Development of a «flash» method based on thin-layer-chromatography for radiochemical purity assessment of ^99mTc-tetrofosmin

Background/objectives:
^99mTc-tetrofosmin (^99mTc-T) is a radiopharmaceutical, mainly used as a tracer of myocardial perfusion in the diagnosis of myocardial ischemia and/or myocardial infarction.
Once prepared, quality controls are carried out on the radiopharmaceutical, including radiochemical purity (RCP), in order to release it. This RCP is assessed by thin-layer chromatography (TLC). The technique described in the summary of product characteristics (SPC) used to determine the RCP is very time-consuming and therefore unacceptable. We created and validated a new, faster TLC RCP analysis technique, using the European Agency for Nuclear Medicine (EANM) guidelines.

Materials and methods:
Our TLC mobile phase is composed of 65%/35% ethyl acetate/acetonitrile on a 6cm x 0.7cm GMCP-SA strip with a 45mm migration distance. The TLC mobile phase of the SPC technique consists of acetone/dichloromethane 65%/35% on a 20cm x 2cm GMCP-SA strip with a 150mm migration distance. We assessed the resolution between reduced ^99mTc (peak 1), ^99mTc-T (peak 2) and pertechnetate (^99mTcO4-) (peak 3) by contaminating the ^99mTc-T solution with ^99mTcO4-. We also evaluated the coefficient of variation (CV) and percentage recovery of our technique. A Student’s t test (5% risk) was performed to compare the migration time (TM) and RCP of our technique with the SPC technique.

Results:
Our method (« flash ») has a resolution between peaks 1 and 2 of 2.85 ±0.35 and between peaks 2 and 3 of 2.35 ±0.37 (n=12). It has a CV of 0.35% (n=12). It also has a percentage recovery of 99.8% (n=6). The RCP of the two techniques are not significantly different (p=0.28 nSPC=6 nflash=12). TM with our technique is significantly shorter (2min 58sec ±22sec n=12) than with the SPC method (27min 29sec ±17sec n=6) (p<0.000001). Radiochromatograph analysis time is also shorter with our technique (1min 3sec) than with the SPC technique (2min 44sec).

Discussion/conclusion:
Evaluated parameters (resolution, CV, percentage recovery, RCP) comply with the EANM validation protocol. As migration and detection times are significantly shorter with our technique, it will enable us to improve patient care at our facility and improve our reactivity in case of ^99mTc-T non-conformity. As the TLC plate is smaller, we will be using less GMCP-SA and smaller volumes of solvent. This will lead to reduce costs. Furthermore, our method avoids staff exposure to dichloromethane, a category 2 carcinogen according to the INRS (French National Institute for Research and Safety), and therefore protects our staff.

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