Chemical digestion and radionuclidic assay of TiNi-encapsulated 32P intravascular brachytherapy sources

A very quantitative, destructive assay procedure was devised for accurately measuring the P-32 activity content of TiNi-encapsulated intravascular brachytherapy sources and was applied to four different sources (termed 'seeds') which were developed and provided by Guidant Intravascular Intervention (formerly NeoCardia). These seeds are intended for use in the prophylactic treatment of restenosis following balloon angioplasty in heart-disease patients. The assays involved the dissolution of the TiNi jacket, extraction of the activity from the internal P-32-containing source material, quantitative solution transfers, and a gravimetrically-based dilution; followed by liquid scintillation (LS) spectrometry of the resulting master solution with H-3-standard efficiency tracing using composition-matched LS cocktails, The LS spectrometry utilized a previously-developed method for resolving the always-present P-33 impurity. The protocol included provisions for accounting for all possible losses of P-32 in the digestion procedure (based on radiochemical tracing experiments), for any unrecovered activity in the remaining source material, and for any residual activity in the solution-transfer and containing vessels. Sections of the TiNi jackets adjacent to the cutoff active seed portions were also assayed for any contained activity. Such destructive assays were required for relating measurements of the absorbed dose spatial distribution for the seeds to theoretic dose modelling and for establishing calibration factors for subsequent non-destructive radionuclidic measurements on the seeds. Published by Elsevier Science Ltd.