The second international in-vivo monitoring intercomparison program for whole body counting facilities by Canadian and United States agencies

The Canadian National Calibration Reference Centre for In-Vivo Monitoring and the United States Department of Energy collaborated to offer a second international in vivo intercomparison program to whole body counting facilities in 1996. This program used a Reference Female phantom shell filled with radioactive tissue-substitute polyurethane to simulate a uniform fission-product distribution in soft tissues. The nuclides used were Cs-137 and Co-60. The phantom also contained K-40 homogeneously distributed in an amount similar to a Reference Female to produce a representative Compton background in the resulting spectra. Participants were asked to identify the nuclides and report activities for all except K-40. They were also asked to measure the precision of counting and supply the MDA for Cs-137 and Co-60. The bias results were in the range of -30% to +80% with most facilities falling inside the range of -25% to +50% (Canadian and U.S. acceptable performance criteria). Results indicated that there was no measurable size dependency for this phantom. All reported precisions were less than 5% but NaI detector based systems seemed to have a systematic uncertainty in addition to Poisson variability. Contrarily, this was not found for Ge detector based systems. MDA data was scattered (14-3,500 Bq for Cs-137 and 9-460 Bq for Co-60) and only suggested that lengthening the counting time improves MDA. Health Phys. 80(3):214-224; 2001.