| Report number | MED-034 |
| Title | Determination of 227Ac impurity in 225Ac using alpha spectrometry |
| Author(s) | Cusnir, Ruslan (Centre Hospitalier Universitaire Lausanne CHUV (CH)) ; Bailat, Claude (CHUV) ; Straub, Marietta (Centre Hospitalier Universitaire Lausanne CHUV (CH)) |
| Publication | 2023 |
| Imprint | 2023-03-20 |
| Number of pages | 2 |
| Keywords | MEDICIS; isotope mass separation; Actinium-225; Actinium-227; Targeted alpha therapy; Dosimetry |
| Abstract | 225 Ac (actinium-225, t 1/2 = 9.9 days) is currently in the spotlight owing to its promising radiotherapeutic applications in nuclear medicine. This alpha-emitter can be produced using an accelerator, however this route involves the formation of an undesirable radionuclidic impurity of 227 Ac (actinium-227, t 1/2 = 21.8 years). The long half-life as well as a complex decay chain of 227Ac which results in five alpha particles call for a thorough radionuclidic purity testing of 225Ac to ensure the safety in pre-clinical and clinical studies. Mass-separation technique at CERN-MEDICIS facility enables the isotopic separation of 225Ac from 227Ac, however the radionuclidic purity of 225Ac produced this way must be proven. It is challenging to demonstrate the absence of 227Ac by a direct measurement at a low concentration using radiometric techniques (only low-energy (< 100 keV) beta emissions present). 227 Ac decays to 227 Th (thorium-227, t 1/2 = 18.7 days), an alpha-emitter which then results in a chain of short-lived alpha-emitters (223 Ra, 219 Rn, 215 Po, 211 Pn, 211 Bi) in a secular equilibrium. The activity of 227Th reaches half of that of 22 Ac after three weeks. We propose to use the ingrowth of these alpha-emitting impurities as an indicator of the presence (or the absence) of 227Ac in 225Ac purified at CERN-MEDICIS. Radiometric techniques such as alpha spectrometry make possible a direct identification of actinides at mBq levels. To enable accurate and quantitative determination of 227Ac, a metrological standard 243 Am (americium243, t 1/2 = 7360 years) will be used. Measuring samples at different time points to allow for an ingrowth of the alpha-emitting impurities will enable to identify infinitely small impurities of 227Ac eventually present in a batch of 225Ac. |
| Submitted by | thierry.stora@cern.ch |
Record created 2023-03-21, last modified 2023-03-21
