Intercomparison of the Reliability of Body Cesium-137 Measurements on Human Beings

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Abstract
As a result of large variations in the 137Cs body burdens reported by the participating laboratories, the Division of Biology and Medicine, USAEC, appointed, in 1962, an ad hoc committee to conduct an intercomparison between these laboratories on the reliability of body 137C measurements on human beings. The intercomparison was divided into three phases: (I) intercomparison with National Bureau of Standards 137C sources to determine variations in the absolute activity of the laboratory standards and to place the laboratories participating in this study on a common basis for future work; (2) determination, at three different distances from the detector, of the ratio between three 137C sources with nominal activities of 1000, 100 and 10 nCi, i.e. between a decade set, to assess the ability of each laboratory to account for all the physical and electronic variables in measurements conducted with whole body counters; and (3) determination of the 137C body burdens of two well-documented subjects (one with a “normal” burden and the other with a burden ∼10 times greater) by the usual procedure of each laboratory to assess the reliability of calibration factors and the control of physiological and other physical variables. Each laboratory (16 of the 17 responded) supplied information in the same form, in order to make the evaluation consistent and convenient. Each participating laboratory compared the old value of its working standard to a new value based on reference to the certified NBS standard. The average of the ratios of new to old value was 1.01 ± 0.04. The ratios of the participating laboratories' values for the decade sources to the corresponding Argonne National Laboratory values averaged 1.00 ± 0.01, for each of three souce to detector distances. The ratios of the body burdens found to the values reported by the Los Alamos Scientific Laboratory averaged 0.96 ± 0.11 for the high 137C burden, and 0.93 ± 0.13 for the low 137C burden. Averages of similar ratios for body potassium were 0.93 + 0.08 (high burden) and 0.90 ± 0.06 (low burden). The conclusion is that these laboratories can be capable of reliable 137C and K body measurements in human beings. Differences which occur in such body measurements appear to be associated with physiological variables (affecting calibration factors, for example) rather than with physical or electronic variables. In view of these results and of the time it has taken to complete this study, it is not clear why the original results were so variable. Since that time, the “normal” 137C burdens have increased, instrumentation has improved, a greater attention has been devoted to calibration factors, and each laboratory has gained much experience. Any and ali of these factors have probably contributed to the state of the art which has been demonstrated by the intercomparison.

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