Strontium 90 in urine: Evaluation of radiotoxicological techniques by international PROCORAD comparison exercises

Strontium 90 (half-life = 28.79 years) is a < leader > of fission products. Through β- disintegration, it leads to yttrium 90 which is a short-term radioactive β- emitter (64 h). Strontium 90 does not exist in a natural state: it is a product of the nuclear fuel cycle. The 90Sr-90Y couple makes up one of the means used in monitoring workers in the nuclear industry. Its quantification in urine serves as a means on confirming the operational radioprotection of nuclear facilities. In France, the Clinical Biochemistry Laboratories (CBL) are in charge of monitoring nuclear sites workers. These laboratories must be accredited and have ministerial certification. The accreditation of radiobioassay analyses notably requires comparison exercises between laboratories. One of the most important is that organized by the PROCORAD association. The specific activity of this association is to provide biological samples overloaded in various radio nuclides to international CBL and to exploit the results obtained by the different laboratories: both statistically and anonymously thanks to a specially-designed software entitled Procostat. The urinary Strontium 90 comparison exercise was initiated at the inception of PROCORAD. It answers a definite demand from laboratories in charge of monitoring workers, since every year more than 40 participants from all over the world sign up to participate . The authors present an overall assessment of the Strontium 90 comparison exercises reviewed over the past seven years (2000-2007) by comparing the mean geometric value of laboratories with a target value, all techniques included. The metrological difficulty leads to a tendency to underestimate its quantification. Analysis of the data through comparison of the couple, techniques and results, enables us to assess performances according to the techniques used. Certain techniques are very well-adapted to the dosage of Strontium 90 in terms of exactitude and reproducibility of the results provided. A specific technique associating chromatography and measurement using a gas beta detector as proportional counter presents an even narrower bias. The gross beta techniques, non-specific, are influenced by gamma emitters that might possibly be present in the samples. The study also deals with other techniques and reviews their performances. Apart from an assessment of the performances of the different laboratories, the urinary Strontium 90 comparison exercises organized by the PROCORAD association enable the Clinical Biochemistry Laboratories to evaluate the techniques implemented in terms of accuracy, reproducibility and specificity. (author)