INTERCOMPARISON MEASUREMENTS OF INCORPORATED RADIONUCLIDES IN MAN BY 4 WHOLE-BODY COUNTERS

Whole-body counting is the most suitable tool to assess the incorporat ion of radioactive substances. Quantitative measurements of the total body activity, however, require the careful calibration of the instrum ent with regard to the varying responses with different body sizes. Th e accuracy of the obtained results can only be checked by interlaborat ory intercomparison. In this study comparative measurements were perfo rmed on eight subjects employing the whole-body counters of KFKI Budap est (Hungary), GSF Frankfurt (Germany), IAEA and Ostereichisches Forsc hungszentrum at Seibersdorf (Austria). Gamma ray spectra obtained were evaluated for body activities of K-40, Cs-134, and Cs-137. On four mo re subjects comparative measurements were carried out at Budapest and Frankfurt. One of these subjects showed additional I-125 thyroid burde n due to a diagnostic investigation. Although these devices have diffe rent arrangements with respect to counting geometry and number of dete ctors and although the subjects investigated were of different size an d weight, generally good agreement of measured activities, i.e. mean o f deviations from the average body activity for each particular subjec t of less than 10%, was obtained between all laboratories. For the two devices at Budapest and Frankfurt excellent agreement was achieved ev en for the I-125 thyroid activity with its low energy photon emission, i.e. only about 2% deviation of the value of thyroid activity measure d at Budapest from the reference value calculated from the retention f unction.