[Show abstract][Hide abstract] ABSTRACT: Most conventional risk analysis methods rely on a single best estimate of
exposure per person which does not allow for adjustment for exposure-related
uncertainty. Here, we propose a Bayesian model averaging method to properly
quantify the relationship between radiation dose and disease outcomes by
accounting for shared and unshared uncertainty in estimated dose. Our Bayesian
risk analysis method utilizes multiple realizations of sets (vectors) of doses
generated by a two-dimensional Monte Carlo simulation method that properly
separates shared and unshared errors in dose estimation. The exposure model
used in this work is taken from a study of the risk of thyroid nodules among a
cohort of 2,376 subjects following exposure to fallout resulting from nuclear
testing in Kazakhstan. We assessed the performance of our method through an
extensive series of simulation tests and comparisons against conventional
regression risk analysis methods. We conclude that when estimated doses contain
relatively small amounts of uncertainty, the Bayesian method using multiple
realizations of possibly true dose vectors gave similar results to the
conventional regression-based methods of dose-response analysis. However, when
large and complex mixtures of shared and unshared uncertainties are present,
the Bayesian method using multiple dose vectors had significantly lower
relative bias than conventional regression-based risk analysis methods as well
as a markedly increased capability to include the pre-established 'true' risk
coefficient within the credible interval of the Bayesian-based risk estimate.
An evaluation of the dose-response using our method is presented for an
epidemiological study of thyroid disease following radiation exposure.
[Show abstract][Hide abstract] ABSTRACT: Little, M.P., Kwon, D., Doi, K., Simon, S.L., Preston, D.L., Doody, M.M., Lee, T., Miller, J.S., Kampa, D.M., Bhatti, P., Tucker, J.D., Linet, M.S., Sigurdson, A.J., Association of Chromosome Translocation Rate with Low Dose Occupational Radiation Exposures in U.S. Radiologic Technologists. Radiat. Res. 182, 1-17 (2014).
Chromosome translocations are a well-recognized biological marker of radiation exposure and cancer risk. However, there is uncertainty about the lowest dose at which excess translocations can be detected, and whether there is temporal decay of induced translocations in radiation-exposed populations. Dosimetric uncertainties can substantially alter the shape of dose-response relationships; although regression-calibration methods have been used in some datasets, these have not been applied in radio-occupational studies, where there are also complex patterns of shared and unshared errors that these methods do not account for.
In this paper we evaluated the relationship between estimated occupational ionizing radiation doses and chromosome translocation rates using fluorescent in situ hybridization in 238 US radiologic technologists selected from a large cohort. Estimated cumulative red-bone-marrow doses (mean 29.3 mGy, range 0-135.7 mGy) were based on available badge-dose measurement data and on questionnaire-reported work-history factors. Dosimetric assessment uncertainties were evaluated using regression-calibration, Bayesian, and Monte-Carlo maximum-likelihood methods, taking account of shared and unshared error, and adjusted for overdispersion.
There was a significant dose response for estimated occupational radiation exposure, adjusted for questionnaire-based personal diagnostic radiation, age, sex, and study group (5.7 translocations per 100 whole-genome cell equivalents per Gy, 95% CI 0.2, 11.3, p=0.0440). A significant increasing trend with dose continued to be observed for individuals with estimated doses <100 mGy. For combined estimated occupational and personal diagnostic medical radiation exposures, there was a borderline-significant modifying effect of age (p=0.0704), but little evidence (p>0.5) of temporal decay of induced translocations. The three methods of analysis to adjust for dose uncertainty gave similar results.
In summary, chromosome translocation dose-response slopes were detectable down to <100 mGy, and were compatible with those observed in other radiation-exposed populations. However, there are substantial uncertainties in both occupational and other (personal diagnostic medical) doses that may be imperfectly taken into account in our analysis.
Radiation Research 06/2014; 182(1):1-17. · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The 1986 accident at the Chernobyl nuclear power plant remains the most serious nuclear accident in history, and excess thyroid cancers, particularly among those exposed to releases of iodine-131 remain the best-documented sequelae. Failure to take dose-measurement error into account can lead to bias in assessments of dose-response slope. Although risks in the Ukrainian-US thyroid screening study have been previously evaluated, errors in dose assessments have not been addressed hitherto. Dose-response patterns were examined in a thyroid screening prevalence cohort of 13,127 persons aged <18 at the time of the accident who were resident in the most radioactively contaminated regions of Ukraine. We extended earlier analyses in this cohort by adjusting for dose error in the recently developed TD-10 dosimetry. Three methods of statistical correction, via two types of regression calibration, and Monte Carlo maximum-likelihood, were applied to the doses that can be derived from the ratio of thyroid activity to thyroid mass. The two components that make up this ratio have different types of error, Berkson error for thyroid mass and classical error for thyroid activity. The first regression-calibration method yielded estimates of excess odds ratio of 5.78 Gy(-1) (95% CI 1.92, 27.04), about 7% higher than estimates unadjusted for dose error. The second regression-calibration method gave an excess odds ratio of 4.78 Gy(-1) (95% CI 1.64, 19.69), about 11% lower than unadjusted analysis. The Monte Carlo maximum-likelihood method produced an excess odds ratio of 4.93 Gy(-1) (95% CI 1.67, 19.90), about 8% lower than unadjusted analysis. There are borderline-significant (p = 0.101-0.112) indications of downward curvature in the dose response, allowing for which nearly doubled the low-dose linear coefficient. In conclusion, dose-error adjustment has comparatively modest effects on regression parameters, a consequence of the relatively small errors, of a mixture of Berkson and classical form, associated with thyroid dose assessment.
PLoS ONE 01/2014; 9(1):e85723. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: PURPOSE: To provide dosimetric data for an epidemiologic study on the risk of second primary esophageal cancer among breast cancer survivors, by reconstructing the radiation dose incidentally delivered to the esophagus of 414 women treated with radiation therapy for breast cancer during 1943-1996 in North America and Europe. METHODS AND MATERIALS: We abstracted the radiation therapy treatment parameters from each patient's radiation therapy record. Treatment fields included direct chest wall (37% of patients), medial and lateral tangentials (45%), supraclavicular (SCV, 64%), internal mammary (IM, 44%), SCV and IM together (16%), axillary (52%), and breast/chest wall boosts (7%). The beam types used were (60)Co (45% of fields), orthovoltage (33%), megavoltage photons (11%), and electrons (10%). The population median prescribed dose to the target volume ranged from 21 Gy to 40 Gy. We reconstructed the doses over the length of the esophagus using abstracted patient data, water phantom measurements, and a computational model of the human body. RESULTS: Fields that treated the SCV and/or IM lymph nodes were used for 85% of the patients and delivered the highest doses within 3 regions of the esophagus: cervical (population median 38 Gy), upper thoracic (32 Gy), and middle thoracic (25 Gy). Other fields (direct chest wall, tangential, and axillary) contributed substantially lower doses (approximately 2 Gy). The cervical to middle thoracic esophagus received the highest dose because of its close proximity to the SCV and IM fields and less overlying tissue in that part of the chest. The location of the SCV field border relative to the midline was one of the most important determinants of the dose to the esophagus. CONCLUSIONS: Breast cancer patients in this study received relatively high incidental radiation therapy doses to the esophagus when the SCV and/or IM lymph nodes were treated, whereas direct chest wall, tangentials, and axillary fields contributed lower doses.
International journal of radiation oncology, biology, physics 04/2013; · 4.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND: Epidemiologic studies have shown consistent associations between obesity and increased thyroid cancer risk, but, to date, no studies have investigated the relationship between thyroid cancer risk and obesity-related single nucleotide polymorphisms (SNPs). METHODS: We evaluated 575 tag SNPs in 23 obesity-related gene regions in a case-control study of 341 incident papillary thyroid cancer (PTC) cases and 444 controls of European ancestry. Logistic regression models, adjusted for attained age, year of birth, and sex were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) with SNP genotypes, coded as 0, 1, and 2 and modeled continuously to calculate P-trends. RESULTS: Nine out of 10 top-ranking SNPs (Ptrend<0.01) were located in the FTO (fat mass and obesity associated) gene region, while the other was located in INSR (insulin receptor). None of the associations were significant after correcting for multiple testing. CONCLUSIONS: Our data do not support an important role of obesity-related genetic polymorphisms in determining the risk of PTC. Impact: Factors other than selected genetic polymorphisms may be responsible for the observed associations between obesity and increased PTC risk.
Cancer Epidemiology Biomarkers & Prevention 10/2012; · 4.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The assessment of potential benefits versus harms from mammographic examinations as described in the controversial breast cancer screening recommendations of the U.S. Preventive Task Force included limited consideration of absorbed dose to the fibroglandular tissue of the breast (glandular tissue dose), the tissue at risk for breast cancer. Epidemiological studies on cancer risks associated with diagnostic radiological examinations often lack accurate information on glandular tissue dose, and there is a clear need for better estimates of these doses. Our objective was to develop a quantitative summary of glandular tissue doses from mammography by considering sources of variation over time in key parameters, including imaging protocols, X-ray target materials, voltage, filtration, incident air kerma, compressed breast thickness, and breast composition. We estimated the minimum, maximum and mean values for glandular tissue dose for populations of exposed women within 5-year periods from 1960 to the present, with the minimum to maximum range likely including 90% to 95% of the entirety of the dose range from mammography in North America and Europe. Glandular tissue dose from a single view in mammography is presently about 2 mGy, about one-sixth the dose in the 1960s. The ratio of our estimates of maximum to minimum glandular tissue doses for average-size breasts was about 100 in the 1960s compared to a ratio of about 5 in recent years. Findings from our analysis provide quantitative information on glandular tissue doses from mammographic examinations that can be used in epidemiological studies of breast cancer.
Radiation Research 01/2012; 177(1):92-108. · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a Bayesian variable selection method for the setting in which the number of independent variables or predictors in a particular dataset is much larger than the available sample size. While most existing methods allow some degree of correlations among predictors but do not consider these correlations for variable selection, our method accounts for correlations among the predictors in variable selection. Our correlation-based stochastic search (CBS) method, the hybrid-CBS algorithm, extends a popular search algorithm for high-dimensional data, the stochastic search variable selection (SSVS) method. Similar to SSVS, we search the space of all possible models using variable addition, deletion or swap moves. However, our moves through the model space are designed to accommodate correlations among the variables. We describe our approach for continuous, binary, ordinal, and count outcome data. The impact of choices of prior distributions and hyper-parameters is assessed in simulation studies. We also examined performance of variable selection and prediction as the correlation structure of the predictors varies. We found that the hybrid-CBS resulted in lower prediction errors and better identified the true outcome associated predictors than SSVS when predictors were moderately to highly correlated. We illustrate the method on data from a proteomic profiling study of melanoma, a skin cancer.
[Show abstract][Hide abstract] ABSTRACT: To determine more accurate regression formulas for estimating peak skin dose (PSD) from reference air kerma (RAK) or kerma-area product (KAP).
After grouping of the data from 21 procedures into 13 clinically similar groups, assessments were made of optimal clustering using the Bayesian information criterion to obtain the optimal linear regressions of (log-transformed) PSD vs RAK, PSD vs KAP, and PSD vs RAK and KAP.
Three clusters of clinical groups were optimal in regression of PSD vs RAK, seven clusters of clinical groups were optimal in regression of PSD vs KAP, and six clusters of clinical groups were optimal in regression of PSD vs RAK and K AP. Prediction of PSD using both RAK andKAP is significantly better than prediction of PSD with either RAK or KAP alone. The regression of PSD vs RAK provided better predictions of PSD than the regression of PSD vs KAP. The partial-pooling (clustered) method yields smaller mean squared errors compared with the complete-pooling method.
PSD distributions for interventional radiology procedures are log-normal. Estimates of PSD derived from RAK and KAP jointly are mos t accurate, followed closely byestimates derived from RAK alone. Estimates of PSD derived from KAP alone are the least accurate. Using a stochastic search approach, it is possible to cluster together certain dissimilar types of procedures to minimize the total error sum of squares.
Medical Physics 07/2011; 38(7):4196-204. · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract In this paper, we describe recent methodological enhancements and findings from the dose reconstruction component of a study of cancer risks among U.S. radiologic technologists. An earlier version of the dosimetry published in 2006 (Simon et al., Radiat. Res. 166, 174-192, 2006) used physical and statistical models, literature-reported exposure measurements for the years before 1960, and archival personnel monitoring badge data from cohort members through 1984. The data and models were used to estimate unknown occupational radiation doses for 90,000 radiological technologists, incorporating information about each individual's employment practices based on a survey conducted in the mid-1980s. The dosimetry methods presented here, while using many of the same methods as before, now estimate annual and cumulative occupational badge doses (personal dose equivalent) to about 110,000 technologists for each year worked from 1916 to 2006, but with numerous methodological improvements. This dosimetry, using much more comprehensive information on individual use of protection aprons, estimates radiation absorbed doses to 12 organs and tissues (red bone marrow, ovary, colon, brain, lung, heart, female breast, skin of trunk, skin of head and neck and arms, testes, thyroid and lens of the eye). Every technologist's annual dose is estimated as a probability density function (pdf) to account for shared and unshared uncertainties. Major improvements in the dosimetry methods include a substantial increase in the number of cohort member annual badge dose measurements, additional information on individual apron use obtained from surveys conducted in the 1990s and 2005, refined modeling to develop annual badge dose pdfs using Tobit regression, refinements of cohort-based annual badge pdfs to delineate exposures of highly and minimally exposed individuals and to assess minimal detectable limits more accurately, and extensive refinements in organ dose conversion coefficients to account for uncertainties in radiographic techniques employed. For organ dose estimation, we rely on well-researched assumptions about critical exposure-related variables and their changes over the decades, including the peak kilovoltage and filtration typically used in conducting radiographic examinations and the usual body location for wearing radiation monitoring badges. We have derived organ dose conversion coefficients based on air-kerma weighting of photon fluences from published X-ray spectra and derived energy-dependent transmission factors for protective aprons of different thicknesses. We tailor bone marrow dose estimates to individual cohort members by using an individual-specific body mass index correction factor. To our knowledge the models and reconstructed doses presented herein represent the most comprehensive dose reconstructions undertaken for a cohort of medical radiation workers.
[Show abstract][Hide abstract] ABSTRACT: To propose initial values for patient reference levels for fluoroscopically guided procedures in the United States.
This secondary analysis of data from the Radiation Doses in Interventional Radiology Procedures (RAD-IR) study was conducted under a protocol approved by the institutional review board and was HIPAA compliant. Dose distributions (percentiles) were calculated for each type of procedure in the RAD-IR study where there were data from at least 30 cases. Confidence intervals for the dose distributions were determined by using bootstrap resampling. Weight banding and size correction methods for normalizing dose to patient body habitus were tested.
The different methods for normalizing patient radiation dose according to patient weight gave results that were not significantly different (P > .05). The 75th percentile patient radiation doses normalized with weight banding were not significantly different from those that were uncorrected for body habitus. Proposed initial reference levels for various interventional procedures are provided for reference air kerma, kerma-area product, fluoroscopy time, and number of images.
Sufficient data exist to permit an initial proposal of values for reference levels for interventional radiologic procedures in the United States. For ease of use, reference levels without correction for body habitus are recommended. A national registry of radiation-dose data for interventional radiologic procedures is a necessary next step to refine these reference levels.
[Show abstract][Hide abstract] ABSTRACT: Current evidence suggests that immune system alterations contribute to the etiology of adult glioma, the most common adult brain tumor. Although previous studies have focused on variation in candidate genes in the adaptive immune system, the innate immune system has emerged as a critical avenue for research given its known link with carcinogenesis. To identify genetic markers in pathways critical to innate immunity, we conducted an association study of 551 glioma cases and 865 matched controls of European ancestry to investigate "tag" single nucleotide polymorphisms (SNP) in 148 genetic regions. Two independent U.S. case-control studies included were as follows: a hospital-based study conducted by the National Cancer Institute (263 cases, 330 controls) and a community-based study conducted by the National Institute for Occupational Safety and Health (288 cases, 535 controls). Tag SNPs (1,397) chosen on the basis of an r(2) of >0.8 and minor allele frequency of >5% in Caucasians in HapMap1 were genotyped. Glioma risk was estimated by odds ratios. Nine SNPs distributed across eight genetic regions (ALOX5, IRAK3, ITGB2, NCF2, NFKB1, SELP, SOD1, and STAT1) were associated with risk of glioma with P value of <0.01. Although these associations were no longer statistically significant after controlling for multiple comparisons, the associations were notably consistent in both studies. Region-based tests were statistically significant (P < 0.05) for SELP, SOD, and ALOX5. Analyses restricted to glioblastoma (n = 254) yielded significant associations for the SELP, DEFB126/127, SERPINI1, and LY96 genetic regions. We have identified a promising set of innate immunity-related genetic regions for further investigation.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have shown that quantitative phenotypes may be influenced not only by multiple single nucleotide polymorphisms (SNPs) within a gene but also by the interaction between SNPs at unlinked genes. We propose a new statistical approach that can detect gene-gene interactions at the allelic level which contribute to the phenotypic variation in a quantitative trait. By testing for the association of allelic combinations at multiple unlinked loci with a quantitative trait, we can detect the SNP allelic interaction whether or not it can be detected as a main effect. Our proposed method assigns a score to unrelated subjects according to their allelic combination inferred from observed genotypes at two or more unlinked SNPs, and then tests for the association of the allelic score with a quantitative trait. To investigate the statistical properties of the proposed method, we performed a simulation study to estimate type I error rates and power and demonstrated that this allelic approach achieves greater power than the more commonly used genotypic approach to test for gene-gene interaction. As an example, the proposed method was applied to data obtained as part of a candidate gene study of sodium retention by the kidney. We found that this method detects an interaction between the calcium-sensing receptor gene (CaSR), the chloride channel gene (CLCNKB) and the Na, K, 2Cl cotransporter gene (CLC12A1) that contributes to variation in diastolic blood pressure.