Specific Correction Factors Research Articles

Monte Carlo calculation of LiF:Mg,Cu,P thermoluminescent dosimeter correction factors for 18F, 131I and 90Y submersion dosimetry

Accurate measurement of absorbed dose from beta-emitting therapeutic radionuclides is important to ensure safe and effective delivery to patients. Thermoluminescent dosimeters (TLDs) are a commercially available option to measure dose, but several confounding factors complicate this process. To preserve their integrity during the measurement, it is necessary to enclose TLDs in a waterproof envelope, which unavoidably attenuates the beta particles. Additionally, the exclusion of radioactivity in the volume occupied by the TLD, the finite volume effect, further complicates the measurement. The purpose of this study is to calculate the correction factors to convert the TLD measured dose to the absorbed dose in water, Dw, for three common radionuclides and the LiF:Mg,Cu,P TLD (Thermo Fisher Scientific™, Waltham, MA). Correction factors were calculated for four different size LiF:Mg,Cu,P TLD dosimeters inside a PMMA cylindrical phantom with 90YCl3, C6H1118FO5, and Na131I aqueous solutions. Specific correction factors are required to account for finite volume, energy, and geometry for each LiF:Mg,Cu,P TLD size, radionuclide, and phantom geometry combination. Additionally, for the PMMA phantom, specific material correction factors are also required to account for the additional materials inside the phantom. The absorbed dose calculations performed with LiF:Mg,Cu,P TLDs showed good agreement with Monte Carlo simulations. Overall, these findings contribute to improving the accuracy of absorbed dose measurements from beta-emitting radionuclides in liquid solutions using TLDs.

Field Validation of the Superelevation Method for Debris‐Flow Velocity Estimation Using High‐Resolution Lidar and UAV Data

AbstractEstimating flow velocities is key to assessing hazards associated with debris flows. One approach to post‐event velocity estimation is the superelevation method, which uses debris‐flow mudlines to measure the cross‐channel surface inclination, or superelevation, produced by centripetal forces acting on the flow in a bend. Flow velocities are then calculated using a subjective parameterization of the forced vortex equation modified to include a debris‐flow specific correction factor. Subjective parameterization of this equation leads to substantial variability and uncertainty in the resulting flow velocities. We present an analysis of the reliability of the superelevation method using a large UAV‐based data set of 14 debris flows with front velocities of ∼0.8–6.5 m s−1 and cross‐channel surface inclinations of ∼0.6–8.5°, as well as a validation for a single debris flow measured using high‐resolution, high‐frequency 3D lidar data fused to video imagery. The validation event indicates that when the flow surface inclination can be measured directly, the forced vortex equation produces excellent results without needing a correction factor for Froude numbers ranging from 0.7 to 1.5. This finding indicates that the main challenge with the superelevation method lies in obtaining accurate measurements of superelevation from the mudlines, and that a correction factor may serve to compensate for measurement difficulties rather than variable flow properties. For very small and highly subcritical flows, the superelevation method may generate a large overestimation of flow velocities.

16: MC simulations of detector type specific output correction factors in the presence of magnetic field

16: MC simulations of detector type specific output correction factors in the presence of magnetic field

Development and Application of Isotope Labelled Internal Standards in a Sum Parameter Method for Ergot Alkaloid Screening of Food

Ergot alkaloids are a group of toxic compounds, formed by fungi on infested grasses. In 2022, the European Commission set into effect maximum levels for the sum of the twelve major ergot alkaloids in multiple foods. To facilitate the laborious and costly individual quantification of the twelve major ergot alkaloids by HPLC–MS/MS or -FLD, we recently reported a sum parameter method (SPM) for ergot alkaloid quantification. Here, derivatization to lysergic acid hydrazide—a derivative of the mutual ergoline backbone in all ergot alkaloids—allowed simplified determination of all ergot alkaloids in flour via HPLC-FLD. For the measurement of more complex matrices like processed foods, we now developed a MS/MS-based SPM. Two internal standards (IS), isotopically labelled at different positions of the molecule, were synthesized and employed in the MS/MS-measurements. Method performance using either the 13CD3-labelled or the 15N2-labelled IS was evaluated on naturally contaminated rye and wheat flour samples as well as on processed food matrices. Employing the 13CD3-labelled IS leads to lower variances and better consistency with the reference data (obtained by the FLD-based SPM) in flour samples compared to the 15N2-labelled IS. The novel method significantly improves the measurement of ergot alkaloids in complex food matrices, due to their increased selectivity and thus lower interferences. Furthermore, the application of isotope labelled IS obviates the need for time-consuming steps like the determination of recovery rate based, matrix specific correction factors as described in the MS/MS-based European standard method for ergot alkaloid quantification (EN 17425).

To what extent do field conditions affect gamma dose rate determination using portable gamma spectrometry?

Field gamma spectrometry is a widely used approach for determining in situ gamma dose rates in dosimetric (i.e., electron spin resonance and luminescence) dating applications. In comparison with laboratory-based determinations, in situ radioactivity measurements typically provide more representative gamma dose rate evaluations for heterogeneous sedimentary environments. However, it is often not possible to perform in situ gamma spectrometry measurements under carefully controlled conditions that are directly comparable to those originally used for equipment calibration.In this study, we use Geant4 Monte Carlo simulations to model gamma spectrometry measurements under a range of field conditions, and examine the relative impacts of the following parameters on dose rate determination using the threshold calibration approach: (i) geometry and depth of the measurement hole in which the probe is inserted, (ii) nature of the sediment or rock materials and their water content, (iii) geometry of the radiation environment surrounding the measurement hole, i.e. closed and partially closed sites (e.g., caves, trenches) versus open-air sites (e.g. plain field excavations, cliff or cutting exposures).Our results show that some differences in calibration and field measurement configurations can significantly bias in situ gamma dose rate determinations. Variations in the depth of probe holes can result in underestimations of infinite matrix gamma dose rates by 5% for a 30 cm-deep hole to 58% for measurements made against sediment surfaces (i.e., 2π geometry). Use of hole shapes that do not match those of the probe can lead to underestimations of infinite matrix dose rates by up to 4%, with these biasing effects becoming more significant for shallow holes. External gamma radiation originating from, and backscattered against, structures in the surrounding environment can contribute significantly to gamma dose rates measured using shallow probe holes. The nature of the mineral materials can have a small effect on the measured gamma dose rate (equivalent to infinite matrix dose rate biases of a few percent), mostly due to differences in the density of different materials. Measurements performed in materials with high water contents can be affected by small gamma dose rate overestimations due to differences between water attenuation factors of centimetre-scale objects such as gamma spectrometer probes and those of relevance for dating smaller objects such as sediment grains. These problems can be resolved by using specific correction factors, by including additional uncertainties during dose rate determination, or by performing in situ measurements at different depths for the same location.

Influence of dosimeter depth on estimating patient's eye lens dose in head computed tomography: A measurement and Monte Carlo simulation study

The distance between the posterior cornea and anterior surface of the lens is approximately 3 mm, and it is unclear whether the dose measured near the ocular surface of the phantom accurately reflects the lens dose without any specific correction factors. This study aimed to investigate the influence of the depth for the estimation of the eye lens doses of the patient during head computed tomography (CT) examination using measurement and Monte Carlo simulation. During the measurement, the absorbed dose on the surface and at a depth of 3 mm from the surface of the cylinder phantom, corresponding to the positions of the right and left eyes, was obtained using optically stimulated luminescence dosimeters at tube voltages of 80 and 120 kV. In the Monte Carlo simulations, an anthropomorphic phantom and custom-made cylinder phantoms, which were made of polymethyl methacrylate (PMMA) and polyurethane, respectively, were used, and absorbed doses were obtained on the surface and at a depth of 3 mm from the surface of the phantoms. In the measurement, the absorbed dose at the 3-mm depth from the surface of the phantom was significantly higher than that on the surface of the phantom for both tube voltages (p < 0.01). In the simulation, the absorbed doses at a depth of 3 mm from the surface of the phantom model were significantly higher than those on the surface of the phantom model regardless of the material and structure of the phantom (p < 0.01). The ratio of the absorbed dose on the surface to that at a depth of 3 mm ranged from 0.93 to 0.95 regardless of the material and structure of the phantom. These results highlight the importance of lens dosimetry considering the depth of the lens.

Dose distributions of the INTRABEAM electronic brachytherapy system measured with traceable detectors

In this work, a methodology to determine the absorbed dose rate to water distribution from electronic brachytherapy (eBT) units is suggested. It involves measuring directly in a full scatter water tank with small active detectors whose energy response at low X-ray photon energies have been previously characterized. Dose distributions of an INTRABEAM PRS 500 system in two configurations — bare needle and with the spherical applicator of 40 mm diameter — were measured in water using the Exradin A26 ionization chamber and the PTW 60019 microDiamond detector. The continuous energy response of these two detectors in terms of air kerma from 5 keV to 70 keV (eBT energy range) was available from a previous calibration at several X-ray radiation qualities. Here, it is converted to the response in absorbed dose to water using correction factors obtained with Monte Carlo (MC) particle transport simulations. The detectors were modelled using the MCNP code. The air kerma calibration factors were simulated and compared with measurements to refine and validate the models. A series of simulations of the experimental arrangement of the INTRABEAM and the detector were carried out for determining the system specific detector correction factors. These values are distance-dependent due to the steep dose gradient and the remarkable spectral changes around the eBT source in water. The dose rate with distance from the source, the radial and the polar distributions of the INTRABEAM are reported and compared with the manufacturers supplied data. This work is an effort to provide traceability for detectors and measurement procedures for the determination of 3D dose distributions as part of the European joint research project “Primary standards and traceable measurement methods for X-ray emitting electronic brachytherapy devices” (18NRM02 PRISM-eBT).

Comparison of Formula-Specific Factors and Artificial Intelligence Formulas with Axial Length Adjustments in Bilateral Cataract Patients with Long Axial Length.

IntroductionTo evaluate and compare the effectiveness for reducing the prediction error (PE) of the second eye using formula-specific factors, artificial intelligence (AI) formulas (PEARL-DGS and Kane), and the Cooke-modified axial length (CMAL) methods in bilateral cataract patients with long axial length (AL).MethodsA total of 98 patients with long AL who underwent sequential bilateral cataract surgeries were retrospectively enrolled. The second-eye IOL power was calculated by the formula-specific factors, AI formulas, and CMAL methods when the first eye suffered from refraction surprise. The correction factors of eight formulas were calculated by regression analysis.ResultsThere was a significant correlation between bilateral preoperative biometric parameters (P < 0.05) as well as bilateral PE (P < 0.05). The Kane formula displayed the lowest median absolute error (MedAE) and highest proportion of PE within ± 0.50 and ± 1.00 D compared with other formulas for the first eye. For the second-eye refinement, all three methods could reduce the second-eye MedAE. The formula-specific correction factors were 0.250, 0.331, 0.343, 0.394, 0.409, 0.452, 0.503, and 0.520 for Kane, Barrett Universal II (BUII), PEARL-DGS, Holladay 2, Holladay 1, Haigis, Hoffer Q, and SRK/T, respectively. The new AI-based Kane and PEARL-DGS with or without the CMAL methods could improve the refractive outcomes of the second eye in sequential bilateral cataract patients with long AL. The Kane, BUII, and PEARL-DGS with specific correction factors displayed higher accuracy compared with the other two methods (P < 0.05).ConclusionsThe new AI-based Kane and PEARL-DGS with or without the CMAL methods could improve the refractive outcomes of the second eye in sequential bilateral cataract patients with long AL. Notably, the Kane, PEARL-DGS, and BUII with specific correction factors displayed higher accuracy.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40123-022-00551-6.

Lifespan Volume Trajectories From Non-harmonized T1-Weighted MRI Do Not Differ After Site Correction Based on Traveling Human Phantoms.

Multi–site imaging consortiums strive to increase participant numbers by pooling data across sites, but scanner related differences can bias results. This study combines data from three research MRI centers, including three different scanner models from two vendors, to examine non–harmonized T1–weighted brain imaging protocols in two cohorts. First, 23 human traveling phantoms were scanned twice each at all three sites (six scans per person; 138 scans total) to quantify within–participant variability of brain volumes (total brain, white matter, gray matter, lateral ventricles, thalamus, caudate, putamen and globus pallidus), and to calculate site–specific correction factors for each structure. Sample size calculations were used to determine the number of traveling phantoms needed to achieve effect sizes for observed differences to help guide future studies. Next, cross–sectional lifespan volume trajectories were examined in 856 healthy participants (5—91 years of age) scanned at these sites. Cross–sectional trajectories of volume versus age for each structure were then compared before and after application of traveling phantom based site–specific correction factors, as well as correction using the open–source method ComBat. Although small systematic differences between sites were observed in the traveling phantom analysis, correction for site using either method had little impact on the lifespan trajectories. Only white matter had small but significant differences in the intercept parameter after ComBat correction (but not traveling phantom based correction), while no other fits differed. This suggests that age–related changes over the lifespan outweigh systematic differences between scanners for volumetric analysis. This work will help guide pooling of multisite datasets as well as meta–analyses of data from non–harmonized protocols.

A modified approach to Industrial Pollution Projection System for the assessment of sectoral pollution loads in Bangladesh.

Industrial pollution in Bangladesh has posed a serious threat to human health, economic activity, and the environment. By emphasizing industries that produce major pollutants, substantial improvements can be made to pollution mitigation measures. In countries where primary pollution data is not readily available, the Industrial Pollution Projection System (IPPS) could be used to calculate the pollution load utilizing total industrial output or employment data. IPPS data, which was designed for developed countries like the USA, had been used directly for other countries without any normalization in previously reported studies. The main purpose of this study is to modify the current IPPS approach for any other country by incorporating specific correction factor for a specific country. In this study, a specific correction factor for Bangladesh was determined, taking into account the country’s major polluting industries, and used to estimate the pollution scenario for the year 2020. The accuracy of the specific pollution intensities was also evaluated by comparing the data obtained using both gross output and employee number. According to this study, the top three air-polluting industries are structural clay products, cement-lime-plaster industry, and iron and steel industry. Similarly, for water pollution, the food industry, paper and paper product industry, and textile industry are the largest pollutant contributors. The detailed pollution load matrix in terms of air and water pollution is also developed, and can be used to predict both short-term and long-term scenarios of industrial pollution in Bangladesh, which eventually will assist the policy makers to adopt appropriate pollution management approach. Moreover, the methods developed in this study will help to tailor the IPPS data for any country and increase the accuracy of the pollution load.Supplementary informationThe online version contains supplementary material available at 10.1007/s10661-022-10073-0.

PO-1564 Detector specific output correction factors in small fields for different 2D detector arrays

PO-1564 Detector specific output correction factors in small fields for different 2D detector arrays

Experimental characterisation of the magnetic field correction factor, for Roos chambers in a parallel MRI-linac

Objective. Reference dosimetry on an MRI-linac requires a chamber specific magnetic field correction factor, This work aims to measure the correction factor for a parallel plate chamber on a parallel MRI-linac. Approach. is defined as the ratio of the absorbed dose to water calibration coefficient in the presence of the magnetic field, relative to that under 0 T conditions, was measured via a transfer to a field chamber at each magnetic field strength from a chamber with known and This was achieved on the parallel MRI-linac by moving the measurement set-up between a high magnetic field strength region at the MRI-isocentre and a low magnetic field strength region at the end of the bore whilst maintaining consistent set-up and scatter conditions. Three PTW 34001 Roos chambers were investigated as well as a PTW 30013 Farmer used to validate methodology. Main Results. The beam quality used for the measurements of was TPR 20/10 = 0.632. The for the PTW Farmer chamber at 1 T on a parallel MRI-linac was 0.993 ± 0.013 (k = 1). The average factor measured for the three Roos chambers on a 1 T parallel MRI-linac was 0.999 ± 0.014 (k = 1). Significance. The results presented are the first measurements of for a Roos chamber on a parallel MRI-linac. The Roos chamber results demonstrate the potential for the chamber as a reference dosimeter in parallel MRI-linacs.

Algorithm to assess neutron HP(10) with estimation of uncertainties using Alnor albedo dosemeters: application in Brazilian nuclear power plants

The Instituto de Radioproteção e Dosimetria (IRD) is implementing an automatic neutron individual monitoring system, which uses albedo dosemeters from the Alnor manufacturer. For practical purposes, the occupational neutron fields have been divided into four application areas, named N1, N2, N3 and N4, as recommended in the German standard DIN 6802-4. For each area, specific Workplace Correction Factor (WCF), as a function of the ratio between photon dose responses measured in the incident and albedo component of the albedo dosemeter (Di/Da), must be used. This study proposes an algorithm for evaluating the photons and neutrons HP(10) values for the Alnor albedo system. It uses WCF × Di/Da curves previously defined by the authors, using MCNPX code simulations of the neutron dosemeter response for several occupational neutron fields. The methodology for calculating all uncertainties involved in the photon and neutron HP(10) assessment is also shown. Before the routine use of this system at IRD, several tests and calibrations are being carried out. This manuscript presents a case study carried out at the Angra I and Angra II power plants in 14 different fields (N1 application area). The results of the Alnor system are compared with those from the albedo system currently in routine use at the IRD. The average value of the ratio between the measurements with the Alnor system and the IRD system was 0.97 for photon HP(10), and 0.84 for neutron HP(10). Considering an expanded uncertainty to 95% confidence level, all results agree with each other.

Monte Carlo-derived ionization chamber correction factors in therapeutic carbon ion beams

The accuracy of electromagnetic transport in the GEANT4 Monte Carlo (MC) code was investigated for carbon ion beams and ionization chamber (IC)-specific beam quality correction factors were calculated. This work implemented a Fano cavity test for carbon ion beams in the 100–450 MeV/u energy range to assess the accuracy of the default electromagnetic physics parameters. The Urban and the Wentzel-VI multiple Coulomb scattering models were evaluated and the impact of maxStep, dRover, and final range parameters on the accuracy of the transport algorithm was investigated. The optimal production thresholds for an accurate calculation of values, which is the product of the water-to-air stopping power ratio and the IC-specific perturbation correction factor, were also studied. The correction factors were calculated for a cylindrical and a parallel-plate IC using carbon ions in the 150–450 MeV/u energy range. Modifying the default electromagnetic physics parameters resulted in a maximum deviation from theory of 0.3%. Therefore, the default EM parameters were used for the remainder of this work. The factors were found to converge for both ICs with decreasing production threshold distance below 5 μm. The values obtained in this work agreed with the TRS-398 stopping power ratios and other previously reported results within uncertainty. This study highlights an accurate MC-based technique to calculate the combined stopping power ratio and the perturbation correction factor for any IC in carbon ion beams.

Wastewater-based epidemiology as a novel tool to evaluate human exposure to pesticides: Triazines and organophosphates as case studies

Production and application of pesticides have risen remarkably in the last few decades. Even if they provide many benefits, they can be hazardous for humans and ecosystems when they are not used cautiously. Human exposure to pesticides is well documented, but new approaches are needed to boost the available information. This work proposes a new application of wastewater-based epidemiology (WBE) to assess the exposure of the general population to organophosphate and triazine pesticides (pyrethroid pesticides have already been validated). Several human urinary metabolites tested as WBE biomarkers, were suitable. Untreated wastewater samples from different European countries were analyzed by liquid chromatography-tandem mass spectrometry. Biomarker concentrations were converted to mass loads and used to back-calculate the local population's exposure to the parent pesticides, using specific correction factors developed in this study. Exposure to organophosphates and pyrethroids showed spatial and seasonal variations. Finally, pesticide exposure was estimated in twenty cities of ten European countries and compared with the acceptable daily intake, concluding that some populations might face health risks. The study confirms WBE as a suitable approach for assessing the average community exposure to pesticides and is a valuable complementary biomonitoring tool. WBE can provide valuable data for public health.

Experimental investigation of the strain‐rate effects on the failure of composite materials with off‐axis tensile tests on unidirectional plies

AbstractThe present study experimentally investigates the mechanical response of T700/M21 Carbon Fibre Reinforced Polymers subjected to coupled shear and transverse tension at intermediate strain rates ranging from 10−3 to 15 s−1. Off‐axis tension specimens with transverse and oblique tabs are used for the various tests. Moreover, the specimen aspect ratio is quite low, since dynamic tests are performed in this study. The axial stress–strain curves are successfully simulated using finite element simulations with a viscoelastic model. Based on these numerical simulations, specific stress correction factors are computed to take the effect of end constraints into account for such low aspect ratio specimens. Finally, an increase in the material strength with the strain rate is observed.

Measuring the dose in bone for spine stereotactic body radiotherapy.

Current quality assurance of radiotherapy involving bony regions generally utilises homogeneous phantoms and dose calculations, ignoring the challenges of heterogeneities with dosimetry problems likely occurring around bone. Anthropomorphic phantoms with synthetic bony materials enable realistic end-to-end testing in clinical scenarios. This work reports on measurements and calculated corrections required to directly report dose in bony materials in the context of comprehensive end-to-end dosimetry audit measurements (63 plans, 6 planning systems). Radiochromic film and microDiamond measurements were performed in an anthropomorphic spine phantom containing bone equivalent materials. Medium dependent correction factors, kmed, were established using 6MV and 10MV Linear Accelerator Monte Carlo simulations to account for the detectors being calibrated in water, but measuring in regions of bony material. Both cortical and trabecular bony material were investigated for verification of dose calculations in dose-to-medium (Dm,m) and dose-to-water (Dw,w) scenarios. For Dm,m calculations, modelled correction factors for cortical and trabecular bone in film measurements, and for trabecular bone in microDiamond measurements were 0.875(±0.1%), 0.953(±0.3%) and 0.962(±0.4%), respectively. For Dw,w calculations, the corrections were 0.920(±0.1%), 0.982(±0.3%) and 0.993(±0.4%), respectively. In the audit, application of the correction factors improves the mean agreement between treatment plans and measured microDiamond dose from -2.4%(±3.9%) to 0.4%(±3.7%). Monte Carlo simulations provide a method for correcting the dose measured in bony materials allowing more accurate comparison with treatment planning system doses. In verification measurements, algorithm specific correction factors should be applied to account for variations in bony material for calculations based on Dm,m and Dw,w.

Scaling the response of armor steel subjected to blast loading

The influence of the strain-rate effect of steel and the mechanical effect of explosive shock load are both key problems to achieving the similarity scaling of a steel plate structure under blast loading. In this research, the scaling of the dynamic response of strain-rate sensitive armor steel subjected to air blast loading was studied further. First, the specific impulse was defined, and the influence of the strain-rate and the geometric scaling ratio on the specific impulse correction factor was analyzed with dimensional analysis. Then, a real air explosion test was carried out to study the response of a full-size armor steel plate during a blast, and the Johnson-Cook constitutive parameters of the armor steel material were obtained using split Hopkinson pressure bar experimental technology, with which the accurate scaling base mode was established. Furthermore, by employing the correction factors of the specific impulse and the total impulse calculated by empirical equations, two correction methods were proven: I-correcting the stand-off distance and II-correcting the charge mass. Then, the relationships between the specific impulse, the total impulse, the stand-off distance and the charge mass are discussed, based on which the explosion load boundary corresponding to the geometric scaling coefficient was determined. The results showed that the prediction of the corrected scaled model was in good agreement with the experimental results, and both methods could achieve the scaling of the response of the armor steel plate subjected to blast loading.

Patient radiation dose from x-ray guided endovascular aneurysm repair: a Monte Carlo approach using voxel phantoms and detailed exposure information

Endovascular aneurysm repair (EVAR) is a well-established minimally invasive technique that relies on x-ray guidance to introduce a stent through the femoral artery and manipulate it into place. The aim of this study was to estimate patient organ and effective doses from EVAR procedures using anatomically realistic computational phantoms and detailed exposure information from radiation dose structured reports (RDSR). Methods: Lookup tables of conversion factors relating kerma area product (PKA) to organ doses for 49 different beam angles were produced using Monte Carlo simulations (MCNPX2.7) with International Commission on Radiological Protection (ICRP) adult male and female voxel phantoms for EVAR procedures of varying complexity (infra-renal, fenestrated/branched and thoracic EVAR). Beam angle specific correction factors were calculated to adjust doses according to x-ray energy. A MATLAB function was written to find the appropriate conversion factor in the lookup table for each exposure described in the RDSR, perform energy corrections and multiply by the respective exposure PKA. Using this approach, organ doses were estimated for 183 EVAR procedures in which RDSRs were available. A number of simplified dose estimation methodologies were also investigated for situations in which RDSR data are not available. Results: Mean estimated bone marrow doses were 57 (range: 2–247), 86 (2–328) and 54 (8–250) mGy for infra-renal, fenestrated/branched and thoracic EVAR, respectively. Respective effective doses were 27 (1–208), 54 (1–180) and 37 (5–167) mSv. Dose estimates using non-individualised, average conversion factors, along with those produced using the alternative Monte Carlo code PCXMC, yielded reasonably similar results overall, though variation for individual procedures could exceed 100% for some organs. In conclusion, radiation doses from x-ray guided endovascular aneurysm repairs are potentially high, though this must be placed in the context of the life sparing nature and high success rate for this procedure.

OR26-05 The Correction Factor for A1C in Anemic Patients

Diabetes can be defined by hemoglobinA1c (A1c), fasting plasma glucose (FPG), and 2-hour plasma glucose (2hPG). Despite that A1c has a tendency for underestimation of the prevalence of diabetes and overestimation of the prevalence of normal glucose tolerance, A1c is the most convenient method, since no preparation required. However, various factors could affect A1c. The objective of this project is to identify the covariates that affect A1c. The study sample included 9,952 adults (age≥20 years old) from the 2005–2016 NHANES. Subjects with established diabetes were excluded, and we analyzed subject’s documented BMI, A1c, FPG, 2hPG, Hemoglobin (Hgb), race/ethnicity, age, education, poverty index, family history of diabetes, and tobacco and alcohol consumption to determine their impact on A1C measurement. Continuous data were expressed as means with standard deviation. Either t-test or ANOVA was used to examine the influence of covariates on continuous variables. We examined the relation of A1c with FPG, 2hPG, and other covariates. With backward regression analysis, we excluded the covariates without significant impact on A1c. All the analyses were conducted in SYSTAT 13, Systat Software, Inc. In the univariate analysis, A1c was significantly corelated with FPG (r=0.5692, P<0.0001) and 2hPG (r=0.5122, P<0.0001). In the backward regression analysis, education, poverty index, and family history of diabetes were excluded for their low impact on A1c. In addition to FPG and 2hPG, gender (r=-0.0527, P<0.0001), age (r=0.1746, P<0.0001), BMI (r=0.0978, P<0.0001), race/ethnicity (r=0.0478, P< 0.0001), current alcohol consumption (r=0.0542, P<0.0001), current smoker (r=-0.0806, P<0.0001), and Hgb (r=-0.1526, P<0.0001) had significant impact on A1c. Due to the significant difference in Hgb between gender, gender-based analyses were performed. In male gender, the impact of other covariates (age, BMI, race/ethnicity, current alcohol consumption, and current smoker) than FPG and 2hPG could be explained at least partially through their impact on Hgb (P<0.0001). Each 1 g/dL decrease of Hgb would falsely decrease A1c by 0.053% (P<0.0001). In female gender, the impact of covariates other than FPG and 2hPG on A1c could be explained by their impact on Hgb (p<0.0001) except for BMI. Each 1 g/dL decrease of Hgb would falsely decrease A1c by 0.047% (P<0.0001). In addition to FPG and 2hPG, A1c could be affected by gender, age, BMI, race/ethnicity, current alcohol consumption, and current smoker through their impact on Hgb, except for BMI in female gender. A1c will be falsely decreased by 0.053% in male gender and 0.047% in female gender for each 1 g/dL decrement of Hgb. Thus, A1c should be interpreted with caution in anemic patients. We propose using the gender specific correction factors for more accurate interpretation of A1c.