arbitrary initial conditions. Computed final fragment size distributions are applied to situations representative of flow karyotypes and pulsed-field gel assays. For human flow karyotypes, the model can be used to obtain misrejoining estimates at doses too high for conventional methods of data analysis. For pulsed-field gel assays in which human chromosomes are digested with restriction endonucleases to form 'cut-somes' (restriction fragments), the model provides a means of misrejoining estimation when the cut-some sizes are non-random. The model suggests that if the cut-some size distribution for unirradiated cells is completely random, misrejoining of radiation-induced DSBs will not be detectable in the final size distribution.

Chromosome Breakage↗

PubMed1998

Threshold models in radiation carcinogenesis.

Cancer incidence and mortality data from the atomic bomb survivors cohort has been analyzed to allow for the possibility of a threshold dose response. The same dose-response models as used in the original papers were fit to the data. The estimated cancer incidence from the fitted models over-predicted the observed cancer incidence in the lowest exposure group. This is consistent with a threshold or non-linear dose-response at low-doses. Thresholds were added to the dose-response models and the range of possible thresholds is shown for both solid tumor cancers as well as the different leukemia types. This analysis suggests that the A-bomb cancer incidence data agree more with a threshold or non-linear dose-response model than a purely linear model although the linear model is statistically equivalent. This observation is not found with the mortality data. For both the incidence data and the mortality data the addition of a threshold term significantly improves the fit to the linear or linear-quadratic dose response for both total leukemias and also for the leukemia subtypes of ALL, AML, and CML.

Cohort Studies↗

PubMed1998

Mortality among US commercial pilots and navigators.

The airline industry may be an occupational setting with specific health risks. Two environmental agents to which flight crews are known to be exposed are cosmic radiation and magnetic fields generated by the aircraft's electrical system. Other factors to be considered are circadian disruption and conditions specific to air travel, such as noise, vibration, mild hypoxia, reduced atmospheric pressure, low humidity, and air quality. This study investigated mortality among US commercial pilots and navigators, using proportional mortality ratios for cancer and noncancer end points. Proportional cancer mortality ratios and mortality odds ratios were also calculated for comparison to the proportional mortality ratios for cancer causes of death. Results indicated that US pilots and navigators have experienced significantly increased mortality due to cancer of the kidney and renal pelvis, motor neuron disease, and external causes. In addition, increased mortality due to prostate cancer, brain cancer, colon cancer, and cancer of the lip, buccal cavity, and pharynx was suggested. Mortality was significantly decreased for 11 causes. To determine if these health outcomes are related to occupational exposures, it will be necessary to quantify each exposure separately, to study the potential synergy of effects, and to couple this information with disease data on an individual basis.

Aerospace Medicine↗

PubMed1998

Recent data obtained by pulsed-field gel electrophoresis suggest two types of double-strand breaks.

The temporal evolution of unrejoined and misrejoined DNA double-strand breaks (DSBs) produced by high doses (80-160 Gy) of X rays has been estimated using pulsed-field gel electrophoresis (PFGE) (Löbrich et al., Proc. Natl. Acad. Sci. USA 92, 12050-12054, 1995). We attempted to fit these data to three models. An RBM ("Revell binary misrejoining") model, based on the usual repair-misrepair and lethal-potentially lethal models, appears to be inconsistent with the data. The main discrepancies are the following: (1) The RBM model predicts that 90% of the misrejoined DSBs form by the time 75% of the DSBs have disappeared, while the data indicate that only 50% are formed by this time; and (2) the model predicts an increasing fraction of DSBs misrejoined at 160 Gy compared to 80 Gy, while the data support approximately equal fractions misrejoined. These discrepancies are alleviated in the Sax subset (SS) and Revell subset (RS) models. In the SS and RS models, two types (or subsets) of DSBs exist: those that are active in misrejoining and those that are not. In the SS model, active DSBs misrejoin by the breakage-and-reunion mechanism described by Sax; in the RS model, active DSBs either repair, or misrejoin according to the complete exchange misrejoining mechanism described by Revell. Both models are consistent with the data set considered.

Animals↗

PubMed1998

Misrejoining of double-strand breaks after X irradiation: relating moderate to very high doses by a Markov model.

Misrejoining of double-strand breaks (DSBs) detected with pulsed-field gel electrophoresis (PFGE) after X irradiation of human cells at very high doses (80-160 Gy) is related to dose-response relationships for chromosome aberrations at moderate doses (1-5 Gy) by the Sax-Markov binary eurejoining/misrejoining (SMBE) model. The SMBE model applies Sax's breakage-and-reunion hypothesis to a subset of DSBs active in binary misrejoining and in binary eurejoining (accidental restitution). The model is numerically consistent with both data on chromosome aberrations and the data obtained by PFGE if proximity effects (restrictions on the range of interactions of DSB free ends) are present. Proximity effects are modeled by partitioning the cell's nucleus into approximately 400 interaction sites, with two active DSB free ends capable of rejoining only if they were produced within the same site. Neglecting one-track action, the SMBE model predicts a quadratic-linear dose-response relationship for DSB misrejoining after exposure to low-LET radiation; i.e., there is a quadratic response at moderate doses which becomes linear as the dose becomes large, rather than vice versa. The linear region results because at very high doses almost all of the active DSB free ends misrejoin rather than eurejoin.

DNA↗

PubMed1995

Ionizing radiation and cancer prevention.

Ionizing radiation long has been recognized as a cause of cancer. Among environmental cancer risks, radiation is unique in the variety of organs and tissues that it can affect. Numerous epidemiological studies with good dosimetry provide the basis for cancer risk estimation, including quantitative information derived from observed dose-response relationships. The amount of cancer attributable to ionizing radiation is difficult to estimate, but numbers such as 1 to 3% have been suggested. Some radiation-induced cancers attributable to naturally occurring exposures, such as cosmic and terrestrial radiation, are not preventable. The major natural radiation exposure, radon, can often be reduced, especially in the home, but not entirely eliminated. Medical use of radiation constitutes the other main category of exposure; because of the importance of its benefits to one's health, the appropriate prevention strategy is to simply work to minimize exposures.

Dose-Response Relationship, Radiation↗

PubMed1994

Decreasing cardiovascular disease and increasing cancer among whites in the United States from 1973 through 1987. Good news and bad news.

OBJECTIVE: Trends in cancer mortality, cardiovascular mortality, and cancer incidence are assessed among US whites to determine whether aging of the population and smoking patterns completely account for increased cancer rates from 1973 through 1987. DESIGN: For mortality, percentage changes in age-specific rates were calculated. For cancer incidence, trends in age-specific rates across time periods and birth cohorts were assessed for several sites. MAIN OUTCOME MEASURES: National US cardiovascular and cancer mortality rates and incidence rates for smoking-related cancer, breast cancer, and all other types of cancer in 10% of the US population covered by the National Cancer Institute's Surveillance, Epidemiology, and End Results Program were analyzed. RESULTS: From 1973 through 1987, cardiovascular mortality decreased 42% in the age group 0 to 54 years and decreased 33% in the age group 55 to 84 years; concurrently, cancer mortality decreased 17% in the younger group but increased 12% in the older group. By 1987, even though proportionally fewer people in the older age groups died, relatively more of them died of cancer. Men born in the 1940s had twice as much cancer as those born in 1888 through 1897 and more than twice as much cancer not linked to smoking; women born during this period had 50% and 30% more of these same cancers, respectively. Rates of smoking-related cancers in recent cohorts of women were five to six times greater than in those born in 1888 through 1897, while rates in men declined. Recent cohorts of women also had more than twice as much breast cancer as those born in 1888 through 1897. CONCLUSIONS: In recent US birth cohorts, our model found that increases in cancer have occurred that are not solely linked to aging of the population and smoking patterns. In light of these results and similar findings in Sweden, changes in carcinogenic hazards in addition to smoking are likely to have occurred and need to be studied further.

Adolescent↗

PubMed1994

Early mortality rate of atomic bomb survivors based on House Reconstruction Survey.

This paper studies the mortality rate experienced by over 23,000 A-bomb survivors in Nagasaki between September 1945 and 1950 when the RERF-ABCC initiated the follow-up of the large LSS cohort. The study is based on the data of the 10-year House Reconstruction Survey. As expected, these data show an increasing mortality rate with increasing proximity to the hypocenter of the bomb. What was not anticipated was a higher mortality rate in the 1400-1699 m band than in the closer distance interval of 1200-1399 m. This suggests a possible selective survival among A-bomb survivors. Whether this affects the cancer risk estimates has not as yet been determined.

Dose-Response Relationship, Radiation↗

PubMed1994

Nonlinearity of dose-response functions for carcinogenicity.

Carcinogenesis data for 315 chemicals were obtained from the National Cancer Institute-National Toxicology Program (NCI-NTP) bioassay programs and were analyzed to examine the shape of carcinogenesis dose-response curves. Tumor site data were more often consistent with a quadratic response than with a linear response, suggesting that the routine use of linear dose-response models will often overestimate risk. Information from in vivo short-term mutagenicity and genotoxicity assays was also obtained for most of these rodent bioassays. It was found that there were no clear relationships between the shape of the carcinogenesis dose-response curve and the result of the short-term test. These observations argue against the concept that carcinogens that are positive in a short-term assay be regulated using a linear dose-response curve and those that are negative be regulated using a sublinear dose-response curve or a safety factor approach.

Animals↗

PubMed1993

Influence of death certificate errors on cancer mortality trends.

BACKGROUND: Evaluation of mortality data is an important tool in assessing both disease time trends and differences in populations. However, the reasons for changes in cancer mortality rates have been controversial. Questions have been raised concerning whether these increases are real or simply the result of changing diagnoses and death certificate reporting. PURPOSE: Our purpose was to determine on the basis of autopsy data if death certificate reporting varies over age, time, and cancer type and to explore the effect of death certificate error on recent cancer mortality trends. METHODS: Data were analyzed from 5886 autopsies collected by the Radiation Effects Research Foundation in Hiroshima, Japan, between 1961 and 1987. Death certificates were linked to autopsy data for analyses. An adjustment factor was calculated as a ratio of the accuracy of these death certificates in identifying cancer (detection rate) and listing cancer (confirmation rate) as the cause of death. This adjustment factor measures bias in mortality rates due to death certification errors and quantifies underestimation and overestimation of cancer mortality rates. RESULTS: Our analyses focused on lymphoma, breast cancer, neoplasms of the brain, multiple myeloma, and melanoma because of reported mortality increases. For these cancers, the adjustment factor decreased significantly (P = .02) over time, implying that death certificate accuracy has improved. This change appears to account for 60% of the observed increase in these cancers during the time period of study. For total cancer, persons 75 years or older have a high adjustment factor but it decreased over time. This decrease suggests an artifactual increase in total cancer mortality rates of about 1% per year for this older group. CONCLUSIONS: The quality of death certificate reporting has generally remained constant for most groups during the period 1961-1987. In the study population, there was a consistent underestimation of total cancer mortality of about 18%. For the five types of cancer studied, there has been less underestimation of cancer mortality since 1976. For some specific cancers and for persons 75 years or older, improvements in death certificate accuracy have occurred over time. These data imply that the total death certificate error rate varies considerably by cancer type, time period, and age at death. IMPLICATIONS: The changes in death certificate reporting for some sites and the elderly appear to have artifactually created increases in cancer mortality rates. These artifacts need to be considered when using mortality data for prevention research and health care planning.

Aged↗