Standardization of 68Ge-68Ga using 4πβ(LS)-γ coincidence counting system for activity measurements

⁶⁸Ga has great scope for use in future for positron emission tomography (PET) imaging due to its very fast blood clearance and fast target localization, even though at present ¹⁸F is widely used. ⁶⁸Ge in equilibrium with ⁶⁸Ga (⁶⁸Ge-⁶⁸Ga) can also be used as a surrogate for ¹⁸F calibration, as ¹⁸F source standardization can be done at national metrology institute (NMI) but, these standards cannot be sent to nuclear medicine centers (NMCs) across India for calibration of isotope calibrators, due to the short half-life of ¹⁸F (110min). Providing ⁶⁸Ge-⁶⁸Ga standards to NMCs requires that first standardization must be carried out at NMI (BARC in India) to provide traceability to the measurements carried out at NMCs. In the present work, standardization of ⁶⁸Ge-⁶⁸Ga was carried out using 4πβ(LS)-γ coincidence counting system and CIEMAT/NIST efficiency tracing technique. The decay scheme correction factors for two gamma windows were calculated by Monte Carlo technique using general purpose code FLUKA. The activity concentration values were normalized by the activity concentration obtained by 4πβ(LS)-γ coincidence counting system using window-1. The final result reported to BIPM for 4πβ(LS)-γ coincidence counting was calculated by taking arithmetic mean of activity concentrations obtained for two gamma windows. The normalized activity concentration obtained by 4πβ(LS)-γ coincidence counting was 0.998±0.005 and that obtained using CIEMAT/NIST efficiency tracing was 1.002±0.007 which are in excellent agreement within uncertainty limits.

Performance demonstration of 4πβ(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme

A standardization of (134)Cs and (131)I was carried out in order to demonstrate the performance and applicability of the 4πβ(LS)-γ coincidence counting system for standardization of radionuclides with complex decay scheme. The coincidence analyzer, capable of analyzing coincidence between beta and two gamma windows simultaneously, was developed and used for the standardization. The use of this dual coincidence analyzer has reduced the total experimental time by half. The activity concentrations obtained using the 4πβ(LS)-γ coincidence counting system, a 4πβ(PC)-γ coincidence counting system, and the CIEMAT/NIST method are in excellent agreement with each other within uncertainty limits and hence demonstrates its performance for standardization of radionuclides decaying with complex decay scheme. Hence use of this 4πβ(LS)-γ coincidence counting system can be an alternative method suitable to standardize radionuclides with complex decay scheme with acceptable precision.