The potential radio-immunotherapeutic α-emitter 227Th – part I: Standardisation via primary liquid scintillation techniques and decay progeny ingrowth measurements. (March 2019)

• Record Type: Journal Article
• Authors: Collins, S.M.; Keightley, J.D.; Ivanov, P.; Arinc, A.; Jerome, S.M.; Fenwick, A.J.; Pearce, A.K.
• Is Part Of: Applied radiation and isotopes. Volume 145(2019:Mar.)
• Page Start: 240
• Page End: 250
• Publication Date: 2019-03
• Subjects: 227Th -- Radioactivity -- Radioimmunotherapy -- Nuclear Medicine -- Standardisation -- Liquid Scintillation -- DCC -- Coincidence -- Radioactive Ingrowth -- Ionisation chambers; Radiology -- Periodicals; Radiation -- Industrial applications -- Periodicals; Nuclear chemistry -- Periodicals; Internet resource; Periodical; 660.298
• DOI: 10.1016/j.apradiso.2018.12.012
• Languages: English
• ISSNs: 0969-8043

Abstract

Abstract: Thorium-227 is a potential therapeutic radionuclide for applications in targeted α-radioimmunotherapy for the treatment of various types of cancer. To provide nuclear medicine departments involved in Phase I clinical trials traceability to the SI unit of radioactivity (Bq), a standardisation of a radiochemically pure 227 Th aqueous solution has been performed at the National Physical Laboratory. This was achieved via two primary liquid scintillation (LS) techniques −4π(LS)-γ digital coincidence counting (DCC) and 4π LS counting. These absolute techniques were supported by the indirect determination of the 227 Th activity via the measurement of the ingrowth and decay rate of the decay progeny by both ionisations chambers and high purity germanium (HPGe) gamma-ray spectrometry. The results of the primary techniques were found to be consistent, both with each other (zeta score = 1.1) and to the decay progeny ingrowth measurements. An activity per unit mass of 20.726 (51) kBq g −1 was determined for the solution. A procedure has been developed that provided an effective separation of the 227 Th from its decay progeny, which was shown by the effective time zero of the 227 Th- 223 Ra nuclear chronometer measured by HPGe gamma-ray spectrometry. Highlights: First primary standardisation of the activity of 227 Th performed. 4π LS counting and 4π(LS)-γ Digital Coincidence Counting techniques employed. Activity of 227 Th determined indirectly via the measurement of the 223 Ra activity ingrowth. Improved procedure for the radiochemical separation of the 227 Th from the decay progeny.