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IAEA intercomparison

 

The IAEA promoted an international intercomparison with the title “Measurement of the quantity ‘activity’ of radionuclides in simulated human organs”. The intercomparison exercise began in 2001 and ended in 2005. The phantoms used were (a) the BOMAB phantom representing a 95-percentile Caucasian male, (b) A torso phantoms representing Asian Reference Man. The torso phantom was provided with five lungs sets, and one overlay plate that simulated a chest wall thickness of approximately 3.5 cm (c) Two thyroid phantoms, each with four inserts: two simulating I-125 and two simulating I-131. An overlay plate was also provided to simulate a layer of tissue over the thyroid insert, and (d) One bone phantom representing a human knee containing four sets of bone inserts that could be placed in the tissue equivalent tissue envelope.

The phantoms were counted in the Whole Body Counting laboratory of the Instituto de Radioproteção e Dosimetria, and the activity in the respective tissues was calculated using VMC in-vivo. The results obtained are shown in the Figure below.

The average bias of the results was 0.2%, and the standard deviation of the biases was 24%. The outlier for the case of Ba-133 in the BOMAB phantom was due to the VMC in-vivo calculation being made for the ANSI BOMAB phantom, and the BOMAB used in the IAEA intercomparison was the 95th percentile phantom, considerably larger than the ANSI phantom.

Conclusions

The testing through international intercomparisons, added to the many years of testing the program with diverse physical phantoms and against other Monte Carlo programs, shows that VMC in-vivo can be used to calculate calibration factors in Whole Body Counter laboratories. Where physical phantoms are available, the physical phantom should be used for the calibration. Where physical phantoms are not available, or to compare the results of Monte Carlo and physical phantom calculations, then VMC in-vivo can be used.

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