The 1993 International In Vivo Intercomparison Programme

The Canadian National Calibration Reference Centre for In Vivo Monitoring [NCRC] and the United States Department of Energy collaborated to offer an international intercomparison program to whole body counting facilities in 1993. The Human Monitoring Laboratory fabricated a phantom shell corresponding to a reference four-year old child and Battelle Pacific Northwest National Laboratory filled the shell with radioactive tissue-substitute polyurethane to simulate a uniform fission-product distribution in soft tissues.

The amounts of the radionuclides on 01-May-93, 1200 PST (Pacific Standard Time) were:

• ⁴⁰K: 851 ± 43 Bq
• ⁸⁸Y: 18.90 ± 0.54 kBq
• ¹³⁷Cs: 4.487 ± 0.076 kBq

Each facility was asked to determine the identity and amount of the radionuclides in the energy range 200 - 2000 keV. Each facility was asked to make an estimate of the "worst case" precision and estimate their minimum detectable activity. The programme had participants from 18 countries for a total of 43 counting systems.

The programme began in April 1993 and ended on 1-Aug-95, when the phantom arrived back at the Canadian National Calibration Reference Centre for In Vivo Monitoring from the last participant's laboratory.

The results of the intercomparison showed that:

• almost all whole body counters are size dependent and this appeared counting geometry independent
• where applied, size correction factors greatly improved results
• no one counting geometry appeared better than another
• although some worst-case-precision results were high, precision of whole body counting is not a problem
• minimum detectable activity results were quite variable showing the differences in facility shielding and ambient background levels

The results of the Intercomparison were presented at IRPA9, Vienna, April 1996 and have been published