engleski

Use of uncollimated gamma camera for emergency whole-body counting

Internal contamination is one of the most important issues in general scenario of nuclear accident. The assessment of body burden and risk from internally deposited radionuclides usually relies on systems for in-vivo measurement of radioactivity (whole-body counters). Since the number and the throughput of available whole-body counters is small and may be the limiting factor, all applicable measuring systems (such as those in nuclear medicine departments) should be at disposal when larger number of individuals are contaminated. The BOMAB (Bottle Manikin Absorption) phantom homogeneously filled with radioactive source of barium-133 (Ba-133), caesium-137 and cobalt-60 was measured by four different counting systems: Canberra Accuscan whole-body counter with one NaI(Tl) detector, and uncollimated Siemens Diacam, Siemens Rota and Marconi Irix single, double and triple NaI(Tl) detector gamma cameras, respectively. During all measurements the distance between anterior detector and bed surface was the same, the acquisition geometry was horizontal scanning bed and the scan length was maximal. The results of intercomparison are given as gross count rates of single anterior detector for the main photopeak of Ba-133 (356 keV, window width 15%), which is a long-lived substitute for radioactive iodine-131 (I-131). In regard to the different detector sizes, measuring geometries and background radiation, relative count rates of single NaI(Tl) detectors of different gamma cameras were about 0.8-3.1 times the count rate of NaI(Tl) detector of a whole-body counter. This work presents very preliminary results of the intercomparison of different imaging systems (gamma camera) used as a counting systems (whole-body counter). Emergency use of gamma camera without a collimator is possible and justified, especially in case of wider-scale accidents with known contaminants, preferably emitting low- and mid-energy gamma radiation. However, great attention should be paid on calibration methodology, in order to substantially improve overall level of emergency preparedness.

unutarnja kotaminacija; mjerenje radioaktivnosti tijela; radioaktivni jod

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