Gamma counting protocols for the accurate quantification of 225Ac and 213Bi without the need for a secular equilibrium between parent and gamma-emitting daughter

EJNMMI Radiopharmacy and Chemistry

Table 1 Overview of the different samples for GC measurements and the activity at the start of the measurements

Sample	²²⁵Ac (in SEq with ²¹³Bi)	Added ²¹³Bi	Experiment
1	1.5 MBq (total)	0 kBq	GC calibration
2	0 kBq	117 kBq	Quantifying down scatter of higher-energy gamma emissions by ²¹³Bi in \({\text{EW}}_{{221_{{{\text{Fr}}}} }}\)
3	94 kBq	55 kBq	Simulating non-SEq conditions between ²²⁵Ac and ²¹³Bi
4	116 kBq	32 kBq	Simulating non-SEq conditions between ²²⁵Ac and ²¹³Bi
5	1–2 MBq	0 kBq	Radiolabeling of [²²⁵Ac]Ac-DOTA and incubation in human serum for 15 min and 24 h
6	1–2 MBq	0 kBq	Radiolabeling of [²²⁵Ac]Ac- DEPA and incubation in human serum for 15 min and 24 h

Specifications of the samples used for determining the linear range of GC measurements and evaluating the impact of different sample volumes on GC measurements is given in the Additional file 1