L. J. Somervaille

In vivo measurement of lead in bone using X-ray fluorescence

The factors affecting the accuracy and minimum detectable concentration of in vivo tibia lead measurement are discussed, and it is demonstrated that the use of a 109Cd source in a backscatter geometry and using the 88 keV coherently scattered photon for normalisation optimizes both criteria. The measurement is shown to be independent of variations in source-sample distance, thickness of overlying tissue and tibia size and shape. Applying the same technique in vitro to samples of human tibia and metatarsals, it is shown that the results are not significantly different (p approximately equal to 0.9) from atomic absorption spectrometry results from another laboratory. The results of Monte Carlo dose distribution calculations are presented and compared with measurements using thermoluminescent dosemeters: the mean absorbed dose to a 20 cm leg section is less than 0.1 mGy (10 mrad) and the maximum absorbed skin dose is 0.45 mGy (45 mrad). For this dose the minimum detectable lead concentration is 10 micrograms g-1. Finally, the technique has been applied to groups of normals and occupationally exposed workers, and the means have been shown to be significantly different, namely 10 and 31 micrograms g-1 respectively. In the normal subjects tibia lead correlated strongly with age (r = 0.63, p less than 0.001).

Lead in Bone: Sampling and Quantitation Using K X-Rays Excited by 109Cd

Lead in bone can be measured in vivo using gamma-rays from a 109Cd source to excite lead K X-rays. Normalization of lead X-ray amplitudes to that of the elastically backscattered 88 keV gamma-rays produces a determination of the concentration of lead in bone mineral that is accurate and insensitive to variations in measurement or bone geometry. For in vivo tibia measurements, a typical precision (1 SD) of +/- 5 micrograms lead (g bone mineral)-1 is achieved for an effective dose equivalent of 2.1 microSv. Measurement can be made of any superficial bone site, but precision will vary approximately as the inverse of the square root of the mass of bone mineral sampled. The apparatus required for this technique is readily transportable, and mobile laboratory facilities are easily established. ImagesFIGURE 7.

In vivo measurements of bone lead-a comparison of two X-ray fluorescence techniques used at three different bone sites

In vivo bone lead measurements have been made on a group of about 120 people, most of whom were lead exposed workers. Two different x-ray fluorescence (XRF) techniques were used to make measurements at three bone sites. Finger lead was measured using 57Co sources, and lead measurements were made in both tibia and calcaneus with a technique based on 109Cd sources. The results of the bone lead measurements correlated strongly with each other and with the index of cumulative exposure, thus confirming the value and reliability of these in vivo measurements as a tool in the study of chronic lead exposure. Measurement precision, +/- 1 standard deviation, was highest for tibia +/- 7.4 micrograms (g bone mineral)-1, +/- 16.6 micrograms (g bone mineral)-1 for the calcaneus and lowest for phalangeal lead +/- 25.0 micrograms (g bone mineral)-1. Maximum absorbed doses to the skin were comparable for all three measurements (1-3 mGy). The mean whole body dose equivalents were all low, but that for the finger measurement, 0.1 microSv, was significantly less than for the calcaneus and tibia measurements 3-5 microSv.

Comparison of two in vitro methods of bone lead analysis and the implications for in vivo measurements

Atomic absorption spectrometry and x-ray fluorescence have been used to determine the lead content of metatarsal and tibia bone samples. For a range of bone lead levels from 6.5 to 83 micrograms g-1 of ashed bone there is no evidence of a systematic difference between the two techniques of more than 1 microgram g-1. There is, however, some evidence that random differences between the two in vitro analyses applied to the same bone sample are larger than can be accounted for by known measurement uncertainties. Variations in bone composition could account for these differences. Because the x-ray fluorescence technique is applied in an identical way to in vivo analysis, it is concluded that the uncertainties in in vivo measurements are small.

Improvements in the precision of in vivo bone lead measurements

The measurement of Pb in bone by X-ray fluorescence using 109Cd gamma -ray to excite K-shell X-rays is considered. Improvements to the basic system performance were made by changing the design of the source collimator and by including data from the Pb K beta 1,3 photopeaks, having used pile-up rejection to reduce background in their region of the spectrum. The summed variances for eight sample measurements are given: two each of four plaster-of-Paris phantoms embedded in wax.

Effect of Occupational Lead Exposure on Serum 1,25-dihydroxyvitamin D Levels

The effects of lead exposure on serum 1,25-dihydroxyvitamin D levels and calcium homeostasis have been studied in 63 males occupationally exposed to the metal in the UK. The exposure indices used were blood lead, reflecting short-term exposure, and an in vivo X-ray fluorescence measurement of tibia lead which reflects cumulative lead exposure. Serum 1,25-dihydroxyvitamin D levels were higher than those in a referent population, who were non-occupationally exposed to lead, and were correlated with both blood lead and tibia lead. Multiple regression analysis suggested that blood lead was the variable responsible for the increase in serum 1,25-dihydroxyvitamin D. There were no other abnormalities in calcium metabolism associated with the degree of lead exposure.

Measurements of Trace Elements In Vivo

When measurements of potentially toxic trace elements are to be made in vivo, the usual constraints of keeping any radiation dose as low as possible and the non-standard, extended shape of humans, are compounded by the fact that the target element is present, by definition, only in small quantities. Lower limits of detection, are often, therefore, vital parameters with which to characterise measurement system peformance.

Estimation and projection of population lung cancer trends (United Kingdom).

AbstractObjective: Reduction of overall cancer mortality in the UK will require a marked decrease in lung cancer incidence and mortality. A method was sought to predict future lung cancer trends at regional and subregional levels to improve planning, aid the monitoring of health promotion strategies, and to assess health gains that might be achieved. Methods: Data on 55,000 lung cancer patients were used in an age-cohort model of lung cancer incidence (1981–95) and a parametric model of survival (1981–91). Indicators of deprivation were included in the models. Prevalence was estimated from the product of incidence and survival. Lung cancer trends were predicted to 2015, both at steady state and with an incidence perturbation. Results: Female lung cancer is predicted to increase, until by 2015 the numbers will almost equal those in men. Cohort coefficients reveal an increasing risk of lung cancer in females born after 1941. Changing these female cohort coefficients to equate to a declining risk after 1941 suggests that, by 2015, around 200 cases per year might be prevented. This would necessitate a marked change in smoking behavior. Survival from lung cancer was significantly associated with social deprivation and health authority of residence. Conclusions: A credible model has been derived which can be used for health service and outcome monitoring. The model results have highlighted a priority area for smoking intervention which currently seems to attract little attention.

In-vivo and in-vitro measurements of lead and cadmium.

Tibia lead is measured in vivo using X-ray fluorescence. A109Cd source is used to excite Pb K X-rays, and this signals is normalized to that from Rayleigh scattering to remove geometrical variations. The lower limit of detection is 10 μg/g for a mean absorbed dose, to the exposed section of the leg, of 100 μGy. Tibia lead correlated positively with age in normal volunteers (r=0.615,p=0.004) and with duration of exposure in occupationally exposed subjects (r=0.847,p=0.0001). When the X-ray fluorescence technique was applied to autopsy specimens previously analyzed by atomic absorption spectrometry there was excellent agreement between measurement techniques.Cadmium is measured in vivo by neutron activation analysis. The detection limit in liver is 6.5 μg/g for a local skin dose equivalent of 0.5 mSv and in kidney is 6.4 mg for a dose equivalent of 0.9 mSv to the skin. Detailed analysis of the γ-ray spectrum will produce only slight improvements in detection limit. Uncertainties in organ position during measurement, even after ultrasonic localization, are likely to produce uncertainties of 20–25% in cadmium measurement. Autopsy samples were measured, using a fast neutron activation method, from people previously measured in vivo. The results are broadly consistent, but show differences greater than those accounted for by counting statistics.

A pilot study using 99mTc to measure lead and platinum in the human kidney

A pilot study has been conducted to investigate the hypothesis that the chemotherapeutic drug, cisplatinum, can mobilize skeletal lead. In vivo measurements of lead and platinum in the kidney of chemotherapy patients were performed with the technique of x-ray fluorescence, using 99mTc in a backscatter geometry. The results of the pilot study were inconclusive; the majority of patients exhibited no evidence of kidney lead at the level of system sensitivity, and negligible blood and urine lead levels.