Determining radiochemical yield of Ac-225 with direct alpha detection
27/02/2025
At a glance
> In our recent webinar, LabLogic presented its findings on optimised radio-TLC scanning for 225Ac-PSMA using the Scan-RAM 2.
> Following recent testing, superb sensitivity was demonstrated by using a ZnS detector for alpha-emitting isotopes instead of a traditional NaI(Tl) detector.
> If you want to learn more, you can access the full webinar by clicking at the bottom of this page.
Addressing the challenges of alpha QC
The development of alpha-emitting radionuclides for targeted radiotherapies are presenting exciting new opportunities to treat cancer, but complex decay chains present challenges. LabLogic is committed to the development of new instruments for the Quality Control of radiopharmaceuticals labelled with alpha-emitters, however, our existing range of instruments are already being optimised for elements such as 225Ac.
Currently, traditional NaI(Tl) detectors are commonly used to scan samples radiolabelled with 225Ac, but because of poor sensitivity to gamma emissions, these scans are run over periods of 15 mins or more. However, following recent testing, LabLogic has been able to determine the optimal settings using a ZnS detector for radio-TLC scanning of 225Ac-PSMA using the Scan-RAM 2.
Faster scanning and superior sensitivity with ZnS SiPM detector
During testing, the Scan-RAM 2 used a Silicon Photomultiplier (SiPM) ZnS scintillation detector which has been designed specifically for total alpha detection and is controlled by Laura Radiopharma. In the radiochromatogram below (Fig. 1), the SiPM ZnS detector was able to detect unbound activity and the radiolabelled PSMA (total activity 1.8 kBq). The chromatogram clearly demonstrates the detector’s superb sensitivity and suitability for 225Ac in place of traditional NaI(Tl) detectors as are commonly used.
Fig. 1: Radiochromatogram using a Scan-RAM 2 with a SiPM ZnS detector. Region 1 in red shows unbound 225Ac. Region 2 in green shows radiolabelled PSMA.
Using lower activity for reduced exposure
As part of a serial dilution, 2 μl of 225Ac-PSMA was spotted onto the TLC plate and was scanned using the SiPM ZnS detector. For radiochemical purity and yield, just 2 kBq of solution on the TLC plate allowed accurate quantitation of low-level impurities, with 1 % impurities being detected as defined by information published to date. This means less sample can be used, reducing potential risks of exposure. Fig. 2 below shows excellent linearity of data.
Fig. 2: Activity (Bq) vs. peak area (counts).
Watch the webinar
Testing has demonstrated that despite the inherent difficulties of working with alpha-emitters, existing systems can be optimised to provide radiopharmacies with the necessary data to release batches safely. You can find out more about Scan-RAM 2 and LabLogic’s work in alpha QC by clicking the button below to watch the full webinar.