On the radioanalytical methods used to assay stainless-steel-encapsulated, ceramic-based 90Sr-90Y intravascular...

Very quantitative radiochemical procedures for the destructive assay of stainless-steel-encapsulated, ceramic-based 90Sr-90Y intravascular brachytherapy sources (termed 'seeds') have been devised. These seeds, developed and provided by Bebig Isotopentechnic und Umweltdiagnostik (Berlin, Germany) in collaboration with the Novoste Corporation (Norcross, GA), are intended for use in the prophylactic treatment of restenosis following balloon angioplasty in heart-disease patients. The procedures were applied to the radionuclidic assay of both the bare-ceramic source materials (of proprietary composition) contained within the seeds and to the stainless-steel (SS) sealed sources. The approach consisted of extracting some arbitrary fraction of the 90Sr activity from the ceramic-like material and assaying the resulting solution by 4pi beta liquid scintillation (LS) spectrometry with 3H-standard efficiency tracing. The fraction of extracted activity was determined by ionization current measurements before and after the chemical extraction. All of the ionization current and LS-based activity determinations were made under the experimentally-verified conditional that 90Y was in radioactive equilibrium with 90Sr. For the assay of the SS-jacketed seeds, the encapsulation was initially dissolved and the resultant solution was also assayed by LS spectrometry to determine the amount of activity removed by the SS dissolution step. The developed protocol included provisions for accounting for all possible losses of 90Sr activity in the chemical and source-handling procedures, for the unrecovered activity in the extracted source material and for any residual activity in the solution-transfer and source-handling tools. These destructive assays were required for relating radiochromic-fill measurements of the absorbed dose spatial distributions for the seeds to theoretic dose modelling and for establishing calibration factors for subsequent non-destructive radionuclidic measurements on the seeds.