Co-57-based intercomparison of TLC scanners and dose calibrators for low-activity radiochemical purity assessment in...

Thin layer chromatography scanners and dose calibrators are commonly used to assess radiochemical purity of radiopharmaceutical preparations. Strict quality assurance programs surveyed by regulatory bodies exist for dose calibrators, but they primarily focus on clinical activity ranges, typically tens to hundreds of megabecquerels (MBq). These programs are not designed to evaluate performance at the lower activity levels used during radiopharmaceutical quality control, in the range of just a few MBq or less. For thin layer chromatography scanners, to our knowledge, no supervised quality control program exists. As a result, current practices may overlook potential inaccuracies at these low but critical activity levels, potentially affecting the reliability of radiochemical purity assessments, guaranteeing radiopharmaceutical quality of patient injections.

To address this gap, in collaboration with the Swiss Federal Office of Public Health, we organized an intercomparison campaign for radiochemical purity testing employing in-house fabricated cobalt-57 (Co-57) strips simulating a chromatogram of a radiopharmaceutical preparation for quality control. Co-57, with its longer half-life, closely simulates the gamma emissions of technetium-99m (Tc-99m), a nuclide widely used in nuclear medicine. Co-57 thin layer chromatography strips were prepared and characterized, before being sent to nuclear medicine centers for measurement and radiochemical purity assessment. 31 centers participated, in total 41 quality control measurements were performed using dose calibrators and/or thin layer chromatography scanners to assess the radiochemical purity. All 27 dose calibrator results were within specifications, except for one result that overestimated the radiochemical purity. Within 14 thin layer chromatography scanner results, 3 were out of tolerance.

Regular participation in intercomparison campaigns is essential for harmonizing practices and ensuring reproducible, reliable results. Thin layer chromatography results can be affected by scanner settings, procedural variations, and subjective peak integration. By comparing thin layer chromatography scanners and dose calibrators, we identified potential instrument biases and methodological discrepancies when values were out of tolerance. Our intercomparison contributed to improving the performance and comparability of radiochemical purity measurements across Swiss nuclear medicine institutions.