Table 2 General overview of important aspects which can be applied when performing a Ac-225 labelling

Addition of quencher(s), dependent on the molecule (Blois et al. 2012; Blois et al. 2014; Larenkov et al. 2023)

 Ex. ascorbic acid/ascorbate/gentisic acid/ethanol/methionine/cysteine (0.35–50 mM*)

Addition of buffer(s), pH, and molecule dependent

 Sodium-Acetate (pH 5, 0.1 M*) (Pretze et al. 2021), TRIS (pH 9, 14 mM*) (Hooijman et al. 2021)

Add a titrated and a biological vector of high chemical purity to be able to obtain the required molar activity (Breeman et al. 2014) and mix carefully. Ensure the absence of metals within the used chemicals and solutions

After dissolving the activity, direct use is recommended to avoid increase of impurities. Addition of the activity should be done as the last step before the labelling. Be aware of the impurities that might be released by the vial due to increased exposure

Preferred final volume depending on the application (~ 500 kBq/140 µL preclinical (Handula et al. 2023) and ~ 10 MBq/0.5–1 mL for a clinical radiolabelling (Hooijman et al. 2021)), note that the smaller the volume, the better the kinetics, large volumes show low labelling yield, smaller volumes show an significant increase of radiolysis

 Optimize conditions → Ex. time and temperature per biological vector

Rapid stabilization with an excess of quencher directly after heating (> 3 × as during labelling*)

 Because of the small volume, radiation in the sample is high, therefore, rapid stabilization should be performed

Excess of DTPA/EDTA (> 10⁴ × more versus Ac-225) to complex all free Ac-225 and recoiled daughters to ensure rapid excretion (Kratochwil et al. 2017)