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 results of the intercomparison are available here. 12 MC is the VMC in-vivo intercomparison number.

The phantoms used were (a) a BOMAB phantom representing a 95-percentile Caucasian male, (b) a torso phantom representing Asian Reference Man. The torso phantom was provided with five lung sets, each set with a different radionuclide, 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) a bone phantom representing the human knee containing four sets of bone inserts, each with a different radionuclide, that could be placed in the tissue equivalent envelope.

The phantoms were counted in the whole-body counting laboratory of the Instituto de Radioproteção e Dosimetria, and the activity each tissue or organ in each phantom was calculated by using VMC in-vivo, as well as by using calibration factors derived from physical phantoms. The summary of the VMC in-vivo results are shown in Figure 1.

Figure 1. VMC in-vivo results in the 2005 IAEA activity intercomparison for lungs, thyroids, BOMAB and knee phantoms.

Conclusions

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 while the BOMAB used in the IAEA intercomparison was the 95th percentile phantom, considerably larger than the ANSI phantom.

After analysis of the IAEA intercomparison results, the VMC in-vivo algorithms were considerably improved.

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