Significance of radiation exposure from work-related chest X-rays for epidemiological studies of radiation workers

BACKGROUND

Previous epidemiologic studies of workers at nuclear weapons facilities have not included X-ray exposures as part of the occupational radiation exposure. The research objective was to determine the contribution of work-related chest X-ray (WRX) exposure relative to the cumulative occupational radiation exposure.

METHODS

Cases and controls were identified from a cohort of workers whose employment began as early as 1943. Medical records for 297 subjects were used to determine the bone marrow dose from their X-ray examinations. Individual dose data, however, were only available for 45 workers. Bone marrow dose estimates were calculated by converting the entrance-skin-exposure (from X-ray procedures) and occupational exposure (from monitoring data) to dose.

RESULTS

Stereoscopic photofluorography delivered a bone marrow dose nearly 100 times that delivered by today's chest X-ray technique. Photofluorography was the predominant radiation source during the 1940s and 1950s. The cumulative WRX dose was, on average, 50 times their occupational doses. No correlation between occupational and WRX dose was found, but may be due to the small study size and incomplete dose data.

CONCLUSIONS

These findings illustrate the importance of including WRX doses in retrospective epidemiological studies of radiation workers, especially if photofluorographic chest X-rays were performed and occupational exposure to ionizing radiation is low.

Solubility of airborne uranium compounds at the Fernald Environmental Management Project

The in vitro solubility of airborne uranium dusts collected at a former uranium processing facility now undergoing safe shutdown, decontamination, and dismantling was evaluated by immersing air filters from high volume samplers in simulated lung fluid and measuring the 238U in sequential dissolution fractions using specific radiochemical analysis for uranium. X rays and photons from the decay of uranium and thorium remaining on the filter after each dissolution period were also directly measured using a planar germanium detector as a means for rapidly evaluating the solubility of the uranium-bearing dusts. Results of these analyses demonstrate that two distinct types of uranium-bearing dusts were collected on the filters depending upon the location of the air samplers. The first material exhibited a dissolution half-time much less than 1 d and was most likely UO3. The dissolution rate of the second material, which was most likely U3O8, exhibited two components. Approximately one-third of this material dissolved with a half time much less than 1 d. The remaining two-thirds of the material dissolved with half times between 230 +/- 16 d and 1,350 +/- 202 d. The dissolution rates for uranium determined by radiochemical analysis and by gamma spectrometry were similar. However, gamma spectrometry analysis suggested a difference between the half times of 238U and its initial decay product 234Th, which may have important implications for in vivo monitoring of uranium.

[Osseous avulsion injury of the extensor carpi radialis brevis tendon from the base of the 3rd metacarpal bone]

An uncommon case of a closed avulsion fracture to the base of the third metacarpal bone by the extensor carpi radialis brevis tendon is described. The dislocation of the small bony fragment was reduced by open reposition and internal fixation with two Leibinger mini-screws.

A new anthropometric phantom for calibrating in vivo measurements of stable lead in the human leg using x-ray fluorescence

A new anthropometric phantom has been developed for calibrating in vivo measurements of stable lead deposited in bone using x-ray fluorescence. The phantom reproduces the shape of the mid shaft of the adult human leg and is fabricated using polyurethanes and calcium carbonate to produce materials that exhibit the same density, energy transmission, and calcium content as cortical bone, bone marrow, and muscle. The phantom includes a removable tibia fabricated using simulants for cortical bone and bone marrow to which a precise amount of stable lead has been added to cortical bone. The formulations used in fabricating the new anthropometric phantom are much more uniform in density and composition than the conventional phantom made from Plexiglas cylinders filled with plaster-of-Paris. The energy spectrum from an x-ray fluorescence measurement of the phantom using a 109Cd source is indistinguishable from an in vivo x-ray fluorescence measurement of the human leg, demonstrating that the materials used in the phantom exhibit the same radiological properties as human tissue. Likewise, results from x-ray fluorescence measurements of the phantom exhibit the same positional dependency as the human leg and vary by approximately 36% when, for example, the phantom containing 54 ppm of stable lead in the tibia was rotated by only 15 degrees. The detection limit for a 30 min 109Cd K shell x-ray fluorescence in vivo measurement is approximately 20 ppm determined from a background measurement using the new phantom containing no added lead in the muscle, bone, or bone marrow. The new anthropometric phantom significantly improves in vivo x-ray fluorescence calibration measurements by (1) faithfully reproducing the anatomy of the human leg, (2) having components that exhibit radiological properties similar to that of human tissue, and (3) providing a realistic calibration standard that can be used for in vivo x-ray fluorescence intercomparison measurements.

Isolation and detection of Listeria monocytogenes using fluorogenic and chromogenic substrates for phosphatidylinositol-specific phospholipase C

The BCM Listeria monocytogenes detection system (LMDS) consists of a selective preenrichment broth (LMPEB), selective enrichment broth (LMSEB), selective/differential plating medium (LMPM), and identification on a confirmatory plating medium (LMCM). The efficacy of the BCM LMDS was determined using pure cultures and naturally and artificially contaminated environmental sponges. The BCM LMPEB allowed the growth of Listeria and resuscitation of heat-injured L. monocytogenes. The BCM LMSEB, which contains the fluorogenic substrate 4-methylumbelliferyl-myo-inositol-1-phosphate and detects phosphatidylinositol phospholipase C (PI-PLC) activity, provided a presumptive positive test for the presence of pathogenic Listeria (L. monocytogenes and L. ivanovii) after 24 h at 35 degrees C. An initial inoculum of 10 to 100 CFU/ml of L. monocytogenes in BCM LMSEB yielded a fluorogenic response after 24 h. On BCM LMPM, L. monocytogenes and L. ivanovii were the two Listeria species forming turquoise convex colonies (1.0 to 2.5 mm in diameter) from PI-PLC activity on the chromogenic substrate, 5-bromo-4-chloro-3-indoxyl-myo-inositol-1-phosphate. L. monocytogenes was distinguished from L. ivanovii by either its fluorescence on BCM LMCM or acid production from rhamnose. False-positive organisms (Bacillus cereus, Staphylococcus aureus, Bacillus thuringiensis, and yeasts) were eliminated by at least one of the media in the BCM LMDS. Using a pure culture system, the BCM LMDS detected one to two L. monocytogenes cells from a sponge rehydrated in 10 ml of DE neutralizing broth. In an analysis of 162 environmental sponges from facilities inspected by the U.S. Department of Agriculture (USDA), the values for identification of L. monocytogenes by BCM LMDS and the USDA method were 30 and 14 sites, respectively, with sensitivity and specificity values of 85.7 and 100.0% versus 40.0 and 66.1%, respectively. No false-positive organisms were isolated by BCM LMDS, whereas 26.5% of the sponges tested by the USDA method produced false-positive results.

Analysis of electret ion chamber radon detector response to 222Rn and interference from background gamma radiation

Environmental radon (222Rn) monitors that incorporate electret detectors are confounded by background gamma radiation, which may cause the electret to discharge by as much as 7.5 volts per mR. Although background gamma corrections were formerly made by multiplying the known background gamma exposure rate with a constant conversion factor, this research demonstrates that doing so introduces an error ranging up to about 20%, especially in high gamma background areas. A new, more accurate method of background gamma correction has been developed that uses an average, voltage-dependent discharge factor, Dgamma (V Kg C(-1)). This factor and its coefficients were experimentally determined by separately exposing groups of electret radon detectors to photons from 60Co and 137Cs. Statistical analysis shows that Dgamma is independent of the orientation of the electret during irradiation but that some dependency on dose rate or energy of the irradiating photons may be expected. The discharge of the electret due only to gamma irradiation, Vgamma is determined by multiplying the total integrated gamma exposure by Dgamma. The discharge of the electret during a radon measurement can then be corrected for background gamma radiation by subtracting Vgamma from the total discharge of the electret resulting in a net discharge due solely to radon. A new equation has also been developed in this study for the radon discharge factor, D(Rn)(V m3 Bq(-1) s(-1)), that is entirely consistent with the gamma discharge factor and was thoroughly evaluated by exposing the electret radon detectors to known concentrations of radon.

Refractory ceramic fiber exposure and pleural plaques

Refractory ceramic fibers (RCF) are manmade vitreous fibers (MMVF) manufactured for high-temperature applications. Between 1987 and 1992, a retrospective cohort and nested case-control study evaluated chest radiographs from 652 workers involved in the manufacture of these fibers for plausibility of a causal relationship between exposure to RCF and chest-radiographic changes. The exposure-response relationship was modeled with three variables: years since first fiber production job, years in fiber production, and cumulative fiber exposure to date of study X-ray. The case-control study used a comprehensive characterization of possible asbestos exposure to investigate asbestos as the potential causative agent of chest-radiographic changes. Chest radiographs of 20 workers (3.1%) demonstrated 19 pleural plaques and one diffuse pleural thickening. Nine of 72 workers (12.5%) with more than 20 yr since their first fiber-production job had plaques (odds ratio [OR] = 9.5; 95% confidence interval [CI] = 1.9 to 48.2). Five of 19 workers with more than 20 yr in fiber-production work (26.3%) had plaques (OR = 22.3; 95% CI = 3.6 to 137.0). Similarly, adjusted ORs demonstrated a progressive relationship between cumulative fiber-months per milliliter (fiber-mo/ml) exposure and plaques. The case-control study confirmed that asbestos exposure did not account for the observed association between fiber exposure and plaques. A validity review of historical films demonstrated biologic plausibility for the association, since sufficient latency existed from the time of first RCF exposure to the development of plaques. There was no significant increase in parenchymal changes consistent with interstitial fibrosis.

Measurement of the attenuation coefficient for Livermore Thoracic Phantom lungs fabricated using contemporary materials

The University of Cincinnati has reproduced the original formulation for the Livermore Thoracic Phantom lungs using contemporary materials and has adopted the linear attenuation coefficient as the primary quality assurance parameter for evaluating the performance capabilities of these new lung phantoms. The Livermore Thoracic Phantom was originally fabricated in 1978 to intercalibrate detector systems used to measure plutonium and other low-energy, photon emitting radionuclides deposited in the respiratory tract. The linear attenuation coefficient is a critical performance indicator for these phantom lungs since the presence of any material with a high effective atomic number (where Z > or = 20) will make a significant change in the photoelectric cross section, the predominant mode of interaction for plutonium x rays. A set of test lungs was fabricated with KCl to introduce a known quantity of 40K in the phantom and to determine, by measurement and calculations, what change would be made to the attenuation coefficient at photon energies below 100 keV as a result of the modified formulation. The KCl increased the linear attenuation coefficient below 60 keV by more than a factor of two, which would produce a substantial systematic error in any subsequent calibration measurements performed with these modified phantom lungs. These results support use of the attenuation coefficient as an important performance indicator for the Livermore Thoracic Phantom lungs and also suggest that KCl not be added to the lung tissue substitute formulation as a means to incorporate 40K in the phantom for low energy calibrations.

Echocardiographic diagnosis of congenital sinus of Valsalva aneurysm with dissection of the interventricular septum

A case is reported in which a congenital aneurysm of the right coronary sinus of Valsalva ruptured and dissected into the interventricular septum. M-mode and cross-sectional echocardiographic examination allowed accurate preoperative assessment of the pathologic anatomy, which was confirmed by angiography, surgery and autopsy. Dissection of the interventricular septum by a congenital sinus of Valsalva aneurysm is a rare lesion, has a poor prognosis, and can be diagnosed noninvasively with echocardiography.

Problems in the differential diagnosis of narcolepsy versus schizophrenia

The authors discuss the problems of accurately diagnosing narcolepsy when patients manifest the auxiliary symptoms of this disorder, i.e., cataplexy, hypnagogic hallucinations, and sleep paralysis, which conclude that misdiagnosis of narcolepsy can be avoided if clinicians are aware that this illness can simulate a psychiatric disorder and if they give careful attention to the histroy of the patient's illness.

Influence of acute hypertension on aortic valve competence

The effect of acutely induced hypertension on aortic valve competence was studied in anesthetized dogs. Aortic pressure was increased by infusion of methoxamine or mechanically; aortic valve competence was evaluated by aortogrphy and by indicator dye. The aortic valve was normally competent; aortic insufficiency appeared with increase of mean pressure by as little as 20-50 mmHg; 6 of 9 animals showed aortic incompetence when mean aortic pressure was elevated 45-70 mmHg, but the valve remained competent in 2 of 9 animals with mean pressure increments of 60-90 mmHg. The aortic root was appreciably less distensible than was the proximal descending aorta; this factor may limit the degree of aortic insufficiency in response to acute hypertension in the dog.